THE PROBLEM; THE MODE OF ITS SOLUTION 21 



Now the first attempts resulted iu artificial classifica- 

 tions, much like our grouping of bats with birds and 

 whales with fish. All animals, like coral animals and 

 starfishes, whose similar parts were arranged in lines 

 radiating from a centre, were united as radiates, how- 

 ever much they might differ in internal structure and 

 grade of organization. But this radiate structure 

 proved again to be largely a matter of adaptation. 



Practically all animals having a heavy calcareous 

 shell were grouped with the snails and oysters as inol- 

 lusks. But the barnacle did not fit well with other 

 mollusks. Its shell was entirely different. It had 

 several pairs of legs ; and no mollusk has legs. The 

 barnacle is evidently a sessile crab or better crustacean. 

 Its molluscan characteristics were only skin-deep, evi- 

 dently an adaptation to a mode of life like that of 

 mollusks. The old artificial systems were based too 

 much on merely external characteristics, the results of 

 adaptation. When the internal anatomy had been 

 thoroughly studied their groups had to be rearranged. 



Reptiles and amphibia were at first united in one 

 class because of their resemblance in external form. 

 Our common salamanders look so much like lizards 

 that they generally pass by this name. But the young 

 salamander, like all amphibia, breathes by gills, its 

 skeleton differs greatly from, and is far weaker than, 

 that of the lizard, and there are important differences 

 in the circulatory and other systems. Moreover, practi- 

 cally all amphibia differ from all reptiles in these 

 respects. Evidently the fact that the alligator and 

 many snakes and turtles (of which neither the young 

 nor the embryos ever breathe by gills) live almost en- 

 tirely in the water, is no better reason for classifying 



