SPERMATOGENESIS OF THE HORSE. 309 



in the equatorial plate it most generally takes a position near 

 them (Figs. 15 and 18), and when the spindle is formed, in a 

 large majority of the cases, it takes a position in, on or near the 

 spindle (Figs. 21-28) as is the case in Pentatoma (Wilson, '13). 

 This, however, is not always the case, for occasionally it is far 

 away from the spindle (Figs. 20 and 29). 



It was in the primary spermatocyte division that the chroma- 

 toid body was first observed. It attracted my attention at the 

 very first glance at the material under low power of the micro- 

 scope and its constant appearance in this stage led me to suppose, 

 at first, that it may be an accessory chromosome. Soon, how- 

 ever, the large, heart-shaped accessory was discovered and for 

 some time I had the impression that this was the .XT-chromosome 

 and the small spherical body the F-chromosome. This tem- 

 porary, erroneous impression was obtained through the peculiar 

 fact that in about ninety per cent, of the cases the chromatoid 

 body passes over to the half of the dividing cell opposite from 

 that containing the large accessory, and in almost a hundred 

 of the first mitotic stages examined not a single case was noticed 

 in which the spherical body was on the same side of the equatorial 

 plate with the accessory chromosome. Even when the first 

 case in which both of the bodies were seen on their way to the 

 same pole was observed, the matter was not taken very seriously. 

 Later, however, when more such cases were seen, my suspicion 

 was aroused and further observations convinced me that besides 

 the supposed ^-chromosome a body identical to it was present. 

 And it was not until the entire history of the body could be traced 

 from the growth-period to the casting-off of the mass of cytoplasm 

 in the final stages of the developing spermatozoon, that I was 

 absolutely certain that the suspicious looking element and the 

 supposed y-chromosome were one and the same thing, namely, 

 the chromatoid body, first described by Wilson in insects. 



In exceptionally rare cases, one (Figs. 23 and 26) or two other 

 small, deeply staining bodies within clear vacuoles occur in the 

 cytoplasm (Fig. 27). However, in cases where such bodies do 

 occur, there is no appreciable difference in the size of the chro- 

 matoid body and therefore it is difficult to determine whether 

 such bodies are simply portions split off from the chromatoid 



