308 



PARASITES OF THE DOMESTIC ANIMALS 



by a looping up of the body, the anterior sucker being again advanced 

 and the process repeated. They can also swim freely by snake-like 

 movements in the water. The body surface is transversely striated, 

 giving the appearance of a large number of segments. The striations, 

 however, are in excess of the true segmentation representing the somites, 

 the primitive segment rings being divided by secondary striations. 

 The alimentary canal has a number of paired sac-like protuberances 

 varj'ing in number according to species. When the leech gorges icself 

 these sacular pockets are filled with blood upon which the animal may 

 live for some time before again feeding. The body cavity is reduced by 

 the connective tissue and musculature to a number of tubular sinuses. 



The leeches are hermaphroditic and copulate reciprocally (cross 

 fertilization). As in the earthworms, certain of the somites at the time 

 of reproduction develop into a clitellum which secretes porous cocoons 

 in which the eggs are deposited. 



The leeches to be considered come under one family, the Gnathobdel- 

 lidas, which have the pharynx provided with three semicircular chitinous 

 plates or jaws, each armed on its free edge 

 with numerous teeth. The Rhynchobdellidse 

 are without jaws. This family contains species 

 which attack fishes and invertebrates and occa- 

 sionally water fowl. 



1. Haemopis sanguisuga. The horse leech. 

 (Fig. 167). Hirudinea (p. 307).— Dorsally this 

 leech is greenish brown or sometimes reddish 

 in color; ventral ly dark gray, reddish gray, or 

 black. Generally the body has four to six longi- 

 tudinal rows of closely set dark points which 

 may be somewhat indistinct. The body is 

 widest in the middle, gradually narrowing an- 

 teriorly, and is composed of ninety-five to 

 ninety-seven segments. It is ro.unded dorsally, 

 flattened ventrally, soft, viscid, and capable of 

 great extension and retraction. The oral sucker 

 is slightl}^ concave, having at its center the 

 mouth which is in the form of a three-rayed 

 star (Fig. 167). Each of these ray-like slits 

 permits the passage of a jaw, the teeth of which wound the mucous 

 membrane and thus enable the leech to suck blood while it holds on 

 by means of the oral sucker. There are ten indistinct eyes located 

 anteriorly on the dorsal surface. The vulva is a transverse slit located 

 five rings behind the male orifice, or between the twenty-ninth and 

 thirtieth rings. 



In fecundation two individuals come together bj' their ventral sur- 



FiG. 167. — Hsemopis san- 

 guisuga. Oral sucker of 

 same at right. 



