A PECULIAR TYPE OF NEPHRIDIA IN NEMER- 



TEANS. 



WESLEY R. COE. 



The excretory apparatus of the nemerteans has long been 

 known to present great variation in form and structure in different 

 members of the group. In many of the smaller and less highly 

 specialized forms the apparatus presents a close similarity to that 

 of the planarians and has evidently been derived from a similar 

 type. In many species a profusely branching system of tubules 

 lying in close proximity to the blood vessels connects with a single 

 excretory pore on each side of the body, while in other forms the 

 number of such efferent openings may be increased to the num- 

 ber of thirty or more on each side, as in some species of the 

 genus Linens. Although limited to the cephalic or a small por- 

 tion of the esophageal region in some species, the system extends 

 throughout the entire length of the body in other forms, as in the 

 fresh-water Stichostemma. In a few species which have been 

 carefully studied the system has not yet been discovered, in some 

 cases perhaps owing to the difficulty of distinguishing the deli- 

 cate nephridial tubules from the branches of the thin-walled blood 

 vessels. 



With the exception of certain species of the genus Tccniosoina 

 (Eitpolici) all nemerteans in which the relationships of the nephrid- 

 ial system are known agree in one important feature, namely, in 

 that these excretory tubules, whatever their structure or position, 

 open and discharge their contents directly upon the exterior of 

 the body. 



Several years ago Punnett, 1 in investigating the anatomy of 

 Tceniosoma quinquelineattim (Enpo/ia melanogramma Punnett), 

 found that this species possesses a considerable number of effer- 

 ent nephridial ducts, some of which open on the exterior of the 

 body, as usual, while others pass inward through the epithelium 



'Punnett, R. C., "On a Collection of Nemerteans from Singapore," Quart. 

 Jotirn. Alicr. Sci., Vol. 44, p. 116, 1900. 



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