390 THE STUDY OF ANIMAL LIFE CHAP. 



its gills after it has developed lungs, while the Ambly- 

 stoma loses them. Both forms may reproduce, and 

 they were originally referred to different genera. But 

 some Axolotls which had been kept with scant water 

 in the Jar din des Plantes in Paris turned into the Ambly- 

 stoma form ; the two forms are different phases of the 

 same animal. It was a natural inference that the Axolotls 

 were those which had remained or had been kept in the 

 water, the Amblystoma forms were those which got 

 ashore. That the matter is more complex than was 

 previously supposed is shoAvn by the fact that both 

 kinds may be found in the water of the same lake and 

 the metamorphosis may take place in the water as well 

 as on the shore. It seems that the Axolotls retain cer- 

 tain larval characters although they have reached their 

 full size and have become reproductive. The same 

 phenomenon occurs in other types, among Amphibians 

 and elsewhere, and is known as psedogenesis. It is a 

 special case of a possibility that is often open to animals 

 with a markedly punctuated life-history the possibility 

 of lengthening out one chapter and shortening another. 

 It is quite likely that some species have arisen in this 

 way, e.g. as persistently juvenile or as prematurely senile 

 forms. 



Another influence of the chemical environment is that 



FIG. 120. SIDE VIEW OF MALE Artemia salina (ENLARGED). 

 (From Chambers's Encyclop.) 



of prompting variations. This is probably illustrated by 

 the story of the brine-shrimps (Arteinia], first told by the 

 Russian naturalist Schmankcwitsch. There is a form 

 called A. salina (see figs. 120 and 121) which has well- 

 developed bristly tail-lobes, and Schmankewitsch found 

 that concentration of the water led to its being replaced 

 by another form (we can hardly say species), called A. 



