26 THE DESCENT OF MAN. 



to examine the tail of a monkey (Macacus), and of a cat, 

 in both of which they found a similarly convoluted body, 

 though not at the extremity. 



The reproductive system oifers various rudimentary struct- 

 ures; but these differ in one important respect from the 

 foregoing cases. Here we are not concerned with the ves- 

 tige of a part which does not belong to the species in 

 an efficient state, but with a part efficient in the one 

 sex, and represented in. the other by a mere rudiment. 

 Nevertheless, the occurrence of such rudiments is as diffi- 

 cult to explain, on the belief of the separate creation of 

 each species, as in the foregoing cases. Hereafter I shall 

 have to recur to these rudiments, and shall show that their 

 presence generally depends merely on inheritance, that is, 

 on parts acquired by one sex having been partially trans- 

 mitted to the other. I will in this place only give some in- 

 stances of such rudiments. It is well known that in the 

 males of all mammals, including man, rudimentary mammas 

 exist. These in several instances have become well de- 

 veloped, and have yielded a copious supply of milk. Their 

 essential identity in the two sexes is likewise shown by 

 their occasional sympathetic enlargement in both during 

 an attack of the measles. The vesicula prostatica, which 

 has been observed in many male mammals, is now universally 

 acknowledged to be the komologue 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 bifurcates, for in the males of 

 these the vesicula likewise bifurcates.* Some other rudi- 

 mentary structures belonging to the reproductive system 

 might have been here adduced, f 



The bearing of the three great classes of facts now given 

 is unmistakable. But it would be superfluous fully to recap- 

 itulate the line of argument given in detail in my " Origin 

 of Species." The homological construction of the whole 



*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. 



f See, on this subject, Owen, "Anatomy of Vertebrates," vol. iii, 

 pp. 675, 676, 706. 



