COE: NEMEKTEANS OF WEST AND NOETHWEST COASTS. 



45 



In this order there is commonly but a single pair of efferent ducts 

 and these pass dorsally to the lateral nerves and then bend sharply 

 downward to open on the ventro-lateral aspects of the body. In A. 

 impavispinosus there are commonly 6 to 8 or more efferent ducts 

 on each side, and in A. fornddahills often more than 20. Not all 

 of them open ventrally, however, for in the latter species nearly all 

 open on the dorsal side of the body (Text-lig. 15) and in the for- 

 mer those ducts situated most anteriorly open ventrally, while those 



Fig. 15. — Amphipoms formidabilis. Transverse section through nephridial 

 region, showing efferent nephridial duct (nd) opening dorsally. Four sec- 

 tions of branched intestinal caecum (tc) are indicated e, pylorus ; Iv, lateral- 

 blood vessel. 



farther back open dorsally. In Tetrasteimna quadrilineaUim the 

 nephridia are situated in the brain region, and the pair of efferent 

 ducts open on the lateral margins of the head in the vicinity of the 

 dorsal ganglia. In T. reticulatum they are situated but little farther 

 posteriorly. 



In Stichostemma and Geonemertes the nephridia extend the 

 whole length of the body, and there are numerous efferent ducts, a 

 portion of which open above, and others beneath, the lateral nerves 

 (Montgomery, '95, and Bohmig, '98). 



C. Bdellonemertea. — In Malacobdella the nephridia form a 

 complex system of branching canals which penetrate the parench\nua 

 in all directions. The single pair of nephridiopores is situated in 

 M. grossa on the ventral side of the body and in M.japorrica on 

 the dorsal side. 



D. Heteronemertea. — In this order the nephridia are usually 

 richly branched, and the tubules often lie side by side with the 



