55S EXTERNAL ANATOMY OF INSECTS. 



in something like a St. Andrew's cross a . In most of 

 the other tribes of this Order the scutellum is a triangu- 

 lar piece, with the vertex to the head, received between 

 two pieces of the dorsolum ; in Psocus it is nearly like 

 that of Tettigonia before described. In the Hymeno- 

 ptera the scutellum is separated from the dorsolum, which 

 it often embraces posteriorly, as the collar does in front, 

 by a suture ; it varies occasionally in shape in the diffe- 

 rent tribes, most commonly it is crescent-shaped, but in 

 many Ichneumonidcs and others it is triangular b ; in the 

 hive bee, &c, it overhangs the succeeding piece of the 

 alitrunk; in Melecta, Crocisa, &c, it is armed with a pair 

 of sharp teeth c ; in others [Oxybelus uniglumis, &c.) with 

 one or more spines, and in some with a pair of long 

 horns d . Before I describe this part in the Diptera, it 

 will be proper to assign my reasons for considering a 

 different piece as its representative, from what has usually 

 been regarded as such, and which at first sight seems 

 the analogue of what I admit to be the scutellum in the 

 Hymenoptera. The dorsolum, and its concomitant the 

 scutellum, belong to the first pair of the organs of flight, 

 which are planted usually under the sides of the former, 

 and in the case of wings, by their Anal Area, connected 

 either mediately or immediately with the latter. Now, if 

 you trace the sides of the piece that I have considered as 

 the part in question in Hymenoptera, you will find that 

 they lead you not to the base of the lower but to that of 

 the upper wings'", and in the saw-flies (Tenthredo L.) 



a Plate IX. Fig. 7- k' . b ibid. Fig. 11, 15. k' . 



c Mon. Ap. Angl. i. t. vi. Apis. ** a./. 2. a a. 

 d Stoll Cigales t. xxviii. /. 164. 

 £ Plate IX. Fig. 12. k'. 



