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CHAPTER IV. 



ARTICULATA, 



§ 1. *drticulatad Animals in general. 



From the Cephalopoda, the transition is easy to the low- 

 est order of vertebrated animals. But previously to pur- 

 suing the analogies which connect these two divisions of the 

 animal kingdom, we have to pass in review a ^^vj exten- 

 sive series of animal forms, constructed upon a peculiar sys- 

 tem, and occupying, as well as the Mollusca, a place inter- 

 mediate between Zoophytes and the more highly organized 

 classes. 



We have seen that even in those Zoophytes which arc 

 distinguished from the rest by a more elaborate conforma- 

 tion of organs, the powers of progressive motion are always 

 extremely limited. Nor are the JNIollusca in general more 

 highly favoured with respect to the degree in which they en- 

 joy this faculty. But the greater number of the animals 

 composing the series we are now to examine are provided 

 with a complete apparatus for motion, and endowed with 

 extensive ca])acities for using and applying it in various 

 ways. While nature has preserved in the construction of 

 their vital organs the simplicity which marks the primitive 

 modes of organization, and has adhered to a definite model 

 in the formation of the different parts of the system, she has 

 nowhere displayed more boundless variety in the combi- 

 nations of the forms whicli she has impressed upon the 

 mechanical instruments, both of prehension and of progres- 

 sion. 



All the tribes of Zoophytes, and by far the greater num- 

 VoL. I. 25 



