THE CLASS OF INSECTS. . 7 



The Worm is long and slender, composed of an irregular 

 number of rings, all of very even size. Thus, while the size of 

 the rings is fixed, their number is indeterminate, varying from 

 twenty to two hundred or more. The outline of the body is a 

 single cylindrical figure. The organs of locomotion are fleshy 

 filaments and hairs (Fig. 3, /) appended to the sides. 



In one of the low intestinal worms, the Tape-worm (Tcenia), 

 each ring, behind the head and "neck," is provided with organs 

 of reproduction, so that when the body becomes broken up 

 into its constituent elements, or rings (as often occurs naturally 

 in these low forms for the more ready propagation of the 

 species, since the young are exposed to many dangers while 

 living in the intestines of animals), they become living inde- 

 pendent boings which "move freely and somewhat quickly 

 like Leaches," and until their real nature was known they 

 were thought to be worms. This and other facts prove, that, 

 in the Worm, the vitality of the animal is very equally dis- 

 tributed to each ring. If we cut off the head or tail of some 

 of the low worms, such as the Flat Worms (Planaria, etc.), the 

 pieces will become a distinct animal, but an Insect or Crab 

 sooner or later dies when deprived of its head or tail (abdomen). 



Thus, in the Worm the vital force is very equally distributed 

 to each zoological element, or ring of the body ; no single 

 part of the body is much honored above the rest, so as to sub- 

 ordinate and hold the other a i> 

 parts in subservience to its 

 peculiar and higher ends in 

 the animal economy. 



The Crustacean, of which 

 the Shrimp (Fig. 9) is a 

 typical example, is com- 

 posed of a determinate 

 number (21) of rings which Fig. n. 



are gathered into two regions ; the head-thorax (cephalo- 

 thorax) and hind -body, or abdomen. In this class there 

 is a broad distinction between the anterior and posterior ends 

 of the body. The rings are now grouped into two regions, 

 and the hinder division is subordinate in its structure and 



FIG. 9. A Shrimp. Pandalus annulicornia. a, cephalothorax ; 6, abdomen. 



