ARRANGEMENT OP THE ANNELIDES. 21 



as are furnished with antennae ; 3. Annelides seden- 

 taires, or such as are fixed to other substances. 



(17.) The arrangement of Milne Edwards is the 

 most recent ; and, although leading to no general re- 

 sults connected with the other classes of the Annulosa, 

 may here be inserted, as disclosing some important 

 facts relative to structure, which may hereafter be 

 turned to good account: although, where no general 

 principles are aimed at, we seldom notice these isolated 

 arrangements. 



(18.) The author in question divides the Anne- 

 lides into two groups: 1. The ANNELIDES APODES, 

 or footless Annelides ; and, 2. The ANNELIDES CHE- 

 TOPODES, which are assisted in their locomotion by 

 setae placed upon pediform tubercles. The former, or 

 ANNELIDES APODES, are very inferior in point of num- 

 bers to the latter, and are distinguished by having a 

 sucker at both their extremities. They constitute two 

 families ; viz. the Hirudimda, or leeches, the body of 

 which is wholly unfurnished with appendages, and 

 these form two tribes ; the Albionnides, in which the 

 oral sucker is but of one piece, and is separated from 

 the body by a constriction, its orifice being evidently 

 longitudinal. Here he places the genus Pontobdella, the 

 species of which are natives of the ocean, and attach them- 

 selves chiefly to the chondropterygeous fishes, as the rays 

 and sharks ; and Piscicola, which inhabits fresh waters, 

 and frequents carps and tench. The second tribe are 

 the Bdelleoides, in which the sucker consists of several 

 pieces, and is scarcely separate from the rest of the 

 body. It has its aperture transverse, forming, as it 

 were, two lips, the interior of which is drawn back. 

 This tribe contains B delta, Hirudo, Erpobdella, Ne- 

 phelys, &c. the most celebrated of which is the medi- 

 cinal leech (Hirudo). They are all inhabitants of fresh 

 water, and some die almost instantly on being with- 

 drawn from it, whilst others will live out of it for a 

 considerable time. Many of them are great enemies to 

 c 3 



