DIGESTIVE ORGANS OF INSECTS. 1,91 



trast, not only in external form, but also in its habits, 

 instincts, and modes of subsistence. The larva 

 is generally remarkable for its voracity, requiring 

 large supplies of food to furnish the materials for its 

 rapid growth, and frequently consuming enormous 

 quantities of fibrous vegetable aliment : the perfect 

 insect, on the other hand, having attained its full 

 dimensions, is sufficiently supported by small quan- 

 tities of a more nutritious food, consisting either of 

 animal juices, or of the fluids prepared by flowers, 

 which are generally of a saccharine quality, and 

 contain nourishment in a concentrated form. It is 

 evident that the same apparatus, which is necessary 

 for the digestion of the bulky food taken in during 

 the former period, would not be suited to the assi- 

 milation of that which is received during the latter ; 

 and that in order to accommodate it to this altered 

 condition of its function, considerable changes must 

 be made in its structure. Hence, it will be in- 

 teresting to trace the gradual transitions in the 

 conformation of the alimentary canal, during the 

 progressive developement of the insect, and more 

 especially, while it is undergoing its different me- 

 tamorphoses. 



These changes are most conspicuous in the 

 Lepidoptera, where we may observe the successive 

 contractions which take place in the immensely 

 voluminous stomach of the caterpillar, while pass- 

 ing into the state of chrysalis, and thence into that 

 of the perfect insect, in which its form is so 

 changed that it can hardly be recognised as the 

 same organ. I have given representations of these 

 three difterent states of the entire alimentary canal 

 of the Sphinx ligustri, or Privet Hawk-moth, in 



