THE CYCLE OF LIFE 463 



the larval frog is never like a young fish. It has no scales, 

 for instance, nor fin-rays supporting the tail-fin, and there 

 are much more fundamental differences. It is an Amphib- 

 ian from first to last. And yet, if we fix our attention on 

 the development of the heart or the circulation, we must 

 admit that the tadpole passes through stages which are 

 permanent in fishes. In other parts of its organogenesis 

 it climbs up its own genealogical tree, and to this extent 

 at least confirms the ' Recapitulation Doctrine '. 



It is very instructive to compare the long drawn out life- 

 history of the common frog with that of some of its relatives. 

 In the Surinam toad (Pipa) and in some Tree-Frogs, the 

 tadpole stage is skipped altogether, while in the Paradoxical 

 Frog (Pseudis paradoxa) the tadpole stage is much more 

 impressive, at any rate, than the adult. In his delightful 

 Infancy of Animals, Mr. W. P. Pycraft tells us that the 

 tadpole is nearly a foot long, nine inches going to the enor- 

 mous tail, and three inches to the head and trunk. During 

 a prolonged fast, and after no little re-modelling, this huge 

 larva is shaped into an adult frog, only two and a half inches 

 in length. 



Retrospect. The general idea which these life-histories 

 suggest, is that the various chapters of a typical life- 

 history are capable of being lengthened out or shortened 

 down according to the conditions of life ; and to some 

 extent, also, that particular conditions of life, may have 

 been sought out to suit particular forms of the life-curve. 

 The various arcs on the span of life are, so to speak, elastic. 

 The line of life is like a telescope with many joints ; it can 

 be drawn out to its full length ; it can be pushed in to a 

 minimum ; or one part can be lengthened and another 

 shortened. Just as some flowers remain, as it were, per- 



