THE NERVOUS SYSTEM OF PELAGIC NEMERTEANS. 



WESLEY R. COE, YALE UNIVERSITY. 



During the past ten years a considerable number of species of 

 bathypelagic nemerteans have been studied anatomically by Brink- 

 mann ('i/) and others and much information has been secured, 



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showing the deviations of the nervous system from the general 

 plan characteristic for the littoral forms. Five new genera, col- 

 lected by the " Albatross " in various parts of the Pacific ocean, 

 which have recently been fully studied by the writer (Coe, '26), 

 proved of particular interest in this respect. One of these species, 

 N euronemertes aurantiaca, possesses a chain of ganglia along the 

 dorsal nerve, a condition almost unique in invertebrates. 



In the modifications of the sense organs also the pelagic nemer- 

 teans (Pelagica) differ widely from any of the littoral and bottom- 

 living species (Reptantia). 



It is to be recalled that bathypelagic nemerteans have been 

 found only in the open oceans, where they swim with sluggish 

 movements or float idly, but always far beneath the surface. 

 Certain of the species are known to be restricted to particular 

 water layers, usually at depths of from 500 to 1,500 meters, and 

 presumably all the species are limited in their vertical range by the 

 conditions of temperature and salinity, and to some extent, per- 

 haps, by the pressure, to which they have become specifically 

 adapted. Their geographical range, on the other hand, may be 

 very wide, since water layers of essentially similar physical and 

 chemical properties extend through vast areas of the oceans and 

 almost from pole to pole. It is in conformity with these en- 

 vironmental conditions that the bathypelagic organisms have 

 evolved. 



Up to the present time 47 species of these aberrant worms have 

 been described, but it is quite possible that some of them may be 

 synonyms. More than half of them have been carefully studied 

 with respect to their anatomical peculiarities, including those of 

 the nervous system. Stiasny-Wijnhoff ('23) has also described 

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