104 GEGENBAUR, ON MEDUS. 
organic residue is left retaining the original form of the 
concretion. Gegenbaur has never observed crystalline forms 
or crystals. 
The number of these marginal vesicles is constant in the 
Geryonide, and also in the minute medusoid forms resembling 
Thaumantias, and which should probably form a distinct 
family from the true Thaumantiade. In the Auginidze their 
number is very variable, and in this group the maximum in 
this respect is probably reached, viz., about 60; though even 
in this family exceptions exist. 
The position of these bodies always indicates an intimate 
relation to the gastro-vascular system, although the cavity of 
the vesicles does not, as might be supposed, communicate 
with the interior of the gastric canals. This relation is 
especially evident in the Cuninide, in which the marginal 
vesicles are always sittiated at the extremities of the gastric 
sac, and never in the interspaces. 
In the Geryonide a marginal vesicle is seated at the base 
of each tentacle. In some species of the family Aiginide 
the vesicle is seated in a depression at the summit of a conical 
eminence, composed of distinct cells, each of which, in a form 
allied to gina, supports a long descending ciliwm. 
Gegenbaur has never witnessed ciliary movement within 
the vesicles, nor in fact motion of any kind, except what 
might be referred to endosmotic action. In this he agrees, 
he says, with all his predecessors, except Kolliker, who 
describes in a species of Oceania the existence of cilia in the 
marginal bodies,—an observation the correctness of which 
Gegenbaur does not doubt, but supposes it to refer to Oceania 
marsupialis (Carybdea marsupialis, Peron), whose marginal 
bodies present very remarkable peculiarities, which he after- 
wards discusses. 
If the rather large marginal vesicles of Geryonia be ex- 
amined, it will at once be seen that the concretion is not free 
in the vesicle, but connected to the wall by means of a short 
peduncle, from which, in fact, a delicate membrane extends 
over and encloses the concretion entirely. Repeated obser- 
vation will occasionally detect a much thicker investment, 
within which, besides the concretion, are contained minute 
molecules, and an oval or rounded corpuscle, resembling a 
nucleus. In fact, there is nothing opposed to the notion that 
the concretion is formed in the secreting cavity of a parietal 
cell which projects into the interior of the vesicle, m the 
same way that other concretions are formed in the lower 
animals, as for instance the renal concretions of the Gastero- 
poda, &e. 
