Microanatomical characteristics of marginal ommatidia in three different size-classes of the semi-terrestrial isopod Ligia exotica (Crustacea / Isopoda)

The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone-, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (= frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length).

Microanatomical characteristics of marginal ommatidia in three different size-classes of the semi-terrestrial isopod Ligia exotica (Crustacea / Isopoda)

The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone-, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (= frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length). (AU)

Possible natural circaseptan rhythm in the beach beetle Chaerodes trachyscelides white.

Activity rhythms in groups of captive beach beetles (Chaerodes trachyscelides White) have been recorded in an actograph over a period of 29 days. Under constant illumination and when no sand was provided for the beetles to burrow in abnormal behaviour occurred. With sand and in constant darkness a strictly nocturnal activity period with apparently circaseptan components superimposed was observed. The beetles in their natural habitat are confined to the debris zone where they feed on washed up seaweed and this debris zone moves up and down depending on the heights of the tides. Circaseptan elements in the beetles' activity may act as adaptations to the weekly alternations between spring- and neap-tides.

Electron microscopy in Jamaica: applications and techniques.

Although the electron microscope was developed about 60 years ago in Germany, its arrival and subsequent use in Jamaica are of considerably more recent date. In this paper, the principles of scanning and transmission electron microscopy (SEM & TEM) are briefly explained, and examples are given of the research done with the electron microscopes at the University of the West Indies (UWI), Mona Campus, Jamaica, especially over the last three years. Detailed descriptions of specimen preparation are provided for both SEM and TEM and particular emphasis is placed on the methodology used in our laboratory, as it sometimes differs from the routine followed in electron microscopy units of temperate countries.

A system of regular ridges instead of nipples on a compound eye that has to operate near the diffraction limit.

A system of regular, radial ridges, spaced approx. 250 nm apart, is reported from the outer corneal surface of the eye of the tiny moth Leucoptera coffeella. Antireflective coatings in larger insects with flatter facets often take the form of corneal nipples. However, evidence is presented that in an insect whose eyes have to operate near the lower diffraction limit and possess strongly convexly-curved corneae a radial arrangement of microridges is just as effective as nipples--and simpler to construct.

Red-white muscle distribution and fibre growth dynamics: a comparison between lacustrine and riverine populations of the southern smelt Retropinna retropinna Richardson.

The myotomal musculature of the common New Zealand smelt Retropinna retropinna from a lacustrine and a riverine population was investigated in an attempt to correlate differences in the fish's maximum body size and migratory habits with differences in muscle morphology and growth dynamics of their component muscle fibres. Based on measurements of cross sections through the fish at 70% fork length, a significant increase in red muscle percentage is recorded between pre- and post-migratory stages in the riverine population. Although lacustrine and pre-migratory riverine smelt possess similar white: red muscle ratios, the red muscle increase in post-migratory, riverine smelt is explained by the requirement for sustained swimming during upstream migration. The growth dynamics of red fibres also appear to be related to functional requirements such as sustained swimming. The slower rates of growth and smaller maximum size (dwarfing) exhibited by lacustrine smelt of basically riverine stock in comparison with diadromous, riverine smelt, are attributed to differences in white fibre growth dynamics. The recruitment of new fibres into the growing muscle mass ceases to be of significance at a shorter fork length in the dwarfed lacustrine form of smelt, with the subsequent result of larger mean diameters of white fibres at all fork lengths compared with those of the riverine form. Hypertrophy of white fibres gradually diminishes in both forms as the mean diameters of white fibres approach 100 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Cephalic structures in the nemertine Parborlasia corrugatus-Are they really eyes?

The opinion as to whether tiny, approximately 0.1 mm large spots around the innermost margin of the cephalic slits in the Antarctic nemertine worm Parborlasia corrugatus represent photoreceptors or not has fluctuated over the years. This first electron microscope study of the enigmatic spots fails to detect any screening pigment granules, rhabdomeres, or lamellae, but reveals that the structure in question is principally made up of two types of cell, characterized by vesicular and vacuolar material of approximately 80 nm and 0.3 mum in diameter, respectively. Filamentous connective tissue strands with gaps for axons surrounds the 'eye-spot' and it is suggested that either exposure to the bright Antarctic summer light has led to a total disintegration of all visual membranes or these structures do not represent eyes at all.

Crystals in supporting cells of pineal organ in larval lamprey not likely to be pure guanine.

Spectrophotometry of larval pineal organs, digested in either 1 M HCl or 1 M NaOH, revealed peak absorbances at 253 nm and 268 nm, respectively. This result is not consistent with the view that the crystals found in lamprey pineals are chemically made of guanine.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis.

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Observations on an accidental case of raw sewage pollution in Antarctica.

The effects of an accidental exposure to saltwater polluted by human wastes on aquarium populations of a variety of Antarctic organisms are described. Only the giant Antarctic slater Glyptonotus antarcticus survived the exposure to the contaminated water unharmed. A comparative analysis of water qualities revealed that total nitrogen and phosphorus levels of the contaminated sample were 15 and 19.5 times higher than those of the control and that the contaminated sample contained high amounts of coliform bacteria, whereas the latter were not identified in the control. Considering the widespread practice in Antarctica of disposing of raw sewage into the sea, the dearth of knowledge concerning the biological impact of such behaviour is seen as worrysome.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis.

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Crystals in supporting cells of pineal organ in larval lamprey not likely to be pure guanine.

Spectrophotometry of larval pineal organs, digested in either 1 M HCl or 1 M NaOH, revealed peak absorbances at 253 nm and 268 nm, respectively. This result is not consistent with the view that the crystals found in lamprey pineals are chemically made of guanine.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis.

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Crystals in supporting cells of pineal organ in larval lamprey not likely to be pure guanine.

Spectrophotometry of larval pineal organs, digested in either 1 M HCl or 1 M NaOH, revealed peak absorbances at 253 nm and 268 nm, respectively. This result is not consistent with the view that the crystals found in lamprey pineals are chemically made of guanine.

Crystals in supporting cells of pineal organ in larval lamprey not likely to be pure guanine

Spectrophotometry of larval pineal organs, digested in either 1 M HCl or 1 M NaOH, revealed peak absorbances at 253 nm and 268 nm, respectively. This result is not consistent with the view that the crystals found in lamprey pineals are chemically made of guanine.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Crystals in supporting cells of pineal organ in larval lamprey not likely to be pure guanine

Spectrophotometry of larval pineal organs, digested in either 1 M HCl or 1 M NaOH, revealed peak absorbances at 253 nm and 268 nm, respectively. This result is not consistent with the view that the crystals found in lamprey pineals are chemically made of guanine.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Nephroblastoma in the clawed frog Xenopus laevis.

One 2.5-3 year old female clawed frog (Xenopus laevis), out of a consignment of 4,000 frogs, was found to have an abnormal abdominal growth, weighing 7.9 g. The growth was examined histologically and on the basis of the abundant stroma and serially-arranged tubules nephroblastoma was diagnosed. The growth is not considered to be transmissible.