62 THE PROBLEM OF EVOLUTION 



means that certain cases occur, in which the 

 individual development of a creature throws light 

 upon the hypothetical development of the race, I 

 am willing to accept the principle, but then it 

 ceases to be a general law. It is an undeniable 

 fact that, among both the higher and the lower 

 animals, instances occur of stages of individual 

 development, which can be explained only by 

 regarding them as temporary traces of a previous 

 stage of development, which was permanently 

 impressed upon certain ancestors. As an example 

 of this, I may refer to the teeth which the embryos 

 of the whalebone-whale still possess, although 

 subsequently they degenerate into whalebone. 

 Geoffrey Saint-Hilaire first observed this fact early 

 in last century, and Kiikenthal has confirmed his 

 statement. If we compare with it the further fact 

 that geology has ascertained, viz. that the whale- 

 bone-whale only in the tertiary period succeeded 

 the toothed whale, which may be regarded as its 

 probable ancestor, the conclusion is obvious. The 

 whalebone-whale is descended from an older toothed 

 whale, and the reason why, in the development of 

 the individual whalebone-whale, there is a stage at 

 which teeth appear, lies in the fact that the ancestors 

 of the present whales passed through this stage of 

 development, and it remains up to a certain definite 

 point in the growth of the embryo. 



Something similar occurs in the case of the 

 Termitoxenia, a very small fly that lives with the 



