418 
MR. T. H. HUXLEY ON THE ANATOMY OF THE MEDUSA. 
therefore, when viewed by transmitted light, appear like four thick fibres. The vesicle 
is about xl^th of an inch in diameter, more spherical in small than in large indivi- 
duals ; it contains a closely-packed mass of strongly-refracting granules 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 p^doncule 
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 derni^re 
est r^flechie. De ce corps il part deux branches qui se dirigent vers le pedoncule du 
corps brim jusqu’a son petit bouton ou tete.” And further on, “ Le corps bifurqu^ 
place a la base du corps brun parait etre im ganglion nerveux, et ses deux branches 
peuvent etre regardees comme des nerfs optiques.” I must confess that, judging by 
what I have observed in Rkizostoma and Phacellophora, 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 Medusae are of two kinds: — 1, those 
which are processes of the outer foundation membrane alone; and 2, those which 
are processes of both inner and outer membranes, and therefore contain a cavity con- 
tinuous with the common cavity of the body. Under the former class must be in- 
cluded the knob-like processes on the convex surface of many Medusae containing 
thread-cells; the papillae on the generative and stomachal membranes of Phacello- 
phora,', 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 Thaunianfias. I will proceed to describe some of 
these more in detail. 
30. The papillae scattered over the generative and stomachal membranes of Pha- 
cellophora 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 the orifice of the 
central cavity, is prolonged at its edges into a great number of short tentacles. Each 
of these is composed of an outer wall, in which immense numbers of thread-cells are 
imbedded, and a central axis made up of large transparent cells. This cellular axis 
extends for some distance beyond the base of the tentacle into the substance of the 
membrane, fig. 7- 
