THE HORNY SKELETON. 235 



central ridge of the same part ; between these roots the muscles of the 

 coxa pass, and between the processes themselves run the pharynx and 

 the nervous cord, and it is to these processes that the connecting 

 muscles of the pronotum and prosternum are attached. In the meso- 

 thorax we first find the prophragma (the same, 3. a), a small, not very 

 high, horny partition, which descends from the anterior margin of the 

 mesonotum, and we next find a delicate ridge which encompasses the 

 whole distinctly separated mesonotum. The mesosternum and scapulae 

 are closely joined in a half ring, and from the central carina of this ring 

 springs a broad strong ledge, which at its upper margin is furnished on 

 each side with a strong process (the same, 6. a, a) ; they form with the 

 ledge a rectangular cross, and serve as points of insertion for the 

 muscles of the coxae of the middle legs, lying on each side contiguously 

 to the central ridge. In Cimbex the cross is very distinct, in Scolia it 

 is merely a ridge, somewhat distended above. The metathorax of the 

 Hymenoptera is more complicated than in the Diptera and Lepidoptera, 

 because in them the abdomen is attached by only one small spot, namely, 

 by the circumference of the aperture beneath the metaphragma, conse- 

 quently there the metathorax encloses more powerful muscles than in 

 the preceding orders. The metaphragma is therefore exposed, and ap- 

 pears, for example, in Scolia, as an equilateral triangle above the arti- 

 culation with the abdomen, upon the very smooth apex of which the 

 abdomen turns (PI. XII. No. 2. f. 1). The apex itself is perforated, 

 and admits a strong band through it, which retains the abdomen (PI. 

 XII. No. 2. f. 3*). In front of this triangle is placed the very narrow 

 metanotum (the same, f. 1 and 2. F, F), and at its posterior margin a 

 triangular process runs inwards (the same, f. 4* and 5*), to which the 

 muscles retaining the abdomen are affixed. Between the metanotum 

 and metaphragma the two large side pieces and their auxiliaries lie, 

 separated from each other by furrows, from which internally strong 

 ridges spring, and to which the muscles of the posterior legs are attached. 

 In the saw-flies, which do not possess a petiolated abdomen, the pleurae 

 join together behind the metanotum (the same, No. 1. f. 1 and 2. 

 H, H), and the metaphragma lies internally as a narrow margin of the 

 metanotum, but the band is a semicircular tense membrane, which is 

 distended by the pleurae, and is very distinct in Cimbex. 



Among the orders with a free prothorax the Hemiptera occupy the 

 lowest place. The entire prothorax is a single, above very broad, 

 beneath narrower ring, from the centre of the pectoral plate of which 



