THE AMPHIBIA OF OKLAHOMA 



Ovaries of specimens collected during October (see Fig. 3) differ little 

 in general features from those of September. There is a small increase in the 

 average size of the oocytes. The only other change noted is a movement of 

 the chromatin nucleoli closer to the centers of the nuclei. 



An increase is found in the diameters of the largest oocytes and of the 

 predominant size of oocytes in the ovaries of frogs of November. (See Fig. 

 4.) A slight differentiation of cytoplasm is seen at this stage. "Yolk nuclei" 

 are few in number, but are occasionally found in the outer region of the cyto- 

 plasm; no general peripheral yolk concentration is seen, however. The chro- 

 matin nucleoli lie closer to the nucleus than in the oocytes of frogs collected 

 in October. 



No outstanding differences are seen between the ovaries of frogs fixed 

 in November and those of individuals of December collections. In the sec- 

 tions studied of the latter a slight retrogression in development is apparent. 

 Reference to comparative ovarian volumetric percentages of the two months 

 shows also a similar slight decrease for December. Cytoplasmic differentia- 

 tion is likewise a little less marked here. 



Ovaries of frogs collected and fixed during January contain oocytes in 

 a stage of growth and development approximately midway between those 

 of frogs taken in September and those taken during the summer months. 

 The range of variation in the sizes of oocytes of these frogs is not so great 

 as in those collected during the months closer to or during the breeding sea- 

 son. (See Table II.) The cytoplasm in the larger oocytes of frogs of January 

 is more dense around the periphery than in the inner region, due to the gath- 

 ering of yolk spherules in the former. No "yolk nuclei" are distinctly seen. 

 The cytoplasm of smaller oocytes, of course, shows no differentiation and 

 no sign of the presence of yolk. The nuclei, numerous at this time, are 

 grouped approximately midway between the periphery of the nucleus and 

 the chromosomes. These darkly staining nucleoli are of various sizes, the 

 larger several times that of the smaller. The chromosomes fit the general 

 description given in the preceding section, that is, they are feather-like in 

 appearance, lightly stained, and lie in the center of the nucleus. 



The mean diameter of oocytes of frogs fixed in February (see Fig. 5) 

 differs little from that of oocytes of frogs of January, although the range of 

 size is greater. The cytoplasm of the larger oocytes is becoming more dense 

 near the periphery. Cytoplasmic differentiation has not advanced far, but 

 the outer region is heavier with yolk than the region immediately surrounding 

 the nucleus. No change is noted in the appearance of the chromosomes, but 

 the chromatin nucleoli are more numerous and lie closer to the chromosomes. 



The general increase in size of the oocytes is considerable. As in all 

 months, however, very young oocytes are present. (See Fig.6.) The yolk in 

 the larger oocytes found during February, and the region of heavy yolk ex- 

 tends closer to the nucleus. Chromatin nucleoli lie slightly closer to the 

 chromosomes. 



The increase in the average size of oocytes in ovaries of frogs collected 

 during April over those found in March is less than was seen in the month 



136 



