SPERMATOGENESIS OF THE HORSE. 307 



much collapsed, owing to the large number of developing sperms 

 which they have nourished. This migration of the sperm back- 

 ward is probably nothing more than a chemotactic response to 

 the food contained in the balls of cytoplasm. 



XI. THE CHROMATOID BODY. 



The behavior of the chromatoid body in the horse bears a 

 striking resemblance to the behavior of the chromatoid body 

 described in Pentatoma (Wilson, '13). Dr. Wilson treats the 

 subject at considerable length in his paper and therefore much of 

 the detail concerning this body in the horse may safely be omitted. 

 However, all the more essential features will be presented here 

 since this is the first case among the vertebrates, according to 

 my knowledge, w^here such an element has been studied in full 

 detail. The reader is advised to familiarize himself with Pro- 

 fessor \Vilson's article in order to appreciate fully the surprising 

 similarity existing in the behavior of the chromatoid body in 

 such diverse classes of animals as the insects and the mammals. 



In speaking of the chromatoid body Professor Wilson ('13) 

 says in part, "As seen during the growth-period and the spermato- 

 cyte-divisions it is of rounded form, dense and homogeneous 

 consistency, and after double staining with hsematoxylin or 

 safranin and light green is at every stage colored intensely blue- 

 black or brilliant red, precisely like the chromosomes of the 

 division-period or the chromosome-nucleoli of the growth-period. 

 In the first spermatocyte-division it may lie anywhere in the cell, 

 sometimes almost at the periphery, but is often close beside the 

 chromosomes. In the latter case it usually lies in, on or near the 

 spindle, lags behind the chromosomes during the anaphases, and 

 in later stages is found near one pole, presenting an appearance 

 remarkably like that of an accessory chromosome (Figs. 8-10). 

 For such in fact I mistook it, even after the discovery that a 

 similar body is often also seen near one pole in the second division 

 (Figs. 22, 23); for I supposed this might be a case like that of 

 Ascaris megalocephala, where, according to Edwards ('10) the 

 .^-chromosome may pass undivided to one pole in either the 

 first or second division. The resemblance is indeed most decep- 

 tive; and these division-figures have often been exhibited to 



