252 Mr. J. W. Fewkes on Deep-sea Mednsce. 



are not characteristic belts of pelagic animals at different 

 depths. 



Witli the question whether tlie recorded depths at which 

 the MedusEe which we shall consider are found are accurate 

 or not we cannot deal. Indeed at this stage of this kind of 

 deep-sea exploration an examination of these methods would 

 be foreign to the purposes of this paper. We take the data as 

 given by the collector and at present leave the improvement 

 of the collecting-apparatus to others. 



Can we not approach this subject from another side ? Are 

 there any characteristics in the Medusae themselves which 

 show that they are preeminently fitted to live at the depths 

 or approximate depths from which they are reported ? Has 

 their habitat left any traces in the modification of their 

 anatomy ? Has the uniformity of conditions in their habitat 

 led to a corresponding simplicity in their structure, and are 

 they nearer the ancestral forms than others with a more 

 varied environment ? An account of the singular structure 

 of one or two typical genera may help us to answer this 

 question, or at all events present certain facts which bear 

 upon it. Let us therefore for illustration consider one or two 

 representatives of the Acraspeda and Siphonophora disco- 

 vered by the ' Albatross ' in the depths of the Gulf-stream. 



Every one familiar with the anatomical structure of the 

 Siphonophoves will recognize how difficult it is to find in 

 those genera like Rhizophysa anything to point to an adap- 

 tation to a deep-sea life. The 'Albatross' has discovered 

 new Physophores closely allied to Rhizophysa^ one of which, 

 Petropliysa, reaches the enormous size of 20 feet in length in 

 alcohol. The float of this animal is larger than that of any 

 true Siphonophore except Physalia. The large size of the 

 float in these Physophores would seem an efl'ective argument 

 against their adaptation to a life in deep water, especially as 

 their nearest ally, Physalia, is preeminently a surface form. 



It is extremely difficult to gather from the structure of the 

 known Siphonophora ascribed to the deep sea anything to 

 indicate an adaptation to such a life. The group can affijrd 

 little satisfaction in our answer to the question of whether 

 there is a nomadic deep-sea life or not. 



The nature of the argument for the existence of Medusan 

 life in bathymetrical zones may be best illustrated by con- 

 sidering a few examples of the Acraspeda. These are not 

 the only instances which might be chosen, and possibly are 

 not the best. They are thought to be as suggestive as any 

 among the Acraspeda which have been ascribed to great 

 depths. 



