The role of androgens in clitorophallus development and possible applications to transgender patients.

BACKGROUND: The clitorophallus, or glans, is a critical structure in sexual development and plays an important role in how gender is conceptualized across the life span. This can be seen in both the evaluation and treatment of intersex individuals and the use of gender-affirming masculinizing therapies to help those born with a clitoris (small clitorophallus with separate urethra) enlarge or alter the function of that structure. OBJECTIVES: To review the role of testosterone in clitorophallus development from embryo to adulthood, including how exogenous testosterone is used to stimulate clitorophallus enlargement in masculinizing gender-affirming therapy. MATERIALS AND METHODS: Relevant English-language literature was identified and evaluated for data regarding clitorophallus development in endosex and intersex individuals and the utilization of hormonal and surgical masculinizing therapies on the clitorophallus. Studies included evaluated the spectrum of terms regarding the clitorophallus (genital tubercle, clitoris, micropenis, penis). RESULTS: Endogenous testosterone, and its more active metabolite dihydrotestosterone, plays an important role in the development of the genital tubercle into the clitorophallus, primarily during the prenatal and early postnatal periods and then again during puberty. Androgens contribute to not only growth but also the inclusion of a urethra on the ventral aspect. Exogenous testosterone can be used to enlarge the small clitorophallus (clitoris or micropenis) as part of both intersex and gender-affirming care (in transmasculine patients, up to 2 cm of additional growth). Where testosterone is insufficient to provide the degree of masculinization desired, surgical options including phalloplasty and metoidioplasty are available. DISCUSSION AND CONCLUSION: Endogenous testosterone plays an important role in clitorophallus development, and there are circumstances where exogenous testosterone may be useful for masculinization. Surgical options may also help some patients reach their personal goals. As masculinizing gender-affirming care advances, the options available for clitorophallus modifications will likely continue to expand and improve.

Clitoral length in immature and mature captive tufted capuchin (Sapajus spp.) females: A cross-sectional study.

Quantitative data on female external genital morphology are sporadic in the primate literature, and the intraspecific and interfemale variation is especially under investigated (e.g., external clitoris length). Since in most anthropoid primate species female external genitals are relatively small and often hidden, for those species whose external clitoris is described as hypertrophic, external genital resemblance may represent a source of confusion in distinguishing the sexes at a distance. This is the case of both captive and wild tufted capuchin (Sapajus spp.) infants. We provided data on external clitoral length and investigated differences in this trait at different ages in a captive female tufted capuchin population. Since likely allometric growth describes changes in relative dimensions of parts of the body that are correlated with changes in overall size, clitoris length has been analyzed by using body weight as a covariate. We measured clitoral length by adapting a technique developed for spotted hyenas (Crocuta crocuta). Our results suggest that the small body size may be only in part responsible of the perception of long clitoris in female infants, since the clitoris is actually longer in immature females compared to adult ones and its size is inversely related to body weight. While the cross-sectional nature of these data does not allow for conclusive interpretation of the results, we tentatively suggest this phenomenon as a transient male-mimicry by immature females. Our study contributed to the description of normative data in a clitoral trait, thus providing foundation for future studies about causal mechanisms and possible adaptive function(s).

Hot spots in fetal human penile and clitoral development.

To better understand how the human fetal penis and clitoris grows and remodels, we undertook an investigation to define active areas of cellular proliferation and programmed cell death spatially and temporally during development of human fetal external genitalia from the indifferent stage (8 weeks) to 18 weeks of gestation. Fifty normal human fetal penile and clitoral specimens were examined using macroscopic imaging, scanning electron microscopy and immunohistochemical localization for the cellular proliferation and apoptotic markers, Ki67 and Caspase-3, respectively. A number of hot spots of cellular proliferation characterized by Ki67 localization are present in the penis and clitoris especially early in development, most notably in the corporal body, glans, remodeling glanular urethra, the urethral plate, the roof of the urethral groove and the fully formed penile urethra. The 12-fold increase in penile length over 10 weeks of growth from 8 to 18 weeks of gestation based on Ki67 labelling appears to be driven by cellular proliferation in the corporal body and glans. Throughout all ages in both the developing penis and clitoris Ki67 labeling was consistently elevated in the ventral epidermis and ventral mesenchyme relative to the dorsal counterparts. This finding is consistent with the intense morphogenetic activity/remodeling in the ventral half of the genital tubercle in both sexes involving formation of the urethral/vestibular plates, canalization of the urethral/vestibular plates and fusion of the urethral folds to form the penile urethra. Areas of reduced or absent Ki67 staining include the urethral fold epithelium that fuses to form the penile tubular urethra. In contrast, the urethral fold mesenchyme is positive for Ki67. Apoptosis was rarely noted in the developing penis and clitoris; the only area of minimal Caspase-3 localization was in the epithelium of the ventral epithelial glanular channel remodeling.

Clitoral development in the mouse and human.

The goal of this report is (a) to provide the first detailed description of mouse clitoral development, and (b) to compare mouse and human clitoral development. For this purpose, external genitalia of female mice were examined by wholemount microscopy, histology and immunohistochemistry from 14 days of gestation to 10 days postnatal. Human clitoral development was examined by these techniques as well as by scanning electron microscopy and optical projection tomography from 8 to 19 weeks of gestation. The adult mouse clitoris is an internal organ defined by a U-shaped clitoral lamina whose development is associated with the prenatal medial and distal growth of the female preputial swellings along the sides of the genital tubercle to form the circumferential preputial lamina. Regression of the ventral aspect of the preputial lamina leads to formation of the U-shaped clitoral lamina recognized as early as 17 days of gestation. While the adult U-shaped mouse clitoral lamina is closely associated with the vagina, and it appears to be completely non-responsive to estrogen as opposed to the highly estrogen-responsive vaginal epithelium. The prominent perineal appendage in adult females is prepuce, formed via fusion of the embryonic preputial swellings and is not the clitoris. The human clitoris is in many respects a smaller anatomic version of the human penis having all of the external and internal elements except the urethra. The human clitoris (like the human penis) is derived from the genital tubercle with the clitoral glans projecting into the vaginal vestibule. Adult morphology and developmental processes are virtually non-comparable in the mouse and human clitoris.

Immunohistochemical expression analysis of the human fetal lower urogenital tract.

We have studied the ontogeny of the developing human male and female urogenital tracts from 9 weeks (indifferent stage) to 16 weeks (advanced sex differentiation) of gestation by immunohistochemistry on mid-sagittal sections. Sixteen human fetal pelvises were serial sectioned in the sagittal plane and stained with antibodies to epithelial, muscle, nerve, proliferation and hormone receptor markers. Key findings are: (1) The corpus cavernosum in males and females extends into the glans penis and clitoris, respectively, during the ambisexual stage (9 weeks) and thus appears to be an androgen-independent event. (2) The entire human male (and female) urethra is endodermal in origin based on the presence of FOXA1, KRT 7, uroplakin, and the absence of KRT10 staining. The endoderm of the urethra interfaces with ectodermal epidermis at the site of the urethral meatus. (3) The surface epithelium of the verumontanum is endodermal in origin (FOXA1-positive) with a possible contribution of Pax2-positive epithelial cells implying additional input from the Wolffian duct epithelium. (4) Prostatic ducts arise from the endodermal (FOXA1-positive) urogenital sinus epithelium near the verumontanum. (5) Immunohistochemical staining of mid-sagittal and para-sagittal sections revealed the external anal sphincter, levator ani, bulbospongiosus muscle and the anatomic relationships between these developing skeletal muscles and organs of the male and female reproductive tracts. Future studies of normal human developmental anatomy will lay the foundation for understanding congenital anomalies of the lower urogenital tract.

Development of the human penis and clitoris.

The human penis and clitoris develop from the ambisexual genital tubercle. To compare and contrast the development of human penis and clitoris, we used macroscopic photography, optical projection tomography, light sheet microscopy, scanning electron microscopy, histology and immunohistochemistry. The human genital tubercle differentiates into a penis under the influence of androgens forming a tubular urethra that develops by canalization of the urethral plate to form a wide diamond-shaped urethral groove (opening zipper) whose edges (urethral folds) fuse in the midline (closing zipper). In contrast, in females, without the influence of androgens, the vestibular plate (homologue of the urethral plate) undergoes canalization to form a wide vestibular groove whose edges (vestibular folds) remain unfused, ultimately forming the labia minora defining the vaginal vestibule. The neurovascular anatomy is similar in both the developing human penis and clitoris and is the key to successful surgical reconstructions.

Evidence of vagus nerve sprouting to innervate the urinary bladder and clitoris in a canine model of lower motoneuron lesioned bladder.

AIMS: Complete spinal cord injury does not block perceptual responses or inferior solitary nucleus activation after genital self-stimulation, even though the vagus is not thought to innervate pelvic structures. We tested if vagus nerve endings sprout after bladder decentralization to innervate genitourinary structures in canines with decentralized bladders. METHODS: Four reinnervation surgeries were performed in female hounds: bilateral genitofemoral nerve transfer to pelvic nerve with vesicostomy (GNF-V) or without (GFN-NV); and left femoral nerve transfer (FNT-V and FNT-NV). After 8 months, retrograde dyes were injected into genitourinary structures. Three weeks later, at euthanasia, reinnervation was evaluated as increased detrusor pressure induced by functional electrical stimulation (FES). Controls included un-operated, sham-operated, and decentralized animals. RESULTS: Increased detrusor pressure was seen in 8/12 GFNT-V, 4/5 GFNT-NV, 5/5 FNT-V, and 4/5 FNT-NV animals after FES, but not decentralized controls. Lumbar cord segments contained cells labeled from the bladder in all nerve transfer animals with FES-induced increased detrusor pressure. Nodose ganglia cells labeled from the bladder were observed in 5/7 nerve transfer animals (1/2 GNT-NV; 4/5 FNT-V), and from the clitoris were in 6/7 nerve transfer animals (2/2 GFNT-NV; 4/5 FNT-V). Dorsal motor nucleus vagus cells labeled from the bladder were observed in 3/5 nerve transfer animals (1/2 GFNT-NV; 2/3 FNT-V), and from the clitoris in 4/5 nerve transfer animals (1/2 GFNT-NV; 3/3 FNT-V). Controls lacked this labeling. CONCLUSIONS: Evidence of vagal nerve sprouting to the bladder and clitoris was observed in canines with lower motoneuron lesioned bladders. Neurourol. Urodynam. 36:91-97, 2017. © 2015 Wiley Periodicals, Inc.

Complex epithelial remodeling underlie the fusion event in early fetal development of the human penile urethra.

We recently described a two-step process of urethral plate canalization and urethral fold fusion to form the human penile urethra. Canalization ("opening zipper") opens the solid urethral plate into a groove, and fusion ("closing zipper") closes the urethral groove to form the penile urethra. We hypothesize that failure of canalization and/or fusion during human urethral formation can lead to hypospadias. Herein, we use scanning electron microscopy (SEM) and analysis of transverse serial sections to better characterize development of the human fetal penile urethra as contrasted to the development of the human fetal clitoris. Eighteen 7-13 week human fetal external genitalia specimens were analyzed by SEM, and fifteen additional human fetal specimens were sectioned for histologic analysis. SEM images demonstrate canalization of the urethral/vestibular plate in the developing male and female external genitalia, respectively, followed by proximal to distal fusion of the urethral folds in males only. The fusion process during penile development occurs sequentially in multiple layers and through the interlacing of epidermal "cords". Complex epithelial organization is also noted at the site of active canalization. The demarcation between the epidermis of the shaft and the glans becomes distinct during development, and the epithelial tag at the distal tip of the penile and clitoral glans regresses as development progresses. In summary, SEM analysis of human fetal specimens supports the two-zipper hypothesis of formation of the penile urethra. The opening zipper progresses from proximal to distal along the shaft of the penis and clitoris into the glans in identical fashion in both sexes. The closing zipper mechanism is active only in males and is not a single process but rather a series of layered fusion events, uniquely different from the simple fusion of two epithelial surfaces as occurs in formation of the palate and neural tube.

Development of the external genitalia: perspectives from the spotted hyena (Crocuta crocuta).

This review/research paper summarizes data on development of the external genitalia of the spotted hyena, a fascinating mammal noted for extreme masculinization of the female external genitalia. The female spotted hyena is the only extant mammal that mates and gives birth through a pendulous penis-like clitoris. Our studies indicate that early formation of the phallus in both males and females is independent of androgens; indeed the phallus forms before the fetal testes or ovaries are capable of synthesizing androgens. Likewise, pre- and postnatal growth in length of the penis and clitoris is minimally affected by "androgen status". Nonetheless, several internal morphologies, as well as external surface features of the phallus, are androgen-dependent and thus account for dimorphism between the penis and clitoris. Finally, estrogens play a critical role in penile and clitoral development, specifying the position of the urethral orifice, determining elasticity of the urethral meatus, and facilitating epithelial-epithelial fusion events required for proper formation of the distal urethra/urogenital sinus and prepuce. Accordingly, prenatal inhibition of estrogen synthesis via administration of letrozole (an aromatase inhibitor) leads to malformations of the glans as well as the prepuce (hypospadias). The effects of prenatal androgens, anti-androgens and impaired estrogen synthesis correlated with the tissue expression of androgen and estrogen receptors.

Morphology of the external genitalia of the adult male and female mice as an endpoint of sex differentiation.

Adult external genitalia (ExG) are the endpoints of normal sex differentiation. Detailed morphometric analysis and comparison of adult mouse ExG has revealed 10 homologous features distinguishing the penis and clitoris that define masculine vs. feminine sex differentiation. These features have enabled the construction of a simple metric to evaluate various intersex conditions in mutant or hormonally manipulated mice. This review focuses on the morphology of the adult mouse penis and clitoris through detailed analysis of histologic sections, scanning electron microscopy, and three-dimensional reconstruction. We also present previous results from evaluation of "non-traditional" mammals, such as the spotted hyena and wallaby to demonstrate the complex process of sex differentiation that involves not only androgen-dependent processes, but also estrogen-dependent and hormone-independent mechanisms.

Effects of intramuscular testosterone undecanoate on body composition and bone mineral density in female-to-male transsexuals.

INTRODUCTION: The most common treatment regimen in female-to-male transsexuals is administration of short-acting testosterone esters intramuscularly every 2 weeks. AIM: The aim of this study was to evaluate the effect of long-acting intramuscular testosterone undecanoate on body composition and bone mineral density during cross-sex hormone therapy in female-to-male transsexuals. METHODS: Forty-five female-to-male transsexuals (FtMs) were treated with injections of testosterone undecanoate 1,000 mg intramuscularly every 12 weeks over 24 months. MAIN OUTCOME MEASURES: Body composition, bone mineral density, hormone parameters, and lipids were compared after 12 months and after 24 months with baseline values. Sonographic findings in the ovaries and endometrium, clinical and adverse effects during the study period were recorded. RESULTS: There was a significant increase in lean mass in the FtMs during the study period in comparison with baseline values, whereas no change in BMI, fat mass, and bone mineral density was observed. There was a significant decline in gonadotropins, estradiol, dehydroepiandrosterone sulphate, sex hormone-binding globulin, and high-density lipoprotein, while testosterone and triglyceride levels increased significantly after 12 and 24 months. Ovaries remained unchanged and no noticeable endometrial pathology was observed. No mortality or morbidity was observed during the study period. We observed a cessation of menstrual bleeding, an increase in clitoral growth, libido, body and beard hair growth, deepened voices and decline in breast size. There was a significant increase in hemoglobin, hematocrit, glutamic-pyruvic transaminase, gamma-glutamyl transferase, and an increase in systolic blood pressure during the study period. CONCLUSIONS: There was an increase in lean mass during the study period in FtMs treated with testosterone undecanoate. Transsexual patients should be monitored for adverse effects on lipid profiles, blood pressure, and erythrocytosis during intramuscular testosterone undecanoate therapy.

A high-resolution anatomical ontology of the developing murine genitourinary tract.

Cataloguing gene expression during development of the genitourinary tract will increase our understanding not only of this process but also of congenital defects and disease affecting this organ system. We have developed a high-resolution ontology with which to describe the subcompartments of the developing murine genitourinary tract. This ontology incorporates what can be defined histologically and begins to encompass other structures and cell types already identified at the molecular level. The ontology is being used to annotate in situ hybridisation data generated as part of the Genitourinary Development Molecular Anatomy Project (GUDMAP), a publicly available data resource on gene and protein expression during genitourinary development. The GUDMAP ontology encompasses Theiler stage (TS) 17-27 of development as well as the sexually mature adult. It has been written as a partonomic, text-based, hierarchical ontology that, for the embryological stages, has been developed as a high-resolution expansion of the existing Edinburgh Mouse Atlas Project (EMAP) ontology. It also includes group terms for well-characterised structural and/or functional units comprising several sub-structures, such as the nephron and juxtaglomerular complex. Each term has been assigned a unique identification number. Synonyms have been used to improve the success of query searching and maintain wherever possible existing EMAP terms relating to this organ system. We describe here the principles and structure of the ontology and provide representative diagrammatic, histological, and whole mount and section RNA in situ hybridisation images to clarify the terms used within the ontology. Visual examples of how terms appear in different specimen types are also provided.

Placental expression and molecular characterization of aromatase cytochrome P450 in the spotted hyena (Crocuta crocuta).

At birth, the external genitalia of female spotted hyenas (Crocuta crocuta) are the most masculinized of any known mammal, but are still sexually differentiated. Placental aromatase cytochrome P450 (P450arom) is an important route of androgen metabolism protecting human female fetuses from virilization in utero. Therefore, placental P450arom expression was examined in spotted hyenas to determine levels during genital differentiation, and to compare molecular characteristics between the hyena and human placental enzymes. Hyena placental P450arom activity was determined at gestational days (GD) 31, 35, 45, 65 and 95 (term, 110), and the relative sensitivity of hyena and human placental enzyme to inhibition by the specific inhibitor, Letrozole, was also examined. Expression of hyena P450arom in placenta was localized by immuno-histochemistry, and a full-length cDNA was cloned for phylogenetic analysis. Aromatase activity increased from GD31 to a peak at 45 and 65, apparently decreasing later in gestation. This activity was more sensitive to inhibition by Letrozole than was human placental aromatase activity. Expression of P450arom was localized to syncytiotrophoblast and giant cells of mid-gestation placentas. The coding sequence of hyena P450arom was 94% and 86% identical to the canine and human enzymes respectively, as reflected by phylogenetic analyses. These data demonstrate for the first time that hyena placental aromatase activity is comparable to that of human placentas when genital differentiation is in progress. This suggests that even in female spotted hyenas clitoral differentiation is likely protected from virilization by placental androgen metabolism. Decreased placental aromatase activity in late gestation may be equally important in allowing androgen to program behaviors at birth. Although hyena P450arom is closely related to the canine enzyme, both placental anatomy and P450arom expression differ. Other hyaenids and carnivores must be investigated to determine the morphological and functional ancestral state of their placentas, as it relates to evolutionary relationships among species in this important taxonomic group.

Development of the penis and clitoris in the tammar wallaby, Macropus eugenii.

The development of the phallus from the indifferent stage to sexual dimorphism has not been described in any marsupial. This study describes the morphological and histological changes occurring in the development of the phallus of the tammar wallaby. The development of the penis and clitoris in the tammar closely follow the most widely accepted model for the development of the same organs in eutherian mammals. The urogenital plate that is present in both sexes at birth hollows out to form a urogenital groove at approximately 70 days postpartum (p.p.). There is then greater growth of the phallus in males than in females, which results in sexual dimorphism in length approximately 100 days p.p. In males, the urogenital groove secondarily closes over at this time and fuses in the midline and by 128 days p.p. the penile urethra is fully formed. In females, the groove remains open. The clitoris changes little morphologically from the time of formation of the urogenital groove until adulthood. The pattern of development of the penis in the tammar is similar to that seen in eutherian mammals. There is strong evidence that penis development is androgen-dependent in the tammar, yet unusually it becomes sexually dimorphic at a time when androgen content of the developing testis is low.

Effects of prenatal testosterone on sexual behavior, reproductive morphology and LH secretion in the female rat.

Sexual differentiation of many brain structures and functions is dependent on levels of testosterone (T) or its metabolites during certain 'sensitive' developmental periods. If T is present during these perinatal periods, masculinization and defeminization of sexual behavior occur; also, reproductive physiology, and central nervous system morphology and function are altered. The purpose of the present study was to characterize the influence of T at specific prenatal developmental intervals on offspring reproductive morphology, physiology, locomotor activity and sexual behavior during postnatal development. To avoid complications induced by endogenous testicular activity, only females were examined. Free T was used because of its relative short half-life, so that the effects induced by its administration on a specific gestational day (GD) could be evaluated. Pregnant rats received a single subcutaneous injection of either sesame oil (controls) or 5 mg of T on GD 16, 17, 18, 19, 20, 21, or 22. Female offspring of pregnant rats exposed to T displayed significant alterations in morphology and behavior. The anogenital distance, measured at 25 days postbirth, was significantly increased if T was administered on GD 16, 17 or 18. T treatment on GD 16 or each day thereafter through GD 20 significantly delayed the normal occurrence of vaginal opening (controls at 37.5 days vs. T treatment which ranged from 38.5 to 41.4 days). Abnormal vaginal morphology (enlarged clitoris) was also observed when T was injected during a similar prenatal interval (i.e. GD 16 to GD 22). Furthermore, prenatal T treatment on GD 18 (and each day thereafter), until GD 22 significantly decreased lordotic behavior compared to control values. However, exposure to T, on any prenatal GD did not alter the animals' ability to exhibit an induced luteinizing hormone (LH) surge. These results suggest that the onset for altered reproductive morphology occurs at least as early as GD 16, whereas the onset of sexual behavior sensitivity occurs precisely at GD 18, and that the normal pattern of adult LH release in females is not altered by prenatal androgen treatment using this specific paradigm.

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 1. Infancy to sexual maturity.

This report is concerned with hormone concentrations accompanying sexual maturation in a highly 'masculinized' female mammal, the spotted hyaena, Crocuta crocuta. Plasma concentrations of testosterone, androstenedione and oestrogen were determined by radioimmunoassay in a longitudinal study of 12 female and eight male hyaenas 2.5-62.5 months old. Concentrations of testosterone were significantly higher in males than in females after 26.5 months of age, but earlier measurements did not differ between sexes. Mean testosterone concentrations in adult female hyaenas (0.4-0.5 ng ml-1) were similar to those in several other female mammals that do not display a 'masculine' profile, but mean concentrations of androstenedione (2.5-5.5 ng ml-1) in female hyaenas were significantly higher than in males (1.0-2.0 ng ml-1), at most ages. Oestrogen could not be detected (less than 0.03 ng ml-1) in females until about 14 months of age and then increased (to approximately 0.13 ng ml-1) between 18 and 30 months; oestrogen remained undetectable in males. This rise in oestrogen in females corresponded to nipple enlargement and to changes in the size and elasticity of the urogenital meatus, permitting copulation and parturition through the clitoris. Gonadectomy (two males and four females) at 4-7 months resulted in nondetectable concentrations of testosterone and oestrogen and a marked attenuation in androstenedione (to approximately 0.39 ng ml-1), indicating that the gonads are the major source of these three steroids. Gonadectomy also eliminated sex differences in weight, nipple development and elasticity of the urogenital meatus.

Differential effects of perinatal androgen treatment on sexually dimorphic characteristics in rats.

Rats were treated with testosterone propionate (TP) or oil (O) beginning in midgestation (group TTT), late gestation (group OTT), neonatally (group OOT), or were left untreated until adulthood (group OOO). At 40 days of age all animals were gonadectomized, received implants of TP in silastic capsules, and were tested in subsequent weeks for masculine copulatory behavior and ex copula phallic responses. Postmortem measures were taken of genital structures and of sexually dimorphic spinal nuclei. Males treated perinatally with androgen were unaffected or exhibited reduced masculinization except on two measures, i.e., number of penile flips and number of cells in the dorsolateral motor nucleus of the lumbar spinal cord, which reflected virilization greater than in normal males. All perinatally androgenized females showed virilization on almost every measure taken of their morphology and behavior. Relative to OOO females, the greatest increases in masculinization were evident in OOT and OTT females. No additional masculinization was detected in TTT females. Only among the TTT rats were males not reliably more masculine than females, but that usually was due to the reduced masculinization of TTT males. Four broad classes of influence characterized the effects of perinatal androgen treatment; these classes may reflect differences in the developmental courses of the variables measured.

Anterior hypothalamic lesions and pubertal development in female rhesus monkeys.

Electrolytic lesions were made in the anterior hypothalamus of 8 prepubertal female rhesus monkeys, aged 1.1-1.7 years. Six unoperated females served as controls. No effects were found of the lesions upon age and body weight at menarche or at first ovulation, as estimated by blood levels of progesterone and laparoscopic observations. From these findings it appears that the neural control of puberty in the female rhesus may not be exerted through the anterior hypothalamus, in contrast with the rat and ferret. Further, an attempt was made to identify biometric correlates of hormonal changes during puberty. Firstly, the well known dip in growth rate, about 0.4 years before menarche, was observed. Secondly, there was a marked spurt in growth of the nipples starting at 0.2 years before menarche. The close temporal association between accelerated nipple growth and menarche suggests that both of these developmental characteristics result from changes in (presumably ovarian) steroid hormone secretion.