THE HORNY SKELETON. 231 



without previously melting, but it is soluble in boiling or heated 

 sulphuric acid. 



Besides the above, small portions of albumen, a peculiar brown 

 colouring matter which dissolves in caustic potass, but not in boiling 

 alcohol, as well as traces of phosphate of iron, have been found in the 

 horny integument of insects, upon different analyses. The albumen 

 belongs doubtlessly to the third tunic, as does the brown colouring 

 matter to the mucous rete : to this also we attribute the chitiiie, 

 whereby the true horny skin, namely, the epidermis, will be found to 

 agree entirely with the horns of the higher animals *. 



163. 



After this general inspection of the horny skeleton, we arrive at the 

 different parts of which it is composed. As we have already, in the 

 first section, in stating the orismological definitions of the insect body, 

 sufficiently exhibited its structure and explained its composition of 

 different pieces, we may here proceed more briefly, and merely add the 

 description of those parts which escape the observer upon an exterior 

 orismological examination. It will suffice then to repeat that the entire 

 body of the insect consists of HEAD, THORAX, ABDOMEN, and the limbs, v 

 namely, six FEET and TWO or FOUR WINGS. 



The HEAD exhibits itself as a single horny bladder with an anterior 

 and posterior aperture. The anterior one is closed by the cibarial 

 organs, and by the posterior one it stands in connection with that of 

 the thorax. 



The THORAX consists of three divisions. The first or PROTHORAX 

 has two or four horny plates; the DORSAL PLATE (pronotum) ; the 

 BREAST PLATE (proslernuin) , and the SHOULDER PLATES (omia). 



The second or MESOTHORAX exhibits four, six, or seven plates. The 

 simple DORSAL PLATE (?nesonotum) ; the sometimes simple, sometimes 

 divided BREAST PLATE (mesosternum}, and the two, also sometimes 

 simple, or likewise divided SHOULDER PLATES (scapula;). In many 

 orders (Diplera, Hymenoptcra}, the three or six last are connate, and 

 form ONE ring. 



The third or METATHORAX has, like the middle one, either two, 



* Compare Aug. Oilier Mem. sur la Composition Cbemique des parties Corn^es des 

 Insectes, in Mem. do la Soc. d' Hist. Natur. de Paris. Par. 1823. T. i. p. 29, Straus 

 Durckheitn, p, 32, and Mr. Children in Zoological Journal, vol. i. Ill -115. 



