30 THE DESCENT OF MAN. [Part I. 



by a mere rudiment. Nevertheless, the occurrence of 

 such rudiments is as difficult to explain on the belief of the 

 separate creation of each species, as in the foregoing cases. 

 Herpafter I shall have to recur to these rudiments, and 

 shall show that their presence generally depends merely on 

 inheritance ; namely, on parts acquired by one sex having 

 been partially transmitted to the other. Here I will only 

 give some instances of such rudiments. It is well known 

 that in the males of all mammals, including man, rudi- 

 mentary mammae exist. These, in several instances, have 

 become well developed, and have yielded a copious supply 

 of milk. Their essential identity in the two sexes is like- 

 wise shown by their occasional sympathetic enlargement 

 in both during an attack of the measles. The vesicula 

 prostatica, which has been observed in many male mam- 

 mals, is now universally acknowledged to be the homo- 

 logue of the female uterus, together with the connected 

 passage. It is impossible to read Leuckart's able descrip- 

 tion of this organ, and his reasoning, without admitting 

 the justness of his conclusion. This is especially clear in 

 the case of those mammals in which the true female ute- 

 rus bifurcates, for in the males of these the vesicula like- 

 wise bifurcates. 41 Some additional rudimentary structures 

 belonging to the reproductive system might here have 

 been adduced. 42 



The bearing of the three great classes of facts now 

 given is unmistakable. But it would be superfluous here 

 fully to recapitulate t]^e line of argument give» in detail 



41 Leuckart, in Todd's « Cyclop, of Anat.' 1849-'52, vol. iv. p. 1415. 

 In man this organ is only from three to six lines in length, but, like so 

 many other rudimentary parts, it is variable in development as well as in 

 other characters. 



42 See, on this subject,. Owen, ( Anatomy of Vertebrates,' vol. iii. pp. 

 675, C76, 706. 



