196 



ZOOLOGY. 



ristics of a fish, acquiring only, as they grow up, those of the 

 reptile (Figs. 147 to 151). 



Now these transitory states of the same individual present 

 frequently a remarkable resemblance to the permanent condi- 

 tion of other species ; and hence it results that the study of 

 these zoological transitions conducts us not only to a know- 

 ledge of a sort of parentage or relationship between animals 

 with forms often extremely unlike, but presents us with a philo- 

 sophic interest of a higher order, for it seems to give us some 

 ideas of the course followed by the Creator of all things in the 

 formation of the so varied products of the animal kingdom. 



353. Out of this tendency to fill up all links in the 

 animal kingdom, there arises the notion of a series or chain 

 of animal life, each form graduating as it were into that 



Fig. 147. 



Fig. 148. 



Fig. 149. Fig. 150. 



Figs. 147 to 151. Metamorphoses of the Frog. 



Fig. 151. 



preceding and that to follow. Sometimes, however, the link 

 seems broken, and there is an interruption between two types, 

 as if a part of the chain were lost or not filled in. Birds, for 

 example, seem isolated; but, generally, the deficient link or 

 hiatus may be found in the fossil remains with which the 

 globe abounds remains of animals, species, and genera which 

 have now ceased to exist. 



Some naturalists have thought that the series or line has 

 always been one uninterrupted series in the same direction, 

 from the monad up to man : they have attempted to establish 

 a zoological scale with these views; but this effort has failed, 

 for the series of animals is not single. Animals appear 

 rather to form a great number of series, which seem some- 

 times to proceed in parallel lines, sometimes to diverge and 

 rise to different elevations. It is even impossible to arrange 



