2 COBBOLD, ON A NAKED-EYED MEDUSA. 
a quarter-inch objective, the external convex surface of the 
umbrella presented a few well-defined and sparsely scattered 
cellules, which were rather irregularly disposed beneath the 
transparent, and, in such situations, slightly elevated, epider- 
mis (fig. 2). No other indications of structure were noticed. 
The ¢entacula, while relaxed and motionless, are fully three 
times the length of the dise—a peculiarity serving to distin- 
guish this Medusa from all other British species, their peculiar 
arrangement (5 x 4+ 4) also constituting a satisfactory 
mark of identification. During the gentle agitation of the 
water it frequently happened that the tentacula stretched 
beyond this length, the trailing filaments assuming an almost 
invisible tenuity, but when violent contraction occurred, the 
threads suddenly acquired the form of minute tubercles, bor- 
dering the circumferential margin of the umbrella. A gradual 
unfolding usually commenced immediately after the contrac- 
tion—-the exciting agent bemg removed—the extension inva- 
riably originating at the base of the filament, and proceeding 
uniformly downwards to the extremity, until each succeeding 
portion was unfurled. Incompletely extended, the tentacles 
always appear clavate at the tip. Amplified 50 diameters, 
they exhibit a finely granular and ringed appearance, analo- 
gous to that of the prehensile labiate organs of hydroida (fig. 
3) ; with an ordinary pocket-lens indications of knotting may 
be seen at the extremity of the cirrhi. To the naked eye the 
tentacular bulbs appear colourless and homogeneous, but under 
a magnification of 300 diameters, the sub-epidermic tissues 
display numerous closely packed fusiform cells, identical with 
those described as lying beneath the cuticle of the umbrella 
(fig. 9). They refracted light very strongly, but the exist- 
ence of nuclei could not be demonstrated. At the bulb the 
cells are irregularly disposed ; a little further down they begin 
to assume symptoms of grouping, co-ordinate with which 
bulgings appear at the margin of the thread. Lower still, 
the fusiform particles acquire an mcompletely linear arrange- 
ment, speedily merging into a definite series of rings or 
knots, placed at regular intervals. While the cirrhus is re- 
laxed the cell-groups are separated by a transparent interspace, 
which is much constricted, but exceeds in length the paren- 
chymatous knot. Near the extremity of the thread the cells 
are more cogently developed, and being placed at a right 
angle to the axis of the filament, appear to stand out from the 
investing epidermis (fig. 4). At the upper part the tentacula 
exhibit lateral lines in their interior, denoting the presence of 
a central canal, the markings becoming more conspicuous 
near the bulb (fig. 9). This last-named structure, viewed by 
