Miscellaneous. 153 



the pairs of glands, the characteristic property of the saliva of the 

 Vertebrata, of rapidly converting feculent aliments into soluble and 

 assimilable glucose. 



In a great many cases (carnivorous insects, Orthoptera, &c.) the 

 oesophagus is dilated into a crop terminated by a narrow valvular 

 apparatus. The food, more or less divided by the organs of the mouth, 

 accumulates in this crop, which is very dilatable, is there impreg- 

 nated by peculiar neutral or alkaline liquids, and undergoes an evident 

 digestive action, the result of which, in carnivorous insects, is the 

 transformation of the albuminoid materials into soluble and assimi- 

 lable substances analogous to the peptones, and, in insects which 

 feed upon vegetable substances, an abundant production of sugar at 

 the expense of starch. This digestion in the crop is very slow ; and 

 until it is terminated the following part of the alimentary tube re- 

 mains empty. 



When the digestion in the crop has come to an end, the materials, 

 subjected to a strong pressure on the part of the walls of the organ, 

 glide or filter, by degrees, through the valvular apparatus (gizzard of 

 authors), being directed in their course by the furrows and chitinous 

 projections of the latter. The vascular apparatus is not a trituratory 

 organ auxiliary to the buccal organs ; for in the carnivorous beetles 

 and in the Locustina, in which it affects a classical form, the animal 

 or vegetable matters which have traversed it are found after the 

 passage in portions of the same size and form as before the opera- 

 tion. 



In the insects which have neither a crop nor a valvular appara- 

 tus, the food passes continuously into the middle intestine. 



In the middle intestine (chylific stomach of authors) the alimen- 

 tary materials which have resisted the action of the crop, or those 

 which have penetrated into it directly in the insects which do not 

 possess the crop and the valvular apparatus, are submitted to the ac- 

 tion of an alkaline or neutral, but never acid liquid, secreted either 

 by special local glands, as in the Orthoptera, or by a multitude of 

 small glandular caeca, as in many Coleoptera, or by a simple epithe- 

 lial lining. This has no analogy with the gastric juice of Vertebrates ; 

 its function is different according to the group to which the insect 

 belongs: in the carnivorous Coleoptera it is an active emulgent of fatty 

 matters ; in the Hydrophilian Coleoptera it continues the transforma- 

 tion of starch into glucose which commenced in the oesophagus ; in 

 the Scarabasida it also gives rise to glucose, but this action is local, 

 taking place in the middle intestine and nowhere else ; in the cater- 

 pillars of Lepidoptera it determines a production of glucose and at 

 the same time acts as an emulgent of fatty matters ; lastly, in the her- 

 bivorous Orthoptera there seems to be no further formation of sugar 

 in the middle intestine, but this body is produced and absorbed en- 

 tirely before passing the crop. 



The middle intestine is generally evacuated slowly and continu- 

 ously into the terminal intestine, the first portion of which, usually 

 long and slender, is very probably the seat of an active absorption. 

 The epithelial lining of the walls in some species seems, however, to 



Ann. & Mag. N. Hist. Ser. 4. Vol. xvi. 11 



