142 ANATOMY. 



baccarum. Occasionally, also, the openings of the gall vessels do not 

 lie by the side of but above each other, for example, in some of the 

 Neuroptera, in which four of the eight biliary vessels enter upon the 

 one side and the other four upon the other side of the intestine (Myr- 

 mccoleori). If many biliary vessels exist their mouths lie contiguously, 

 above and below each other, or although more rarely, all upon one side 

 (Acliet(i), or else they unite into a tolerably long evacuating duct, 

 (for example, Gryllotalpa). 



In form these vessels are generally narrow, cylindrical, filiform, and 

 twisted, but they are not always of the same dimensions throughout : 

 many commence narrowly and afterwards double in size; some, by means 

 of a spiral furrow, resemble a turned slip ; others have alternately 

 small vesicular distensions (Musca) ; a few have long rectangular pro- 

 cesses, which are occasionally furcate (Melolontha vulgaris). 



There are generally FOUR in number, never fewer, unless entirely 

 wanting (Chermes, Aphis), sometimes there are six or eight, and they 

 are even, occasionally, innumerable. These differences in number are 

 regulated by the order to which the insect belongs as well as by its food, 

 whether it be vegetable or animal, as is shown in the following table : 

 I. No biliary vessels, Chermes, Aphis. 

 II. Few (4 8) biliary vessels. 

 } . Four biliary vessels. 



a. Free at the end; most Diptera, as well as the families 



Termiiina, Psocina, and Mallophaga, of the order 

 Dictyoloptera. 



b. Anastomosing ; many Coleoptcra, Hemiptera, and 



Diptera. 



2. Six biliary vessels. 



a. Anastomosing ; many Coleoptcra, for example, Ce- 



rambycina and Chrysomelina. 



b. Free at the end, Lepidoptera. 



3. Eight free biliary vessels, Neuroptera. 



III. Many biliary vessels, Hymenoplera, Orthoptcra, and the Dic- 

 tyotoptera subnlicornia. 



Occasionally the biliary vessels join the intestinal canal at a second 

 place, but this union takes place only with the exterior muscular mem- 

 brane, for it is attached by means of solitary fibres, but a second open- 

 ing into the intestine does not occur. This union is found chiefly in 



those insects furnished with a clavate intestine (the analogue of the 







