316 INSECTA. 



likewise communicate with the commencement of the oesophagus, so that 

 the Lepidoptera have, as it were, two mouths, or rather two separate 

 methods of imbibing nourishment one through the common canal 

 formed by the junction of the whip-like jaws, the other through the 

 cavities of the filiform maxillae themselves ; such an arrangement, how- 

 ever, which would be quite anomalous, may reasonably be doubted. 

 In this mouth, therefore, all the parts, except the maxillae, would seem 

 at first sight to be wanting ; they may nevertheless be detected upon a 

 very careful examination, and rudiments of the upper lip, of the man- 

 dibles, of the lower lip, as well as of the labial and maxillary palpi, be 

 distinctly demonstrated. 



(830.) The last kind of mouth to which we shall advert is that met 

 with in the Louse tribe (Pediculi) ; but, from the extreme minuteness 

 of the parts composing it, the details of its structure are only imperfectly 

 known. It seems to consist of a slender external tube, wherein a sharp 

 sucker, armed with barbs adapted to fix it securely during the act of 

 sucking, is lodged ; when feeding, the barbed piercer is denuded and 

 plunged into the skin, where it is retained until a sufficient supply of 

 nourishment has been obtained. 



(831.) Inviting as the subject is, we are compelled, by the strictly 

 general character of our investigations, to abstain from entering upon 

 further details concerning the mouths of perfect insects, and consequently 

 to omit noticing innumerable secondary modifications in the mechanical 

 structure of the oral organs of these little animals. When we turn 

 our attention to the consideration of their internal viscera, connected 

 with the preparation and digestion of so many different materials, we 

 may well expect to find equal variety of conformation ; and, in fact, 

 the course, dimensions, and relative proportions of the alimentary canal 

 will be seen to be different, to a greater or less extent, in almost every 

 species. Considered as a whole, the internal digestive apparatus of 

 insects must be regarded as a delicate membranous tube, in which the 

 digestion of the substances used as food is accomplished partly by 

 mechanical and partly by chemical agency. For the former purpose, 

 gizzard-like muscular cavities are not unfrequently provided; and to 

 fulfil the second, various fluids are poured into the canal in different 

 parts of its course. The arrangement of the cavities and the nature of 

 the secreting vessels will, however, be modified in conformity with the 

 necessities of the case, and certain parts will be found to exist, or to be 

 deficient, as circumstances may require ; it would be absurd, therefore, 

 to attempt to describe particular examples ; our observations must be 

 of general application, and such as will enable the reader to assign its 

 proper function to any organ which may present itself to his notice. 

 The first part of the digestive apparatus is disposed in the same manner 

 in all insects, and is a slender canal arising from the mouth and passing 

 straight through the thorax into the cavity of the abdomen ; this por- 



