ALIMENTARY CANAL OF INSECTS. 



317 



tion represents the oesophagus (fig. 159, a a ; fig. 160, o). The stomach 

 and intestine succeed to this ; and if the body of the insect be very 

 thin, their course also passes nearly in a direct line to the tail. But in 

 those families which have the abdomen thick and largely developed, 

 especially if herbivorous, the intestine becomes much elongated and 

 winds upon itself in various convolutions; nevertheless, however tor- 

 tuous the canal may be, its windings are never sustained by any 

 mesentery or peritoneal investment : the air- tubes (that, as we shall 

 afterwards see, permeate the body in all directions) form a sufficient 

 bond of connexion, and one which is better adapted to the wants of 

 these animals. 



(832.) We must now examine more minutely the different portions 

 of which the alimentary canal may consist, premising at the same time 

 that the structures mentioned do not invariably exist together, as some- 

 times one part and sometimes another may be entirely wanting, or only 

 found in a very rudimentary condition. They are, the crop, the gizzard, 

 the stomach, the small intestine, and the large intestine. 



(833.) The crop, or sucking -stomach, as it is called by some writers, 

 is only met with in Hymenoptera, Lepidoptera, and Diptera insects 

 which have no gizzard*. In Bees, Wasps, and other Hymenoptera, it 

 is a simple bladder-like distention of the oesophagus (fig. 159, b) ; in 

 Butterflies and Moths it forms a 

 distinct bag, that opens into the 

 side of the gullet (fig. 160, v v) ; 

 while in the Diptera it is a de- 

 tached vesicle, appended to the 

 oesophagus by the intervention of a 

 long thin duct. This organ, which 

 in Bees is usually called the honey- 

 bladder, is regarded by Burmeister 

 (who founds the opinion upon the 

 result of experiments made by 

 Treviranus upon living insects) as 

 being not merely a receptacle for 

 food, resembling the craw of birds, 

 as llamdohrt and Meckel consider 

 it, but as being a sucking instru- 

 ment for imbibing liquids, by be- 

 coming distended, as he expresses 

 it, and thus, by the rarefaction of 

 the air contained within it, facili- 

 tating the rise of the fluids in the proboscis and oesophagus. It must, 

 however, be confessed that there is something very anomalous in the 

 * Burmeister, op. tit. p. 125. Treviranus, Vermischte Scliriften. 

 t Kamdohr, Ueber die Verdauungswerkzcugo der Insekten. Halle, 1811. 



Alimentary canal of the Honey Bee, Apia 

 melliftca. a a, resophagus ; b, the crop or suck- 

 ing-stomach ; c, d d, the stomach proper; e e, 

 small intestine;/, large intestine; g, anal ori- 

 fice ; A h, biliary vessels ; i i, auxiliary glands. 



