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THE AMERICAN NATURALIST [Vol. LVI 



true nature of the embryonic male gonad lias sufficient 

 time to manifest itself before being supplanted by the 

 definitive gland. 



We come now to a discussion of the nature of Bidder's 

 organ in Bufo, for this is the classical example of ovi- 

 form degeneration of racially senescent germ cells. Here- 

 tofore, this embryonic sex gland rudiment has been re- 

 garded as characteristic of toads, but such is not the 

 case. In frogs the pro-testis or larval gonad is a Bid- 

 der's organ, destined to be replaced by the definitive male 

 gonad developing within ; in male toad larvae on the other 

 hand, the functional gonad arises behind the pro-testis 

 or Bidder's organ, consequently this structure persists 

 as a degenerate gonadic rudiment attached to the func- 

 tional gland. 



According to the writer's view, Bidder's organ in Bufo 

 is simply a vestigial larval gonad persisting throughout 

 life and has the same sex as the definitive gonad behind 

 it — male in males, female in females. It is just as 

 though the pro-nephros of tadpoles persisted as a non- 

 functional and degenerate rudiment at the end of the 

 mesonephros. That many such larval and embryonic 

 rudiments do persist through adult life in various ani- 

 mals is a commonplace of embryologj^ and their per- 

 sistence in one species and total disappearance in another 

 related one, is also well known. Bidder's organ in Bufo 

 then, is a persisting, in frogs a transitory, embryonic 

 sex gland rudiment, a relic of a phylogenetically earlier 

 sexual condition. The functional gonads are more re- 

 cently acquired structures (like the larval mesonephros) 

 superimposed upon the older degenerate glands. Briefly 

 stated, the evidence for the view that Bidder's organ is 

 homologous to the pro-testis of frogs and that it is not 

 a rudimentary ovary except in female animals is as fol- 

 lows : 



1. The cells of Bidder's organ in Bufo are unquestion- 

 ably germ cells. The gland appears very early in em- 

 bryonic life (two weeks after hatching) and its cells far 



