302 J. E. WODSEDALEK. 



VII. SPERMATIDS. 



The division of the secondary spermatocytes gives rise in the 

 one case to spermatids containing nine chromosomes (Figs. 46, 

 55 and 56), and in the other case nine plus the one accessory or 

 ten chromosomes (Figs. 39-41). All of the chromosomes except 

 the accessory are bivalent in nature (Figs. 23-41, 54-56), so 

 that in reality we have the equivalent of eighteen chromosomes 

 in the one kind of spermatid and eighteen plus the accessory in 

 the other. All of the foregoing evidences indicate that eighteen 

 is the reduced number of chromosomes. 



The accessory is usually out of the main mass of chromosomes 

 (Figs. 40 and 41). Soon after the secondary spermatocyte di- 

 vides the chromosomes become massed together and the nuclear 

 wall begins to form (Figs. 57-59). In the resting stage half the 

 spermatids contain a large nucleolus which is the same thing as 

 the accessory chromosome, since it can be traced through all 

 the stages in the formation of the nucleus (Figs. 63-65). The 

 other half of these cells lack such a body (Fig. 62). In some 

 cases this nucleolus persists in the developing stages of the 

 spermatozoon (Figs. 72 and 73). Especially is this true in 

 material which has not been destained too much. In favorably 

 stained material the centrosome surrounded by a clear layer can 

 be seen within the centrosphere (Figs. 64-66). The chromatoid 

 body is still very distinct (Figs. 55-67). 



VIII. DEVELOPMENT OF THE SPERMATOZOA. 



The development of the spermatozoon in the horse is essen- 

 tially the same as the development of the spermatozoon in the 

 pig (Wodsedalek, '13). The centrosome surrounded by a clear 

 area emerges from the sphere (Fig. 67) and soon divides into two 

 spherical bodies (Fig. 68). The anterior one comes in contact 

 with the nuclear wall, while the posterior one which remains 

 spherical passes down the developing axial filament (Figs. 69, 

 70, 71, 73, 74). This posterior body which is quite small never 

 assumes the shape of a ring as it does in the pig. It passes far 

 down the filament and often no trace of it is left (Fig. 79). Then 

 again it retains a size just enabling detection (Fig. 73). As a 

 rule, however, a sufficient amount of it is left to be sloughed off 



