﻿2 BRITISH BEETLES. 



difficulty can well arise about it, except, perhaps, in the 

 case of the Tortoises {CheJonia) among the Reptiles, which 

 might puzzle a superficial observer; their shell, however, 

 is merely an abnormal development of the ordinary ver- 

 tebrse, ribs, and chest-bones. 



The Invertebrata are again composed of three sec- 

 tions, — the Mollusca, Articulata (to which insects be- 

 long), and Radiafa, with which the animal kingdom 

 terminates, as far as we know. 



The Mollusca (whereof the Cuttle-fish, Nautilus, Snail, 

 Whelk, Oyster, and Ship-Avorm are familiar examples) 

 are comparatively mere lumps of muscular fibre, mostly 

 contained in a shell, which is either single, bivalve, or 

 tubular; they have no articulated limbs or solid lever 

 points except their shells ; their blood is either devoid 

 of colour, or slightly bluish, circulation being effected by 

 a muscular heart, with a system of arteries and veins ; 

 the nutritive organs occupy the greater part of the body, 

 through which the nervous system is vaguely distributed ; 

 and in habit they are both terrestrial and aquatic, the 

 land species breathing air, and those that live in the 

 water having branchise, or gills ; the latter are by far the 

 most numerous portion, — some inhabiting salt water, 

 others fresh. 



The Articulata have the body and limbs composed 

 of different segments or rings, to the inner side of which 

 the muscles are attached, — in short, they may be said to 

 carry their skeletons outside. Most of them have hard 

 outer coverings; but in the lowest class the body is soft, 

 formed of skin folded into many rings, and sometimes 

 not possessing any distinct head or jaws, wherein they 

 differ from the other articulated animals. It is remark- 

 able, by the way, that the jaws of the Articulata open 



