CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANGHS. 285 
apparently at rest, the cells have passed completely over from 
the first into the second spermatogenetic period. The com- 
mencement of this metamorphosis is marked by an increasing 
fineness of the reticulum in the nuclei, which continues to 
increase until cells with nuclear elements like that represented 
in fig. 835 are seen, and about the same time there appears a 
curious secondary nucleolus surrounded by a vacuole (fig. 31 n’), 
which, so far as I can ascertain, is in these fishes diagnostic of 
the change. After a while the nuclear threadwork again 
grows coarser and thicker, displaying at the same time a 
peculiar tendency to contract to one side of the nucleus, leaving 
a great clear space (fig. 39) across which stretch numerous 
linin filaments. The contraction is not so marked when the 
cells have been preserved with osmic acid, nor on the outside 
of sections which have been preserved with Flemming’s fluid, 
where the osmium has acted directly upon the cells. I have, 
however, seen it in elements of Torpedo which were simply 
immersed in dilute glycerine ; and whether it exists in nature 
or not, the cells display at this period, and at no other, a 
remarkable tendency to have their chromatin contracted, in 
consequence of some internal change which renders these 
nuclear figures diagnostic of the particular period in question. 
Similar figures have been obtained at corresponding periods in 
the spermatogenesis of Amphibia, Mammals, Nematodes,! 
and various Arthropods,’ and I do not think it probable that 
the contraction in many of these cases has anything to do with 
the reagents used. 
20. In the cytoplasm the conversion from the first to the 
second spermatogenetic period is marked by a gradual increase 
in the small dark zone about the centrosomes, until it eventu- 
ally attains the dimensions of a veritable spermatic ‘‘ Neben- 
kern” or archoplasm (figs. 85, 36,37), and from what has been 
said (§ 12) it follows that this body is here of an entirely 
cytoplasmic origin. The archoplasm, with its contained cen- 
1 Brauer, loc. cit. (pl. ix, figs. 12—18). 
2 See Toyama, “On the Spermatogenesis of the Silkworm,” ‘ Bull. Agric. 
Coll. Imp. University Tokio,’ vol. ii, No. 3, 1894, pl. iv, figs. 25, 26. 
