PHYLUM ANNULATA 



497 



with the surrounding water, and the skin becomes a highly efficient 

 respiratory organ. The space between the epidermis and the 

 enteric canal is filled by a peculiar form of connective-tissue, 

 consisting of a gelatinous matrix with interspersed cells and fibres, 

 many of the former large and branched. More immediately 

 surrounding the enteric canal is the peculiar and charac- 

 teristic botryoidal tissue (b. t.) consisting of branched canals, the 

 walls of which are formed of large cells loaded with black pigment. 

 This system of canals is in communication on the one hand with 

 the blood-vascular system and on the other with the greatly 

 reduced ccelome. 



Numerous unicellular glands are produced from the epidermis : 

 the gland-cells themselves lie in the connective-tissue, and are con- 

 tinued into long ducts which open on the surface. Special glands 

 in the ninth, tenth, and eleventh segments secrete the substance 

 from which the cocoon is formed (vide infra, p. 503) : the segments 

 in question therefore constitute the clitellum. 



The muscular system is well developed, and consists of an 

 outer layer of circular (c. m.) and an inner of longitudinal (I. m.) 

 fibres. There are also dorso-ventral fibres 

 (d. v. m.) passing vertically between the 

 pouches of the crop (vide infra), and radial 

 fibres extending from the wall of the enteric 

 canal to the integument : these take the 

 place of the septa of Chsetopods. 



The alimentary organs are greatly 

 modified in accordance with the blood- 

 sucking habits of the animal. Surrounding 

 the mouth are three jaws, one median and 

 dorsal (Fig. 415, d.j.), the other two ventro- 

 lateral (v. I. .?.). Each (Fig. 413) has the 

 form of a compressed muscular cushion, 

 with a sharp, evenly curved, free edge 

 covered with chitin, which is produced into FIG. 413. one of the jaws of 

 numerous serrations or teeth : by means of its 

 muscles each jaw can be moved backwards 

 and forwards through a certain arc, and the three, acting together, 

 produce the characteristic triradiate bite in the skin of the animal 

 upon which the Leech preys. 



The mouth leads into a muscular pharynx (Figs. 414 and 415, 

 ph.) situated in the fourth to the eighth segments. Radiating 

 muscles pass from its walls to the integument, and by their con- 

 traction dilate its cavity and suck in blood from the wounds made 

 by the jaws. Around the pharynx are numerous unicellular 

 salivary glands, which open close to the mouth : their secretion 

 has the effect of preventing the coagulation of the blood taken as 

 food. 



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