INSECTA. g[l 



lives on the back and under the skin of homed cattle, and feeds on the pus 

 which is formed by the tumors occasioned by their residence. Other larvae 

 ot the same genus are found in the stomach of the horse, around the pylorus, 

 and sometimes in the intestines ; and sheep, horses, and oxen feed the larvae 

 of another species of ceslrus in their frontal sinuses, on the fluid which 

 exudes from the nose. In short, no animal seems free from the depreda- 

 tions of insects ; and some larvae live even in the interior of the body of 

 other species, as the large family of the ichneumons, the cinips of Geoffroy, 

 and the sphex of Linnaeus. 



The organs of deglutition, in insects, present nothing very remarkable. 

 The oesophagus is a straight canal, passing between the brain and the first 

 nervous ganglion. It is surrounded by the nervous matter which joins the 

 two principal organs of sensation. This part of the oesophagus is perhaps 

 the seat of the organs of taste. In the gnawing insects, the alimentary 

 matters, after having been cut and reduced to snic.ll portions by the action 

 of the mandibles, are carried to the pharynx. In the suckers, the nutritive 

 fluids are carried there by the pressure of the sucker. 



The organs of digestion comprise the stomach and the intestinal canal. 

 These are, according to M. Marcel de Serres, formed of three membranes. 

 The stomach presents great variety in point of form, and has been distin- 

 guished by Latreille, into three kinds, which he distinguishes as simple, 

 double, and multiple. The stomach of the first form occurs in the greater 

 part of the insects. In some it is simply membranous ; in others it is mus- 

 cular; and in a third group it is not evident, that is, the oesophagus is not 

 dilated. Those which have the stomach membranous and dilated, live 

 generally on the nectar of plants, such as the bees, butterflies, &c. ; those in 

 which the stomach is muscular, are chiefly the hemiptera ; and those in which 

 this viscus is not dilated, feed commonly on leaves or roots, which they 

 gnaw and eat. The insects which have a double stomach are the coleoptera 

 which feed on living prey, such as the hydrocanthari, the cicindeletce and the 

 carabidcB. The greater part of the orthoptera are remarkable for the appa- 

 rent multiplicity of their stomachs. The mole cricket of gardens has four. 

 This insect and others analogous have been considered as ruminating 

 insects, or as having the faculty of returning again to their mouth the ali- 

 ments in their organs of digestion. In insects, it is to be remarked, there 

 often exist great differences in the structure of the intestinal canal, properly 

 so called, in the state of larvae, and in the perfect insect. Thus, in the 

 caterpillar of the butterfly there is an oesophagus dilated abruptly to form a 

 cylindrical stomach, with three transverse rows of ccecums totally different 

 from the form of the same parts in the perfect insect. Similar differences 

 nave been observed in the larva of the bee, and indeed occur in many 

 groups. This change of structure is necessary for the accommodation of 

 the animal to its changes of food; but when the larvae and the perfect insect 

 feed on the same materials, this alteration in organization does not take place. 



