THE POLYCH^TA. 209 



13). Each tooth has a little projection upon its convex edge, 

 which is connected by a short strong ligament with the cor- 

 responding projection of another tooth ; and the one pair of 

 teeth, thus connected, works vertically against the opposite 

 pair. In Nereis, there are two powerful teeth which work 

 horizontally, besides minute accessory denticles. In Syllis, 

 the chitinous lining of the pharynx is produced into a circle 

 of sharp teeth anteriorly, and there is, in addition, a much 

 stronger triangular median tooth. In Glycerol, which pos- 

 sesses a pair of teeth, the extremity of the protruded pro- 

 boscis is covered with very remarkable papilla?. The most 

 complex arrangement of teeth, however, is that presented by 

 the JEunicidce. In Ewnice, there are altogether nine distinct 

 pieces : two large, flat, more or less calcified portions united 

 together below, and three cutting and tearing teeth on the 

 right side working against four on the left. As has has been 

 already stated, the tubicolar Annelids possess neither probos- 

 cis nor teeth. 



No special hepatic gland appears to exist in the Annelida, 

 unless the intestinal caeca perform that function, and the 

 secretion of the bile is doubtless effected by the glandular 

 tract, which extends for a greater or less distance in the walls 

 of the alimentary canal. A pair of glandular caeca, the func- 

 tion of which is not known, is appended to the base of the 

 proboscis in Nereis. 



The general cavity of the body, or perivisceral cavity, 

 which is included between the parietesof the alimentary 

 canal and those of the body, is filled with a fluid which con- 

 tains corpuscles, which are usually, as in the Invertebrata in 

 general, colorless. They are red, however, in Glycera, and 

 in a species of Apneumea (De Quatrefages). The parapodia, 

 the cirri, the branchiae, and all the other important appendages 

 of the Polychoeta, contain a cavity continuous with the peri- 

 visceral cavity, and are therefore equally filled with the blood. 

 The circulation of this fluid is effected partly by the contrac- 

 tion of the body and its appendages, partly by the vibratile 

 cilia, with which a greater or less extent of the walls of the 

 perivisceral cavity is covered. 



In a great number of the JPolychceta no part of the body 

 is specially adapted to perform the function of respiration, 

 the aeration of the blood probably taking place wherever 

 the integument is sufficiently thin ; and, even when distinct 

 branchiae ordinarily exist, members of the same family may 

 be deprived of them. In Polynoe squamata, ciliated spots 



