294 



THE EARTHWORM AND OTHER ANNULATA 



located at certain points, cause the blood to flow in appropriate 

 circuits. There arc, however, five pairs of so-called hearts, 

 consisting of specially developed contractile vessels in segments 

 seven to eleven inclusive, and running dorso-ventrally. By 



b.^ 



b. T 



Fig. 142. — Neiihridium of earthworm. 



Above, diagram of an entire nephridium, drawn with coils somewhat separated. Below 

 (left), portion of nephridium showing blood supply; and (right) the nephridial funnel or 

 nephrostome by which the nephridium communicates with the coelome. 



bl, bladder-like muscular portion; b.v., blood vessel; c.t., connective tissue surrounding 

 tubules; d.l., dorsal lip; e.p., peritoneal epithelium; /, funnel or nephrostome; I, lumen; 

 n, nephridium; n.p., nephridiopore or external opening of nephridium; s, septum; t, 

 tubule; v.L, ventral lip. (Redrawn with modifications from Howes, "Atlas of Zootomy," 

 copyright, 1902, by Macmillan and Co.', Ltd., printed by permission.) 



means of this system the blood circulates through the larger 

 vessels and the capillaries throughout the body. The terms 

 "arteries" and "veins" are hardly applicable, because there is 

 no specialization of blood vessels leading to and from a central 

 heart. 



