SPERMATOGENESIS OF THE HORSE. 297 



together. The finer details of the cells, too, were not as easily 

 made out as in the other material, this being undoubtedly due to 

 the fact that the material was not fixed until about an hour after 

 it was removed from the animal. The chromatoid body, how- 

 ever, was very distinct and could be traced throughout its entire 

 history the same as in the more favorable material. The acces- 

 sory chromosome, too, could easily be identified, especially 

 through the first spermatocyte division. 



III. GENERAL ARRANGEMENT OF THE GERM CELLS. 



The structure of the testes of the horse differs from the pig 

 in that the seminiferous tubules as well as the corresponding 

 cells in the various degrees of development are much smaller 

 and the interstitial cells are much fewer in number. The con- 

 tinuous network of connective tissue walls is present, but the 

 chambers formed by this network and filled with coiled tubules 

 are much larger in the horse and, therefore, a section through one 

 of the chambers as a rule reveals many more sections of the 

 tubules. These chambers in the horse testes do not show the 

 same regularity in size as is the case in the pig testes. In 

 some cases a group of over a hundred sections through the 

 tubules are surrounded by the connective tissue wall and then 

 again a count of only a dozen or so can be made. The arrange- 

 ment of the cells in the tubules is similar to that of the other well- 

 known mammals, particularly the pig. 



IV. SPERMATOGONIA. 



As a rule the spermatogonia lie in a single layer next to the 

 wall of the tubule, though occasionally some of the cells are 

 crowded out. At times the cells are far apart, in which case they 

 are flattened out on the tubule wall. The cells also differ con- 

 siderably in size and appearance, depending on the stage of 

 development they are in (Figs. 1-3). 



During the resting stages a large nucleolus is invariably 

 present. As a rule it assumes a somewhat heart-shaped appear- 

 ance; especially is this true in the larger cells and in those in 

 which the chromosomes are beginning to form. A much smaller 

 spherical nucleolus also appears to be fairly constant (Figs. I 



