106 J. M. ESSENBERG. 



to say, but merely wishes to point out that the claim is inappli- 

 cable in case of Xiphophorus helleri. The primordial germ cells 

 reach the body cavity en masse by passive displacement brought 

 about by developmental processes of adjacent musculature and 

 at no time do germ cells fuse with cells of peritoneal epithelium. 



Causes of Sex-Reversal. 



A case of complete sex-reversal in ring dove was described by 

 Riddle (1923). The autopsy revealed that the viscera of the 

 bird were seriously affected by tuberculosis which, together with 

 other cases observed by Riddle, led him to the conclusion that 

 tuberculosis is the immediate cause of sex-reversal. Based on 

 the fact that the male bird has a higher metabolic rate than the 

 female, Riddle assumes that the function of tuberculosis is to 

 increase the metabolic rate of the diseased female bird. When 

 once the metabolic rate has been increased, the diseased animal, 

 according to Riddle, has nothing to prevent it from acquiring 

 the anatomy and physiology of the opposite sex. 



The data gathered from fishes undergoing sex-reversal do not 

 seem to favor the claim that there is an increase of metabolic 

 rate prior to, or during, transformation of sex. Indeed there 

 are definite indications that the opposite is true. The trans- 

 forming fishes become very inactive, probably take no food 

 during early stages and are incapable of adapting themselves to 

 changing environment even if the change be very slight. 



Another case of complete sex-reversal in birds was describe 

 by Crew (1923). This bird, a Buff Orpington hen, was als( 

 affected with tuberculosis of the viscera. Crew claims that 

 sex-reversal is preceded by some disease such as tuberculosis, 

 hemorrhage, tumor growth, etc. The disease affects the ovarian 

 secretion and the general metabolism of the bird in such a way 

 that the conditions favorable for the differentiation and growth 

 of spermatic tissue are created. 



It is definitely known that the fishes described in this paper 

 were not diseased, certainly not by tuberculosis. Every trans- 

 formed fish has been sacrificed to establish this very point. 

 A number of diseased fishes have been observed, but none of 

 these have become subject to sex-reversal. A case of complete 



