102 EIGHTEENTH REPORT. 



THE PKOCESS OF OVrLATION IN AMPHIBIA. 



BERTRAM G. SMITH. 



Ill all vertebrates, there is discoiitinuity between tUe ovaries and 

 the ducts which convey the eggs to the exterior — a lack of adapta- 

 tion which becomes intelligible only in the light of studies con- 

 cerned with the origin and evolution of the coelomic cavity. In 

 the higher vertebrates, the approximation of the funnel-shaped 

 inner end of the oviduct to the ovary safeguards to a considerable 

 extent the passage of the eggs into their proper channel; but in 

 the amphibia the two organs are widely separated, and the prob- 

 lem of how the eggs find their way into the oviduct has been a 

 puzzling one. As a result of some observations on Cryptobranchus 

 and Rana pipiens, I have become convinced that the generally-ac- 

 cepted explanation of this process is incorrect. In connection with 

 this study some observations of minor importance were made on 

 the escape of the eggs from the ovary of Cryptobranchus. 



1. The escape of the eggs from the ovary. Judging from the 

 published accounts, direct observations on the escape of the am- 

 phibian egg from the ovary are rare. Brandt ('76) examined the 

 outer surface of the ovary of Rana temporaria as the eggs were 

 about to pass into the body cavity and found a small round hole 

 above each egg through which a larger or smaller part of the egg 

 protruded. Recently I have observed various stages of the process 

 in several different adult females of Cryptobranchus which had been 

 killed by pithing and the body cavity iminediatelj^ opened. 



A very small portion of the egg first protrudes as a minute 

 spherical exovate connected by a very narrow stalk with the re- 

 mainder of the egg which is still covered by the ovarian wall and 

 follicle. Very slowly the exovate becomes larger. Under the con- 

 ditions noted the process has not been observed to go very far; 

 perhaps the pressure of surrounding parts on the ovary, and 

 especially the movements of the viscera during locomotion, are 

 normally required to comjjlete the ex])ulsion of the egg. But slight 

 pressure with an instrument on the portion bf the egg still in the 

 ovary completes the process as follows: The exovate increases in 

 size until it equals the part of the egg still in the ovary; at this 

 time the egg is shaped like an hour-glass. Then the enclosed part 

 of the egg flows out with remarkable suddenness, and the entire 



