ANIMAL BIOLOGY 



these terms are applicable. What are the 

 ventral and dorsal surfaces of a fish, a frog, 

 a bird, a horse, a man ? 



The name "worm" is often carelessly applied 

 to various crawling things in general. It is prop- 

 erly applied, however, only to segmented animals 

 without jointed appendages. 

 Although a caterpillar crawls, 

 it is not a worm for several 

 reasons. It has six jointed 

 legs, and it is not a developed 

 animal, but only an early stage 

 in the life of a moth or but- 

 terfly. A " grubworm " also 

 has jointed legs (Fig. 167). 

 It does not remain a grub, but 

 in the adult stage is a beetle. 

 A worm never develops into 

 another animal in the latter 

 part of its life ; its setae are 

 not jointed. 



The Food Tube. — The earthworm has 

 no teeth, and the food tube, as might be 

 inferred from the form of the 

 body, is simple and straight. On 

 account of slight variation in size 

 and structure, its parts are named 

 the pharynx (muscular), gullet, 

 crop, gizzard (muscular), and the 

 long intestine extending through the last three 

 fourths of its body (Fig. 72). The functions of 

 the parts of the food tube are indicated by their 

 names. 



Circulation. — There is a large dorsal blood 

 vessel above the food tube (Fig. 73). From the 



Fig. 72. — Food 

 TUBE of earth- 

 worm. (Top 

 view.) 



Fig. 73. — Food 

 Tube and 

 Blood Ves- 

 sels of earth- 

 worm showing 

 the ring-like 

 hearts. (Side 

 view.) 



