THE ANNELIDES OR ENTOMOZOABIA. 365 



which, typifying the genus, is entitled to that character. 

 Lastly, it is in them that a portion of the nervous system 

 acquires a development equal to the production of electricity ; 

 and in certain of the class it is that we find the remains of a 

 skeleton, the tegumentary, which in the extinct world pre- 

 vailed to an extent of which we now can scarcely form an idea. 



" In the ganoid or mailed extinct fishes, the skeleton which, 

 from its connexion with the skin, may be called tegumentary 

 or dermoid (but to which probably the more appropriate name 

 of neuro-skeleton, as protecting the extremities of the nervous 

 papillae might be better applied), reached its highest develop- 

 ment as regards the class fishes ; in the present or living 

 zoology, only two genera of fishes exhibit a similar arrange- 

 ment of the tegumentary skeleton, namely, the lepidosteus of 

 the Ohio, and the polypterus of the Nile. In the sturgeon we 

 find a very complete tegumentary skeleton, but not arranged 

 in the admirable mechanical manner of the extinct ganoid 

 fishes." R. K.] 



SECOND PKIMAET DIVISION. 

 THE ANNELIDES OR ENTOMOZOARIA. 



507. The animals composing this division are so distinct 

 from the preceding as to be recognised at a glance. Their 

 bodies, in fact, are composed of segment-like rings, placed in 

 a file behind each other. In some, this annulated appearance 

 is confined to the existence of a certain number of transverse 

 folds grooving the skin and engirdling the body, but in most 

 the animal is enclosed in a sort of solid armour, composed of 

 a series of rings united to each other, or so articulated as to 

 admit of motion. This armour serves the purpose in some 

 measure of a skeleton, for it determines the general form of 

 the body, protects the soft parts, offers points of attachment 

 for the muscles, and performs the office of levers : thus, it is 

 often called an external skeleton. But it must not be for- 

 gotten that it is merely the skin hardened and become rigid, 

 or even encrusted with a calcareous epidermis, and thus is, 

 at most, a tegumentary skeleton. 



508. In certain of the articulata or annelides, as in the 



