208 GERM-CELL CYCLE IN ANIMALS 



a posterior region which becomes an ovary or testis. 

 Bidder's Organ persists in the adult of males, where 

 it lies just anterior to the testis, but in the females 

 of Bufo variabilis, B. cinereus, B. clamita, and B. 

 lentiginosus it disappears at the end of the second 

 year. Bu^o vulgaris seems to differ from the other 

 species since here Bidder's Organ persists, becom- 

 ing small and shrunken during the winter (Ognew, 

 1906) and regenerating during the summer months 

 (Knappe, 1886). At first the cells in both the 

 anterior and posterior portions of the genital ridge 

 are similar, all possessing a polymorphic nucleus, 

 and dividing mitotically, but later those of Bidder's 

 Organ begin to divide amitotically and assume the 

 characteristics of young oocytes with rounded nuclei. 

 Knappe (1886) claims that these cells never become 

 functional ova because they are unable to form yolk. 

 King (1908), however, does not consider this prob- 

 able, but traces their differentiation to irregularities 

 in the synizesis stage. 



By most investigators Bidder's Organ is regarded 

 as a rudimentary ovary. Others believe that the 

 Amphibia were derived from hermaphroditic ances- 

 tors and that in the male it is a rudimentary ovary 

 and in the female a rudimentary testis. This seems 

 more probable than Marshall's suggestion that this 

 organ is the result of degenerative processes proceed- 

 ing backward from the anterior end of the genital 

 ridge, or than that it represents the remains of a 

 sex gland possessed by the larvae of ancestral toads 

 when they were paedogenetic, as Axolotl is at the 



