ANELLATA. 



133 



Leech. 



the shells of Mollusca ; but differing in being quite external to the 

 integument, and not organically attached to the animal, which can 

 quit and return to its tube. Most species of Serpulis, as the Serjy. 

 contortuplicata, which coats the shells of oysters and other bivalves 

 with its characteristic dwelling, have a pedunculated operculum for 

 closing the entry of the tube. 



The organisation of the integument has been studied chiefly in the 

 naked Anellides. It consists, in the leech, of a strong, smooth 

 whitish epithelium, and of a cellular corium divided into short segments, 

 and having many pigmental cells of a brown or greenish colour, 

 except in the intervals of the rings. The muscular fibres have a 

 tendinous lustre : those of the outer layer are transverse ; those of 

 the next layer cross each other 

 diagonally, and form a fine re- 

 gular reticulation : beneath these 

 are the longitudinal fasciculi, 

 which form the most conspicu- 

 ous stratum. There are also 

 other smaller muscular fascic- 

 uli in the under surface of the 

 body, besides those which spe- 

 cially regulate the action of the 



terminal suckers and the dentated jaws (^Jig- 69. h). 

 The mouth of the leech (^fig^ 69.) is triangular, and 

 is armed with three crescentic jaws (a, a), presenting 

 their sharp convex margin towards the oral cavity, 

 which margin is beset with sixty small teeth (^fig. 

 70.). It is by the action of these 

 little saws upon the tense integument 

 seized by the labiaF sucker, that the 

 characteristic triradiate bite of the 

 leech is made. 



The oesophagus (^fig. 71. ^) is short, 

 and terminates in a singularly com- 

 plicated stomach, divided by deep 

 constrictions into eleven compart- 

 ments, the sides of which are produced into caecal 

 processes (c, c\ progressively, though slightly, in- 

 creasing in length to the tenth, and disproportion- 

 ll \W-d ^^^^y elongated in the eleventh, compartment. The 



l! 1| first gastric chamber is the smallest. In the eight 



posterior compartments the anterior part of each 

 slightly expands to form a pair of small accessory 

 K 3 



Jaw and teeth. 

 Leech . 



Leech. 



