34 THE THEOKY OF EVOLUTION 



it entirely from all other classes. That the beak con- 

 tained teeth while the present birds no longer possess 

 them, that the caudal vertebrae had not yet become 

 united as is now the case, shows that it was a different 

 bird from the present ones, but otherwise demonstrates 

 nothing. We are, however, accustomed to find in the 

 first representatives of any type divergent and (by com- 

 parison with the present ones) curious characteristics. 



It must therefore be assumed that the Birds bore 

 teeth for a long period and only gradually lost them. 

 In that case we should have here a so-called apparent 

 regression (see p. 44). 



3. Some palceontological 'laws' according to which 

 the transformation proceeded within defined 

 (narrower) groups (families, genera). 1 



(1) The law of increase of size. 



In the previous matter we have repeatedly called 

 attention to the fact that the first representatives 

 of a newly appearing group are often small and 

 insignificant individuals compared with the later and 

 sometimes gigantic forms within the same group. This 

 is observed ' almost invariably in all classes of the animal 

 world, but we find more numerous and clearer applica- 

 tions of the law in the group of Vertebrates than in 

 that of the Invertebrates/ By careful investigation 

 Neumayr, Waagen, Mojsisovics, and Hyatt have deter- 



1 We rely in this section particularly upon Deperet-Wegner's Die 

 Umbildung der Tierwdt, chaps, ix. and x., where the whole literature of the 

 subject is dealt with. 



