578 



matozoa depending presumably upon whether the original spermatid 

 did or did not receive the odd chromosome. By careful focussing, 

 in favorable preparations, the head of the adult spermatozoon was 

 seen to contain a beading of highly refractive transparent masses 

 separated and surrounded by the more deeply staining portions of 

 the transformed nucleus as already described for the pigeon and the 

 guinea. Fig, 34 represents a portion of a head showing these bodies 

 or areas. 



As soon as the developing spermatozoa approach the mature con- 

 dition they shift in such a way as to become closely attached to the 

 nurse or Sertoli cell. There seems to be a mutual attraction between 

 the cytoplasm of this cell and the spermatozoa, for ordinarily the 

 former lies quiescent at or near the wall of the seminiferous tubule 

 but when spermatozoa are maturing it sends out a column of cyto- 

 plasm which extends inward between the adjacent cells until it meets 

 the spermatozoa that in the mean time have started to move toward 

 it. The head of the spermatozoa become deeply imbedded in the 

 cytoplasm of the Sertoli cell and seem to mingle their own cytoplasm 

 with it (Fig. 35) for there is no discernible boundary between the 

 two. Under such conditions the cytoplasmic mass of the Sertoli cell 

 seems to be considerably augmented and the nucleus may move inward 

 and take up a position nearer to the heads of the spermatozoa. At 

 this stage the cytoplasm of both the Sertoli cell and the developing 

 spermatozoa seems to be in a highly plastic condition and the boun- 

 daries are devoid of definite cell walls so that they readily fuse 

 together when they come into contact. Fig. 35 is drawn from a smear 

 preparation and shows the Sertoli cell and the imbedded heads of 

 the spermatozoa. The tails of the latter have been omitted from 

 the drawing. When the spermatozoon is finally mature the head is 

 considerably smaller than during its period of attachment to the 

 nurse cell. 



Summary. 



1) An accurate count of the spermatogonial chromosomes is very 

 difficult to make ; seventeen is probably the correct number, although 

 it is safer simply to affirm that there are not less than fifteen, nor 

 more than nineteen. 



2) Nine chromosomes ordinarily appear in the prophase of the 

 first division of the spermatocytes. Of these, eight are presumably 

 bivalent. The other which is the "odd" or "accessory" chromosome 

 has not paired at this time but is nevertheless probably a compound 

 body consisting of three elements. 



