THE CATERPILLAR AND THE MOTH 



from the blood the waste products containing nitrogen, 

 and discharge them into the intestine along with the waste 

 parts of the food from the stomach. Ordinarily the Mal- 

 pighian tubules are of a whitish color, but just before the 

 tent caterpillar is ready to spin its cocoon thev become 

 congested with a bright yellow substance. Under the 

 microscope this is seen to consist of masses of square, 

 oblong, and rod-shaped crystals (Fig. K7). At this time 

 the caterpillar has ceased to feed and the alimentary canal 

 contains no food or food refuse. The intestine, however, 



Fig. 1 c8. A piece of the fat-body of the fall webworm 

 a, a, globules of fatty oil in the cells; Nu, Nu, nuclei of the cells 



becomes rilled with the yellow mass from the Malpighian 

 tubules; and this is the material with which the tent 

 caterpillar plasters the walls of its cocoon, giving them 

 their yellowish color and stiffened texture. The yellow 

 powder of the cocoon, therefore, consists of the crystals 

 from the Malpighian tubules. 



We now come to the question of why the caterpillar eats 

 so much. It is almost equivalent to asking, "Why is a 

 caterpillar?" The caterpillar is the principal feeding 

 stage in the insect's life; eating is its business, its reason 

 for being a caterpillar. It eats not only to build up its 

 own organs, many of which are to be broken down to 

 furnish building material for those of the moth, but it 

 eats also to store up within its body certain materials in 

 excess of its own needs, which likewise will contribute to 

 the growth of the moth. 



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