THE ORGANS OF NUTRITION. 143 



ilium), for example, the Cerambyclna, most of the Neuroptera, and the 

 Cicadaria. 



The length of the biliary vessels is in direct proportion to their num- 

 ber, for when there are but few they are very long, indeed the longest 

 of all (for example, Melolontha) ; but they are short, on the contrary, 

 where they are numerous, for example, in Gryllotalpa, Libellula, &c. 

 The long biliary vessels lie generally around the intestine ; they first 

 ascend parallel to the stomach as far as the pharynx, they then return 

 and form a thick knot of vessels around the ilium ; where there are many, 

 some return upwards along the stomach, and the rest below along the 

 ilium. The length also of the single biliary vessels sometimes varies, 

 for example, in the Cerambycina, in which they form concentric circles, 

 but the two opposite sides are always of the same length. 



The biliary vessels are also always more simply constructed than the 

 intestinal canal, for they appear to consist of but a single skin, which, 

 besides, is very delicate and transparent, so that their contents can be 

 distinctly recognised as a finely granulated mass. The delicacy of the 

 smooth shining case is proved by the difficulty of removing the biliary 

 vessels from the enveloping fatty substance, and by their being very 

 easily torn, even when the greatest precaution is used. 



In colour they generally resemble the yellowish white of the intes- 

 tinal canal ; in some beetles (for example, Carab^ls, Dyticus,} they are 

 of a dark brown, but which becomes paler as it approaches the opening. 

 In many caterpillars, while parallel with the stomach they are whitish, 

 but at the intestine of a saffron yellow ; Swammerdam thence applied 

 the name of saffron vessels to them. 



It may be here remarked, at the close of our observations upon 

 the biliary vessels, that some insects in which they are numerous, 

 for example, the bees and wasps, have in their larvae state but few 

 (4 6) long and thick ones, which, by degrees, whilst during the pupa 

 state the remaining gall vessels are forming, shrink up, and become 

 shorter until they contract to the same length as the rest *. Do they 

 not perhaps entirely disappear, and are replaced by the shorter ones ? 

 Perhaps they are very different vessels possessing a different function, 

 which probably disappears when the intestine and anus become formed 

 in the insect. 



* See Raradohr, PI. XIT. 



