THE ORGANS OF NUTRITION. 125 



Meloe, Chrysomda, Blatta, and the grasshoppers (PI. XXI. f. 2 and 

 3), internally covered with short stiff setae and teeth ; the muscular 

 fibres of the exterior membrane generally lie regularly above each 

 other, but they sometimes form a loose confused net-work from open 

 spaces remaining here and there between them. 



The separation of the oesophagus from the stomach is effected some- 

 times by a positive constriction (Diptera, PI. XVIII. f. 3.) ; it occa- 

 sionally passes insensibly into it, and sometimes the crop intervenes 

 between them, as the organ of transition ; in this case the oesophagus 

 expands by degrees into a sack-shaped CROP (ingluvies, PI. XVIII. 

 f. 1. B, B,) which] takes the place of a first stomach, and prepares the 

 swallowed food for digestion. In GryUotalpn it occurs as a perfectly 

 sack-shaped appendage of the oesophagus * (PL XXI. f. 7-)- To 

 facilitate this the inner surface of the crop is covered with glands (for 

 example, in Dyticus, Blatta, &c.), the secretion of which has the func- 

 tion of a preparing juice. Such an expansion of the oesophagus before 

 the proventriculus might readily be considered as analogous to the 

 crop of the higher animals, of the birds, for example; an opinion which 

 Ch. L. Nitzsch has already propounded-]-. The expansion, however, 

 without a contemporaneous proventriculus, is of a different and peculiar 

 kind, namely, the sucking stomach, indicated by G. R. Treviranus, 

 and which we proceed to describe. 



* 



THE SUCKING STOMACH. 

 103. 



The Hymenoptera, Lepidoptera, and Diptera are the orders in which 

 the proventriculus is deficient, but they possess, nevertheless, a bladder- 

 shaped distension of the oesophagus (PI. XVII. and XVIII. c, c,), 

 which in the first lies directly in front of the cardia ; in the second it 

 forms a distinct bag, which opens into the oesophagus, contiguous to 

 the cardia; and in the third it hangs appended to the oesophagus by 

 means of a long thin duct, frequently far in front of the opening of the 

 stomach. This organ is the before-named sucking stomach. Its function 

 does not consist in being a receptacle for nutriment, but in promoting 

 the suction of food, by distending, at the will of the insect, and thus, 

 by the rarefaction of the air contained within it, facilitating the rise of 



See Sucko\v,in Reusing. Zeitschrift. f. d. Org. Php. vol. 3. p. 53. PI. II. f. 134. 

 f Gattungen dcr Tliier-Inseckten, Germar's Magaz. iii. p. 280. 



