390 Introduction to Animal Morphology. 



of grouping into larger series.* There are retractors and 

 occlusors of the spiracles, and numerous muscles for the 

 limbs and wings, which nearly fill the entire thorax. 



The pharynx has often lobate processes [epi- and 

 hypo-pharynx) on its under surface, not to be con- 

 founded with outer movable processes of the tongue 

 or paraglossa. The oesophagus is often dilated into a 

 crop which may be a thin-walled and pedunculate,t 

 lateral sucking stomach ; double in Chrysis and Lepi- 

 doptera ; the proventriculus, or gizzard crop, has mus- 

 cular walls and chitinous teeth, absent in suctorial 

 insects ; the thin-walled stomach has no chitinous lin- 

 ing, but is glandular, often with caeca or villi within. 



The small intestine, or ilcinn, which follows, ends in the 

 rectum, at whose lower end are 4-6 longitudinal ridges, on 

 which rectal glands open. The length of the intestine 

 varies with the solidity as much as with the nature of the 

 food ; thus the vegetable-feeding suctorial Cicada has a long 

 intestine, while the grasshopper has a much shorter one. In 

 larvae the gastric region is long, and the intestinal short, 

 while in the adults these conditions are more than reversed, 

 and the intestine generally becomes curled. The stomach 

 may have caeca along its entire extent, or only at its origin 

 (Orthoptera), two (Locusts and Crickets), six (Acrididae), 4-8 

 (Perlidse), none (Earwig and Phasma) ; the stomach itself 

 may be long and convoluted, as in Melolontha, Bees, &c. 

 The rectum generally dilates at its pre-anal end, and there 



* Each wall of the caterpillar of the cabbage butterfly consists from within 

 outward of— first, two layers of longitudinal ; second, superficial and deep 

 internal obliques ; third, superficial and external obliques ; fourth, a super- 

 ficial rectus, fifth, another layer of oblique fibres ; sixth, triangular diagonal 

 fibres ; seventh, transverse fibres in several layers. 



t Where the duct of this sucking stomach joins the oesophagus there is 

 a flat muscular sucking dis:. 



