362 
PROFESSOR E. RAY LANKESTER. 
and which is called tentacle root/’ we find the same large cells 
as those in the axis of the free part. 
The root at first expands a little at its insertion into the disc, 
but tapers as it approaches the wall of the marginal canal, and 
becomes rounded ofi* (see PL XXX, fig. 5 TRj and woodcut, 
fig. 3). There is, however, no discontinuity of the tissue where 
the tentacle root ceases and the marginal ring commences, but 
rather a very rapid transition or change in the form of the en- 
dodermal cells, which equally constitute the tentacle axis and 
the marginal cartilage ring. 
The cells, in fact, diminish very much in size whilst exhibit- 
ing a characteristic polygonal form (PI. XXX, fig. 6). In 
place of the large vacuoles filled with gelatinous substance which 
are presented by the large cells of the tentacle-axis, we find, 
within the small polygonal cells, block-like deposits, one or two 
to a cell, of a pale greenish tint and homogeneous structure. 
The greenish colour of the contents of these cells shows through 
the superficial ectoderm cells, and gives the whole ” marginal 
ring ” a greenish-yellow appearance. It is most strongly de- 
veloped in the velo- marginal cells which form an inferior limit 
to these modified endodermal cells of the ring-canal’s wall. 
It cannot be disputed that in the character of these cells, as 
compared with those of the adumbraLwall of the marginal canal 
(PI. XXX, fig. 7), we have a very well-marked distinction. 
These adumbral cells are metamorphosed by the intracellular 
deposit of a homogeneous greenish substance, so as to form a 
sort of cartilaginous tissue, which acts the part of and morpho- 
logically represents the cartilage-ring ” of higher Trachyline 
Medusse. In order to appreciate their special character ^ it is 
only necessary to compare them with the lining cells of the 
adumbral wall of the marginal canal (PI. XXX, fig. 7). 
I am not able at present to state definitely whether the simple 
rudimentary cartilage-ring of our Medusa is the actual limiting 
wall of the ring-canal, or whether a second layer of endoderm 
cells exists deeper than it, and actually bounding the cavity of 
the ring- canal. 
This question I hope to decide by the preparation of sections. 
Comparison of the arrangement of the tissues of the marginal 
ring and tentacle root with those of typical Trachyline Medusae, 
and with structures found in the Leptomedusoe. — If we compare 
with what has just been described the arrangement of the homo- 
logous parts in such a Trachyline Medusae as Cunina, we find 
very considerable differences, which, however, appear to me to be 
differences of degree, our new Medusa exhibiting in a simple form 
* Cells of the same character as those of the endoderm of the marginal 
ring occur in parts of the stomach-wall. 
