168 J. W. Fewkes — Deep-Sea Medusae. 



crust, perhaps lava flows or geological oscillations ;* but midway 

 between these two places, equally removed from both, dis- 

 turbing causes only rarely penetrate and conditions remain 

 more constant year by year. Can we not expect to find here 

 a corresponding uniformity in the fauna as compared either 

 with the highly organized animals of- the surface or those of 

 the depths of the ocean % Is that fauna more uniform than any 

 other in the ocean ? 



JSTo group of animals is better suited for a study of the 

 questions which suggest themselves concerning the bathy met- 

 rical zones of characteristic animals, free-swimming at differ- 

 ent depths in the ocean, than the medusae. The group is a 

 large and very variable one. It is confined, with but few ex- 

 ceptions, to the ocean. Moreover it is probable that its ances- 

 tors were oceanic animals. No group of marine animals 

 presents fewer difficulties in studying the questions which 

 we have stated than this. 



It was with the impetus of a new enthusiasm for the study 

 of these questions that I undertook, by the advice of Prof. 

 Verrill, the examination of the rich collections of deep sea 

 medusae made in the Gulf Stream by the " Albatross." It 

 seemed to me that the examination revealed much of general 

 scientific interest. 



I shall not consider in this discussion the Hydroida, as the 

 members of this group are for the most part attached to the 

 ground, and the problems connected with them are the same 

 as those which pertain to all deep-sea animals attached or par- 

 tially living on the ocean bed. We shall also pass by, in silence, 

 the Ctenophora, no genus of which has yet been ascribed to the 

 deep-sea. I propose to consider a few of those jelly-fishes 

 which are known as the Acraspeda and incidentally the Si- 

 jphonopTiora. 



The history of the study of the deep-sea medusae belonging 

 to these divisions is a very brief one. In many of the mono- 

 graphs on these groups we have isolated mentions of medusae 

 which are ascribed to the deep-sea. The jelly-fishes thus men- 

 tioned were commonly washed into shallow water by ocean cur- 

 rents, by storms or unusual events in the ocean, and the depths at 

 which they were supposed to live could only be conjectural. 

 The specimens themselves were, for the most part, in a mutila- 

 ted condition. 



The first and only paper on the Siphonophora of the deep- 

 sea is by Prof. Studer,f who describes new species and genera 

 of these animals which were found twisted on ropes and wires 



*Such changes might take place even if the oceans have practically been the 

 same in past geologic times as at present. 



f Zeitschrift fur Wissenschaf tliche Zoologie, vol. xxi. 



