APPARATUS OF MOTION. 



53 



158. A variety of appendages are attached to these 

 rings, such as jointed legs, or in place of them, stiff bristles, 

 oars fringed with silken threads, wings either firm or mem- 

 branous, tentacles or antenna?, movable arms which per- 

 form the office of jaws, &c. But, however diversified this 

 solid apparatus may be, it is universally the case that the 

 rings, to which every part may be referred as to a type, 

 constitute but a single simple cavity, in which all the organs 

 are enclosed, the nervous system as well as the organs 

 of vegetative life (63). 



159. The muscles which move 

 all these parts have this peculiar- 

 ity, that they are all situated within 

 the solid parts, and not on their ex- 

 ternal face, as in the vertebrates ; 

 and also that the muscular bundles, 

 which are very considerable in 

 number, have the form of ribbons, 

 or fleshy strips, with parallel 

 fibres of remarkable whiteness. 



Figure 27 represents the disposi- Fig. 27. 



tion of the muscles of the caterpillar which destroys the 

 willow, (Cossus ligniperdd). The right side represents 

 the superficial layer of muscles, and the left side the deep- 

 seated layer. 



160. The Vertebrata, like the articulated animals, have 

 solid parts at the surface, as the hairs and spines of mam- 

 mals, the feathers and claws of birds, the bucklers and 

 scales of reptiles and fishes, &c. But they have besides 

 this, throughout the interior of the whole body, a solid 

 framework not found in the other departments, well known 

 as the SKELETON. 



161. The skeleton is composed of a series of separate 



5* 



