GEGENBAUR, ON MEDUSZ. 105 
If this be the true state of things, there can be no question 
as to the non-existence of motion in the concretions, and in 
great measure the analogy fails, which would place the 
marginal bodies of the Meduse in the same category with 
the auditory organs of the Acephala and Cephalopoda. 
6. Pigment-spots (ocelli). 
Coloured spots on the base of the tentacles occur only in 
the Oceanidz and Thaumantiad, both of which families 
(certainly the former) are medusoid forms of polypes. Con- 
sequently, except in Oceania turrita, coloured spots and mar- 
ginal vesicles are not found to coexist. 
The spots themselves consist of dense agglomerations of 
yellow, red, brownish-red, or black pigment-cells, placed upon 
a more or less prominent elevation on the base of the 
tentacle. Except in Tiaropsis, their number corresponds 
with that of the tentacles. 
In Lizzia, Bougainvillea,—Oceanide, with the tentacles 
disposed in groups,—the ocelli are always situated on the 
under side of the tentacles in the form of a crescent. 
In Cladonema and the allied Eleutheria of Quatrefages, a 
spherical, highly refractive corpuscle is lodged in the midst 
of the pigment. In Eleutheria this body is of considerable 
size, and projects above the surface. 
B. Marginal bodies of the higher Meduse. 
In the lower Meduse we have seen the two forms of 
marginal bodies existing in distinct families, but in the 
higher or steganophthalmatous group we see indications of 
the union of the two into a single organ. 
In the simplest form of these bodies, as in Pelagia and 
Cassiopeia, they constitute vesicles of an oval form, somewhat 
acuminate at the free end, and wider at the opposite, sup- 
ported on a short stem in the incision and between the lobes 
of the disc. Immediately above the notch in which the 
marginal body is lodged, runs a canal communicating with 
the contiguous prolongation of the gastric cavity. The canal 
at this point is slightly dilated and furnished with distinct 
walls. It enters the stem of the marginal body, running 
downwards in it for more than one third of its length, ulti- 
mately curving round nearly at a right angle with the longi- 
tudinal axis of the marginal vesicle. 
The marginal body itself encloses an oval cavity also 
surrounded by a well-defined layer of tissue. The curved 
canal of the peduncle opens into this space, which would, in 
fact, represent a sudden dilatation of it. Thus, in the 
