OF INSECTS. 139 



certain neuropterous groups, such as the Hemerobii, 

 and, in maity instances, particularly among the Or- 

 thoptera and Hymenoptera, they amount to a hun- 

 dred and fifty. Their length generally bears some 

 proportion to their number, a deficiency the one 

 way being compensated by an increase in the other 

 The longest surpass the dimensions of the body five 

 or six times. Although commonly of the same dia 

 meter throughout their whole extent, they are occa- 

 sionally attenuated at one or both extremities. Nu- 

 merous constrictions at regular intervals, in a few 

 instances, give them the appearance of being granular 

 or warty. One of tie most notable deviations from 

 their generally simple construction is witnessed ii 

 the cockchafer, in wh?ch they appear fringed with a 

 double row of thickset projecting processes of equai 

 length, some of which are furcate ; (PL II. fig. 3, e, e.) 

 their composition, also, is greatly more simple than 

 that of the alimentary canal, the coat consisting of a 

 single membrane of great delicacy. It is likewise 

 transparent, permitting the view of the contained fluids, 

 which are most frequently brown or saffron yellow ; 

 the prevalence of the latter induced Swammerdam tc 

 call the whole organs saffron-vessels. 



The last system of vessels which we shall notice 

 at present in connection with the alimentary tube, is 

 that formed by the urinary vessels. In their general 

 aspect they almost seem to repeat, at the anal ex- 

 tremity of the body, the salivary vessels appended to 

 the head. But their presence seems to be far less 

 general, or at least they are more difficult to detect* 



