i-l^j 



ZOOLOGY 



animals that depend upon currents of water to bring them 

 food have a mode of feeding that is incompatible with living 

 in the air, they have given rise to no terrestrial species. 



The newt well illustrates the changes of form and structure 

 that an aquatic animal must undergo in adapting itself to the 

 land. The young newts, as they hatch from the eggs Ij-ing in 

 the water, are thin-skinned animals with dehcate, bushy gills 



extending out from the 

 side of the head. The 

 legs are very small, or 

 absent, and locomotion 

 is by a large fin on the 

 tail. By the move- 

 ment of this fin the 

 animal is propelled 

 through the water very 

 much as a fisherman 

 sculls a boat. By the 

 time the newt has left 

 the water and has become adjusted to the moist air of the 

 damp ground on which it lives, the outer la.yers of its skin 

 have become somewhat horny and the bushy gills have become 

 lost (Fig. 309). Respiration now takes place in the throat, or 

 in other cases in pockets formed from the throat and known 

 as the lungs. Four legs directed downward support the body 

 alaove the ground, and the tail-fin withers away, so that only a 

 rouhd.ed tail remains. 



The transformation that the indi^'idual newt undergoes in 

 its lifetime is an epitome of the evolution of many terrestrial 

 forms. Thus, in the tropics, certain shore crabs ha^'e come to 

 live in the upper part of the beacli antl eventually in the forests 



Fk;. .'309. — A female newt {DcsmognaOtus 

 fuscus) guarding its eggs in a hole Vjy the side 

 of water. Nat. size. After Wilder. 



