INSECTA. 295 



it to soar into the air and quit for ever the raft so singularly pro- 

 vided for its use. 



(340.) Having thus become acquainted with the various con- 

 ditions under which insects arrive at maturity, and the principal 

 forms that they exhibit during the different stages of the meta- 

 morphosis, the reader will be prepared to investigate more mi- 

 nutely the changes in progress during the process, and the gradual 

 developement of the organs which successively make their appear- 

 ance. On examining the viscera of a Caterpillar, they are found 

 scarcely at all to resemble those of the butterfly or moth, into 

 which a larva of this description is ultimately matured. The 

 jaws (Jig. 136, i, 6), widely different both in structure and 

 office from the proboscis which represents them in the perfect 

 insect (Jig. 115), are strong and horny shears adapted to cut 

 the leaves of vegetables and other coarse materials used as food ; 

 the oesophagus (j%. 134, g, h) is strong, muscular, and capa- 

 cious ; and the stomach (A, i), in capacity corresponding with 

 the extraordinary voracity exhibited by the larva, passes insen- 

 sibly into a wide intestine (i, w), the line of separation being 

 only indicated by the entrance of the biliary vessels (k) that wind 

 in numerous convolutions around the posterior half of the alimen- 

 tary canal. It is sufficient to contrast this arrangement of the 

 digestive organs with what we have already described in the but- 

 terfly (Jig. 117), to appreciate the amazing dissimilarity: it would 

 be difficult indeed to imagine, did not anatomy convince us of the 

 fact, that the digestive apparatus of the imago, with its slender 

 oesophagus, dilated crop, short sacculated stomach, long and con- 

 voluted small intestine, and capacious colon, was derived from a 

 gradual modification of such viscera as those we have just been 

 considering. The salivary glands of the caterpillar (Jig. 134, q, r) 

 are large cylindrical caeca, and their ducts (p) pour into the 

 mouth an abundance of saliva proportioned to the coarse nature 

 of the materials used as food. 



The sides of the body are traversed by the wide longitudinal 

 tracheae, a, 6, c, that communicate on the one hand with the 

 lateral spiracles, and on the other give off at regular intervals 

 the air-tubes (d, e, e, e, e), which ramify most minutely over all 

 the viscera, and convey the atmospheric air throughout the entire 

 system. 



Besides the above organs, there are other viscera, which, al- 

 though of considerable importance to the caterpillar, would be 



