CTENOPHORA. 



All these forms which are of so very great interest both for the morphology and the phylo- 

 geny of the Ctenophora and have given rise to long discussions concerning the interrelations between 

 the Ctenophora and other groups of animals, especially the Polyclads, are, with the exception alone 

 of the somewhat problematic Gastrodes, as yet only known from the Coasts of the Indo-Pacific Ocean, 

 those tracts so rich in all zoological wonders; not one of them is known to occur in the Atlantic 

 Ocean (though Gastrodes will doubtless prove to occur there). - - It is further a curious fact that 

 all these remarkable types were discovered by Russian naturalists, so that it almost seemed to be 

 their privilege to make such discoveries; to be sure, Ctenoplana has been rediscovered by Willey 

 and Coeloplana by Abbott, but no new types 1 ), only some new species, were discovered by them. - 

 At length, however, such a remarkably deviating type of Ctenophore has been discovered in the At- 

 lantic, and this time by a Scandinavian Naturalist, Ad. S. Jensen. Thus the Atlantic Region has 

 also been proved to be the home of at least one transformed Ctenophoran type, and even one of the 

 most transformed and which affords quite unusually great interest, both from a morphological and a 

 phylogenetic point of view. 



The animal was found by Mr. Ad. S. Jensen on the stems of some Umbellula Lindahlii K611. 

 in the Umanak Fjord, West Greenland, where when trawling in a depth of 475 575 M., he came over 

 a whole forest of this magnificent Pennatulid. His other duties not leaving him any time for observ- 

 ing the remarkable looking animal more closely, he preserved some specimens in formaline. On his 

 return he asked me to undertake the study of the animal. I beg him to accept my sincerest thanks 

 for leaving to me this most interesting task, and hope that he and my fellow-workers will find that I 

 have treated the rare animal in a way not too much out of harmony with its inquestionably great 

 morphological importance. 



At first, the animal puzzled me very much, as, indeed, also my colleagues, with whom I dis- 

 cussed the question to which class of animals it belonged. Only two possibilities seemed to offer 

 themselves -- that it was a Coelenterate or a Tunicate. For the latter view something in the whole 

 appearance was in favour; in fact there is, as I have said in my preliminary notice, something recalling 

 the peculiar sessile Salp, Octacnemus ; also for its being a compound Ascidian something might be said 

 viz. the four pairs of knobs along the upper side, each having a small opening, while another single 

 small opening was found in the middle of the upper side. It was, however, soon found that the ana- 

 tomy of the animal did not in the slightest way support the suggestion of its being a Tunicate. 

 There was then evidently no other possibility than that it was a Coelenterate. But also for a Coelen- 

 terate its organisation seemed most unusual. On studying its anatomy more closely I soon observed, 

 however, that some roundish knobs on the sides of the animal contained embryos, and the most 

 developed of these were found to be typical Ctenophores in the Cydippe-stage. Then the riddle was 

 solved, and the whole anatomy of the animal proved to be in full accordance with its nature as a 

 Ctenophore; though transformed in a most remarkable manner, it was not difficult to trace all its features 

 to the typical Ctenophoran structure, especially the different developmental stages showing the way 

 along which the transformations take place. 



') The Hetcroplana Newtoni Willey regarded by the author as related to Coeloplana and Ctenoplana is, in any case, very 

 doubtful as being really a Ctenophoran. A. Willey. On Heteroplana, a new genus of Planarians. Quart. Journ. Micr. Sc. 

 N. S- Vol. 40, 1898, p. 203 205). 



