RUDIMENTS. 27 



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 i-ather late embryonic period, 

 : and being inherited at a corresponding period, how it is 

 that the embryos of wonderfully different forms should still 

 retain, more or less perfectly, the structure of their common 

 progenitor. No other explanation has ever been given of 

 the marvelous fact that the embryos of a man, dog, seal, 

 bat, reptile, etc., can at first hardly be distinguished from 

 each other. In order to understand the existence of rudi- 

 mentary organs, we have only to suppose that a former pro- 

 genitor possessed the parts in question in a perfect state, 

 :and that under changed habits of life they became greatly 

 reduced, either from simple disuse, or through the natural 

 selection of those individuals which were least encumbered 

 with a superfluous part, aided by the other means pre- 

 viously indicated. 



* Prof. Bianconi, in a recently published work, illustrated by ad- 

 mirable engravings ("La Theorie Darwinienne et la creation dite in- 

 dependante," 1874), endeavors to show that bomological 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, 

 bow admirably such structures are adapted for their final purpose ; 

 and this adaptation can, as I believe, be explained through natural 

 selection. In considering the wing of a bat, he brings forward (p. 

 218) what appears to me (to use Auguste Comte's words) a mere met- 

 aphysical principle, namely, the preservation "in its integrity of the 

 mammalian nature of the animal." In only a few cases does he dis- 

 cuss 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 ani- 

 mal. 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 

 mammae of male quadrupeds, or the wings of certain beetles, existing 

 under the soldered wing-covers, or the vestiges of the pistil and 

 tamens in various flowers, and many other such cases. Although I 

 _greatly admire Prof. Bianconi 's work, yet the belief now held by 

 most naturalists seems to me left unshaken, that homological struct- 

 ures are inexplicable on the principle of mere adaptation. . 



