PEOF. Q. J. ALLMAN ON LIMNOCODIUM VICTORIA. 137 



interval from the outer ectodermal walls of the sporosac, is quite 

 in favour of the endoderm being the seat of their origin. 



The marginal nerve-ring can be traced running round the whole 

 margin of the umbrella, and in close relation with the lithocysts*. 

 A filament is given off from it in each of the four interradial 

 spaces, and thence ascends in the subumbrella between the radial 

 canals. Ocelli are not present. 



The refringent body which occupies the interior of the litho- 

 cyst consists of an aggregation of highly refringent spherical cor- 

 puscles. I have counted from five to ten such spherules in a 

 single lithocyst. This structure becomes very obvious in speci- 

 mens which have remained for a day or two in a weak magenta 

 solution f. 



The generic characters of Limnocodium may be brought together 

 as follows : — 



Genus Limnocodium (\[fxvr)=pond, KioZuv—bett). 



Hadial canals 4, each carrying a single reproductive sac ; manu- 

 brium destitute of peduncle, 4-lipped ; marginal tentacles filiform, 

 solid, very numerous, adnate to the outer side of the umbrella 

 for some distance from their insertion into its thickened and 

 sinuous margin ; marginal vesicles each sending into the velum a 

 tubular extension, which terminates blindly at the free edge of 

 this membrane. 



* The terms " otocysts " and " otolites," employed for the marginal bodies of 

 a medusa, are very unsatisfactory. Their significance depends on the assumption 

 that these bodies are organs of hearing. Their being endowed with an auditory 

 function, however, is very far from having been proved. Mr. Busk had long 

 ago given morphological reasons for regarding them as organs destined to 

 receive and transmit impressions of light, while the recent beautiful physiolo- 

 gical experiments of Mr. Eomanes give results whicb point quite in the same 

 direction. Though observation is thus in favour of ascribing to the marginal 

 bodies of the Hydroid Medusae a photaesthetic function, the very convenient 

 term of "lithocyst" proposed for them by Prof. Huxley, involving, as it does, 

 no idea of disputed function, may be adopted with advantage. 



t To this peculiar structure of the otolite my attention was first called by 

 Mr. Busk. 



LINN. JOTJltN. — ZOOLOGY, TOL. XV. 11 



