spermatogenesis 485 



the spireme in the growth period. One spermatocyte division is 

 reducing and the other equational. In the anaphase, the chromo- 

 somes again become massed together (Fig. 34) and the nucleus is 

 reconstructed by the formation of a nuclear membrane (Fig. 35). 

 The "Zwischenkorper" is again noticeable in this telophase. 



In the young spermatid (Fig. 36), the chromatin is still massed 

 together and stains deeply. The spindle material remains as the 

 "Nebenkern," as first described by v. La Valette St. George ('86) 

 for insect spermatids. The chromatin soon scatters through the 

 nucleus in definite clumps and it is evident that half of the sperma- 

 tids contain a smooth round darkly-staining body (Fig. 37), while 

 the other half do not (Fig. 38). Through several succeeding 

 stages, this same fact is noticeable; ;. e., when the chromatin 

 becomes more diffuse (Figs. 39 and 40), when it forms a pale net- 

 work and the axial filament has grown out (Figs. 41 and 42), and 

 even when the chromatin has begun to condense to form the head 

 of the spermatozoon (Figs. 43 and 44). The method of deter- 

 mining whether this body is in only half the cells or in all is as 

 follows: cysts of spermatids in various places were picked out and 

 the number of cells with and without this body were counted in 

 each cyst. In studying sections, it must be remembered that parts 

 of some cells are in another section, so even if this body (x) were 

 actually present in all the cells, it would not appear in all in any one 

 section of a cyst. On the same principle, if it were actually in only 

 half the cells, it would appear in less than half in any one section. 

 In Entilia, this body appears in a few less than half of the sperma- 

 tids. It always takes the chromatin stains, deep blue with thionin, 

 and green with the Auerbach. As it resembles the odd chromo- 

 some of the first spermatocyte rest stages in staining reaction and 

 contour, and as it appears in not more than one-half of the sperma- 

 tids, a condition which the odd chromosome necessarily fulfills 

 from the fact of its not dividing in the first spermatocyte division, 

 we seem to be justified in concluding that the body x of the sperma- 

 tids is a derivative of the odd chromosome of the spermatocyte. 

 There is nothing unusual about the formation of the spermatozoon. 

 The "Nebenkern" forms the sheath of the axial filament (Fig. 41), 

 the acrosome differentiates from the cytoplasm at the apex of the 



