320 



TEXT-BOOK OF ENTOMOLOGY 



ment, and is more or less eversible. It is protected above in cater- 

 pillars, and other insects with 10 free abdominal segments, by the 

 suranal plate. It is bounded on the sides by the paranal lobes, while 

 beneath is the infra-anal lobe. 



The anus is wanting in certain insects, and where this is the case 

 the hind-gut, owing to a retention of the embryonic condition, is 

 usually separated from the mid-intestine. (See p. 300.) 



Some remarkable features of the digestive canal in hemipterous insects are 

 noteworthy. In the Coccidfe, according to Mark, the anterior end of the long 



mid-intestine forms, with the hinder end of the oesoph- 

 agus, a small loop, whose posterior end is firmly 

 grown to the wall of the rectum, and forms a cup- 

 like invagination of the latter. Then the rest of the 

 tube-like stomach turns sidewise and forms a large 

 loop, which turns back on itself and occupies a large 

 part of the body-cavity. This loop receives on the 

 anterior end, near the oesophagus, the two urinary 

 vessels, and forms just below the opening into the 

 rectum a short caecum. 



In other homopterous genera (Psyllidse and some 

 Cicadidse) Witlaozil describes nearly the same peculi- 

 arity, the mid-gut and part of the intestine forming 

 a loop growing together for a certain distance and 

 winding round each other (Fig. 321). 



Histology of the digestive canal. In all the 



divisions of the digestive canal of insects the 

 succession of the cellular layers composing 

 it is the same : 1st, a cuticula ; 2d, an epithe- 

 Hum ; 3d, connective tissue ; 4th, muscular 

 tissue. In the locust, the first division of the 

 canal (fore-gut), there are two muscular coats, 

 an internal longitudinal and an external cir- 

 cu ] ar coa t . the fibres are all striated. The 

 lining epithelium is not much developed, but 

 forms a thick, hard, and refringent cuticula, which is thrown up 

 into spiny ridges. In the second division (mid-gut, "stomach") the 

 epithelium is composed of very high columnar cells, which make up 

 the greater part of the thickness of the walls, while the cuticula 

 is very delicate, slightly refringent, with no ridges, and is probably 

 not chitinous; the fibres of the muscular coats are not striated, 

 while this division is also distinguished by the presence of glandular 

 follicles and folds. The stomach and the csecal appendages have 

 all these peculiarities in common, while no other part of the canal is 

 thus characterized. 



, 



i !lrt 



321 - Enteric canal 

 / S?lSS,- 



nary 'vessdsT'f th<J 



a^T'th^ mnst in anterior 

 "f 1 '"' "i'-'testine. - 



. 



After Witlaczil, from Lang. 



