22 



SILKWORMS. 



and thither over the body, branching as they go, and serve as 

 channels by which air can obtain access to all parts of the 

 organism. The mere muscular movements of the body are 

 sufficient to effect the necessary change of air in them. 



Of legs, as we have already said, there are eight pairs, three 

 pairs just behind the head, and five others of a totally different 



a 



Fig. 7. Legs of Caterpillar, a, a single leg, b, a pair. 



form farther down, the last pair being situated on the last segment. 

 The first three pairs, which are the only true legs, are little five- 

 jointed things (Fig. 7), the last joint being sharp-pointed and 

 curved inwards. They are very useful for holding and steadying 



the food while the jaws play 

 upon it. The other five pairs, 

 or prolegs, are not jointed, but 

 are fleshy, cylindrical pillars, 

 with a circle of strong, curved 

 hooks set around their free end 

 (Fig. 8). These require the aid 

 of a lens to make out the form 

 and arrangement ; and when 

 they are thus viewed, there will 

 cease to be any wonder at the 

 extraordinary tenacity of grip 

 which the caterpillar can mani- 

 fest in clinging to any support. 

 The last pair are rather differ- 

 ently shaped, because they are 

 scarcely separate from the seg- 

 ment on which they are placed, 



Fig. 8. -Pair of prolegs of a Caterpillar anc | o f which they Seem tO be 

 clasping a twig. . , J 



a mere continuation. 



During its fifth and last age the caterpillar eats far more 

 voraciously than ever, and grows rapidly and enormously. After 



