EFFECTS OF GONAD GKAFTS IN CHICKS 17 



ostium is the last to disappear." My observations agree in 

 general with this statement. The process of retrogression does 

 not proceed regularly from the posterior end, but begins in one 

 or several places in the ducts irregularly so that intact portions 

 are left between thread-like degenerated portions. The anterior 

 end at the level of the wolffian body remains intact longer than 

 other regions of the ducts in most embryos. The time at which 

 retrogression begins is more or less variable; sometimes the 

 process has already begun in six-day old embryos while in other 

 cases one duct, but generally not both, may still persist in twelve 

 or thirteen-day-old embryos in a nearly intact condition. In 

 the majority of cases the right miillerian duct retrogresses more 

 rapidly than the left one. Both ducts completely disappear 

 between the seventeenth day of incubation and the time of 

 hatching. 



In the female, the left miillerian duct persists and continues 

 to develop, eventually differentiating into a functional oviduct. 

 The process of degeneration of the right duct is, hoTvever, quite 

 different from that in the male. 



The degeneration of the right miillerian duct was investigated 

 by Gasser C74). Gasser states that the duct ceases to develop 

 soon after the eighth day; that by the twelfth day it is no longer 

 present in the region of the sex-glands; by the fifteenth day it 

 has disappeared from the region occupied by the wolffian body, 

 and that after this time there remain only traces of the duct 

 along its course together with a small lumen close to the cloaca. 

 According to my observations, however, the degeneration of the 

 duct does not take place as regularly as described by Gasser. 

 In the first place it is somewhat doubtful that the development 

 of the duct ceases after the eighth day; a differentiation of the 

 posterior end, a widening similar to that occurring in the left 

 duct, is always noticeable subsequent to this time. In fact, 

 this differentiation of the posterior end may continue for a con- 

 siderable length of time, even though degeneration is progressing 

 at the anterior end. Consequently, in advanced stages, after 

 retrogression is completed, the posterior end of the right miiller- 

 ian duct is still present as a short widened tube with a small 



