THE DISCOPHORA. 123 



radiating series of thickenings of the oral wall of each cham- 

 ber.^ 



All the other Dlscophora^ which are what are commonly 

 known as " Jelly-fish," are free, and some attain a very large 

 size. In the adult (Fig. 18) the umbrella is thick and divided 

 by small marginal notches into as many (usually eight) lobes. 

 At the bottom of each notch, often protected by special lob- 

 ules, is an oval lithocyst, supported by a cylindrical pedun- 

 cle, the cavity of which is in direct communication with 

 one of the radiating canals of the umbrella (Fig. 28, IV.). 

 This canal communicates with the exterior on the aboral side 

 of the base of the peduncle.'' The thick mesoderm of which 

 the great mass of the umbrella consists is composed of a ge- 

 latinous connective tissue, in the meshes of which is a watery 

 fluid, containing numerous nucleated cells which exhibit amoe- 

 boid movements. On the oral face there is a broad zone of 

 striped muscle, made up of fusiform fibres placed side by 

 side. In Aurelia aurita^ the angles of the four-sided hy- 

 dranth are produced into long foliaceous lips, the margins 

 of which are beset with minute solid tentacula (Fig. 18). 

 The gastric cavity contained in the hydranths terminates, be- 

 neath the centre of the umbrella, in a somatic cavity which 

 passes into four radially-disposed, wide offshoots, or genital 

 sinuses, the oral walls of which constitute the roof of the gen- 

 ital chambers (Fig. 18, II.). From their margiris the narrow 

 branching radial canals are given off. The peripheral ends 

 of these unite when they reach the margin. 



Each genital chamber is a recess, surrounded by a thick 

 wall of the oral face of the umbrella, in the centre of which 

 only a small aperture is left (Fig. 18, I., Gr). The roof of 

 this cavity is the floor of the genital sinus ; it is much plaited 

 and folded, and the genital elements are developed in it. Its 

 inner or endodermal wall is beset with small tentacular fila- 



1 The relations of Luc&rnarla with the DlscopJiora were sho-^-n in my lect- 

 ures, Medical Times and Gazette^ 1850. Kefei\stein, " Untersuchungen iiber 

 niedere Seethiere" (18()2\ in his monoOTaph on the ffenus, fully "confirms 

 this view, and Prof II. J. Clark arrived independently at the same conclusion : 

 '"'• Lucernaria the Co'notype of the Acalephoe^^ ("Proceedings of the Boston 

 Society of Natural Hist:ory," 1862'^. The Lncernaria {Carduella^ Allman) 

 cyathiformis of Sars differs much from the ordinary Lncertmrice^ especially in 

 the position of the genital organs as longitudinal thickeninfrs in the walls_ of 

 the gastric cavity. 8ee Allman, " On the Structure of Carduella cyathiformis'''' 

 ("Transactions of the Microscopical Society," viii.). 



2 The circular canal of the nectocalyx" communicates with the exterior by 

 apertures on the summits of papillose elevations in some medusoids. 



