CHANGES IN REPRODUCTIVE CELLS OF ELASMOBRANCHS, 279 
splitting in this threadwork or the granules which com- 
pose it, like that given by Brauer! in the corresponding stage 
of the spermatogenesis of Ascaris. The individual granules 
(microsomes) become completely massed together into axial 
cores, from which delicate filamentous radii of linin (figs. 12, 
13, /.) spread in all directions, and the continuation of this me- 
tamorphosis in the chromatin results eventually in the for- 
mation of one or two long chromatin threads coiled round the 
inner surface of the nuclear membrane (figs. 14, 15), the nu- 
cleolus lying a little more within. 
These threads, as soon as they are found, break up appa- 
rently simultaneously into twenty-four bent rods, which form 
the twenty-four chromatic elements characteristic of the 
divisions of the first spermatogenetic period ; and at the same 
time the nucleolus, becoming smaller and smaller, breaks up 
and disappears. 
6. Concomitantly with the above intra-nuclear changes, the 
centrosomes, originally occupying the focus of the cytoplasmic 
radiations, separate from one another and pass successively 
through the positions represented in ¢., figs. 11, 12, 13, 14. 
Owing to the absence of the archoplasmic constituent of the 
sphere, there is in these cells no real archoplasmic spindle 
formation (as in the spermatocytes of Salamandra described 
by Hermann’). Each centrosome, with its crown of radiations, 
simply travels away from the other, until, at the period of the 
nuclear evolution reached in the last paragraph, they lie on 
opposite sides of the nucleus, with almost the whole diameter 
of the cell between them (cf. c., figs. 12, 13, 14). 
7. As soon as the cytoplasmic conditions just described have 
been attained, the nuclear wall becomes irregular and dis- 
appears, while the chromosomes, collecting under the con- 
traction of their connecting linin filaments, form a long oval 
mass stretched across the nuclear sap between the centrosomes 
(figs. 15, 16, 17). 
1 «Zur Kenntniss der Spermatogenese von Ascaris megalocephala,” 
‘Arch. fiir mikr. Anat.,’ Bd. xlii, pp. 153—208, figs. 3—5, Taf. xi. 
9° 
2 «Arch. fiir. mikr. Anat.,’? Bd. xxxvii. 
