Cii. XL. DESCENT OF ANIMALS. 421 



Plan. — Another reason was that curious agreement in the 

 bones of different animals which had become more and 

 more noticed ever since the time of John Hunter, and Avhich 

 Geoffroy St.-Hilaire insisted upon so strongly. Why should 

 the animals of one class (such as the vertebrate or back- 

 boned class) be formed all on one plan even to the most 

 minute bones ; so that the wing of a bat, the front leg of a 

 horse, the hand of a man, and the flapper of a porpoise, are 

 all made of the same bones, which have either grown together, 

 or lengthened and spread apart, according to the purpose 

 they serve? And, more curious still, why should some 

 animals have parts which are of no use to them, but only 

 seem to be there because other animals of the same class 

 also have them. Thus the whale has teeth like the other 

 mammalia, but they never pierce through the gum ; and the 

 boa- constrictor has the beginnings of hind legs hidden under 

 its skin, though they never grow out. Here again it seemed 

 extraordinary, if a boa-constrictor and a whale were created 

 separately, that they should be made with organs which 

 are quite useless ; while, on the other hand, if they were 

 descended from the same ancestor as other reptiles and 

 mammalia who have teeth and hind legs, they might be 

 supposed to have inherited these organs ; just as, for ex- 

 ample, a child sometimes has a mole or other mark upon its 

 body in exactly the same place as its great grandfather had 

 before it. 



Embryos of Animals alike in Structure.— Another still 

 more remarkable fact was that pointed out by Von Baer, 

 that the higher animals, such as quadrupeds, before they are 

 perfectly formed, cannot be distinguished from the embryos 

 of other and lower animals, such as fish and reptiles. If 

 animals were created separately why should a dog begin 



