274 THE PRINCIPLES OF [Part II. 



the same sex. With tortoise-shell cats the females alone, 

 as a general rule, ai*c thus colored, the males being rusty- 

 red. With most breeds of the fowl, the characters proper 

 to each sex are transmitted to the same sex alone. So 

 general is this form of transmission that it is an anomaly 

 when we see in certain breeds variations transmitted equal- 

 ly to both sexes. There are also certain sub-breeds of the 

 fowl in which the males can hardly be distinguished from 

 each other, while the females difier considerably in color. 

 With the pigeon tlie sexes of the parent-species do not 

 difier in any external character; nevertheless in certain 

 domesticated breeds the male is differently colored from 

 the female." The wattle in the English Carrier-pigeon 

 and the crop in the Pouter are more highly developed in 

 tlie male than in the female ; and altliough these chax'acters 

 have been gained through long-continued selection by man, 

 the difFerence between the two sexes is wholly due to the 

 form of inheritance which has prevailed ; for it has arisen, 

 not from, but rather in opposition to, tlie Avishes of the 

 breedei". 



Most of our domestic races have been formed by the 

 accumulation of many slight variations ; and as some of 

 the successive steps have been transmitted to one sex 

 alone, and some to both sexes, we find in the difierent 

 breeds of the same species all gradations between great 

 sexual dissimilarity and complete similarity. Instances 

 have already been given with the breeds of the fowl and 

 pigeon ; and under Nature analogous cases are of fre- 

 quent occurrence. With animals under domestication, but 

 whether under Nature I will not venture to say, one sex 

 may lose characters proper to it, and may thus come to 

 resemble to a certain extent the opposite sex ; for in- 

 stance, the males of some breeds of the fowl have lost 



"^^ Dr. Chapuis, ' Lc Pigeon Voyageur Beige,' 1865, p. 87. Boitard 

 ct Corbie, ' Les Pigeons dc Voliore,' etc., 1824, p. 173. 



