Introduction. 



It is now forty years since the first pelagic nemerteans 

 were brought to light during the voyage of the "Chal- 

 lenger", and although new finds have subsequently been 

 made by various other expeditions, notably that of the 

 "Valdivia", the material has throughout been but scanty 

 in amount, and only partly available for thorough investi- 

 gation. With regard to this peculiar animal group there- 

 fore, interesting as it is from the point of view of general 

 zoology on account of the remarkable transformations 

 occasioned by the need of adaptation to pelagic life, our 

 knowledge is still irregular and incomplete in the extreme. 

 It has even, in several cases, been found quite impos- 

 sible to identify species previously described, owing to 

 the superficial character of the original descriptions. 



The "Michael Sars" expedition brought home a 

 very rich amount of material of this group, for the most 

 part in a good state of preservation; this materiel has 

 since been placed at my disposal by the Norwegian 

 Director of Fisheries, Dr. Johan Hjort, who was in 

 command of the expedition, conjointly with Sir John 

 Murray. 



I had then already, some ten years before, com- 

 menced the study of the pelagic nemerteans, specimens 

 of which I had received from several Danish expeditions, 

 and in course of the work other collections came to 

 hand. It was the material from the "Michael Sars" 

 however, which rendered it possible to make a thorough 

 investigation into the taxonomy, distribution and anatomical 

 structure of this group. 



Any work dealing with nemerteans must necessarily 

 be based upon highly detailed treatment of the subject 

 by means of serial sections, and should, moreover, if it is 

 to prove of real value to subsequent investigators, include 

 exhaustive descriptions, supplemented, as regards anatomy, 

 by a great amount of illustrative matter. Such a method 

 of proceeding would however, in the present instance, 

 involve a demand for space altogether transcending the 

 limits assigned to this chapter in the report of the expe- 

 dition, and disproportionate to the small number of species 

 treated; the scope of the work has here therefore been 

 very essentially curtailed. The plan now adopted, after 

 consultation with the Editor, Dr. Hjort, is to give a 

 fairly detailed diagnosis of all new or little-known species, 

 with a statement of their respective geographical distri- 

 bution as indicated by the material. The entire subject 

 will thereafter be treated at length, with the requisite 

 illustrations, in a separate monograph on the pelagic 

 nemerteans shortly to be issued among the publications 

 of the Bergen Museum. In this latter work will be found 

 the full explanation of the classification also employed in 

 the present report, a system based upon a number of species 

 over and above those here concerned, and, in the case 

 of several species, upon a considerably greater number 

 of specimens than furnished by the expedition. 



With regard to the terminology employed, it will 

 suffice to mention that this is in all essentials identical 

 with that formulated by Burger (3) in his monograph on 

 the nemerteans. 



Bergen, June 1915. 



Aug. Brinkmann. 



