Animals Before Man 



equal in importance if not in size, just as Rhode 

 Island and Texas, though very different in area, 

 are both States of the same rank so far as in- 

 dependence and form of government are con- 

 cerned. But while " invertebrates " is no longer 

 used to denote one of the primary divisions of 

 the animal kingdom, it is still a most useful and 

 comprehensive term for all the creatures vrhich 

 have no back-bone. 



Owing to the vast numbers of invertebrates 

 and their numerous divisions, it will be possible 

 to mention only a few of our great primary 

 groups or phyla, bearing in mind that each of 

 these phyla corresjDonds in the degree of its im- 

 portance to that including all vertebrates. 



The highly specialized structure of the 

 squids and cuttlefishes comprising the class 

 Cephalopoda is generally considered as placing 

 the mollusks next to the vertebrates ; and while 

 we usually associate the term mollusk with 

 animals covered with a shell, forgetting the 

 fact that the name means soft, yet among the 

 highest living members of the group only the 

 nautilus and argonaut are thus protected. On 



42 



