TRACHYMEDUSjE — GERYONIA. 427 



Nagel, 1893, 94, states that in Geryonia the ectoderm of the subumbrella and the manu- 

 brium is insensitive to chemical, but very sensitive to mechanical, stimulation; whereas the 

 tentacles are more sensitive to chemical than to mechanical stimuli. The mouth is extended so 

 as to touch any part of the bell-margin which may be stimulated, thus behaving in a manner 

 similar to that found to be the case by Romanes in his "Tiaropsts mdtcans." 



Stschelkanowzeff, 1906, finds that, in the Mediterranean, Geryonia proboscidalis is the 

 host of the parasitic larvae of two species of Cunina, C. proboscidea and C. rhododactyla. 



Mass, 1908 (Verhandl. deutsch. Zool. Gesell., p. 114), gives the results of some important 

 observations and experiments upon the development and structure of the egg in Geryonia and 

 Liriope. In Geryonia three distinct regions can be recognized in the unfertilized egg: an inner 

 mass of gelatinous material, surrounded by a coarsely foam-like cytoplasm, and a peripheral layer 

 of fine structure. The polar coordination of the larva is not determined in the 2-layered stage 

 wherein the larva consists of ectoderm and entoderm, but is determined by the polarity of the 

 unfertilized egg itself. Mass finds in accord with Zoja that the isolated blastomeres of the 2-cell 

 stage each develop into perfect medusae. The 4 blastomeres of the 4-cell stage give a larva with 

 a closed entodermal sac, with differentiated entoderm on its subumbrella side but no mouth- 

 opening. The 8 and 1 6-cell blastomeres resemble even more closely the planula condition in the 

 most advanced stage of development to which they are capable of attaining. Unfortunately, 

 this important paper has appeared too late to be adequately reviewed here and should be con- 

 sulted in the original. 



Geryonia "elephas." 



Geryones elephas, Haeckel, 1879, Syst. der Medusen, p. 294, taf. 18, fig. 7. 



Bell globular, fuller than a hemisphere, 50 mm. wide, 40 mm. high. This medusa is said to 

 be distinguished from G. proboscidalis by its long, narrow, cylindrical peduncle, apparently 3 

 times as long as the bell-diameter, instead of being about the same length, as in G. proboscidalis. 

 Moreover, the gonads are much wider than in G. proboscidalis and are 6-sided, nearly touching, 

 covering almost the entire area of subumbrella. The gonads extend along the 6 radial-canals 

 from base of peduncle to ring-canal. No centripetal canals ( ?) Found off the coast of South 

 Africa (Indian Ocean ?). 



Described by Haeckel from a preserved specimen. I am inclined to suspect that this so- 

 called species may be a specimen of G. proboscidalis with its bell unnaturally contracted 

 through the influence of preservative reagents. (See text -fig. 283.) 



a 



