JMOLLUSCA. 519 



lengthened, approaching to cylindrical. The body is di- 

 vided into rings by transverse strictures more or less dis- 

 tinctly marked. Even the different appendices of the skin 

 frequently exhibit their annulose structure. 



The annulose animals form two groups, which, while 

 they indicate the closest affinity in the nervous system 

 and divisions of the body, exhibit at the same time remark- 

 able distinctive characters. These characters indeed are 

 so obvious, as to have been perceived by all naturalists, 

 and to have induced them to assign to each a separate place 

 in their systems. The first group, the species belonging 

 to which have articulated limbs, is identical with the fifth 

 class in the LINNEAN system, termed Insecta. The se- 

 cond group, containing animals destitute of articulated 

 limbs, includes genera of the different orders of the class 

 Vermes of the same system. As the remarks which appear 

 necessary to be made on one group, must differ widely 

 from those applicable to the other, it will be proper to con- 

 sider each apart. 



Subdivision I. ANNULOSE ANIMALS WITH ARTICULATED 



LIMBS FOR LOCOMOTION. 



The SKIN of the animals of this group serves the double 

 purpose of protection and support, and represents the cuta. 

 neous and osseous systems of the vertebral animals. Its 

 structure appears much more simple than in the .higher 

 classes, as it can neither be said to possess a mucous or cel- 

 lular web or true skin. It bears the nearest resemblance to 

 the cuticle of the skin of the higher classes, or rather, all 

 the laminae of perfect skins are here incorporated into one 

 uniform plate. It exhibits very remarkable varieties of 

 texture. In some genera it is soft and pliable ; while, in 

 others, as some of the weevils, it approaches the consistence 



