INSECTS. 39 



species place their eggs on nettles, others on the parsnip, 

 others on the cabbage, &c., and it is found that if the 

 caterpillars produced, are transferred from one of these 

 plants to the other, they in most cases die of starvation, 

 or improper food, being unable to partake of any other, 

 except that on which they are found. 



The young caterpillar is at first exceedingly small, 

 being often less than a line in length. As they enlarge 

 in size their skins, being at first somewhat elastic, are 

 stretched so as to accommodate their growth. But this 

 part growing more firm with age, finally refuses to yield 

 any further to the growth of the animal. It is then cast 

 off in the following manner. The worm fastens the old 

 skin to the side of a leaf, and then breaks through that 

 part which covers the head, and liberating its fore feet, 

 gradually draws the body out, the skin remaining sta- 

 tionary. But before this is done, a new skin has been 

 prepared underneath, more capacious than the former, 

 and which again for a time allows the insect to grow. 

 This, however, in its turn becomes too small ; or rather 

 the caterpillar becomes again too large for its skin, and 

 the same process is repeated four or five times before the 

 full size is attained. 



When the larva is fully grown, and therefore when 

 there is no further necessity for a new skin, it makes a 

 much more decided and important change than those it 

 had before undergone ; for although it had thrown off 

 coat after coat, it still had become nothing more than a 

 worm. But now it not only strips itself of the cater- 

 pillar's skin for the last time, but so changes its form as to 

 have no appearance of what it was before. It is wrap- 

 ped in a shroud of skin, presenting no vestige of its form- 

 er legs, mouth, or any oth^r member. It is fixed in its 

 place by a rope of silk, or wound up in a cocoon of the 

 same material, and presents, in either case, scarcely any 

 signs of life. In this condition it is said to be in its pupa, 

 or chrysalis state. 



What is said of the different plants on which the butterfly lays her 

 eggs 1 What change takes place when the larva passes to the chrysalis 1 



