Mr. J. W. Fevvkes on a new Fhysopfiore. .j^l 



III. Homology of the iZboc^ o/Ploeophysa. 



The horaologue of the hood is to be found among other 

 Physophores in the nectostem of which it is an outgrowth. 

 It assumes in certain genera a variety of shapes. In Rhizo- 

 pliysa gracilis, Fewkes, in which, as in all Rhizophjsidse, 

 the polyp-stem is very long, the hood appears as a small 

 transparent hernia-like bud with air-bubbles at the base of 

 the float, as figured in my paper on the jellyfishes of l^or- 

 tugas *. In Plenro'pliysa the nectostem does not bear necto- 

 calyces ; but instead of bells it carries small buds or tubercles 

 on one side. In this genus the hood has been elongated into 

 a nectostem, but does not yet bear nectocalyces. In Rail- 

 phyta we have the same condition as in Pleuropliysa as far as 

 the modified hood is concerned \. It can readily be seen 

 that in these two genera the hood has assumed the shape of a 

 nectostem, which, in genera like ^9'rt/wrt, bears nectocalyces f. 

 It seems, then, that we have in the so-called nectostem of 

 Pleurojihysa and Halipliyta an indication of the homology of 

 the hood of Ploeophysa. 



In the Ehizophysid^e, as_ before recorded, the nectostem is 

 ordinarily reduced to nothing or wanting. The hood, how- 

 ever, may be represented in the structure at the base of the 

 float of R. gracilis. In Pterovliysa, a giant genus over twenty 

 feet in length, a differentiation of the nectostem from the 

 polyp-stem has begun to take place, and in the allied Batliy- 

 physa ahyssorum (Studer) Hseckel, both nectostem and 

 polyp- stem are well differentiated. 



In Pterophysa^ we find at the base of the floa<^, in about 

 the same position as the bud already mentioned on the float 

 of Rhizvphysa gracilis, a cluster of taster-like bodies homo- 

 logous with the so-called tasters [ts) of Ploeophysa. These 

 bodies indicate the position of the nectostem and are homo- 

 logous with similar bodies, called nectotasters, found on the 



* Loc. eif. 



t The great ditference between these two genera is the absence of 

 hydrophyllia in Pleurophysa and the character of the polypites, 



X I was at first led to suppose that nectocalyces once existed on the 

 nectostem of Haliphyta and that tlie small knobs indicated their former 

 attachment. That opinion is now abandoned, and I now think they were 

 never there. I am confident of this so far as Pleurophysa is concerned. 



§ My figure of Pterophysa, drawn from a beautiful specimen over 

 twenty feet long, shows no nectocalyces or hydrophyllia. In none of the 

 specimens which I have studied are there any signs of nectocalyces or 

 covering-scales, nor of the attachment of these structures. Moreover, a 

 long nectostem does not exist. I cannot therefore follow Haeckel when 

 he refers my Pterop/iysa to the Forskalidte. 



