ANNELIDS IN GENERAL 251 



teeth make incisions in the skin thus permitting the blood and lymph 

 to flow freely. At the same time sahvary secretions are introduced 

 into the wound which prevent coagulation of the blood. 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 pouches 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 intes- 

 tine for absorption. 



There are other leeches which have a protrusible proboscis in place 

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

 these are not parasitic but are predatory species which feed upon worms, 

 snails, and insect larvae. Snails, fish, and turtles are among the forms 

 most commonly parasitized, 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 sperfnatophores 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 

 ovo 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. 



287. 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. 158). Some show traces 

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

 through degeneration. 



288. 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 

 certain 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. 



