56 GENERIC DISTINCTIONS. 



tures. Each appendage is enveloped in a thin pellicle. 

 Green is the commonest colour in the pupal state. 

 Sometimes there are yellow or orange spots on the 

 abdomen, but only if these colours were present in the 

 larva. The pupa state does not last over twelve or 

 fourteen days, as a rule, and may be shorter. When 

 the perfect state is reached the insect does not leave 

 the cocoon until its wings, &c., have hardened, and 

 the pupal skins have been got rid of. It quits the 

 cocoon by cutting off one end, which is done in 

 Nematus, &c., by cutting out the end roughly, but 

 with Lophyrus and Oimbex a neat lid is cut, which 

 remains attached to the cocoon by one end after the 

 insect has left. 



Generic and Specific Distinctions. 



It must be said that it is not at all an easy matter 

 to find characters that will differentiate clearly the 

 larger groups and the genera, and even if we are able 

 to do so with European species difficulties arise when 

 exotic species are taken into account. Thus, Strong y- 

 logaster and Selandria are tolerably distinct and well 

 defined if we only regard our own species, but when 

 we come to arrange the Central American species all 

 distinction between the two breaks down. Similarly, 

 by following too closely the alar-cell structure in 

 fixing the genera species otherwise dissimilar are 

 placed together, and removed from among species 

 with which they agree in other peculiarities of struc- 

 ture. 



Peculiarities in the antennae, thorax, legs, and 

 abdomen appear to afford the best characters for 

 defining the tribes. For the sub-tribes the neuration 

 of the wings is of use. The genera may be defined by 

 peculiarities in most parts of the body, but more 

 especially in the (a) antennae, as regards the number 

 of the joints, their relative length, and their covering; 

 (b) the neuration of the wings, and more especially the 



