'126 PHYSIOLOGY. 



hours 150 times its own weight ; but the common caterpillar of Euprepia 

 Caja, which weighed thirty-six grains, and every twelve hours rejected 

 from fifteen to eighteen grains of excrement, increased only one or two 

 grains in weight in the same space of time *. The increase in weight 

 appears to be much greater in carnivorous larvae, for, according to 

 Redi t, the maggots of the flesh-flies, which at first weighed one grain, 

 so increased, that each, on the following day, weighed seven grains, 

 which gives a proportion of increase, in twenty-four hours, of from 

 1 to 200. 



After the third moulting, when the larva has acquired its full size, 

 the rudiments of the wings begin to form beneath the skin, upon the 

 first and second segments. They at first present themselves as short 

 viscous leaves, the substance of which greatly resembles that of the 

 mucous tunic, and to which many delicate tracheae pass, which dis- 

 tribute themselves throughout them. These rudiments increase with 

 the growth of the caterpillar, and betray themselves, even externally, 

 by both the segments of the caterpillar, upon which these rudimentary 

 wings are found, appearing swollen and spotted. Their enlargement 

 probably takes place by the assistance of the blood flowing into them. 

 Simultaneously with the perfecting of these rudiments the intestinal 

 canal increases in compass, and, as a consequence of this increase there 

 is a greater accumulation of the fatty mass. A transformation is also 

 taking place in the anterior feet of the caterpillar, for the larger legs 

 of the butterfly begin to form. But, as a similar transformation is 

 going on in the oral organs, the caterpillar loses its desire to eat and 

 power of mastication, it ceases to receive food, and prepares itself for 

 its last moulting, viz., for its change into the pupa. It seeks for this 

 purpose an appropriate place where it can lie, hang, spin, or attach 

 itself, and it accomplishes this, its last business, the same as its earlier 

 ones, with great care and consideration. After its situation and web 

 are prepared it reposes a few days, then strips off its skin, and now 

 presents itself as a pupa, with the visible limbs of the butterfly. 



It is striking that insects, notwithstanding such a great, and, we might 

 almost say, unexampled, capacity of production which is exhibited both 

 in their rapid growth and the increase of the body in mass as well as 

 in the development of new parts and the enlargement of the old ones 

 during the pupa state, display but very slight traces of a power of re- 



* Kirby and Spence, vol. i. t De General. Insectorum, p. 27. 



