STUDIES ON THE CELLS OF CATTLE. 2Q5 



studied in this animal, only the phases pretaining to the chromo- 

 some numbers and their behavior are emphasized in this paper. 



i. Spermatogonia. 



The spermatogonia usually lie in a single layer next to the wall 

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

 out, thus forming a second layer which is always very irregular. 

 The cells which undergo the last spermatogonial division (Figs. 

 5-12) are usually beyond the first layer, though occasionally 

 they may be found next to the tubule wall along the entire 

 section of the tubule. At times the cells are far apart, in which 

 case they are flattened out on the tubule wall. The cells also 

 differ considerably in size and appearance, depending on the 

 stage of development they are in. 



During the resting stage a large nucleolus is invariably present. 

 As a rule it assumes a somewhat heart-shaped appearance; 

 especially is this true in the larger cells and in those in which the 

 chromosomes begin to form. At the conclusion of the resting 

 stage numerous large chromatin granules appear and arrange 

 themselves along fine threads in an entangled mass. The chro- 

 mosomes soon become distinct and mitotic figures are fairly 

 numerous. And while, as a rule, there is considerable over- 

 lapping and massing of the chromosomes in the early spermato- 

 gonial divisions, hundreds of cells were found in which there was 

 little or no overlapping, making accurate counts possible. 



Thirty-seven chromosomes appear in the late prophase of the 

 spermatogonial division (Fig. i). Thirty-six of these are vari- 

 ously shaped, mainly oblong or slightly curved, and differ 

 somewhat in size. One which is much larger is triangular in 

 form or heart-shaped. This is the accessory or sex-chromosome, 

 and is the same thing as the large nucleolus which appears in the 

 resting stages. This point is certain, as. the body can be easily 

 traced through the various stages of the cells. A similar condi- 

 tion was reported by Guyer ('10) in man, Wodsedalek in the pig 

 ('13) and in the horse ('14). Several other investigators have 

 reported it in other forms since. During division each chromo- 

 some, including the sex-chromosome, divides in two (Figs. 3 

 and 4). 



