246 METAZOAN PHYLA 



attaches itself to another animal for the purpose of securing blood these 

 teeth are brought into play as a means of scarifying the surface and thus 

 permitting the blood and lymph to flow freely. At the same time sali- 

 vary secretions are introduced into the wound which prevent coagulation 

 of the blood. Consequently the wound produced by a leech bite is 

 usually very irritating. The blood is sucked up by the action of a 

 muscular pharynx and passed into a crop, which is very long and provided 

 with lateral branches that give it great capacity. It has been stated that 

 a medicinal leech can take in three times its own weight of blood and 

 that this supply will last it for nine months. The blood which is stored 

 in the crop is from time to time passed on into the stomach, where it is 

 digested; from here it goes into the intestine for absorption. 



There are other leeches which have a protrusible proboscis in place 

 of jaws, and still others which lack both jaws and proboscis. They 

 attack animals of various groups but more particularly the vertebrates. 

 Snails, fish, and turtles are among the forms most commonly preyed 

 upon, but mammals entering the water also become victims. There 

 are land leeches, occurring chiefly in the tropics, which are serious pests. 

 One species of European land leech feeds upon earthworms. 



Leeches are hermaphroditic, but, as in the case of the earthworm, 

 cross-fertilization takes place. The sperm cells are collected in bundles 

 called sper7natophores which are passed from one worm into the body of 

 another. The eggs of many leeches are deposited in chitinous cocoons 

 that are attached to the surface of hard objects in the water where they 

 form brown, elliptical, moderately convex objects. Some leeches are 

 viviparous. Others carry their eggs attached to the ventral surface of 

 their bodies, and when the young are hatched they remain with the 

 parent for a time, attached by the posterior sucker. 



285. Gephyrea. — The affinities of this group are uncertain but it has 

 more resemblance to the annelids than to any other phylum recognized 

 in this text. Its members are all marine (Fig. 148). Some show traces 

 of metamerism while others do not, but they may have lost this feature 

 through degeneration. 



286. Metabolism. — The food of some annelids is made up entirely of 

 small animals; that of others includes both microscopic plants and ani- 

 mals; that of still others consists of any organic detritus; while that of 

 leeches is only blood and lymph. The alimentary canal of all annelids 

 shows a high degree of specialization. Circulation is carried on by 

 means of coelomic cavities and blood vessels. Excretion takes place 

 into both the coelomic fluid and the blood, and elimination is accom- 

 plished by means of nephridia. These in some cases have no opening 

 into the coelom and so eliminate only liquid waste. Respiration always 

 takes place through the body surface but may be more or less limited to 

 certain areas, as to the parapodia or the tentacles about the head. 



