6 



The Unity of the Organism 



The centrioles (2, figure 37) are "almost always double and 

 occupy a place in the spermatid close beneath the surface of the 

 cell." ' The pair is typically so placed that the axis joining them 

 is perpendicular to the surface of the spermatid, the member 



a.f. 



FIGURE 39. SPERMATID OF FUR SEAL (AFTER OLIVER). 



h.c., head cap. n., nucleus, p.c., proximate centriole. d.c., distal 

 centriole. a.f., axial filament, s., remnant of sphere. 



toward the surface being known as the distal centriole and the 

 one toward the center of the spermatid the proximal centriole 

 (figure 39 d.c. and p.c.). 



As to the part played by each of these in the development of 



FIGURE 40. SPERMATID OF FUR SEAL (AFTER OLIVER). 



n., nucleus, c.h., chromatin granules, c.t.f., caudal tube filaments. 



the sperm we learn that after migrating inward until they 

 come to lie very near the nucleus, if not in actual contact with 

 it, the centrioles begin their development with the following out- 

 come: "The proximal centriole . . . divides into two portions, 

 closely adherent to the nuclear wall, each connected by a fila- 

 ment to one distal group. The distal centriole divides into an 



