IV 



VERMES NEPHRIDIA 



235 



IX. Excretory Organs Nephridia. 

 (Occasionally Ducts for the transmission of the Sexual Products.) 



Nemertina. The excretory apparatus, which is always paired, 

 consists of canals lined with epithelium and mostly ciliated, which as 

 a rule rise in the blood sinuses of the body and open externally. 



It is limited to the anterior portion of the bod 

 always lie laterally over the longitudinal trunks 

 of the nervous system. Its arrangement differs 

 greatly in details. In all Nemertina, the epithelial 

 walls of the excretory canals (nephridia) are 

 glandular. 



In Carinella (Paleonemertina) an excretory 

 portion separates itself from the lateral vessels 

 of the blood-vascular system, and falls into two 

 parts, a glandular part and a reservoir. On the 

 one side it is connected with the lateraL vessels 

 at two points, on the other with a canal which 

 opens externally. In Carinoma the nephridium 

 on each side consists of (1) a very short longi- 

 tudinal canal which communicates with the lateral 

 vessels at three points, and (2) an efferent duct 

 which opens externally. In Carinina also the 

 nephridial system on each side consists of two 

 parts : (1) a compact mass of small canals, which 

 projects inwards towards the blood sinus of the 

 cesophageal region, and which (2) is connected 

 with a nephridial cavity narrowing at its posterior 

 end into a canal which opens externally. 



While in the Paleonemertina (with the excep- 

 tion of Carinina) the nephridia are in__gpea- com- 

 munication with the blood- vascular- system, such anterior 



The efferent ducts 



TUf 



portion of the 

 a communication has till now not been proved in body of a Nemertian, dia- 



.-, -, r ,. -r ,1 n i i grarurnatic. n, Longitudinal 



other i\emertma. In the bcluzonemertum on each cana is of the nephridial 

 side of the anterior region of the body there system; np, lateral apertures 

 is either a single longitudinal canal or else a 



of the same ; na, 

 ducts ; vd, dorsal vessel ; vl, 

 longitudinal network of canals, m which, however, lateral vessel ; gs, transverse 



one principal canal can generally be distinguished, vessels between the dorsal 

 These longitudinal canals, which lie in or on the a 

 blood sinuses or lateral vessels on the inner side of the longitudinal 

 muscle layers, reach the exterior on each side either (1) posteriorly 

 through an efferent duct, or (2) through two ducts opening near the 

 middle of their course, or (3) through several often very numerous 

 lateral ducts which are more or less metamerically arranged. 



In the Hoplonemertina and Malacobdellidce also, on each side, in 

 the anterior region of the body, a longitudinal canal is found. This 



