STUDIES ON THE CELLS OF CATTLE. 



were corroborated in the tissue obtained from cows and heifers, 

 although the adult tissue was not nearly as satisfactory. Most 

 excellent material was found in the ovaries of a four and a half 

 inch fcetus and one six-inch fcetus. These were fixed in the 

 Benin's plus chromic acid fixing fluid. The oogonia were ap- 

 parently in extreme activity at the time of fixation. Mitotic 

 figures are abundant and the chromosomes are very distinct, 

 especially in the late prophase and early metaphase stages which 

 are numerous (Figs. 44-46). In general these cells resemble the 

 last spermatogonial cells (compare Figs. 44 and 10), except that 

 the oogonia are somewhat larger. 



In well fixed and favorably stained material the oogonia in 

 the resting stage invariably show two large nucleoli each corre- 

 sponding to the single nucleolus of the resting stage of spermato- 

 gonial cells (Fig. 41). These retain their individuality during the 

 spireme stage though at times they are somewhat distended 

 (Fig. 42). When the spireme breaks up the chromosomes are 

 long and narrow and variously curved (Fig. 43). In the late 

 prophase they become shorter and thicker and appear evenly 

 distributed throughout the large nuclei (Figs. 44 and 45). In 

 this stage as well as in the early metaphase stages of division 

 (Fig. 46) hundreds of accurate counts were possible. The two 

 sex-chromosomes can be easily distinguished in all of the prophase 

 stages (Figs. 41-45). 



Thirty-eight chromosomes are present in the oogonia (Figs. 

 43-46). Thirty-six are the ordinary chromosomes corresponding 

 to the thirty-six ordinary chromosomes in the spermatogonia of 

 the male. The two other elements are the sex-chromosomes. 

 When the chromosomes arrange themselves in the equatorial 

 plate for division the sex-chromosomes are always at the 

 periphery (Figs. 46 and 47). During division all of the chromo- 

 somes, including the sex-elements, divide in two (Fig. 48). All 

 of the figures of the oogonial cells were made from the same 

 section (Figs. 41-48). 



On account of the great significance of the two sex-chromo- 

 somes in the femal tissue a tremenduous amount of time was 

 devoted to this particular phase of the problem; this was also 

 true of the studies in connection with the chromosomes of the 



