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NORTH AMERICAN SPHINGID^E. 115 



flower simply by its color ; that it can traverse fields and regions in the night time 

 where the most varied vegetation is intermixed, and select the appropriate food plant 

 of its young with the certainty of an educated botanist, without the aid of some 

 special sense. And it is plain too, that the determination of the food plant, is not 

 arrived at in the two states in the same manner. The larva never rejects a substi- 

 tuted food until it has first tasted it, and the imago has no organs of manducation 

 with which to determine the food plant by the sense of taste. The selection is the 

 result of the action of different senses, perhaps more developed in one of its states than 

 in the other. It would not be hazarding too much to say, that in consequence of 

 being invariably placed in the midst of its appropriate nourishment, and but rarely 

 compelled from accidental causes to seek it, we would expect to find the sense of 

 taste specially developed in the larval state ; and from the acts of selection by the 

 imago, we should look in it for that of smell as well as taste, as important sensorial 

 endowments. Whilst this may be admitted in general, the specification of the organs 

 devoted to specific functions, will doubtless be objected to, and I am well aware that 

 a subject so interesting physiologically should be approached cautiously, However, 

 in describing the accessory organs of the head, the question of their functions naturally 

 arises, and when this is not immediately obvious, it should be an object with every 

 student to endeavor to ascertain them, both by microscopic examinations and dissec- 

 tions, and by experimental observation. I regret my own efforts towards this end 

 have been too few and too recent to justify, perhaps, positive inductions, but such 

 as they are, they will be given in the hope that others may be induced to pursue the 

 subject. 



The most noticeable organs belonging to the head of caterpillars are two corneous, 

 strong, central, horizontally-acting mandibles, or upper jaws, which meet each other 

 on the median line of the body. These are the only instruments of manducation 

 of the mouth, and their opposite faces form surfaces almost smooth, or present 

 cavities and irregularly arranged ridges ; or they are thin, and overlap each other, 

 and are furnished with serrated or toothed edges adapted for cutting or gnawing. 

 These are the only forms I have observed in the larva. These organs are covered 

 superiorly on their upper surface by the 



Labrwm or upper lip. This is attached to the lower edge of a triangular or lance- 

 shaped piece, placed in the lower portion of the median suture of the head, and may 

 be called the clipeus. The labrum consequently is placed in the centre of the head, 

 overhanging the mandibles, and is in contact with them. The upper portion is mem- 

 branous, and the lower consists of a subcorneous plate, at least externally, which is 

 excised or deeply emarginate centrally, and therefore presenting an obtusely rounded 

 lobe on each side of the median line. This subcorneous portion is capable of being- 

 retracted and depressed by two bundles of muscles with long tendons, which are 



