§52 EXTERNAL ANATOMY OF INSECTS, 
varies in the different Orders. In the beetle tribes it 
has generally a sinus taken out of its anterior margin, 
and it approaches more or less to a trapezium; in Blatta 
it is transverse and somewhat arched; in Gryllotalpa it 
is nearly square, and distinguished besides on each side 
by a minute aperture, fitted with a tense membrane, 
which perhaps covers a respiratory apparatus. In the 
locusts it is more or less triangular, and in Mantis and 
Phasma long and slender. In the Hemiptera the dorso- 
lum appears to consist of several pieces, variously cir- 
cumstanced, separated by sutures, corresponding with 
which are as many ridges on the inside of the crust?. 
In the Lidellulina it is rhomboidal®; in Panorpa nearly 
hexagonal; in the Ephemerina it is ample and oblong; 
in Sialis and the Trichoptera this part is represented by 
three subtriangular pieces, the scutellum constituting a 
fourth, with the vertices of the triangles meeting in the 
centre®; in the Lepidoptera the part in question is large, 
and receives the scutellum into its posterior sinus*. The 
Hymenoptera usually exhibit a very ample dorsolum, 
mostly subtriangular with the vertex rounded or trun- 
cated, and pointing in some (Vespa) to the head*, and 
in others (Apzs) to the anus; in the Dzptera, except in 
Tipula, the parts of the mesothorax are not separated by 
any suture, but only indicated by impressed lines or chan- 
nels; in the genus last mentioned, however, the dorso- 
Jum is distinct, subrhomboidal, and received by an angu- 
‘lar sinus of the scuéellum, which last, I think, is not the 
@ Pirate VIII. Fic. 16. 20. 7’. baPrars TX) Fic..7. 7’. 
© Ibid. Fie. 10. 7. #’. “Ibid; Fic. 1. 7. #. 
® Ibid. Fic. 11.7. 
