608 EXTERNAL ANATOMY OF INSECTS. 
the Flgorelle they incline to a trapezium, sometimes to 
a pentagon *; in the Cicade they approach to an obtuse- 
angled triangle; and in others of the tribe they are nearly 
wedge-shaped ”. ‘ 
6. Neuration. ‘The circumstance that most strikingly 
distinguishes tegmina from elytra is their neuration or 
veining ; which adds much to their strength, without in- 
creasing their weight so much as to render them unapt 
for flight. To look at these organs in Blatta Petiveriana, 
you would imagine them at first to be deprived of this 
distinction ; but if you observe them attentively, particu- 
larly their white spots, you will soon detect their ner- 
vures; and if you further examine their lower surface, 
you will find them very visible. The gibbous Blatte 
also, Blatia picta and affinities, the analogues of Erotylus 
amongst the Coleoptera, have tegmina which, except at 
their apex, exhibit but faint traces of the nervures of 
their tribe, and approach to elytra besides by the in- 
numerable minute impressed points that cover them. In 
the Orthoptera and some Homopterous Hemiptera the 
nervures may be divided into longitudinal ones more or 
less ramified, and traversing ones. In the Blatte the 
traversing nervures cut the longitudinal ones nearly at 
right angles, but not at regular intervals, so as to cover 
the tegmen with quadrangular areolets; in Mantzs pre- 
caria and affinities the longitudinal nervures of the Anal 
Area diverge from the base, and are traversed nearly as 
in Blatta, while those of the Costal diverge from the 
mediastinal nervure, but the traversing ones form innu- 
* Stoll Cigales t.i. f. 1, 5—5. and ¢. vi. f. 31. 
> Ibid. ¢. iii, f. 12—15. and ¢. xvii. f. 92. 
