632 EXTERNAL ANATOMY OF INSECTS. 
are none*; in many, as Prosopis, Nomada, Andrena®, 
though there is the usual number, they are incomplete 
and do not reach the margin. The dasal areas are of 
little importance in assisting to determine genera; they 
are most commonly ¢wo in number, but in Cynips, &c., 
there is only one‘. The shape and other circumstances 
of the areolets vary considerably in different genera and 
species : upon these however I shall not enlarge further, 
but proceed in the next place to consider very briefly 
the wings of the Diptera Order as to their neuration. 
These are not so easily made subservient to a genera 
plan. The basilar areolets are now reduced considerably 
in length, occupying merely the base of the wing 4; the 
medial are become less numerous and important*; and 
the apical, in a variety of instances, are the most con- 
spicuous ; in some wings, as in those of Scatopse, the 
Intermediate Area has no nervures or areolets, or only 
spurious ones; in Psychoda the nervures diverge from 
the base almost without branching, so as to form no 
closed areolets §; in many, the lower medial areolets are 
very long, resembling the basilar in Hymenoptera® ; these 
are often crowned by a single small one, as in the Stra- 
tyomide, Tipula, &c., from which numerous branches 
proceed to the margin'; but in Musca two large ones 
approach the margin, the anterior one having an angle 
open to it*; in the Hippoboscide almost the whole of 
* Jurine Hymenopt. t. iv. Gen. 23. 
» Ibid. Gen, 30—32. ° Ibid. t. v. Gen. 40. 
4 Prater X. Fie. 12, 15, e. 
© Ibid. Fie. 15. f. f Ibid. Fic. 12. g-. 
® Ibid. Fie, 13. h Ibid. Fic. 15. c. 
i Jbid, d. * Ibid. Fre. 14, e, 
