Mr. J. W. Fewkes on Deep-sea Medusce. 257 



which bring information of the thermal limits at which the 

 Medusfe can live. 



It would be profitable, if space permitted, to consider other 

 genera of Acraspeda made known bj the ' Albatross ' in their 

 bearings on the question which is the title of this paper. 

 The three genera already considered present us the strongest 

 arguments which can be found in the modification of external 

 and internal anatomy, as indicative of a deep-sea habitat. 



" Those Medusffi," writes Ha^ckel, " may be regarded with 

 greater probability as permanent and characteristic inhabitants 

 of the deep-sea, which have either adapted themselves by 

 special modifications of organization to such a mode of life, 

 or which give evidence by their primitive structure of a re- 

 mote phylogenetic origin." He then enumerates those which 

 he places in this category, among which are the two remark- 

 able genera Atolla and Nauphanta. "It is by no means 

 certain," writes Ha^ckel, " that all the eighteen Medusae 

 described below (Report on ' Cliallenger ' Medusse) are con- 

 stant inhabitants of the deep sea.'" We have discussed the 

 argument drawn from two of the most characteristic of the 

 Acraspeda, viz. Atolla and Naujj/ianta, and can readily sub- 

 scribe to this statement as far as these are concerned. 



The resemblance of Naupka^itopsis and Atolla to Ephyra 

 is believed to have a morphological significance ; Ephyra is 

 thought to be the ancestral form of the Acraspeda, and these 

 so-called deep-sea Medusse still preserve the ancestral form 

 with small modifications, except in size, repetition of organs, 

 and certain other characters. Of the development of Atolla 

 or of the Collaspidse we know nothing, and yet a knowledge 

 of this subject is possibly to reveal the solution of important 

 questions. If the mode of growth should prove to be a direct 

 development without a Scyphostoma, it would certainly in- 

 crease my belief that these Medusaj somehow resemble the 

 ancestral forms. I have already elsewhere shown that among 

 the Hydromedusce with alternation of generations and those 

 with a direct development, the latter method is normal, while 

 the former is a secondary modification. Among Acraspeda 

 also the direct development of Pelagia is the ancestral 

 method, while the formation of a Scyphostoma is a secondary 

 modification. We should expect to find in Atolla a direct 

 development if it be an ancestral genus. From its mode of 

 life in the high seas we should also expect tlie same *. 



* I believe the Luceruariaus are degenerate adult Acraspeda, which 

 have attached themselves to the bottom much in the same way as Cas~ 

 siopea frondosa, and become modihed in consequence. While it may be 

 said that they are homoloiious to the Scyphostoma stage, it is not thouglit 



