THE AMPHIBIA OP OKLAHOMA 



actual time of ovulation is great, particularly during the summer. The breed- 

 ing period seems definitely to have passed in October. 



The cytological changes in the gonads which accompany the beginning 

 of breeding behavior in Bufo has been previously noted. 



Fisher and Richards noted peculiar nucleolar changes in the oocytes of 

 Acris crepitans. These changes are similar in gross features to those in B. 

 cognatus and B. w. woodhousii. Though no definite cyclic changes in the 

 ratio of small to large nucleoli were observed, there was a migration of 

 nucleoli from the outer edge of the nucleus toward the chromosomes and a 

 gradual increase in their abundance from the fall months to the next ovula- 

 tion period in July. They believed that these nuclear inclusions are probably 

 "chromatin nucleoli," clumps of chromatin migrating along linin threads to 

 several common points. 



Rogers (1942), in her study of the nucleolar changes accompanying 

 oocyte growth in the zebra fish, Brachydauio icrio, first described the young 

 nucleus as bearing one to five basophilic nucleoli which, though they remain 

 near the nuclear membrane almost constantly, undergo processes similar in 

 many respects to those which have been described for Bujo cognatus and 

 Bu]o w. woodhousii. Numbers of nucleoli increase by fragmentation, lose 

 their intense staining reaction, and become vacuolated. In B. rerio the 

 nucleolar events seem to indicate a utilization of this material during yolk 

 formation. 



While the nucleolar variations described in detail by Rogers are not 

 entirely the same as those indicated for B. cognatus and B. tv. woodhousii 

 in our section on the microscopic structure of the ovaries, they are paralleled 

 in an increase in the numbers of nucleoli, in small basophilic discharges (in 

 B. cognatus and B. w. woodhousii these are produced away from, as well as 

 toward, the center of the nucleus) and the disappearance of the nuclear 

 inclusions. 



Painter and Taylor (1940) described oocytes of a toad in which small 

 nucleolar-like bodies develop as pseudopods from the germinal vesicle during 

 yolk synthesis and are cut off into the cytoplasm. In a few oocytes of B. 

 cognatus, though not in B. w. woodhousii , a similar process was seen. The 

 infrequency of this occurrence indicates, however, that it is not a typical 

 feature in development, even in B. cognatus. 



The pattern by which yolk is deposited near the periphery of the cell 

 in fine granules and then in heavy spherules as accumulation continues to- 

 ward the nucleous is in keeping with that described for Acris crepitans. The 

 presence of "yolk nuclei" was originally described by King (1908) in Bujo 

 lentiginosus^ as "irregular, granular masses" appearing in the otherwise 

 homogeneous cytoplasm of young oocytes. These structures, which seemed 

 to arise from a previously formed generation of cytoplasmic bodies called 

 "vitelline bodies" by King, were believed by her to be responsible tor the 

 initiation of yolk formation in Bufo. Fisher and Richards failed to find 

 "vitelline bodies," but laid considerable stress on the function of the "yolk 

 1 Probably the toad nmv known as E. tcrrcstns amcru\uuis Holbrook. 



150 



