Fine structure in every stage of spermatogenic cells of the squalen shark, Centrophorus atromarginatus Garman, from Suruga Bay was observed by means of an electron microscope. Selachian spermatogenesis, as in other vertebrates, consists of two periods, spermiocytogenesis and spermiohistogenesis. The former is similar to that of mammalians but different from that of teleost fishes. While the latter has special characteristics compared to other vertebrates, especially in the form of mature spermatozoon. These two periods of selachian spermatogenesis are discussed in comparison with mammalians, reptilians, amphibians and teleost fishes.
Morphological and ecological studies on two forms of Oncorhynchus rhodurus Jordan et McGregor living in Lake Biwa and adjoining inlets were conducted. The fluviatile form (the amago) and the lacustrine form (the biwamasu) showed morphological differences in number of pyloric caeca, transverse scales, ventral fin rays and red spots on lateral body. The fluviatile form lives in the upper waters of inlets to Lake Biwa, but the lacustrine form leaves the streams as fry and lives in Lake Biwa almost all its life. In addition to this, there are ecological differences in maturity age, growth rate and food habits between the two forms. It is presumed that the fluviatile form and the lacustrine form living in this lake and adjoining inlets consist of different populations.
The leptocephali of Conger japonicus Bleeker are shallow-bodied, reaching125.5mm in standard length at the fully grown stages.The larvae are similar to those of C.myriaster (Brevoort) in general appearance and meristic characters except that they have a more slender body but do not have any conspicuous black spots on the midlateral body side.The developing leptocephali, longer than64mm, can be divided into two stages by the dentition and body size, and the meta-morphosing leptocephali, into five stages by the dentition, position of the origin of dorsal and anal fins, pigmentation and body size.The present study shows that metamorphosing leptocephali occur mainly from August to November.
In order to clarify the mechanism of osmoregulation of the larval red seabream Pagrus major (Temminck et Schlegel), chloride cells of the larvae were observed from immediately after hatching to 15 days using the silver staining technique.Numerous silver-stained cells, round or elliptical in shape and 7.5-14.9 μ in diameter, were noticed as black small bodies on the whole integument of larvae.The cross section indicated that these cells were found within the epithelium.The central part of silver-stained cells was more blackly stained, where a lip or rent-like structure was found as an orifice.The network binding the silver-stained cells was also observed on the body surface. The fluctuation of the number of silver-stained cells with different developmental stages was summarized as follows: The cells were already found on the all body surface in larvae im-mediately after hatching.Silver-stained cells increased in number up to 5 days, then decreased after about 8 days, and disappeared around 15 days after hatching. Silver-stained cells are likely to be chloride cells, according to previous findings.If this assumption is true, seabream larvae are provided with chloride cells in the epithelium of the skin to regulate osmotic pressure.