HEREDITY AND SEX 187 



the testes, and this stimulus is essential, not merely for the 

 initiation of the horn growth, but for its continuance, the 

 horns ceasing to grow whenever the testes are removed." 



" The removal of the ovaries from young ewes belong- 

 ing to such a breed does not lead to the development of 

 definitely male characters, except possibly in an extremely 

 minor degree." 1 



Arkell 2 crossed Merino ewes with a Southdown ram 

 (hornless). The sons of this cross had horns. The 

 factor for horns in this case must have been present in 

 the Merino mother, herself hornless, but the full develop- 

 ment of horns cannot take place except the male glands 

 are present and functional. 



175. Effect of transplanting sexual glands. The in- 

 vestigations already described seem clearly to point to the 

 conclusion that some stimulus to the development of the 

 secondary sexual glands exists in the testes and ovaries. 



Steinach transplanted ovarian tissue from a female 

 guinea pig to the tissues of a castrated male. The result 

 was to cause the rudimentary mammary glands of the 

 male greatly to enlarge and the male came to resemble 

 the female in certain characters. 3 



A remarkable experiment is described by Goodale 4 in 

 which the ovaries of a female Mallard duck were entirely 

 removed and the plumage became like that of the male 

 Mallard. 



176. Effect of internal secretion. The secretions 

 of various internal organs have a profound influence 

 upon the development of the individual. These secre- 



1 Marshall, Proceedings Royal Society (London), ser. B, 85, 

 1912. 



2 Arkell, New Hampshire Agr. Exp. Sta., Bui. 160. 



3 Morgan, " Heredity and Sex," 1913, p. 140. 



4 Goodale, Journal Experimental Zoology, 10. 



