84 Snail-Leeches. 



This organ consists of a branched membrane attached to 

 the body walls ; it is furnished with five or seven pairs of 

 pouches, or gastric cgeca. In these pouches it is evident that 

 the juices must be assimilated. An Italian writer (De Filippi) 

 says he has noticed special channels of communication between 

 these casca and the blood-vessels through which the imbibed 

 blood of the victims passes almost directly to the vascular 

 system (?). The general form of the stomach of a snail- 

 leech may be seen in Plate 2, Fig. 1 ; the dark- coloured con- 

 tents of which (as seen in Plate 1, Fig. 1) clearly enough 

 reveal the branching caeca — the last pair of which is much 

 larger than the others, and is always directed downwards 

 towards the posterior extremity. 



The intestine, like the stomach, is divided into branching 

 casca, four being the normal number. The intestine ends in 

 a perforation situated on the dorsal surface, at the point of 

 juncture between the posterior sucker and the body. 



The circulation in these animals, though clearly seen, 

 especially in young specimens, is difficult to ascertain precisely. 

 It may be enough to remark that the heart is represented by a 

 dorsal vessel extending throughout the entire length of the 

 leech ; there is also a corresponding ventral one. The cir- 

 culating fluid, which is colourless, is propelled by the contrac- 

 tion of the dorsal heart into a number of radiating vessels, 

 which carry it to a couple of lateral canals, one on each side of 

 the animal. 



In the red-blooded leeches it is the lateral vessels which 

 contract, in the Grlos siphons the dorsal one acts the part of a 

 heart. The blood is no doubt oxygenated by coming in con- 

 tact with the air contained in the water, principally in the 

 attenuated margins of the body, which are beset with innumer- 

 able small blood-vessels. A snail-leech may often be seen to 

 create currents of a fresh supply of water by attaching its 

 suckers to the glass vessel in which it is confined, and by 

 undulating the intervening portion of the body in a vertical 

 direction. 



The nervous system is simple, and the entire cord may with 

 care be dissected out. It consists of a double chain of nervous 

 matter with ganglionic knots occurring at irregular intervals 

 (See Plate 2, Fig. 7). 



The ovary (Plate 2, Fig. 6) consists of a double sac-like 

 lobe,* situated in the anterior portion of the body. The 

 enclosed vitelli are attached to a long twisted cord, funiculus 

 (Fig. 5), but fall from it before exclusion. The mode in which 

 the eggs are deposited, and their development, is full of 

 interest, and readily observed at the proper season of the year. 



* A single lobe only is represented in the engraving. 



