Chap. I. THE DESCENT OF MAX. 31 



having been partially transmitted to the other. Here 

 I will onlv srive some instances of such rudiments. It 

 is well known that in the males of all mammals, in- 

 cluding man, rudimentary mammae exist. These in 

 several instances have become well developed, and have 

 yielded a copious supply of milk. Their essential iden- 

 tity in the two sexes is likewise shewn by their occa- 

 sional sympathetic enlargement in both during an 

 attack of the measles. The vesicula prostatica, which 

 has been observed in manv male mammals, is now uni- 

 versally acknowledged to be the homologue of the 

 female uterus, together with the connected passage. It 

 is impossible to read Leuckart's able description 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 uterus bifur- 

 cates, for in the males of these the vesicula likewise 

 bifurcates. 42 Some additional rudimentary structures 

 belonging to the reproductive system might here have 

 been adduced. 43 



The bearing of the three great classes of facts now 

 given is unmistakeable. But it would be superfluous here 

 fully to recapitulate the line of argument given in detail 

 in my ' Origin of Species.' The homological construction 

 of the whole frame in the members of the same class is 

 intelligible, if we admit their descent from a common 

 progenitor, together with their subsequent adaptation 

 to diversified conditions. On any other view the simi- 

 larity of pattern between the hand of a man or monkey, 

 the foot of a horse, the flipper of a seal, the wing of 



42 Lenckart, 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 a^ well 

 as in other characters. 



43 See, on this subject, Owen, ' Anatomv of Vertebrates,' vol. iii. pp. 

 675, 676, 706. 



