Chap. I. 
THE DESCENT OF MAN. 
31 
eluding 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 prostratica, which 
has been observed in many 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 . 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 unmistakeable. But it would be superfluous here 
fully to recapitulate the line of argument given in detail 
in my 4 Origin of Species.’ The homological construction 
of the w r hole 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 
a bat, &c., is utterly inexplicable. It is no scientific 
41 Leuckart, in Todds 1 Cyclop, of Anat/ 1849-52, yol. iv. p. 1415. 
In man this organ is only from three to six lines in length, bnt, like 
so many other rudimentary parts, it is variable in development as well 
as in other characters. 
42 See, on this subject, Owen, 4 Amatomy of Vertebrates/ vol. iii. pp. 
675, 676, 706. 
