SPERMATOGENESIS OF SQUILLA ORATORIA a20 
9. How the tetrads are formed could not be determined. | It 
is probable that the tetrad arises by two successive longitudinal 
splittings of each bivalent chromatin thread. 
10. The number of chromosomes appearing in the division of 
the primary spermatocyte is twenty-four. 
11. The chromatoid body may be found throughout all of 
these sucessive spermatogonial and spermatocyte stages, scarcely 
undergoing any modification; during mitoses it is situated out- 
side the spindle. 
12. After the division of the secondary spermatocyte the 
nucleus exhibits a reticular appearance and then, after going 
through a series of fairly complicated changes, it becomes uni- 
versely granular in appearance and loose in consistency. 
13. The centrosome wanders toward the nucleus and becomes 
completely enclosed within the latter. 
14. A vacuole appears in the cytoplasm and enlarges to 
occupy by far the greater part of the cell, so that the nucleus 
becomes quite eccentric in situation, and finally comes into 
contact with the cell membrane. 
15. The centrosome within the nucleus is divided into two 
halves, of which one representing the proximal centrosome 
becomes rod-shaped, while the other, representing the distal 
centrosome, remains unmodified. 
16. Hand in hand with the changes of the centrosome, the 
nucleus increases its consistency and stains very heavily, and, 
further, appears entirely homogeneous and compact. 
17. A conical prominence representing the perforatorium 
develops from the nucleus at the point where this is in associa- 
tion with the cell membrane, and the rod-shaped proximal cen- 
trosome takes the axial position in it. 
18. In the spermatid are a chromatoid body and a mito- 
chondrial mass; they do not appear to play any important part 
in the formation of the mature spermatozoon. 
19. The mature spermatozoon is a spherical vesicular cor- 
puscle, at one pole of which the head is attached; the head 
consists of two distinct parts, namely, a main part with homo- 
geneous consistency and a subordinate part, or the _perfora- 
