296 J. E. S.. MOORE. 
cephalic point to the spermatazoon head. The nuclear jacket 
(figs. 88, 89, 90, .v.), formed by the sap separating the nuclear 
chromatin from the nuclear wall, continues well marked even 
at maturity, and the swelling on the cell membrane, where 
the flagellum originally passed out, remains (fig. 90, md.) as 
the little bead at the hinder end of the Mittelstiick. 
The spermatogenesis is now practically complete, and the 
facts of the second spermatogenetic period which appear to be 
of primary comparative importance are: 
I. The transformation of the cells of the first spermatogenetic 
period into those of the second, which I have termed the 
Synapsis, is accomplished while the celis are in complete 
repose, and is marked by a peculiar evolution in the chromatin 
with the formation of peculiar nucleoli (which are repeatedly 
characteristic of the succeeding cellular generations) and by the 
formation of an archoplasmic constituent round the centro- 
somes. 
II. The evolution during the prophases of the first and 
second divisions of the second spermatogenetic period of 
twelve ring chromosomes, which split transversely to form the 
same number, twelve, in each daughter-cell. 
III. The differentiation of the spindle during the diastral 
figure into an outer and an inner fibrous sheath, which coalesce, 
forming a delicate connecting thread between the attraction 
spheres of both daughter-cells. 
IV. The existence during the synapsis of a peculiar evolu- 
tion among the constituents of the attraction sphere, whereby 
the centrosomes are brought to its exterior surface, beneath 
the membrane of the cell. 
V. The repetition of the process in a more pronounced 
manner, after the first heterotype division in the second sperma- 
togenetic period, so that a short flagellum is protruded from 
the centrosomes through the membrane of the cell. 
VI. The origin of the long whiplash tail of the spermato- 
zoon in a similar manner, after a corresponding metamor- 
phosis of the sphere during the formation of the final cellular 
generation. 
