DIGESTIVE ORGANS OF MOLLUSCA. 193 



gizzard, which is developed only in the moth, at 

 G, Fig. 328. 



It will be seen that in the caterpillar, (Fig. 320), 

 the stomach forms by far the most considerable 

 portion of the alimentary tube, and that it bears 

 some resemblance in its structure and capacity to 

 the stomachs of the Annelida, already described.* 

 This is followed by a large, but short, and per- 

 fectly straight intestine, to the coats of which are 

 appended a great number of membranous processes 

 containing masses of fat; a substance which ap- 

 pears to be laid up as a store of nutriment to meet 

 the great demands of the system consequent on the 

 rapid growth of the larva, its frequent renovation 

 of integument, and its subsequent metamorphosis 

 into the pupa state, when it is deprived of the 

 means of taking food. The quantity of fat thus 

 accumulated is more considerable in the larvae 

 which inhabit cold climates, and which have to 

 remain in this state of inactivity during a long 

 winter. No provision of this kind, or scarcely any, 

 is made in the larvai of those insects which undergo 

 only a semi-metamorphosis, and which, not having 

 to pass through the state of a chrysalis, continue 

 uninterruptedly to consume food. 



The digestive organs of the pupa (Fig. 327) have 

 undergone considerable modifications ; the whole 

 canal, but more especially the stomach, being 

 contracted both in length and widthf : the shorten- 



* See the figures and description of those of the Nais and the 

 Leech, p. 91 and 92. 



t Carus states that he found the stomach of a pupa, twelve days 

 after it had assumed that state, scarcely half as long, and only one- 

 sixth as wide as it had been in the caterpillar. 

 VOL. II. O 



