ON THE ANATOMY OF THE FAMILY OF THE MEDUSA 1 3 



In the Cryptocarpae, the common cavity may be either small 

 {Thaujnatitias) or large {Oceania) ; from it there proceed a number of 

 straight unbranching canals which open into a circular canal running 

 round the margin of the disc. 



In the Phanerocarpae the general arrangement is similar, but the 

 canals frequently branch {Medusa aurita, Phacellophora) and anasto- 

 mose in a reticulate manner. 



In many of the Monostome Medusje the centre of the under sur- 

 face of the disc projects into the " common cavity " as a rounded boss 

 (fig. 1 1 (?.), and according to its form and size will seem to divide the 

 former more or less into secondary cavities. This appears to me to be 

 the origin of the multiple stomachs of Medusa aurita as described by 

 Ehrenberg. 



19. In the Rhizostomidae, the canals of the branched processes 

 unite and open by four {Rhizostoma, Cephea) or eight {Cassiopea ?) 

 distinct trunks into a wide curiously-shaped cavity, from whence 

 anastomosing canals are given off to all parts of the disc (figs. 

 26, 26 (7.). The circular vessel exists, but is not particularly 

 obvious in consequence of anastomosing branches being given off 

 beyond it. 



20. In very many of the Cryptocarpae {Carybdoa, Oceania (fig. 5 a. 

 and b?), Polyxenid) there is a circula^r, valvate, muscular membrane 

 developed from the inner and under edge of the disc. In tlie Phanero- 

 carpae such a membrane does not seem to be present, but in Rhisostoma, 

 and Cephea it is evidently replaced by the inflexed edge of the disc 

 fig. 26 a. 



21. Of the Marginal Corpuscles. — In the Cryptocarps the marginal 

 corpuscles are sessile upon the circular vessel, figs. 8, 9, 10. They are 

 soheroidal vesicles, containing a clear fluid, and one or more spherical 

 strongly-refracting bodies occasionally included within a delicate cell. 

 The. marginal vesicles are placed between the inner and outer mem- 

 branes of the circular vessel. 



In the Phanerocarpae {Phacellophora) the marginal corpuscle (figs. 

 25, 25 a.) is placed at the extremity of a short double-walled tubular 

 pedicle projecting downwards or towards the ventral surface of the 

 disc ; the under margins of the fissure in which it is lodged are pro- 

 longed into two overlapping fringes. The cavity of the pedicle is con- 

 tinuous with that of a canal which runs from the common cavity 

 directly towards the corpuscle. Its walls are continuous, the inner 

 with the inner wall of the canal, the outer with the substance of the 

 disc. The pedicle is in fact a mere process of the system of canals, so 

 that the position of the marginal vesicle is relatively to this system 



