﻿NORTH AMERICAN SPHINUID^E. 117 



which likewise extends nearly to the articulation of the head with the body. 

 This may probably be called the mentum, or chin, and articulates anteriorly with the 



Labium, or lower lip. This lies usually in a depression or pocket, at the point of 

 articulation with the mentum, and from which it can be thrust outward, so as to be 

 in advance even of the mandibles, especially in the spinners. It is a small, fleshy, 

 cushion-like lobe, having next its articulation with the mentum a corneous half 

 circle, which tapers within the head into slender processes on each side, and to which 

 are attached numerous sets of small muscles. In the middle of this movable lobe 

 will be found the spinneret, or a little tube, in which terminate the silk vessels, and 

 from which the silk liquid issues in the process of spinning. At each side of the base 

 of this tube, and almost in contact with it, are two minute, generally cylindrical, 

 jointed palpi, each terminating in a seta. These are the pair of 



Labial palpi, which sometimes attain such an excessive development in the imago. 

 In the spinners these organs are quite distinct, but in Ceratomia quadricornis the spin- 

 neret is surrounded by a collection of fimbriae which quite conceals it ; and the labial 

 palpi, which are applied against its sides, are also fimbriated at their extremities. 

 These might more properly, perhaps, be called filiform papillae, for they are fleshy 

 and soft, and unprovided with an investing tunic of corneous substance. The minute- 

 ness of the labial palpi in the caterpillar is quite worthy of observation ; and their 

 position, with reference to the spinneret, seems to connect their function in the 

 ' embryo, with the uses to which this latter instrument is applied. Whether the 

 structure of the organs of the labium, in larvae that do not spin, is similar to that of 

 G. quadricornis, I am unable to say ; but, in all the spinners I have examined, the 

 palpi are cylindrical and distinct. The labium is situated just beneath the inferior 

 point of contact of the mandibles, and is separated by a transverse sulcus from another 

 lobe, the greater portion of which lies within the mouth, and forms its lower surface. 

 This is the analogue of the inferior maxillm or lower jaws, in the mandibulated 

 orders, but in this I think it undoubtedly corresponds in function to the 



Tongue. It extends within the mouth to the commencement of the pharynx, and 

 is very distinctly divided by a sulcus in the median line. When viewed as a trans- 

 parent object, or even in place with a half inch lense, it is found to be covered with 

 minute fleshy papillae, which are also distributed over the portion exterior to the 

 mandibles. The superior part of the labium, however, is perfectly smooth, and pre- 

 sents no evidence of papillae. From the structure, position and use of this organ, I 

 judge it is endowed with the function of taste, and I cannot regard the fact as won- 

 derful or surprising, that it should be developed in the perfect insect, into an organ 

 obviously possessing the same function, and modified in form and physical appearance 

 agreeably to the requirements of a new existence. 



This organ in the perfect insect, {see figs. 3, 4, st.,) also called spiral maxilla;, anflin. 



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