SHAPE OF DIGESTIVE CANAL RELATED TO FOOD 301 



Newport, while stating that the length of the alimentary canal in larvae is not 

 in general indicatory of the habits of the species, makes this qualification after 

 describing the digestive canal of Calandra as compared with that of Caiosoma : 

 "The length and complication of the intestines, therefore, appear to have some 

 reference to the quality of the food to be digested, since it is well known that 

 the food of these latter insects (weevils) is of difficult assimilation, being as it 

 is chiefly the hard ligneous fibres of vegetable matter ; but they cannot be re- 

 ceived as always indicatory of a carnivorous [or] vegetable feeder, since, as 

 above remarked, the length of the canal is considerable in one entirely carnivo- 

 rous larva, while it is much shorter in some herbivorous, and particularly in 

 pollenivorous larvae, as in the Melolontha and the apodal Hymenoptera." 



Newport also contends that the length of the alimentary canal is not more 

 indicative in the perfect insect of the carnivorous or phytophagous habits of the 

 species than in the larva. It is nearly as long (being from two to three times 

 the length of the whole body), and is more complicated, in the rapacious 

 Carabid* (Fig. 302) than in the honey-sipping Lepidoptera, whose food is en- 

 tirely liquid. Referring to the digestive canal of Cicindelida?, which is scarcely 

 longer than the body, he claims that "we cannot admit that the length of the 

 digestive organs, and the existence of a gizzard and gastric vessels, are indica- 



FIG. 802. Digestive canal of a carabid beetle: I, oesophagus; c, crop; d, proventriculus ; /, 

 mid-intestine, or " chyle-stomach," with its coeca ; (/, posterior division of the stomach ; i, the two 

 pairs of urinary tubes ; /;, intestine ; k, rectum ; I, anal glands. After Dufour, from Judeich and 

 Nitsche. 



tory of predacity of habits in the insect, because a similar conformation of parts 

 exists often in strictly vegetable feeders. The existence and length of these 

 parts seem rather to refer to the comparative digestibility of the food than to its 

 animal or vegetable nature." Newport then refers to the digestive canal of 

 Forficulidse (in which the gizzard is present, the canal, however, passing in an 

 almost direct line through the body, making but one slight convolution), "-a 

 farther proof that the length of the canal must not be taken as a criterion 

 whereby to judge of the habits of a species." He adds this will apply equally 

 well to the omnivorous Gryllidae, in which there exists a short alimentary canal, 

 but a gizzard of more complicated structure than that of the Dytiscidse. 



In larval insects and others (Synaptera, Orthoptera, etc.), in which 

 the digestive canal is simplest, it is scarcely longer than the body, 

 and passes through it as a straight tube. 



In the caterpillar, which is a voracious and constant feeder, the 

 digestive canal is a large straight tube, not clearly differentiated into 

 fore-stomach, stomach, and intestine ; but in the imago, which only 



