Ontogeny of the nasolacrimal apparatus and nasal sensory systems of the American alligator (Alligator mississippiensis).

The nasolacrimal apparatus (NLA) is a feature common to many sauropsid amniotes. It consists of an orbital Harderian gland (HG)whose secretions drain into the nasal cavity, in the vicinity of the vomeronasal organ (VNO), an accessory olfactory organ derived from the olfactory epithelium, and a connecting nasolacrimal duct (NLD). Though not all features are present in all posthatchling sauropsids (i.e., no VNO in crocodilomorphs), it is not clear if this system either never existed or failed to develop during the embryonic stages. The purpose of this study is to histologically describe the ontogeny of the NLA and the main olfactory organ in Alligator mississippiensis. Alligator specimens, from embryonic stage 9 to hatchling, were serially histologically sectioned, stained, photographed, and segmented into different tissues using Abobe Photoshop and then reconstructed using Amira for 3D analysis and quantitative nasal epithelial distribution. Though there was no evidence of a VNO, the rest of the NLA was present. The development of the NLA could be subdivided into four phases: (1) inception of NLD, (2) establishment of orbitonasal connections of NLD, (3) bone development, and (4) nasal cavity growth. Glands mature during this last phase and the nasal region rapidly grows, rotates, and is displaced anteriorly. The gradual proportional increase in nonolfactory epithelial distribution during ontogeny is consistent with the literature. Alligator embryonic nasal and NLD growth differs from that of mammals and squamates. The NLD is connected to the anterior third of the nasal region during its initial attachment, but as anterior nasal growth exceeds posterior growth, it is gradually displaced into the posterior third of the nasal region by hatching. It is unknown whether this is a derived archosaur condition or just another example of the morphological variation seen within sauropsid amniotes.

Ontogeny of the American alligator (Alligator mississippiensis) prenatal head: A morphometric approach.

Variation in vertebrate cranial morphology is both extensive and functionally significant. Morphometric analysis attempts to explain such variation in form in evolutionary and functional contexts. Developmental morphometric analyses of vertebrate crania are less common, and many taxa are underrepresented. For example, the published morphometric studies of crocodilian cranial development focus mainly on posthatchling head development, with few, incomplete morphometric analyses of prehatchling heads. To further explore ontogenetic changes in the alligator head, we recorded and analyzed six linear cranial measurements in 77 preserved embryonic and hatchling American alligators (Alligator mississippiensis) representing 20 different stages. Examination of individual measurements revealed nonlinear changes in growth rate during development, suggesting a level of dynamic complexity worthy of further analysis. Using principal components analysis, we identified three distinct phases in prenatal alligator head growth. The second (intermediate) phase disrupts an otherwise monotonic developmental trajectory and represents a phase of reduced snout growth. Although this is a detailed description of prehatchling ontogenetic trajectory of the alligator head, further studies in other crocodilians are needed to assess evolutionary patterns among crocodilians.

Whale tear glands in the bowhead and the beluga whales: Source and function.

Orbital glands are found in many tetrapod vertebrates, and are usually separate structures, consisting of individual glands lying in the eyelids and both canthi of the orbit. In cetaceans, however, the orbital glandular units are less distinct and have been described by numerous authors as a single, periorbital mass. There are few histochemical and immunhistochemical studies to date of these structures. In this study, we examined the orbital glandular region of both the bowhead whale (Balaena mysticetus: Mysticeti) and the beluga whale (Delphinapterus leucas: Odontoceti) using histological, histochemical, and immunohistochemical techniques. Histologically, in the bowhead, three glandular areas were noted (circumorbital, including Harderian and lacrimal poles), palpebral (midway in the lower eyelid), and rim (near the edge of the eyelid). In the beluga, there was only a large, continuous mass within the eyelid itself. Histochemical investigation suggests neither sexual dimorphism nor age-related differences, but both whales had two cell types freely intermingling with each other in all glandular masses. Large cells (cell type 1) were distended by four histochemically distinct intracellular secretory granules. Smaller cells (cell type 2) were not distended (fewer granules) and had two to three histochemically distinct intracellular secretory granules. The beluga orbital glands had additional lipid granules in cell type 1. Counterintuitively, both lipocalin and transferrin were localized to cell type 2 only. This intermingling of cell types is unusual for vertebrates in whom individual orbital glands usually have one cell type with one to two different secretory granules present. The heterogeneity of the orbital fluid produced by cetacean orbital glands implies a complex function, or series of functions, for these orbital glands and their role in producing the tear fluid.

The role of desmosomes in the ear plug formation in the bowhead whale (Balaena mysticetus).

The external acoustic meatus (EAM) of most baleen whales accumulates cellular debris annually in the lumen as whales age, forming a lamellated ear plug. The bowhead whale ear plug is formed from annually molting lining of the EAM as the entire epithelium releases at the level of the stratum basale during the spring migration. Epithelial regeneration is mostly completed by the fall migration, remaining intact for 6-7 months before being torn off the following spring. Desmosomes are integral to cell-cell adhesion with connecting desmosomal cadherins desmoglein (dsg) and desmocollin (dsc). Paraffin sections of the oral cavity and EAM lining of spring and fall adult bowhead whales, as well as the EAM of spring-caught juvenile, were immunohistochemically examined for the presence of these cadherins. In all fall specimens, both cadherins occurred in all layers except the superficial keratinous layer of the oral cavity. In spring, three different conditions existed: (a) oral cavity of spring-caught adults had reduced cadherins, with superficial fissuring in its keratinized layer and vacuolation in the upper stratum spinosum; (b) EAM of juvenile spring-caught whales displayed fissuring with accompanying reduction of both cadherins in its superficial lining; and (c) EAM lining of spring-caught adults displayed deep fissures, reduced cadherins, and absence of dsc1 in the fissuring zone. These results suggest that shedding of skin layers in mammals, whether normal molting, pathological, or the result of injury and wound repair all revolve around desmosome function. The specific role, structure, and location of these two cadherins need to be further addressed.

Isolation and characterization of abundantly-expressed cDNAs from the Harderian gland of the garter snake (Thamnophis sirtalis: Colubridae).

The Harderian gland (HG) is an orbital structure whose proteinaceous secretions pass through the nasolacrimal duct to the vomeronasal organ (VNO). Though these three structures occur in many tetrapod vertebrates, the garter snake (Thamnophis sirtalis) is one of the few vertebrates in which the passage of the proteinaceous secretions have been experimentally shown. Secreted proteins from the HG may function as transporters for chemical signals to the VNO epithelium. To investigate the proteins being produced by the HG of the garter snake, cDNA libraries were constructed from HG mRNA, and several individual cDNAs were analyzed by sequencing, RT-qPCR, and PCR on genomic DNA. Two of the three cDNAs that were characterized are abundantly expressed only in the Harderian gland and contain putative signal sequences for secretion, which makes them candidates for transporter proteins secreted from the HG. One is a member of the large lipocalin family of proteins, based on its similarity to other members of that protein family. Many lipocalins are binding/carrier proteins for a variety of ligands. The other is a family of proteins, with five members identified so far, all of unknown structure and function and present in the garter snake genome but not in other squamate genomes.

A major review on disorders of the animal lacrimal drainage systems: Evolutionary perspectives and comparisons with humans.

PURPOSE: To provide a systematic review of the literature on the disorders and management of the lacrimal drainage system (LDS) in few of the species of the animal kingdom. METHODS: The authors performed a PubMed search of all articles that were published in English with specific reference to lacrimal drainage disorders in animals. Data captured include demographics, presentations, investigation, diagnoses and management modalities. Emphasis was also on anatomical differences, evolutionary perspectives and addressing the lacunae and potential directions for future research. RESULTS: The lacrimal drainage system is a terrestrial adaptation in vertebrates. Evolutionary development of the LDS is closely linked to the Harderian gland and the vomeronasal organ. Variable differences in the clinical presentations and management of lacrimal drainage disorders (LDD) are noted in comparison to humans. These are secondary to unique structural and pathophysiological differences. Uniformity in usage and reporting of disease terminologies is required. Diagnostic challenges in clinical examination can be met with the development of customized lacrimal instruments. Contrast dacryocystorhinography is a very useful investigation in the diagnosis of LDD. Multiple bypass procedures like conjunctivorhinostomy, conjunctivobuccostomy and conjunctivomaxillosinosotomy have been described for nasolacrimal duct obstruction (NLDO). Advances of endoscopy and radiological techniques are paralleled by minimally invasive lacrimal interventions. The search for an ideal animal model for human LDS is far from over and the choice of the animal needs to be customized based on the research objectives. CONCLUSION: The lacrimal drainage system is an ancestral feature in tetrapod vertebrates and it is present, in some form or another, in most descendant species. The lacrimal drainage system has evolved considerably, adapting to the needs of the species. It is essential to understand the lacrimal drainage disorders of domestic animals so that the animal and human lacrimal sciences contribute more meaningfully to each other.

Structure of the external auditory meatus of the Bowhead whale (Balaena mysticetus) and its relation to their seasonal migration.

The external auditory meatus (EAM) in many species of mysticete whales is filled with a waxy ear plug. Though this lamellated structure is often used to age a whale, its formation and development remain undescribed. It is thought that growth layer groups (GLGs) are laid down annually, thereby increasing the size of this structure. Since some mysticete whales are migratory and many undergo molting, we hypothesized that the cyclical production of these GLGs may be related to these processes. The epithelia of both EAM and glove finger (a part of the tympanic membrane protruding into the EAM) of one juvenile and multiple adult bowhead whales from both fall (October: non-molting) and spring (May: molting) seasons were dissected and examined anatomically and histologically. These tissue samples were compared with the adult oral epithelia at the same time periods. These epithelia shared a similar basic broad structure, though there were differences in thickness and presence of intraepithelial structures. All epithelia in the October specimens were rich in both glycogen and lipid. The parakeratinized epithelium of the oral cavity in the juvenile and some May specimens shed via the production of several superficial epithelial fissures. Other adult May specimens exhibited deep epithelial fissures, reminiscent of pressure ulcers, which would cause the detachment of the entire epithelium from the dermis. We propose that sloughed epithelial lining is the source of the GLGs in the ear plug. Correlating a potential molting sequence with these observations explained the presence of epidermal glycogen, deep epidermal fissures and dermal glycolipid, and to some extent calls into question the origin and structure of the ear plug itself. Further morphological characterization of ear plugs in bowheads is needed to better understand cell origin and ear plug formation.

Ontogeny of the Orbital Glands and Their Environs in the Pantropical Spotted Dolphin (Stenella attenuata: Delphinidae).

The nasolacrimal duct (NLD) connects the orbital (often associated with the Deep Anterior Orbital gland: DAOG, a.k.a. Harderian gland) and nasal regions in many tetrapods. Adult cetaceans are usually said to lack an NLD, and there is little agreement in the literature concerning the identity of their orbital glands, which may reflect conflicting definitions rather than taxonomic variation. In this study, we examined an embryological series of the pantropical spotted dolphin (Stenella attenuata), and report numerous divergences from other tetrapods. Underdeveloped eyelids and a few ventral orbital glands are present by late Stage (S) 17. By S 19, circumorbital conjunctival glands are present. In S 20, these conjunctival glands have proliferated, eyelids (and scattered palpebral glands) have formed, and a duct similar to the NLD has appeared. Subsequently, both the palpebral glands and the NLD are progressively reduced by S 22, even as the conjunctival glands exhibit regional growth. In most tetrapods examined, the ontogeny of the NLD follows a series of three stages: Inception of NLD, Connection of orbit and nasal cavity by the NLD and Ossification (i.e., formation of the bony canal surrounding the NLD, emerging into the orbit via the lacrimal foramen in the lacrimal bone). In contrast, the dolphin NLD originates at the same time as the lacrimal bone, and a lacrimal foramen fails to develop. The cetacean fossil record shows that a lacrimal foramen was present in the earliest ancestral amphibious, freshwater forms, but was soon lost as the lineage invaded the oceans. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:77-87, 2018. © 2017 Wiley Periodicals, Inc.

Membranous Support for Eyes of Strepsirrhine Primates and Fruit Bats.

Living primates have relatively large eyes and support orbital tissues with a postorbital bar (POB) and/or septum. Some mammals with large eyes lack a POB, and presumably rely on soft tissues. Here, we examined the orbits of four species of strepsirrhine primates (Galagidae, Cheirogaleidae) and three species of fruit bats (Pteropodidae). Microdissection and light microscopy were employed to identify support structures of the orbit. In bats and primates, there are two layers of fascial sheets that border the eye laterally. The outer membrane is the most superficial layer of deep fascia, and has connections to the POB in primates. In fruit bats, which lacked a POB or analogous ligament, the deep fascia is reinforced by transverse ligaments. Bats and primates have a deeper membrane supporting the eye, identified as the periorbita (PA) based on the presence of elastic fibers and smooth muscle. The PA merges with periostea deep within the orbit, but has no periosteal attachment to the POB of primates. These findings demonstrate that relatively big eyes can be supported primarily with fibrous connective tissues as well as the PA, in absence of a POB or ligament. The well-developed smooth muscle component within the PA of fruit bats likely helps to protrude the eye, maintaining a more convergent eye orientation, with greater overlap of the visual fields. The possibility should be considered that early euprimates, and even stem primates that may have lacked a POB, also had more convergent eyes than indicated by osseous measurements of orbital orientation. Anat Rec, 299:1690-1703, 2016. © 2016 Wiley Periodicals, Inc.

Early development and differentiation of the Laysan albatross (Phoebastria immutabilis (Rothschild, 1893): Procellariiformes).

Bird incubation is subdivided into two phases: differentiation (embryonic phase) and growth (fetal phase). Most birds have a relatively short incubation period (20-30 days) with the phase transition occurring midway through the incubation period. The Laysan albatross (Phoebastris immutabilis) is a large pelagic bird with a long incubation period. The purpose of this study was to document the differentiation phase with the aim of ascertaining the impact of a lengthened incubation on embryonic development. Eighty-two previously collected albatross embryos were examined, measured, and staged. The albatross was found to develop more slowly than smaller birds, with a rate similar to other long-incubating birds. Legs and wings grow at similar rates but exhibit variation in growth among their anatomical components. While the albatross embryos shared some morphological stages with chickens, they were more similar to ducks and pelicans. Special features of the albatross not shared with the Gallianserae (chickens and ducks) included an alligator-like curved tail, narial tubes, and a cloacal bulge. Further examination of other larger pelagic birds with long incubation periods are needed to determine the uniqueness of the Laysan albatross embryonic development. Although much embryonic phase growth was documented in the postnatal period, little is known about the later, fetal phase in Laysan albatross. Future studies should involve examination of later (post day 32) fetuses. J. Morphol. 277:1231-1249, 2016. © 2016 Wiley Periodicals, Inc.

Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function.

The nasolacrimal apparatus (NLA) is a multicomponent functional system comprised of multiple orbital glands (up to four larger multicellular exocrine structures), a nasal chemosensory structure (vomeronasal organ: VNO), and a connecting duct (nasolacrimal duct: NLD). Although this system has been described in all tetrapod vertebrate lineages, albeit not always with all three main components present, considerably less is known about its ontogeny. The Mongolian gerbil (Meriones unguiculatus) is a common lab rodent in which the individual components of the adult NLA have been well studied, but as yet nothing is known about the ontogeny of the NLA. In this study, serial sections of 15 fetal and three adult Mongolian gerbil heads show that the development of the NLA falls into three fetal stages: inception (origin of all features), elongation (lengthening of all features), and expansion (widening of all features). No postnatal or juvenile specimens were observed in this study, but considerable growth evidently occurs before the final adult condition is reached. The development of the orbital glands and the VNO in the Mongolian gerbil is largely consistent with those in other mammals, despite a slight nomenclatural conundrum for the anterior orbital glands. However, the Mongolian gerbil NLD follows a more circuitous route than in other tetrapods, due mainly to the convoluted arrangement of the narial cartilages, the development of a pair of enlarged incisors as well as an enlarged infraorbital foramen. The impact of these associated features on the ontogeny and phylogeny of the NLA could be examined through the approach of network science. This approach allows for the incorporation of adaptations to specific lifestyles as potential explanations for the variation observed in the NLA across different tetrapod clades.

An examination of the sensory structures in the oral cavity of the American alligator (Alligator mississippiensis).

The location and distribution of mucosal sensory structures of the crocodilian oral cavity are poorly understood. Although there are several descriptions of these structures in adults, nothing is known about their development. The purpose of this study was to document location, morphology, and relative abundance of these mucosal sensory structures in both hatchling and subadult alligators. Numerous mucosal sensory structures and pale staining dome-shaped papillae were observed only in the upper palate and tongue. In hatchlings, these papillae, which house either mechanoreceptive or chemosensory (taste buds) structures, were larger and more prevalent on the tongue than the upper palate. In the subadult, however, these papillae housed primarily mechanoreceptive structures and possibly degenerate taste buds. Although the presence of the mechanoreceptive structures in the palates of the suabadult alligator are to be expected, the loss of most taste buds is hitherto undocumented. Thus, there is morphological support for an ontogenetic shift in the role of the sensory palate, from a prey detection gustatory sensory system in hatchlings to a prey-manipulative mechanoreceptive system in subadults.

Mapping bone cell distributions to assess ontogenetic origin of primate midfacial form.

Midfacial reduction in primates has been explained as a byproduct of other growth patterns, especially the convergent orbits. This is at once an evolutionary and developmental explanation for relatively short snouts in most modern primates. Here, we use histological sections of perinatal nonhuman primates (tamarin, tarsier, loris) to investigate how orbital morphology emerges during ontogeny in selected primates compared to another euarchontan (Tupaia glis). We annotated serial histological sections for location of osteoclasts or osteoblasts, and used these to create three-dimensional "modeling maps" showing perinatal growth patterns of the facial skeleton. In addition, in one specimen we transferred annotations from histological sections to CT slices, to create a rotatable 3D volume that shows orbital modeling. Our findings suggest that growth in the competing orbital and neurocranial functional matrices differs among species, influencing modeling patterns. Distinctions among species are observed in the frontal bone, at a shared interface between the endocranial fossa and the orbit. The medial orbital wall is extensively resorptive in primates, whereas the medial orbit is generally depositional in Tupaia. As hypothesized, the orbital soft tissues encroach on available interorbital space. However, eye size cannot, by itself, explain the extent of reduction of the olfactory recess. In Loris, the posterior portion of medial orbit differed from the other primates. It showed evidence of outward drift where the olfactory bulb increased in cross-sectional area. We suggest the olfactory bulbs are significant to orbit position in strepsirrhines, influencing an expanded interorbital breadth at early stages of development.

A re-examination and re-evaluation of salamander orbital glands.

The amphibian integument contains numerous multicellular glands. Although two of these, the nasolabial and orbital glands and the associated nasolacrimal duct (NLD), have historically received considerable attention, interpretation of the original observations can be problematic in the context of current literature. Salamanders, in particular, are frequently regarded as at least indicative of aspects of the morphology of the common ancestor to all extant tetrapods; hence, an understanding of these glands in salamanders might prove to be informative about their evolution. For this study, the orbitonasal region of salamanders from three families was histologically examined. Three themes emerged: (1) examination of the effect of phylogeny on the nasolabial gland and NLD revealed a combination of features that may be unique to plethodontid salamanders, and may be correlated to their nose-tapping behavior by which substances are moved into the vomeronasal organ; (2) ecology appears to impact the relative development of the orbital glands, but not necessarily the nasolabial gland, with smaller glands being present in the aquatic species; (3) the nomenclature of the salamander orbital gland remains problematic, especially in light of comparative studies, as several alternate possibilities are viable. From this nomenclatural conundrum, however, it could be concluded that there may be a global pattern in the location of tetrapod orbital gland development. Molecular questions in terms of ontogeny and genetic homology affect the nature of the debate on orbital gland nomenclature. These observations suggest that rather than reflecting an ancestral condition, salamanders may instead represent a case of specialized, convergent evolution.

Histology of melanic flank and opercular color pattern elements in the Firemouth Cichlid, Thorichthys meeki.

Dark melanic color pattern elements, such as bars, stripes, and spots, are common in the skin of fishes, and result from the differential distribution and activity of melanin-containing chromatophores (melanophores). We determined the histological basis of two melanic color pattern elements in the integument of the Firemouth Cichlid, Thorichthys meeki. Vertical bars on the flanks were formed by three layers of dermal melanophores, whereas opercular spots were formed by four layers (two lateral and two medial) in the integument surrounding the opercular bones. Pretreatment of opercular tissue with potassium and sodium salts effectively concentrated or dispersed intracellular melanosomes. Regional differences in epidermal structure, scale distribution, and connective tissues were also identified.

Eye size at birth in prosimian primates: life history correlates and growth patterns.

BACKGROUND: Primates have large eyes relative to head size, which profoundly influence the ontogenetic emergence of facial form. However, growth of the primate eye is only understood in a narrow taxonomic perspective, with information biased toward anthropoids. METHODOLOGY/PRINCIPAL FINDINGS: We measured eye and bony orbit size in perinatal prosimian primates (17 strepsirrhine taxa and Tarsius syrichta) to infer the extent of prenatal as compared to postnatal eye growth. In addition, multiple linear regression was used to detect relationships of relative eye and orbit diameter to life history variables. ANOVA was used to determine if eye size differed according to activity pattern. In most of the species, eye diameter at birth measures more than half of that for adults. Two exceptions include Nycticebus and Tarsius, in which more than half of eye diameter growth occurs postnatally. Ratios of neonate/adult eye and orbit diameters indicate prenatal growth of the eye is actually more rapid than that of the orbit. For example, mean neonatal transverse eye diameter is 57.5% of the adult value (excluding Nycticebus and Tarsius), compared to 50.8% for orbital diameter. If Nycticebus is excluded, relative gestation age has a significant positive correlation with relative eye diameter in strepsirrhines, explaining 59% of the variance in relative transverse eye diameter. No significant differences were found among species with different activity patterns. CONCLUSIONS/SIGNIFICANCE: The primate developmental strategy of relatively long gestations is probably tied to an extended period of neural development, and this principle appears to apply to eye growth as well. Our findings indicate that growth rates of the eye and bony orbit are disassociated, with eyes growing faster prenatally, and the growth rate of the bony orbit exceeding that of the eyes after birth. Some well-documented patterns of orbital morphology in adult primates, such as the enlarged orbits of nocturnal species, mainly emerge during postnatal development.

The orbitofacial glands of bats: an investigation of the potential correlation of gland structure with social organization.

The facial glands of bats are modified skin glands, whereas there are up to three different orbital glands: Harderian, lacrimal, and Meibomian glands. Scattered studies have described the lacrimal and Meibomian glands in a handful of bat species, but there is as yet no description of a Harderian gland in bats. In this study we examined serial sections of orbitofacial glands in eight families of bats. Much variation amongst species was observed, with few phylogenetic patterns emerging. Enlarged facial glands, either sudoriparous (five genera) or sebaceous (vespertilionids only) were observed. Meibomian and lacrimal glands were present in most species examined (except Antrozous), though the relative level of development varied. Two types of anterior orbital glands were distinguished: the Harderian gland (tubulo-acinar: observed in Rousettus, Atribeus, Desmodus and Miniopterus) and caruncular (sebaceous: observed in Eptesicus and Dieamus). The relative development of the nasolacrimal duct and the vomeronasal organ did not appear to be correlated with the development of any of the exocrine glands examined. There does, however, appear to be a correlation between the presence of at least one well developed exocrine gland and the level of communality and known olfactory acuity, best documented in Artibeus, Desmodus, and Miniopterus.

"A new lachrymal gland with an excretory duct in red and fallow deer" by Johann jacob Harder (1694): English translation and historical perspective.

The Harderian gland is an enigmatic orbital gland that has been described for many tetrapods, although a consistent definition of this structure has remained elusive. In particular, an unambiguous distinction between the Harderian gland and the nictitans gland, which may both occur in the anterior aspect of the orbit of mammals, remains problematic. These glands were first distinguished in 1694 by Johann Jacob Harder, a Swiss physician and anatomist. To facilitate a renewed examination of the anatomical and developmental relationships of the anterior orbital glands, we review the historical context of Harder's discovery, and provide Harder's original Latin text as well as an English translation.

The primate Harderian gland: Does it really exist?

The Harderian gland, an anterior orbital structure, is either absent or vestigial in primates. This is based upon gross anatomical observations of scattered adult specimens. Though largely absent in the adult human, it is present in the fetal and neonatal stages. Thus, histological examination of the orbital region of neonatal material was undertaken in other primates. The orbital region of neonatal specimens of 12 species of strepsirrhines (Lemuriformes and Lorisiformes), and haplorhine (tarsiers and callitrichids) was examined. The Harderian gland is ensconced in either periorbital fat or connective tissue and thus was not readily identifiable gross anatomically. Thus, it may have been missed in the anatomical studies. Tarsal glands are present in all neonatal primate eyelids. The relative size of the neonatal primate Harderian gland can be subdivided into five separate categories, ranging from large to absent (tarsiers), with no apparent phylogenetic trends. Thus, the Harderian gland is present in numerous primates at birth, quite possibly all strepsirrhines. The positive findings on callitrichids question whether any anthropoids lack the Harderian gland postnatally. The enigmatic tarsier appears to possess another apomorphic trait in lacking a Harderian gland. Further study is required to determine the role of this gland and its relationship with the tarsal glands.

Morphology of the Harderian gland of some Australian geckos.

This study of the morphology, histology, histochemistry, and ultrastructure of the Harderian gland in Geckos (Squamata, Gekkota) revealed previously unreported variation. The gecko Harderian gland is unlike that of other squamates in that each cell of the secretory epithelium has both lipid and protein secretory granules. Lipid secretion has not been reported previously for the squamate Harderian gland. The structure of the protein granules resembles that described for a scincomorph lizard (Podarcis, Lacertidae). Differences between representatives of the subfamilies Gekkoninae and Diplodactylinae suggest possible phylogenetic constraints in the structure or function of Harderian glands within gekkotan lineages. The structural relationship between the Harderian gland and the lacrimal duct supports previous suggestions of a possible functional link between the Harderian gland and the vomeronasal organ. J Morphol 231:253-259, 1997. © 1997 Wiley-Liss, Inc.