PHYLUM ANNULATA 



519 



by growths of connective-tissue, of an originally continuous coelome. 

 In the Rhynchobdellids in general the coelomic spaces remain 

 fairly extensive, and are lined by a coelomic epithelium. Another 

 interesting condition occurs in Nephelis (3), in which the middle 

 region of the body contains a series of paired, metamerically ar- 

 ranged spaces (c.), surrounded by botryoidal tissue and containing 

 the nephrostomes. Development shows that these cavities are 

 derived from true coelomic spaces in the embryo, formed, as in 

 Chaatopoda, by a splitting of 

 the mesoderm in each seg- 

 ment. Acanthobdella, already 

 referred to as exceptional in 

 the possession of setae, is also 

 the only member of the class 

 which has a well-developed 

 and spacious coelome, divided 

 by mesenteries into a number 

 of segments. 



In most instances the skin, 

 with its abundant supply of 

 capillaries, constitutes the only 

 respiratory organ, but in 

 Branchellion (Fig. 413, 3) a 

 Rhynchobdellid parasitic on 

 the Electric Rays (Torpedo and 

 Hypnos) and on one of the Aus- 

 tralasian Skates (Raja nasuta}, 

 differentiated respiratory or- 

 gans or gills (br.) are present 

 in the form of delicate lateral 

 outgrowths of the segments. 



In most members of the 

 class the nephridia are formed 

 on the same general type as 

 those of Hirudo, but differ in 

 the structure of the ciliated 

 funnels, which- may be more 

 or less modified, as in Hirudo. 



The funnels, where they occur, never open into the nephridial 

 canals. Each funnel leads by a narrow ciliated duct into a re- 

 ceptacle, in which leucocytes laden with waste matters are received 

 from the coelomic spaces and sinuses, subsequently to undergo 

 degeneration and absorption (Fig. 415). By its outer side this 

 receptacle is in close relation to the inner end of the nephridium, 

 and the waste-matters from the disintegrated leucocytes are no 

 doubt received into the nephridial canals and thus passed out to 

 the exterior. In Hirudo and Herpobdella (Nephelis) the recep- 



IV 



FIG. 415. Ciliated funnel of Herpobdella 

 (Clepsine). cr. crown-cells of funnel ; ex. 

 terminal cell of the nephridium ; Ic. leuco- 

 cytes ; at. duct leading to receptacle ; w. wall 

 of receptacle. (From Meiseuheimer, after L. 

 von Graff.) 



