360 
PROFESSOR E. RAY LANKESTER. 
a considerable flexure of the cartilaginoid axis at the point 
where its free and inserted portions unite^ becomes necessary. 
This is shown in the diagram woodcut, figure 3, where tenta- 
cles of three horizons are shown bent mouthwards by the 
pressure of the cover-glass. The recurved axis-roots {tr) of the 
two larger tentacles are seen by transparency through the 
substance of the disc passing towards the margin, where they 
become continuous with the centripetal upgrowths of the tissue 
of the marginal ring {MR), 
The smaller tentacles spring almost directly from the mar- 
ginal ring, and have therefore no length of axial root. This 
enables the small (which are the younger) tentacles to assume 
more readily the dependent mouthwardly directed carriage ; 
they are not mechanically directed into the vertical upright 
position by the elasticity of a vertical axial root. 
Tissue of the nettle-ring and peroniay and of the cartilage- 
ring and tentacle-roots. — In order to obtain a satisfactory view 
of these structures witli the microscope, it is necessary to get 
the margin of the disc in such a position when prepared for 
examination that the optical plane is tangential to the concave 
surface of the disc. Under these circumstances such a view as 
that drawn in PI. XXX, fig. 4, may be obtained. This re- 
presents the part as seen from the supra umbrellar surface. In 
PI. XXX, fig. 5, I have represented the same parts seen with 
a deeper focussing, the optical plane now passing near to the 
subumbrella surface. 
The surface of the marginal ring and peronia is seen to be 
formed by a continuation of the large-celled ectodermal tissue 
of the supraumbrellar surface, but the cells which constitute 
it differ from those of the general surface in being loaded with 
thread-cells. The continuous marginal ring of nettle-cells thus 
constituted is entitled to the name of nettle-ring,^^ though it is 
only one cell deep and does not exhibit the marked specialisation 
and thickening observed in some Trachomedusae and Narcome- 
dusae. It may be regarded as a rudimentary condition of the 
structure which is more highly developed in other Trachyline 
Medusae. 
The same simple but, as it appears to me, distinct character, 
is exhibited by the prolongation of this nettle-ring centripetally 
towards the point where the tentacle becomes free of the disc. 
The masses of thread-cells forming these little peronia"’^ are not 
merely due to the continuation of the character of the ectoderm 
cells which clothe the free portion of the tentacle. Por the first 
])ortion of the free part of the tentacle is almost devoid of thread 
cells. 
It is not a little difficult, on a first examination of this region. 
