Snail-Leeches. 83 



semi-crustaceous, and one species soft and flabby ; some of the 

 species when taken out of the water roll themselves up oniscus- 

 like (PL 1, Fig. 4), while one has the habit of putting out its 

 tongue or syphon when handled (Fig. 9). These creatures 

 live upon the juices of various aquatic animals, such as small 

 worms, gnat-larvae, and molluscs. The proboscis is inserted 

 into the body of the victim, and the nourishing liquid pumped 

 out. All the species are oviparous, depositing their ova upon 

 submerged bodies, and sedulously incubating them, as in O. 

 complanata, marginata, and tessellata, or else they carry 

 them about within the cavity of the abdomen, formed by 

 the folding inwards of the margins, as occurs in G. bioou- 

 lata and hyalina. Observers having noticed the young 

 completely closed in by the folds of the abdomen, have erro- 

 neously described certain kinds as viviparous. The whole 

 family is oviparous. The curious incubating habit already 

 mentioned appears to have been first noticed by Baker, who, I 

 think, observes that the young frequently leave their mother's 

 pouch and return again to their shelter. I have not witnessed 

 this latter circumstance. None of the family are capable of 

 swimming, so far as I have observed ; all the members locomote 

 by attaching one extremity of the body to the ground or the 

 surface of leaves, etc., and by drawing the other extremity up 

 to that point. The closely allied genus, Piscicola, common as 

 a parasite on fish, both swims and moves in the manner above 

 described. 



Having made these general observations, let us glance at 

 some of the parts belonging to the internal structure of these 

 creatures. The species O. complanata is perhaps- as good as 

 any to operate upon. Having put our subject under the 

 influence of chloroform, we place him in a small shallow trough 

 of fresh water, and by means of a couple of pins, one at either 

 extremity, fasten him down on his back. The form of the 

 mouth is readily seen under the lens ; with a little skilful mani- 

 pulation, we shall see that the mouth is connected with the 

 characteristic proboscis by means of a delicate membranous 

 cesophagus, with which it is continuous, and by which it is 

 included : when the animal protrudes this tube the membrane 

 is drawn over it, like the unfolding of a glove from the finger. 

 In form this tube is cylindrical, minutely segmented at the 

 apex, and sometimes bulbous at the extremity (PL 2, Fig, 2) ; 

 its reticulated muscular structure is seen in Fig. 3. The juices 

 which constitute the food of the snail-leech proceed down this 

 tubular organ (which is protruded at the time it is feeding, and 

 which is fixed in the soft integuments of the animals preyed 

 upon), and flow into another delicate membrane situated at the 

 bottom of the tubular bulb, and thence into the stomach. 



