170 FOREST ENTOMOLOGY. 



Similarly, the cubital area shows, practically without exception, 

 either, as here, two, or perhaps more often three, nerves connecting 

 the radius with the cubitus {i n, j p). These, as crossing the cubital 

 field, are called the cubital nerves (1st, 2nd, &c.), and the divisions 

 into which they cut up that field are the cubital cells. (Three seems 

 to have been the original number of the cubital nerves. Where only 

 two appear, either the first or second of the original three has 

 vanished. Thus in Emphytus the first has gone, leaving only the 

 second and third ; whereas in Dolenis the two surviving nerves are 

 the first and third, the second being absent.) 



"Although these radial and cubital transverse nervures give, both 

 as to their number and direction, obvious and easy characters for 

 distinguishing both genera and species, they are unluckily liable, as 

 already mentioned, to considerable variation, — disappearance, duplica- 

 tion, displacement (within certain limits), irregular (atavistic) reap- 

 pearance, &c., in particular specimens, or even in one wing of a 

 specimen and not in the other ; so that it is very unsafe to trust 

 wholly, or even chiefly, to them in 'determinations.' 



" Very much more constant and trustworthy are the characters to 

 be drawn from the three nervures which cross the median field — viz., 

 I q (perhaps the most important nerve in the whole wing), the dis- 

 coidal nerve, m s, and on the medial nerves (1st and 2nd), the two 

 latter being better known probably to English readers as the 1st and 

 2nd 'recurrent,' and the former as the 'basal.' The characters of 

 these nerves can hardly ever mislead i;s, and are of the utmost con- 

 sequence in determining not merely genera or species, but families 

 and tribes, — such characters, e.g., as whether the discoidal nerve 

 strikes the sub-costa close to the origin of the cubitus (as in fig. 159), 

 or considerably before it {i.e., between the points h and I in that figure), 

 or Avhether it strikes {e.g., in Lyda, &c.) not the sub-costa at all, but 

 the cubitus ; and again, whether the discoidal and 1st medial nerves 

 are convergent (upwards) or sub-parallel, whether the two medial 

 nerves are received in the same cubital cell or in two different ones, 

 (I'c. The importance of these points for ' determination ' will appear 

 abundantly when we come to construct our future tables. Two more 

 transverse nerves only appear in my figure — viz., r, ic, the areal nerve 

 (called by Thomson rather oddly nervus transversus ordinarius, and by 

 Mr Cameron — e.g., see his Tables of Species for Empihytiis — the 

 transverse median), and t, x, the anal nerve. Of these the former is 



