INSECT A. 379 



and dilated, and provided with two lateral conical glandular bodies.* 

 Hunter made experiments to determine the function of the appen- 

 diculated crop. " I kept a flj," he says, " for twelve hours without 

 food, and then gave it milk and killed it, and found no milk in the 

 crop, but it had got through almost the whole tract of intestines : 

 here the animal had immediate occasion for food, therefore the milk 

 did not go into the crop. This experiment at the same time shows 

 that every part of the intestine digests." Another time Hunter killed 

 his flies after they had drunk their fill, and found the crop full, as 

 well as the stomach and intestines : he suspects, therefore, that the 

 crop serves as a reservoir, and " that when there is more food than 

 what is immediately necessary, then it is thrown into the crop to be 

 used in future.'' f 



The result of Hunter's first experiment, and the absence of the 

 crop in the flea and some other suctorial insects, negative the idea of 

 Burmeister that the crop in Hymenoptera, Lepidoptera, and Diptera 

 promotes the suction of food by a voluntary power of self-expansion, 

 if even the structure of the part justified the idea; but, on the con- 

 trary, they prove it to be a receptacle of nutriment. 



In the Cicadidae the chyUfic stomach is of great length, intestini- 

 form, looped, and its termination is connected, penetrating in Cicada 

 beneath the muscular tunic of the first stomach, but it does not 

 conmiunicate therewith : the chymified fluids pass at once from its 

 termination into the intestine. 



The entire alimentary canal consists of three tunics, — an external, 

 fine, membranous, or peritoneal layer ; a compact muscular coat com- 

 posed of a layer of longitudinal and a layer of circular fibres, most 

 developed at the two extremes of the canal ; and an internal mucous 

 coat, the chitinous epithelium of which is thickest at the pharynx 

 and the rectum. Between the muscular and epithelial coats, in the 

 intestinal division, there is a white spongy layer of tissue, composed 

 of aggregated cells, compared by Ramdohr to transuded chyle, and 

 which is sometimes the seat of gastric glands. 



The several divisions and convolutions of the alimentary canal are 

 supported and attached to the adjoining parts by the air-vessels: 

 there is no mesentery. 



At least three kinds of glands add their secretions to those of the 

 caeca and follicles of the alimentary canal. The first kind open in or 

 near the commencement of the canal, and are regarded as salivary 

 glands. They are classified by Professor Burmeister as follows: — 



* Prep. No. 2123. , 



f Physiol. Catalogue of Hunterian Collection, vol. L p. 189. 



