44 THE DESCENT OF MAN 



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 rudimentary structures belonging 

 to the reproductive system might have been here adduced." 

 The bearing of the three great classes of facts now given 

 is unmistakable. But it would be superfluous 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 similarity 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, etc. , is utterly inexplicable. " 

 It is no scientific explanation to assert that they have all 

 been formed on the same ideal plan. "With respect to de- 

 velopment, we can clearly understand, on the principle of 

 variations supervening at a rather late embryonic period, 

 and being inherited at a corresponding period, how it is 



" 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. 



^5 See, on this subject, Owen, "Anatomy of Vertebrates," vol. iii. pp. 6t5, 

 6t6, Toe. 



'^ Prof. Bianconi, in a recently published work, illustrated by admirable 

 engravings ("La Theorie Darwinienne et la Creation dite independante, " 18T4), 

 endeavors to show that homological structures, in the above and other cases, 

 can be fully explained on mechanical principles, in accordance with their uses. 

 No one has shown so well how admirably such structures are adapted for their 

 final purpose ; and this adaptation can, as I believe, be explained through natu- 

 ral selection. In considering the wing of a bat, he brings forward (p. 218) whal 

 appears to me (to use Auguste Comte's words) a mere metaphysical principle, 

 namely, the preservation "in its integrity of the mammahan nature of the ani- 

 mal." In only a few cases does he discuss rudiments, and then only those 

 parts which are partially rudimentary, such as the little hoofs of the pig and 

 ox, which do not touch the ground; these he shows clearly to be of service to 

 the animal. It is unfortunate that he did not consider such cases as the minute 

 teeth, which never cut through the jaw in the ox, or the mammse of male quad- 

 rupeds, or the wings of certain beetles, existing under the soldered wing-covers, 

 or the vestiges of the pistil and stamens in various flowers, and many other 

 such cases. Although I greatly admire Prof. Bianconi's work, yet the belief 

 now held by most naturahsts seems to me left unshaken, that homological 

 structures are inexplicable on the principle of mere adaptation. 



