CH. XLI. DESCENT OF ANIMALS. 459 



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 

 lioise, the hand of a man, and the- paddle 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 example, a child sometimes has a mole or other 

 mark upon its body in exactly the same place as its great 

 grandfather had before it. 



Another still more remarkable fact was that pointed out 

 by Von Baer, that the embryos of 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 separ- 

 ately, why should a dog begin like a fish, a lizard, and a 

 bird, and have at first parts which it loses as it grows into 

 its own peculiar form ? 



These were facts entirely belonging to living creatures, 

 but now others sprang up about fossil species which were 

 equally puzzling. We know that certain animals are 



