14 ON THE ANATOMY OF THE FAMH.Y OF THE MEDUSA 



the same as in the Cryptocarpje. A similar remark holds good with 

 regard to the Rhizostomidae. 



22. In Cephea and Rhizostonia the organ is placed in a notch between 

 two lobe-like processes of the margin of the disc, and looks upwards. 

 On the upper surface a semilunar fold extends from one lobe to the 

 other and covers in the corpuscle ; below, the edges of the lobes are 

 thinned and overlap, figs. 33, 34. 



23. There are some peculiarities in Rliizostonia which deserve to 

 be noticed more fully. On the dorsal surface, behind the semilunar 

 fold above mentioned, there is a large heart-shaped depression (fig. 33) 

 with its base towards the corpuscle. Its surface is thrown into 

 prominent arborescent folds, and is very richly ciliated. The deepest 

 part of the depression is towards its base, and seems to take the 

 direction of the base of the pedicle of the marginal corpuscle, which is 

 just below it. I could not pass a needle from the depression into the 

 cavity of the pedicle, but I have no doubt that they communicate, as 

 on a lateral view the deepest part of the depression seems to project 

 into the cavity of the pedicle. Furthermore, on pressure, the granules 

 usually contained in the cavity of the pedicle sometimes passed into 

 the depression. 



24. Ehrenberg describes apertures in Mediisa mirita by which the 

 system of canals communicates with the exterior, but they are 

 alternate with the marginal corpuscles, not under or above them. 

 In Cepliea Wagneri, again, according to Will, the canals open beneath 

 the marginal vesicles. I did not observe this in the Cephea ocellata. 



25. On the ventral surface a much slighter semilunar fold connects 

 the base of the two lobes, fig. 34. In the centre, behind this, there is 

 an elevation of the substance of the disc, to which the muscular bands 

 which run along the under surface of the disc converge. 



26. The canal which runs to the marginal vesicle gives off branches 

 on each side, then opposite the base of the vesicle forms a dilatation 

 rather larger than the cordate depression ; from this a caecal process 

 passes off into each lobe, and so terminates. The termination of the 

 canal in Cephea and Pliacellophora is similar, but in the latter the caeca 

 gives off lateral anastomosing branches, fig. 25. 



27. In Rliizostoma the pedicle is somewhat bent and enlarged at 

 its upper half The inner membrane is richly ciliated, and the cavity 

 which it encloses usually contains a number of rounded cell-like bodies 

 floating about in incessant motion. There is a considerable space 

 between the inner and outer membranes, which are thick, and there- 

 fore, when viewed by transmitted light, appear like four thick fibres. 



The vesicle is about yi-uth of an inch in diameter, more spherical 



