112 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



tions, not of the theory, but of the theorists of 

 transformism. It was at Zurich, after the appear- 

 ance of the last volume of his Handbuch, that Zittel 

 set forth before the International Congress of 

 Zoology, with entrancing clearness and eloquence, 

 the uncertainties and deceptions of palaeontological 

 evolution. Phylogeny, Ontogeny, and System, such 

 is the suggestive title of this memorable lecture, 

 which made such a noise in the palseontological 

 world that it seems indispensable to give at least 

 a sketch of it. 



The theory of descent rests to some slight de- 

 gree on palseontological facts. The most solid 

 argument consists, as Neumayr had already said, 

 in the series of similar species which can be followed 

 from individual to individual through geological 

 formations, and show at least the probability of a 

 phylogenetic descent. Nevertheless, these series 

 do not generally form a continuous chain of which 

 the links are joined to one another, mutation to 

 mutation, and species to species ; there are often in- 

 termittent series, the ends of which are all modi- 

 fied in a given direction, and establish the stages of 

 an evolution crowned by recent or existing forms. 

 One can describe similar series more or less close to 

 each other in the Camelidse, the Suidse, and the 

 Ruminants among Mammals, in the Crocodilians 

 among Reptiles, and in the Amiadae and the 

 Physostomes among Fishes. 



The terminal types of these series are in general 

 distinguished from their ancestors by a more marked 

 differentiation, which makes them more specialized, 

 and, so to speak, more finished beings. The theory 



