ANIMAL PEDIGREES 215 



only ; while in succeeding ages they gradually 

 increased in size and in complexity. The palaeon- 

 tological series thus agrees with the developmental 

 series of stages through which the antlers of a stag 

 pass at the present day before attaining their full 

 dimensions. 



There is another point of view from which 

 fossils acquire special interest in connection with 

 the Recapitulation Theory. If the theory is 

 correct, it must apply not merely to the animals 

 now living on the earth, but to all animals that 

 ever have lived ; and it becomes a matter of 

 considerable interest to enquire whether we have 

 any evidence whereby we can test this point, and 

 determine whether or not the fossil animals in 

 their own individual development repeated the 

 characters of their ancestors. 



At first sight the enquiry does not seem a 

 promising one, for it may well be asked what 

 possibility there is of determining the embryology 

 or mode of development of animals which are 

 only known to us through the chance preservation 

 of their bones or shells as fossils. In most cases 

 it is true that such determination is impossible, 

 but in some groups as for example the Trilobites, 

 great numbers of well preserved specimens have 

 been obtained, not merely of adults, but of young 

 forms in various stages of growth ; and the study 

 of these young forms has already yielded results 

 of considerable interest. According to Barrande, 

 to whom our knowledge of ' these early stages 

 is mainly due, four chief types of development 



