226 HALIDAY ON 



she can find no footing on them. As they are accessible, and 

 not defended by hair or a tough coat, the borer itself is short 

 and delicate. A summary of these particulars will afford the 

 most comprehensive notion of the group. 



An acquaintance, though imperfect, with the economy of the 

 insects composing it, has afforded, in the relation which 

 subsists between this and the form of the parts in the imago, 

 some data for estimating the comparative importance of their 

 several variations. In the general considerations we have, 

 consequently, ventured to overlook distinctions such as else- 

 where are of much significance, and to assemble species 

 offering considerable diversity in the antennae, wings, and 

 feelers. Hence we may be prepared to find the influence of 

 similar variations modified and subdued, to a certain extent, 

 in contiguous groups ; while, in pursuing the chain a little 

 further, some or all of these organs may affect a determinate 

 character, through a protracted series of affinities. In the 

 present family, generally, the antennae may be said to vary 

 indefinitely with sex and species ; and, where we detect the 

 tendency to a typical number, there is room to suspect an 

 approach to one or other of the remaining Parasitic families, 

 which has (if I may express it so) communicated its character 

 to such adjacent groups. These approaches are few and 

 evanescent, and while they may serve to indicate the external 

 relations of the family, do not seem applicable, in a primary 

 degree, to the further subdivision of it. The cells of the 

 wings, by their number, figure, and position, afford distinctions 

 generally precise and easily apprehended, constant in the 

 sexes, and whose variations may be referred to a limited 

 number of types ; but these are not so readily generalized, 

 and, on account of the abrupt transitions between them, some- 

 times yield no clew to the connexion of the groups which they 

 distinguish. At the same time they furnish most convenient 

 characters for the separation of the minor groups ; and, if 

 carefully compared with the variations of other parts, will be 

 often of the highest value as obvious indications of characters 

 more influential, but also more difficult of investigation. The 

 mouth, whose structure enters so largely into most systems, 

 does not exhibit much variety of development among insects 

 whose instruments of industry and weapons of defence are 

 seated elsewhere, and which scarcely seem to require nourish- 



