Class 1. Chcatopoda. 175 



Class 2. DisCOphora {Leeches). 



Tlie body is always flattened witli sharp lateral edges^ rarely 

 cylindrical. The segments are externally divided^ each into several 

 small a n n u 1 i, by transverse furrows, so that the number of segments 

 appears many times greater than it is in reality (the same thing occurs 

 in some Chsetopods) . Parapodia and c h a e t se are always 

 wanting ; with few exceptions, no branchige are present. The 

 posterior end of the body is modified into a sucker ; around the mouth 

 there is also an adhesive disc, which in some is cup-shaped like the 

 hinder one, whilst in others, it consists of a long, jointed upper lip, 

 and a shorter underlip. 



The digestive tract consists of three sections : the pharynx, 

 the crop, and the rectum. In one group, the Gnathobdellidse, 



Fig. 137. Digestive tract, nervous system and excretory organs of a Leech in ontline. 

 a anus, 6 diverticulum, c cerebral ganglion, e rectum, g sub-oesophageal ganglion, m sucker, 

 .96 nephidium. — After Leuckart. 



the pharynx is muscular, and furnished in front with jaws, 

 three prominent, longitudinal, chitinous ridges, with teeth on 

 their sharp edges, which work like little saws to cut holes in 

 the skin of the prey, so that the fluids may be pumped out of its 

 body by the pharynx. In the other division, the Ehyncobdellidee, on 

 the other hand, a thin, muscular tube, the proboscis, is attached 

 to the end of the thin-walled pharynx. It may be stretched out from 

 the mouth and pointed, so as to bore through the integument of the 

 prey. The crop is a straight, wide tube, which is almost always 

 provided with a number of paired diverticula; the capacity of the 

 crop and its diverticula allows of the ingestion of a large amount of 

 food. The intestine is narrow, and opens dorsally above the sucker. 



A number of eyes is always present upon the anterior end of the 

 animal; in some Fish-leeches on the hind margin of the posterior 

 sucker also. 



The Leeches are always hermaphrodite; they possess two long 

 or round ovaries, which open far forward on the ventral side in a 

 common efEerent duct : albumen glands open into the oviduct. The 

 round testes are present in great numbers, 6 — 12 pairs, one pair in a 

 segment ; on either side there is a long vas deferens, into which all the 

 testes of the same side open by short ducts : the two vasa def erentia 



