EXTERNAL ANATOMY OF INSECTS. 553 



tunity, by an extended examination of living subjects, to 

 verify or disprove this suspicion, I shall merely mention 

 it, and conclude this head by observing, that the collar 

 varies most in the Hymenoptera order, and that its most 

 remarkable form is in Vespa, Cimbex, Dorylus, &c, in 

 which it bends into an ample sinus that receives the 

 dorsolum a . 



2. Dorsolum h . Where there is no apparent collar, 

 the dorsolum (dorslet) is the Jirst piece of the mesothorax, 

 and where there is one, the second; it bears the elytra 

 or other primary organs of flight. It varies in the dif- 

 ferent Orders, particularly with respect to its exposure. 

 In Coleopterous insects it is most commonly, but not 

 invariably , covered entirely by the shield of the protlio- 

 rax, the scutellum alone being visible; as it is also 

 in the Orthoptera (with the exception of Mantis and 

 Phasma, in the first of which it is partially, and in the 

 latter intirely exposed), and the Heteropterous, and 

 most of the Homopterous section of the Hemiptera. 

 The scutellum is likewise covered in Gerris, Hydrome- 

 tra, and Velia, and the whole of the back of the alitrunk 

 by a process of the prothorax in Acrydium F., Centro- 

 tus, &c. But in the remaining Orders, and the tribe 

 of Tettigonia in the Homopterous Hemiptera, the dor- 

 solum is not hidden by the thoracic shield. It is usually 

 less elevated than the scutellum; in Necrophorus, and 

 some other beetles, however, the latter is most depressed. 

 With regard to its substance, it is generally not so hard 



a Plate IX. Fig. 11. g. b Plates VIII. IX. i. 



c When the prothorax is separated from the elytra by a kind of 

 isthmus, as in Semites, Passalas, &c, the dorsolum is more or less 

 uncovered. 



