ON THE ANATOMY OF THE FAMILY OF THE MEDUS/E 1 5 



in small than in large individuals ; it contains a closely-packed mass 

 of strongly-refracting granules .r 5^'ooth of an inch, more or less, in 

 diameter. The outer membrane of the pedicle can be traced over the 

 vesicle, and the inner probably passes under it, separating the cavity 

 of the pedicle from the vesicle : the dense mass of granules prevents 

 this from being actually seen, but from analogy with Mesonema, &c., I 

 have no doubt of the fact. 



28. Ehrenberg, in his description of the Medusa aurita, says, " Le 

 pedoncule est attache a une vesicule, dans lequel on remarque, sous le 

 microscope, un corps glanduleux, jaunatre lorsque la lumiere le 

 traverse et blanchatre lorsque cette derniere est refl^chie. De ce corps 

 il part deux branches qui se dirigent vers le pedoncule du corps brun 

 jusqu'a son petit bouton ou tete." And further on, " Le corps 

 bifurque place a la base du corps brun parait etre un ganglion nerveux, 

 et ses deux branches peuvent etre regardees comme des nerfs optiques." 

 I must confess that, judging by what I have observed in Rhizostoma 

 and PhacellopJiora, it appears to me that these so-called nervous 

 branches passing on each side of the pedicle towards its head, are 

 nothing more than the optical expression of the thickness of the two 

 membranes of which the pedicle is composed ; and a very similar 

 explanation may, I think, be given of his intertentacular ganglia, which 

 appear to be nothing more than the optical expression of the thickened 

 walls of the circular canal. 



29. Of the Tentacles.- — The tentacles of the Medusse are of two 

 kinds : — i, those which are processes of the outer foundation mem- 

 brane alone ; and 2, those which are processes of both inner and outer 

 membranes, and therefore contain a cavity continuous with the common 

 cavity of the body. Under the former class must be included the 

 knob-like processes on the convex surface of many Medusae con- 

 taining thread-cells ; the papillae on the generative and stomachal 

 membranes of Phacellophora ; the thickened margin of the stomachal 

 membrane in Oceania ; the buccal tentacles of Mesonema ; the tentacles 

 of the fringe of Rhizostoma and Cephea, and probably the marginal 

 tentacles of Thaumantias. I will proceed to describe some of these 

 more in detail. 



30. The papillae scattered over the generative and stomachal mem- 

 branes of Phacellophora are spherical, and connected with the membrane 

 by a somewhat narrower neck. The substance of this, as well as of 

 the body itself, is made up of large clear cells, but the surface of the 

 body is covered with an immense number of round thread-cells, figs. 

 20, 20 a. 



In Mesonema, the perpendicular membrane, which depends from 



