THE METAMORPHOSIS. 441 



and the ventral plates, pro-, meso-, and metanotum. But why do the 

 thighs articulate with the vertebrae itself? why not with the shoulder- 

 blade, as it is present ? These questions could be suggested only by a 

 superficial observer, with reference to the posterior femur, for upon, 

 the anterior and intermediate pairs the shoulder-blade actually forms a 

 portion of the articulating socket *. The posterior femur also, or 

 rather its ball, which is usually called the hip, joins the parapleura 

 above, and this forms a portion of the articulating socket f. Likewise 

 in the downward bent margin of the parapleura the small articulating 

 socket is formed for the round ball of the top of the femur which 

 revolves in the large hip socket. Lastly, the aperture through which 

 the muscles of motion pass into the thorax is always found between 

 the pleura and the sternum, and is partly encompassed by the former 

 and partly by the latter. 



Thus the composition of the insect body and the analogy of its 

 individual plates with the bones found in the vertebrata, is fully proved, 

 and we obtain as the result that 



The head consists of two vertebrae, the one of which is twisted in 

 opposition to the other J. 



The thorax consists of three vertebral rings, each of which is sub- 

 divided into the true vertebra, the shoulder-blades and a sternum. 



The abdomen consists of nine vertebrae, each of which again consists 

 of the true vertebra and its arch, which are either the analogies of 

 the ribs or frequently merely represent the transverse processes of the 

 vertebra and the ventral sternum, the horny ventral covering. The 

 last of these vertebral rings, namely, the anal and sexual vertebra, is 

 also twisted, so that the vertebra with the anus lies above, and the 

 ventral plates with the sexual apertures lie beneath. These abdominal 

 vertebrae have no internal processes ; they retain their original most 

 simple larva form, and generally present themselves as simple but 

 more frequently halved rings. In some cases, for instance, in the 

 locusts, from the lateral parts of the half ring other free moveable half 

 arches project into the cavity of the abdomen, which both in situation 



See PI. IX. No. 2. f. 2., No. 3. f. 5.; PI. X. No. 1. f. 6., No. 3. f. 5. 



f PI. IX. No. 3. f. 5. 



I This composition of the head from two vertebra or rings is confirmed by Ratzeburg's 

 observations upon the development of the larvae of the Hymenoptera. See Darstellung 

 und Beschreibung dor Arzneithicrc, vol. ii. p. 175, PL 23, f. 47 50 and f. 815 91 



