551 EXTERNAL ANATOMY OF INSECTS. 



and rio-id as the scutellum, but in most Coleqptera harder 

 than in the other Orders in which it is covered ; in 

 the Hemiptera, except in Tettigonia, it approaches to 

 membrane. As to shape and other circumstances, it 

 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 a . 

 In the Libellulina it is rhomboidal b ; 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 c ; in the Lepidoptera the part in question is large, 

 and receives the scutellum into its posterior sinus d . The 

 Hymenoptera usually exhibit a very ample dor solum ^ 

 mostly subtriangular with the vertex rounded or trun- 

 cated, and pointing in some {Vespa L.) to the head e , 

 and in others {Apis) to the anus ; in the Diptera, except in 

 Tipula, the parts of the mesothorax are not separated by 

 any suture, but only indicated by impressed lines orchan- 



a Plate VIII. Fig. 16. 20. i'. h Plate IX. Fig. 7- i. 



c Ibid. Fig. 10. i. k' . rt Ibid. Fig. 1. i. k' . 



c Ibid. Fig. 11. i'. 



