284 



COELHELMINTHES 



origin of these vessels from the ccelom the following points are in favor, (i) 

 The ventral cord is enclosed in the ventral blood sinus; (2) the flagellate funnels, 

 just alluded to, lie in the blood lacunas, usually in ampullar spaces between the 

 ventral and lateral blood sinuses. Further relations are shown by Acanthobdella 

 pelcdina, parasitic on fishes. This has both blood-vessels of the oligochaetes, a 

 body cavity divided by septa, and chaetae. On the other hand, it is leechlike 

 in other features; two suckers and sexual apparatus on the Hirudinean pattern. 

 Branchiobdella, parasitic on the gills of the crayfish, is a chstopod devoid of 

 bristles and furnished with a sucker in correlation with its habits. 



Order I. Gnathobdellidse. 



The jawed leeches include Hirudo medicinalis, once extensively used for 

 blood-letting, now little employed. Hivmadipsa includes land leeches of the 

 tropics. Nephelis* soft jaws. Macrobdella* includes our largest species. 



Order II. Rhynchobdellidae. 



Without jaws. CLEPSPINID^; mostly feed on snails and fishes. Clepsine* 

 Hcementaria ghiliani of South America is poisonous. ICHTHYOBDELLID^E,* 

 cylindrical, occur in salt and fresh water, parasitic on fishes. Ichthyobdella,* 

 Pontobdella,* marine; Piscicola, fresh water. 



Class IV. Polyzoa (Bryozoa). 



In external appearance the Polyzoa closely resemble the hydroids, 

 so that the inexperienced have difficulty in distin- 

 guishing them. Like them by budding they form 

 colonies which are either incrusting sheets or assume 

 a more bush -like character. Further they have a 

 crown of ciliated tentacles which can be spread out 

 or quickly retracted. In internal characters the two 

 groups are greatly different. The Polyzoa have a 

 complete alimentary canal, with its three divisions, 

 which is bent upon itself so that the anus lies near 

 the mouth. The central nervous system lies be- 

 tween mouth and anus, and the single pair of nephri- 

 dia empty by a common opening. Beyond this it is 

 difficult to go, since the two groups Entoprocta 

 and Ectoprocta differ widely. The Entoprocta 

 have no ccelom, resembling in this respect the 

 Rotifera; the Ectoprocta are true Ccelhelminthes 

 and by way of Phoronis show resemblances to the 

 Sipunculoida ('Prosopygii,' p. 281) and also to the 

 Annelida. 



Sub Class I. Entoprocta. 



The single individuals of the Entoprocta (fig. 273) are shaped like a wine- 

 glass and are placed on stalks which rise from (usually) creeping stolons. The 



FIG. 273. Loxosoum 

 sinidare (after Nit- 

 sche) in optical sec- 

 tion. A, rectum; Ga, 

 ganglion; /, intes- 

 tine; T, tentacles; V, 

 stomach. 



