THE ANIMAL KINGDOM 419 



The mouth of the earthworm is without teeth. It leads to 

 a muscular pharynx, which seems to be the principal agent in 

 drawing food into the mouth. Food or earth passes from the 

 pharynx to a narrow esophagus into which the secretions of 

 two pairs of calciferous glands is discharged. This secretion 

 contains calcium carbonate and serves to neutralize the strongly 

 acid condition of the food. From the esophagus the food passes 

 to a muscular gizzard, where it is pulverized, and then into a 

 stomach-intestine, where it is digested and absorbed. The 

 digestive fluid contains proteolytic and lipolytic enzymes. 

 Earth and other indigestible material taken into the alimentary 

 canal are eliminated at the anus. 



CLASS IV. GEPHYREA. Marine worms without parapodia; 

 unsegmented in the adult stage. The body cavity is undivided 

 and the nephridia are reduced to a single pair. A few setae 

 may be present. They are dioecious and there is a trochophore 

 stage in development. 



Example: Thalassema melitta, found on the coast of North 

 Carolina. 



CLASS V. HIRUDINEA. The Hirudinea, or leeches, lack 

 parapodia, tentacles, and setae, but have sucking disks: one 

 surrounding the mouth and another at the posterior end of 

 the body. The body is flattened dorsoventrally and is marked 

 externally by two or more grooves to a segment. The body 

 cavity is partially filled with a vacuolated parenchyma. In 

 some leeches there are three sharp chitinous plates in the 

 pharynx that are used in drawing blood. Others, lacking jaws, 

 can pierce the integument by means of a proboscis that can be 

 thrust out of the pharynx. The salivary glands of leeches pro- 

 duce a substance called hirudin, which prevents coagulation of 

 the blood. It acts apparently by preventing the action of 

 thrombin upon fibrinogen and may therefore be considered an 

 antithrombin. 



In many leeches the crop and stomach are provided with 

 capacious pouches that become greatly distended after a meal. 

 The food consists principally of the blood or body fluids of 

 various animals. Leeches live in the water or in moist ground 

 and vegetation. They completely devour small aquatic 

 worms, insect larvae, etc.; and from larger animals, such as 

 fishes, amphibians, turtles, and mammals, they draw blood. A 



