REPORT ON THE SIPHOTSTOPHOR^E. 105 



the Eudoxidaa. The first group, Diplophysidse, possess a smooth umbrella with rounded 

 surface, never prismatic; hemispherical or mitriform in Diplophysa and Eudoxella, conical 

 or spathiform in Cucubcdus and Cucullus. The second subfamily, Aglaismidae, has a poly- 

 hedral or prismatic umbrella with angular surface ; it is more or less cuboidal in Cuboides 

 and Af/laisma, wedge-shaped or similar to a prompter's box in Sphenoides and Amphiroa. 

 The cuboidal form (Pis. XL., XLII.) is of special interest as a reminiscence of the quadri- 

 radial structure in the orisjmal umbrella of the ancestral Medusa. 



Bracteal Cavity. — Whilst the superior or proximal face of the bract is convex, and 

 corresponds to the exumbrella of the Medusa, its inferior or distal face is concave and 

 comparable to the subumbrella. In the fundus of this cavity hangs the siphon, like the 

 manubrium or gastral tube of the Medusa. Its point of insertion is usually dislocated 

 towards the dorsal side. The single tentacle, which arises from the base of the siphon, 

 is placed between this and the dorsal wall of the subumbrellar cavity. The greater 

 ventral part of the cavity is occupied by the gonophore. 



The form of the bracteal cavity has sometimes preserved the original hemispherical 

 form of the subumbrella ; but usually it is more campanulate or conical, and often at the 

 same time bilateral, more rarely asymmetrical. Its basal opening, or the bracteal mouth, 

 is usually oblique, more or less bevelled off, sometimes armed with prominent teeth. 



Phyllocyst.- — The central part of the subumbrella, where the siphon is inserted, con- 

 tains in each Eudoxia a caecal diverticulum of the entoderm, which is in direct communi- 

 cation with the basal part of the siphon, and in the young sessile Eudoxia with the 

 central canal of the stem. This phyllocyst (bursa centralis bractese) is comparable to the 

 apical canal, which in certain Medusae (Codonidae, &c.) ascends vertically from the base 

 of the manubrium, and ends blindly in the jelly of the umbrella. 



The cavity of the phyllocyst is usually small, lined by large clear vacuolated entoderm- 

 cells, which are polyhedral from mutual pressure. The apical part of the phyllocyst usually 

 contains an oleocyst (co), an oil-globule, which has a hydrostatic function. The phyllocyst 

 of the bract is, therefore, similar to and comparable with the somatocyst of the nectophore. 



The phyllocyst is sometimes a simple cylindrical caecal canal or an ovate sac, placed 

 in the vertical axis of the bract, or somewhat excentric ; as in Diplophysa, Cucubalus, 

 and Cucullus. But usually some nutritive canals arise from its base, which enter into 

 the jelly mass of the bract. The number and disposition of these phyllocyst canals are 

 characteristic of the different genera, and of interest as remnants of the four radial canals, 

 which run in the subumbrella of Medusae towards its margin. Eudoxella (PL XXXII.) 

 and Aglaisma (PL XL.) still possess all four canals ; two of them are placed in the sagittal 

 plane (one dorsal and one ventral), two others symmetrically on both sides (one right 

 and one left). The latter are preserved too in Cuboides (PL XLII.) and in Amphiroa (PL 

 XXXVI.), whilst the two sagittal canak are lost. Sphenoides (PL XXXVIII.) possesses 

 only a single canal, descending on the dorsal side ; the three others have disappeared. 



(ZOOL. OHALL. EXP. PART LXXVII. — 1888.) Hhhh 14 



