MR. T. H. HUXLEY ON THE AFFINITIES OF THE MEDUS.®. 
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in being composed of a single membrane covered with thread-cells, and having a 
cellular axis. 
63. The second kind of tentacle is homologous with the prehensile organs of the 
Diphydae and Physophoridse with the peculiar clavate processes of Plumularia, and 
so far as I can judge from descriptions of their structure, with the tentacles of 
Hydra. 
All the organs here mentioned commence their development as bud-like processes 
of the two primary membranes, elongating and attaining the forms peculiar to their 
perfect state as they grow older. The tentacles of the Medusae are usually developed 
(as in most Monostomatae) from the circular vessel of the disc, sometimes {Phacello- 
phora)fvom the diverging canals, sometimes, finally, from the neck of the stomach 
Lymnorea, Javonia). The prehensile organs of the Physophoridae also have consider- 
able variety in position. In Porpita, Vitella, Angela (?), they are developed from the 
margin of the float ; in PJiysophora and many others from the base or the pedicle of 
the stomach. The prehensile organs of the Diphydae are always developed either 
from the base or the pedicle of the stomach. The peculiar clavate organs of Plumu- 
laria are developed from the common tube independently of the stomach. 
64. The adult forms of these organs have all the same structure, being composed 
of two membranes, with a vast number of thread-cells of larger or smaller size, 
seated in the substance of the outer membrane or between the inner and the 
outer. 
65. The “clavate organs” of Plumularia deserve especial notice, as I am not 
aware that they have been hitherto described, and as they exemplify in a very beau- 
tiful manner the “ unity of organization” manifest among these families. 
I have found them in two species of Plumularia obtained by the dredge at Port 
Curtis ; they were of two kinds, the one attached to the cell of the polype, the other 
to the pedicle of the ovary, figs. 43, 44, 45. In each species there were three pro- 
cesses of the former kind, two above proceeding from near that edge of the aperture 
which is towards the stem, the other below from the front part of the base of the cell ; 
they were conical in the one species, club-shaped and articulated in the other, and 
consisted of an external horny membrane open at the apex, and an internal delicate 
membrane inclosing a cavity, all these being continuous with the corresponding 
parts of the stem. At the apex of each, and capable of being pressed through the 
aperture, lay a number of thread-cells ; with moderate pressure the threads only of 
these organs were pressed out. 
I found the second kind of organ in the species with conical processes. It con- 
sisted of a stem proceeding from the pedicle of the ovary, bearing a series of conical 
bodies having the same constitution as those just described, fig. 45. The perfect 
resemblance between these and the prehensile organs of the Diphydae cannot be 
overlooked. 
66. The structure of the generative organs is still more instructive. In the 
Medusae I have endeavoured to show that there are always processes of the two 
