354 ORGANS OF DIGESTION. 



form biliary vessels (B. m. m. /.). The small intestine 

 (B. u.) originates from a coecal cavity below the crop, and 

 forms a narrow convoluted tube, which dilates into a small oval 

 colon (B. h.) near the anus. This tubular anastomosing form 

 of the stomach, with four similar sacculated biliary vessels en- 

 tering its commencement, is seen in the aphrophora salicina 

 and other insects of this family. In the dorthesia characias, 

 the biliary vessels enter the narrow middle portion of a 

 similar anastomosing convoluted . gastric tube, and the 

 stomach describes the same circular course in the psylla ficus 

 where the biliary vessels are reduced, as in many other 

 insects, to four short isolated follicles. 



The salivary glands are nearly as general in the class of 

 insects, as the biliary vessels, and they are often accompanied 

 in predaceous insects, as in the nepa, with distinct poison- 

 glands, which present the same simple follicular structure. 

 Although the biliary vessels are most frequently four or six 

 in number, and terminate generally in the phyloric extremity 

 of the stomach, they often exceed a hundred, and terminate 

 around two or more distinct parts of the lengthened gastric 

 cavity. Where these primitive tubuli biliferi are very nu- 

 merous, as in many orthopterous, neuropterous and hyme- 

 nopterous insects, they are generally small, short, and separate 

 at their distal extremity ; where they are more lengthened 

 and complicated they often anastomose at their free ends, as 

 in the glands of higher animals. In most of the coleopterous 

 insects with two sets of biliary vessels, whether simple or 

 rammed, the ends of the anterior set anastomose with the 

 posterior as in separate lobules. By the low and oblique 

 insertion of the small intestine into the wider inferior portion, 

 a distinct and often capacious coscum-coli, analogous to that 

 of vertebrated animals, is formed in many insects, as in 

 pelogonus marginatus, ranatra linearis, nepa cinerea, and 

 other species. The lower part of the intestine, also, fre- 

 quently receives one or more urinary follicles, or tubuli urini- 

 feri, which are found to secrete urea as in higher animals, 

 and on which a small vesicle or urinary bladder is sometimes 

 distinctly formed as in ditiscus marginalis and several other 

 coleopterous insects. The alimentary canal of insects termi- 

 nates in the cloaca along with the genital organs, as in ovipa- 

 rous vertebrata. 



