The Rev. P. Keith 07t ihe Structure of Animals. 7 



four in number, are attached, forming in their ensemble the 

 skeleton or carpentry of the body. Animals of this class are 

 said to be vertebrate, Vertehata. They have red blood ; a 

 muscular heart; a mouth, the origin of the intestinal canal ; 

 two horizontal jaws; distinct organs of sight, smelling, hear- 

 ing, tasting, situated in the cavities of the head ; a generally 

 diffused tact or circumscribed touch ; the locomotive muscles 

 attached to bones ; the viscera lodged in the head and trunk ; 

 the head distinct from the body; and the sexes in separate 

 individuals. Of this general model there are many varieties, 

 the descending gradations of which may very easily be traced 

 from man to the meanest reptile. 



The second division of the descending animal scale includes 

 the Mollusca, namely, individuals which consist of a soft and 

 gelatinous mass, and exhibit a structure less complex than 

 that of the Vertebrata, The body is without a skeleton, and 

 without a distinct head ; the muscles being attached to the 

 skin, forming a soft and contractile covering, (which in many 

 species is encrusted with a shell), in which envelope the viscera 

 are contained, together with the nervous system, which in these 

 animals takes the form of scattered masses of threads. The 

 chief of these masses lies in [or around] the oesophagus, and 

 is called the brain. Of the senses common to the Vertebrata, 

 they seem to possess only taste and vision ; with the exception 

 of one family — Sepice — which exhibits also organs of hearing. 

 But they have an apparatus for circulation, respiration, di- 

 gestion and secretion, scarcely less complicated than that of 

 the preceding division. 



The third division of the descending animal scale is that of 

 worms and insects, designated by the appellation of articulated 

 animals, Articidata, exhibiting a structure still less complicated 

 [?] than that of the Mollusca. Their nervous system consists of 

 two cords, extending along the belly, and expanding at regu- 

 lar intervals into knots, ov ganglia. The first of these, placed 

 on the oesophagus, is called the brain, though not much larger 

 than the rest. The covering of the body, in some cases soft, 

 in others hard, is divided by transverse folds into a certain 

 number of rings, with the muscles attached to the interior; 

 and hence their appellation of Articulafa, or, as MacLeay 

 would rather call them, Annulosa *. Many of them have la- 

 teral and articulated limbs, originating in pairs, while others 

 are wholly destitute of limbs. They have not a real circu- 

 lation, except, says Kirby, the Arachnida and Annelida f . 

 They have not lungs, but spiracles. They have organs of 



* Linn. Trans,, vol. xiv. Part I. [or Phil. Mag. vol. Ixii.pp. 192,255.] 

 f Introd. to Kntomol., vol. iv. p. 80. 



