148 E VOL UTION AND DISEASE. 



many suppose, especially when each suspected case is 

 submitted to rigid analysis. I shall, however, first of 

 all consider atavism in relation to secondary sexual 

 characters, and then proceed to the study of super- 

 numerary digits and limbs, and supernumerary mammae 

 and nipples. It will be to the reader's advantage 

 before perusing those sections to study carefully 

 the remarks made on dichotomy, for of all examples 

 mistaken for atavism, dichotomy claims by far the 

 greatest number. 



Atavism in relation to Secondary Sexual characters. 

 As Darwin points out, two distinct elements are in- 

 cluded under the term " inheritance " the transmission 

 and the development of characters. The distinction is 

 so important, especially in its bearing on the question 

 of atavism, that the two conditions will be illustrated 

 by concrete examples. 



In most species of the deer tribe it is the rule for the 

 male alone to possess antlers, yet it is a well attested 

 circumstance that under certain diseased conditions of 

 the sexual organs, especially atrophy or degeneration 

 of the ovaries, rudimentary horns which are never shed 

 appear in the female. 



This shows us that the female is in possession 

 of secondary sexual organs in virtue of transmission, 

 yet they remain latent as a rule, and only become 

 developed under extraordinary circumstances. The 

 same holds good for those cases of hens who for years 

 lay eggs, yet eventually cease to do so, put on one side 

 the plumage proper to their sex, and adopt more or less 

 completely that of the cock. 



