BEGINNERS' ZOOLOGY 



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 appe?idages. 

 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 a but- 

 terfly. A " grubworm " also 

 has jointed legs (Fig. 167). 

 It does not remain a grub, but 

 in the adult stage is a beetle. 



KS. 



Fig. 72. — Food 

 TUBE of earth- 

 worm. (Top 

 view.) 



A worm never develops into «.s 

 another animal in the latter a 

 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. Its 

 parts, recognizable because of 

 slight differences in size and 



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Fig. 73. — Food 

 Tube and 

 Blood Ves- 

 sels of earth- 

 worm showing 

 the ring-like 

 hearts. (Side 

 view.) 



The last cx- 



structure, are named the pharynx 

 I* (muscular), gullet, crop, gizzard 

 (muscular), and stomach-intestine 

 tends through three fourths of the length of the 

 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 



