216 THE VITAL FUNCTIONS. 



small triangular teeth in each row. All the 

 teeth contained in this organ are of a brown 

 colour and horny texture, resembling tortoise- 

 shell. 



The same insect, as we have seen, often 

 exhibits, at different periods of its existence, 

 the greatest contrast, 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 dimen- 

 sions, is sufficiently supported by small quantities 

 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 concen- 

 trated form. It is evident that the same appa- 

 ratus, which is necessary for the digestion of the 

 bulky food taken in during the former period, 

 would not be suited to the assimilation 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 interest- 

 ing to trace the gradual transitions in the confor- 

 mation of the alimentary canal, during the pro- 

 gressive developement of the insect, and more 



