56 TRANSFORMATIONS OF INSECTS. 



some other larv?e. Lyonct found that the larva of Cossiis lig- 

 niperda, which remains about three years in that state, in- 

 creased to the amount of 72,000 times its first weight. This 

 amazing increase is occasioned chiefly by a prodigious accumu- 

 lation of fat, which exists in a greater quantity in this than in 

 most other larvcie. We have ourselves removed forty-two grains of 

 fat from one specimen, which was more than one-fourth of the 

 whole weight of the insect. The occasion for this prodigious 

 accumulation is chiefly to supply the insect during its continuance 

 in the pupa state, while the muscular structure of the limbs and 

 other parts of the body are in the course of development, and 

 also to serve, perhaps, as an immediate source of nutriment to the 

 insect at the period of its assuming the perfect state, and more 

 particularly during the rapid development of its generative func- 

 tions ; since, when these have become perfected, the quantity that 

 remains is very inconsiderable. But all larvae do not increase in 

 these amazing proportions, although their actual increase may be 

 more rapid. Those in which the proportion of increase is the 

 greatest are usually those which remain longest in the pupa state, 

 as in the species first noticed. Thus Redi observed in the maggots 

 of the common flesh flies a rate of increase amounting to about 

 200 times the original weight in twenty-four hours ; but the 

 proportion of increase in these larvae does not at all approach that 

 of the Sphinx and Cossus. From observations made on the larva 

 of one of the wild bees, Anthophora rctusa, Ave believe that this is 

 also the case with the Hymenoptcra. The weight of the Q.g^ of 

 this insect is about the 150th part of a grain, and the average 

 weight of a full-grown larva is six and eight-tenths grains, so 

 that its increase is about 1,020 times its original M-eight, which, 

 compared with that of the Sphinx of medium size, is but as 

 one to nine and three quarters, and to a Sphinx of maximum 

 size, only as one to a little more than eleven. 



" The changes of skin which a larva undergoes before it enters 

 the pupa state are more or less frequent in different species. In 

 the generality of lepidopterous insects it occurs about five times, 

 but in one of the Tiger-moths, Arctia caja, according to Messrs. 

 Kirby and Spence, ten times. A few hours before the change 

 is to take place the larva ceases to eat, and remains motionless, 



