APPARATUS OF MOTION. 



77 



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, antennas, movable pieces which perform the office 

 of jaws, &c. But however diversified this solid apparatus 

 may be, it is universally the case that the rings, to which 

 every segment of the body may be referred as to a type, com- 

 bine to form but a single internal cavity, in which all the or- 

 gans 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 enclosed with- 

 in the more solid framework, and 

 not external to it, as in the verte- 

 brates ; and also that the muscular 

 bundles, which are very consider- 

 able in number, have the form of 

 ribbons, or fleshy strips, with par- 

 allel fibres of remarkable white- 

 ness. Figure 27 represents the g< '' 

 disposition of the muscles of the caterpillar which destroys 

 the willow, (Cossus ligniperda.) 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 horns of mam- 

 mals, the coat of mail of the armadillo, the feathers and claws 

 of birds, the bucklers and scales of reptiles and fishes, &c. 

 But they have besides this, along the interior of the whole 

 body, a solid framework not found in the invertebrates, well 

 known as the SKELETON. 



161. The skeleton is composed of a series of separate 

 bones, called vertebrae, united to each other by ligaments. 



