SUMMARY OF CUEEENT EESEAECHES. 107. 



rnent starts the hormone is not always able to check it. Some strains 

 of leghorns and minorcas produce a large percentage of spurred female 

 offspring. 4. Castrated ducks of botli sexes showed no change in 

 voice, but castrated fowls are disinclined to give voice to any kind of 

 sound. Capons can utter all the sounds of which the cock is capable, 

 but they rarely do so. 5. As far as Goodale's observations go, castra- 

 tion with one exception has not influenced the moult of the capon. On 

 the other hand, castrated ducks lose the power of developing the summer 

 plumage. 6. Castration is without influence on the colour of the 

 male duck's mandible, but ovariotomy results in the disappearance of 

 certain pigments from the mandible of the female. 7. Completely 

 castrated individuals of all kinds are on the whole negative in behaviour 

 as compared with normal adults. The behaviour of castrates corresponds 

 rather closely to that of young birds shortly before they become mature. 

 The birds eat, drink and move about rather quietly. 



Male characters, such as spurs, large comb and wattles, and a 

 " neck ring " in ducks, sometimes occur in otherwise normal females. 

 Instances of the occurrence of female characters in males, strictly com- 

 parable to those just referred to, are uncommon or wholly lacking. The 

 only character of this sort among capons is the brooding instinct. 

 Some female-like characters in males are juvenile characters. It is 

 probable that while some secondary sex- characters are absolutely depen- 

 dent on the internal secretion of the gonad, others are partially, at least, 

 independent. Hen-feathered males illustrate juvenile, rather than 

 female characters of plumage. Neither the assumption of male plumage 

 by the female nor the development of the accessory reproductive organs 

 need be considered evidence that the female is a suppressed herma- 

 phrodite, because the secretion of the ovary clearly controls their 

 development. On the other hand, it is clearly proven that the female 

 is a suppressed josei<f/o-hermaphrodite. 



The influence exerted by the gonads on the secondary sex-characters 

 differs in diff'erent groups. In insects the secondary sex-characters are 

 independent of the gonads. In certain Crustaceans the conditions are 

 the reverse of those found in birds. In Mammals removal of the testes 

 produces an effect very similar to that on the male bird, while the 

 female undergoes little change in her secondary sex-characters. 



On the whole, the relation between the gonads and the secondary 

 sex-characters appears to be specific and not general. Although more 

 striking, their relation is essentially of the same order as other morpho- 

 genetic secretions, such as that of the thyroid. Indeed, the morpho- 

 genetic activity of the gonads is by no means confined to the secondary 

 sex-characters, but produces other well-known effects. 



The three luost important results are : 1. If the ovary of a domestic 

 bird be removed completely, many of the secondary sex-characters of 

 the male appear (and always of the male of the same race). Some 

 individuals become nearly complete replicas, of the male, others im- 

 perfect imitations of the male. 2. If the testes be removed, the 

 majority of the secondary sex-characters of the male develop, though a 

 few may remain in an infantile condition. 3. Castrated drakes lose the 

 power of developing the summer plumage. 



