556 EXTERNAL ANATOMY OF INSECTS. 



of which are immoveable, there seems really to be no 

 scutellam. Generally speaking, as was lately observed, 

 but not always, it is distinguished from the dorsolum by 

 being more elevated : this is particularly conspicuous in 

 the genus Mater, in which it is a flat plate elevated 

 from the dorsolum by a pedicle; in Sagra the latter part 

 is horizontal, while the scutellum is vertical : and even in 

 cases where the distinction is not so striking, these parts 

 are separated either by a line, or some difference in their 

 sculpture and substance. In this Order this part varies 

 greatly, and often in the same tribe or genus, both 

 in size and shape; being sometimes very large a , and 

 sometimes very minute; sometimes very long, and some- 

 times very short; sometimes nearly round, at others 

 square; now oval or ovate, heart-shaped, triangular, 

 acuminate, intire, bifid, &c. In the Ortkoptera, though 

 less conspicuous, it still is present as a triangular eleva- 

 tion of the middle of the posterior part of the dorsolum, 

 with the vertex either pointing towards the head, as in 

 Blatta, or towards the tail, as in Locusta Leach b . In 

 the Heteropterous section of the Hemiptera (which, in 

 columns of Mandibulata and Haustellata, appear to bear 

 the same reference to the Coleoptera, that the Hymeno- 

 ptera do to the Diptera, and the Homopterous Hemi- 

 ptera to the Ortkoptera c ) the part we are considering is 

 mostly very large and conspicuous, quite distinct from the 



a In Macraspis MacLeay it is often half as big as an elytrum. 



" Plate VIII. Fig. 12. It . 



c Mr. W. S. MacLeay opposes the Hemiptera to the Ortkoptera, 

 the Homoptera to the Neuroptera, and the Aptera to the Coleoptera: 

 but if analogous structure be made the guide, I think my arrange- 

 ment will be found most correct. Hor. Entomolog. 367. 



