216 



MEDUSAE OP THE WORLD. 



As A. Agassiz says: 



"The action of the light and increase of temperature of the surface is sufficient to kill them in 

 the course of half an hour; the moment they are brought to the surface, the bell loses its transpar- 

 ency, the genital organs become dull and the medusa is soon completely decomposed. This action 

 is much more rapid than anything of the kind which I have noticed, even in Ctenophora;, Mertensin 

 being the only genus in which the decomposing effects of light and heat are at all equal to what is 

 produced here. This jelly-fish must be a deep-water species, as they have only been found during 

 a single autumn, and then only for a few days, when they seemed quite abundant." 



f ' 



.-... :^, 



Fin. lo<).Ptychogtna " f>!nnulata"= P. laflea, after Haeckel, in "Report. Challenger Expedition, Deep-Sea Medusa. 



v, velum; w, subumbrella; al, lips; urn, umbrella-margin; r, stomach cavity; ob, marginal clubs; gs, ciliated 

 perradial cruciform furrow in the aboral wall of the central stomach; en, outer part of one of the radial-canals; 

 ck, distal funnel-like part of one of the radial-canals; j, gonad; u, umbrella; 1, tentacles. 



