174 INSECTS. 



Boerhaave subjected the eggs of some butterflies 

 to a cold of twenty-three degrees below zero, (pro- 

 duced by a freezing mixture) but he found that they 

 were hatched, as usual, in due season, and the cat- 

 erpillars appeared as strong as any others. On 

 examining the contents of the eggs at the above low 

 temperature, he found that they had remained quite 

 liquid, whilst insects themselves were killed at four- 

 teen and sixteen degrees, and their members became 

 as hard as ice. 



The caterpillar, whose life is one continued scene 

 of changes, often moults its skin before it attains its 

 full growth, and it is not merely the skin which is 

 renovated, for at each moult the caterpillar acquires 

 a new skull, new jaws, and all the exterior parts 

 both scaly and membraneous which compose its 

 upper and under lip, antennae (or horns), palpi (or 

 feelers), and even those crustaceous pieces within 

 the head, which serve as a fixed basis for a number 

 of muscles, spiracles, claws, sheaths of the anterior 

 legs, and in fact all of the exterior which is visible. 

 This change is effected by the insect withdrawing 

 itself from the old skin, which at the proper time 

 splits along the back. The accomplishment of this 

 change is a work of much time and exertion, and 

 apparently causes much pain. It fasts sometime 

 before moulting. The caterpillars of butterflies and 

 moths, excepting the few already mentioned, are 

 destitute of all means of defence, and are the prey of 

 birds and other small animals. Many of them feed 

 close to the ground or under the surface, subsisting 

 on the under parts and roots of plants, and for this 

 reason they are seldom seen and remain unknown. 

 Many, also, are similar in color to the leaves of the 

 plants on which they feed, and hence they are with 

 difficulty discovered by their enemies. A large 

 number of them are green of different shades, some- 

 times beautifully contrasted with other colors, but 

 the beautiful coloring of the caterpillar is no indi- 



