358 
PROFESSOR E. RAY LANKESTER. 
points, and first of all discuss the structure of the peronia and 
tentacles. 
Naked-eye appearances . — When the Medusa is seen swim- 
ming in the water, the observer is at once struck by the manner 
in which the tentacles are carried. Though they can be de- 
pressed and directed towards the subumbrella surface, they 
are, as a rule, carried nearly at right angles to the horizontal 
plane of the disc and directed upwards. This carriage of the 
tentacles is more particularly noticeable when the Medusa is at 
rest after a certain number of pulsations, but is also seen be- 
tween each one of a series of pulsations. An opaque crenated 
line along the margin of the disc (fig. 1, 3/i2.) is very readily 
observed, even without any magnifying glass. This line is the 
marginal ring, consisting externally of ectoderm cells charged 
with thread-cells, and more deeply strengthened and supported 
by the thickened wall of the marginal or ring canal, the endo- 
derm cells of which are converted into a cartilaginoid tissue, 
having a yellowish-green tint when seen by transmitted light 
with the microscope. These yellowish cartilaginoid cells have 
led Professor Allman to speak of the margin of the disc as being 
loaded with brownish-yellow pigment-cells."” 
The layer of thread-cells along the margin of the disc, although 
not bulky in this small form, yet undoubtedly corresponds to the 
^^nettle-ring” (Xesselring) of the typical Trachyline Medusae, 
whilst the subjacent cartilaginoid tissue corresponds to the ‘‘'ring- 
cartilage ” (Eingknorpel) of the same group. 
The crenations or centripetal projections of the opaque mar- 
ginal ring are in relation to the insertions of the tentacles. 
They have the same superficial structure as the superficies of the 
ring itself, and, so far as any definition can be given to the term 
“ peronium,” the centripetal prolongations of the nettle-ring 
passing from that structure to the point where a tentacle springs 
from the disc, are entitled to the name. Below the peronia we 
find in each case an extension of the peculiarly modified endo- 
dermal cartilaginoid tissue of the ring-canal, which passes with 
rapid gradation into the cartilaginoid tissue of the tentacle- 
root. 
The power of contraction and expansion possessed by the ten- 
tacles is no doubt, as Professor Allman has pointed out, greater 
than that possessed by the most highly differentiated of the 
Trachyline Medusae. At the same time the stiff erect carriage 
to which I have alluded, is quite unlike anything seen in Lepto- 
medusae, and as I shall point out below the solid axis of the 
tentacles, though not so firm a tissue as the corresponding tissue 
of Cunina, is very appropriately described by the term “ carlila- 
ginoid,” and more distinctly resembles “notochordal tissue” 
