102 CARNEGIE INSTITUTION OF WASHINGTON. 



have not assumed the summer plumage. Among the females there 

 was one individual, castrated late last fall when four weeks of age, 

 that is particularly interesting for two reasons. First, she has never 

 developed the duck's voice. Her usual voice is quite like that of the 

 drake, and even when especially stimulated, she only succeeds in 

 producing a sort of half quack. This bird did not assume the entire 

 plumage of the male, a few brown feathers remaining in the breast, 

 but after a molt early in the summer assumed the summer plumage 

 of the drake. Just at present she is undergoing a second molt and 

 this time is assuming the normal breeding-plumage of the male. This 

 is the first case that Dr. Goodale has found to behave in this way. 

 Another duck developed the plumage of the male perfectly, but, 

 although molting, did not take on the summer plumage of the male. 

 In respect to his experiments with fowl Dr. Goodale reports as 

 follows : 



Altogether, I have had eight pullets which have developed the male 

 plumage to a greater or less extent. One individual which was castrated 

 last summer was reported as having started to develop the male's plumage, 

 and then after a time was found to have begun reverting to the female's. 

 An examination was made, and it was found that there was a bit of ovarian 

 tissue attached to the posterior side of the oblique septum. There were 

 also three ova, each about 10 mm. in diameter, lying on the original site 

 of the ovary. The ovarian tissue attached to the transverse ligament was 

 removed, but the other left in place. During the present summer it was 

 observed that this bird again began to develop the male plumage, and, to 

 all appearances, the complete male plumage would have eventually replaced 

 the female. On autopsy it was found that all trace of ovarian tissue was 

 lacking. 



Two other females developed the complete plumage of the male, but the 

 combs and wattles still remain small. This plumage includes a cock's tail 

 which was lacking in the first bird in which these results were obtained. 

 Except for the small comb and wattles, these birds are much better speci- 

 mens than the original. 



Observations have been continued on the two capons which were cas- 

 trated in the spring of 1911. Their combs and wattles remained small for 

 18 months, but after this period they grew considerably, and now have 

 reached a size about that of a Brown Leghorn pullet just before she com- 

 mences to lay. Early in the spring, when 2 years old, they were observed 

 to crow, although this reaction occurred only a few times. In the absence 

 of normal males, they tread the hens. It is important to note that these 

 responses developed late in life and that externally the birds were capons 

 for over 18 months, or half again the usual age for keeping capons. 



MUTATIONS AND ABERRATIONS. 



No student of evolution by experimental methods can doubt the 

 importance of mutations. Our work has shown that they are some- 

 times due to irregularities in the behavior of the chromosomes during 

 maturation, and the hypothesis seems warranted that they are always 



