Introduction. 



It natnralh- follows from the difficulty of preserxing Cteuophores in a toleraljle condition only 

 that this group of animals has been rather neglected by most of the great Expeditions. Thus the 

 "Challenger"* Expedition has evidently brought home no serviceable material, and the same appears 

 to be the case with e. g. the Norwegian North Sea Expedition, the "Blake" Expedition a. o., even the 

 material collected by the Plankton Expedition was only for a \er\- small part in a condition which 

 made it possible to identify it with certainty'). The Danish "Ingolf" Expedition does not make an 

 exception from the general rule. Most of the material was simply preserved in alcohol, which no 

 Ctenophore can stand ; if onl)- formaline had been used, the results would certainly have been a good 

 deal better, and results of considerably greater value might have been obtained. The Ctenophore-Fauna 

 of the North Atlantic is certainly by no means so rich as that of the warmer regions, but it is cer- 

 tain that there is yet much to learn about it, l^oth as regards the distribution of the forms 

 already known and the occurrence of forms altogether unknown or not hitherto known from these 

 regions. The recent discovery of a new form, Pleurobrachia criiiita Moser, at Greenland indicates 

 sufficiently the incompleteness of our knowledge of the North Atlantic Fauna of Ctenophores. 



While there is after all not much prospect of finding new forms representing types of great 

 morphological importance among the Ctenophores of the surface of the North Atlantic, the case is 

 quite different with the deep-sea forms. Chun, in his report on the Ctenophores of the Plankton 

 Expedition (p. 3) was the first to suggest that such might possibly exist, and he had the satisfaction 

 of being also the first to prove their existence-). On the German Deep-Sea Exijedition he found two 

 different forms of peculiar Deep-Sea Ctenophores, one of which has recently been described by Moser 

 under the name Mertcnsia C/nini. the other still remaining undescribed. It ma\' not be too hardy 

 to suggest that many other Deep-Sea Cteuophores will prove to exist, and that also the North Atlantic 

 will contain such seems equalh' probable. This highly interesting problem remains as yet unsolved; 

 likewise the question of the vertical distribution of the Ctenophores has as yet scarcely received any 

 attention. A quite new problem regarding Ctenophores, viz. the existence of forms adapted to life at 

 the bottom as sessile or creeping organisms, has been raised by the unexpected discovery by Mr. 

 Ad. S. Jensen of the extremely interesting ses.sile Ctenophore which I have i^reliminarily described 



•) C. Chun. Die Ctenophoren des Plankton-Expedition. Ergebnisse d. Plankton Exp. d. Huniboldt-Stiftung. II. K. 

 iSgS. p. 4— 5, i) C. Chnn. Aus den Tiefen des Weltmeeres. 2. Aufl. 1905. p. 545. 



The Ingolf-hxpeilition. V, 2. 



