THE ALIMENTARY CANAL. 



1 1 



larvae, this canal in all insects is terminated by a mouth at one end 

 and an anus at the other. The mouth opens upon the pharynx, 

 which, in the Coleoptera, is merely a slightly widened commence- 

 ment of the (esophagus, and need not be considered as distinct 

 from the latter. The oesophagus is a simple tube, varying in size 

 and length ; it is largest in those insects which feed on solid, 

 usually vegetable, food, and smallest in those living on liquid food : 

 it merges into the crop, but the latter is not always present, being 

 merely an enlargement, under special conditions, of the end of the 

 oesophagus, lined internally with a muscular coat. According to 

 Packard the crop is very large in locusts and other Orthoptera (with 

 the exception of the Piiasmidjs), in the Dermaptera, and most of 

 the imagines of the Coleoptera. In the larvae it is sometimes present 

 and sometimes wanting ; it exists in the larva of Ccdandra, for 

 instance, but not in that of Calosoma ; also, according to Beau- 

 regard, it is wanting in the pollen-eating beetles Zonitis, Sitaris, 

 and Mylabris, while in Meloe it is highly developed (Kolbe). 



In some orders of insects a thin pouch is present connected by 

 a sleuder neck with the end of the oesophagus : this is called the 

 " sucking stomach"; by older writers it was considered not to be 

 a receptacle for food, but to promote the suction of food " by dis- 

 tending at the will of the insect, and thus, by the rarefaction of 

 the air contained within it, facilitating the rise of fluids in the 

 proboscis and oesophagus." Graber, however, has proved that, 

 though generally found to contain nothing but air, it is simply a 

 reservoir for the temporary reception of food. This he did by 

 feeding flies with a coloured sweet fluid, and observing that the 

 organ could " be seen tilling itself fuller and fuller with the 

 coloured fluid, the sac gradually distending until it occupied half 

 the hind-body." * 



The so-called " sucking stomach," however, does not occur iu 

 the Coleoptera. In this order the oesophagus, or the crop, if 

 present, is followed by the proventriculus or fore-stomach, a small, 

 narrow, tubular, or subglobose cavity, furnished w T ithin with rugose 

 folds, teeth, spines, or horny ridges. This organ is well developed 

 in all the carnivorous and wood-feeding beetles (notably the 

 Carabine, DvTisciDiE, and Scolytii)^:), and in fact, in all man- 

 dibuiate insects which feed on hard and indigestible substances ; it 

 has usually been considered to correspond with the gizzard of the 

 gallinaceous birds, and this opinion is still held by many, although 

 some think that its function is rather that of straining than tritu- 

 rating, and others consider that the teeth, etc. are merely used to 

 pass the food backward into the mid-intestine, which follows just 

 behind the proventriculus. 



The " mid-intestine," " ventriculus," " chylific ventricle," or 

 "chylific stomach" is very differently described by different authors, 

 owing to its variability. Sometimes, as Dr. Sharp says, it is very 



* See Packard, A Text-Book of Entomology, p. 305. 



