104 A Sketch of Comparative Embryolegy, [¥February, 
Like the eggs, or thelybiasts, the spermatozoa are developed out 
of cells, each cell forming not one sexual element, 
as in the case of the egg, but several. Hence sev- 
eral young elements appear within the interior of 
one cell at once; therefore this one cell is called 
the spermatocyst} while the young elements which 
are to become spermatozoa, are called spermato- 
blasts, and lie within the mother-cell or the cyst. 
The spermatoblasts appear at first as cell-like, 
spherical bodies, which may multiply by division 
Fic. 7.—Sper- within the mother-cell. Their development pro- 
matophore of ; ; x 
Cyclops quadri- gresses in the ordinary type of spermatozoon by a 
et s cubrane gradual elongation, the nucleus forming the greater 
shell; ss, part of the head, and the protoplasm, the tail, as 
Spermatozoa. has been described in the Narurauist for July, 
1877 (p. 397). These changes are so striking that they have 
absorbed the attention of investigators; hence the relation of the 
spermatoblasts to the parent-cell has been far less studied than its 
importance demands. At present, certainly, it is impossible to 
give any general account of the development of the spermatozoa. 
I shall, therefore, confine myself to a résumé of Semper’s obser- 
vations of the process in the sharks, his being the most complete 
special account of which I know. The principal stages are rep- 
resented in Fig. 8, which are taken from eee stained 
with hzmatoxiline. 
In the earliest stage the spermatic follicle, or ampulla, a, is a 
cavity occupied by the remnants of a cell, which soon disappears. 
This cavity is lined bya layer of cells with large spherical, granular 
nuclei, and enclosed by an outer layer of cells with smaller dark, 
oval nuclei. The inner layer alone is directly concerned in the for- 
mation of the spermatozoa. In each one of the inner cells, which 
are the spermatocysts, the nucleus begins to multiply, as shown 
in 4, c, d, e, dividing every time into two parts, one of which 
remains at the inner extremity of the cell and preserves the 
character of the parent nucleus, while the other recedes towards 
the outer end. The parent nucleus then again divides, until finally 
the spermatocyst contains one mother nucleus (smutterkern), and 
several daughter nuclei, which are easily distinguished by their 
1 The term spermatocyst has been used in various senses, but I believe the defini- 
tion above en accords with the usage most widely accepted. 
