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PROFESSOR E. RAY LANKESTER. 
the marginal bodies, and their capsules (referred to above as 
otocysts^^ and velar canals I am also able to give some 
conclusive observations on the embryonic condition of Limnoco- 
dium. I have not, as I have the intention of doing later, 
studied this Medusa by means of sections, but in the living state 
and with the aid of that invaluable reagent, osmic acid. 
The account of the structure of this Medusa, published by 
Professor Allman, is as follows : 
The umbrella varies much in form with its state of contrac- 
tion, passing from a somewhat conical shape with depressed 
summit through figures more or less hemispherical to that of a 
shallow cup or even of a nearly flat disc. Its outer surface is 
covered by an epithelium composed of flattened hexagonal cells 
with distinct and brilliant nucleus. The manubrium is large ; 
it commences with a quadrate base, and when extended projects 
beyond the margin of the umbrella. The mouth is destitute of 
tentacles, but is divided into four lips, which are everted and 
plicated. The endoderm of the manubrium is thrown into four 
strongly-marked longitudinal plicated ridges. 
The radial canals are four in number; they originate each in 
an angle of the quadrate base of the manubrium, and open dis- 
tally into a wide circular canal. Each radial canal is accom- 
panied by longitudinal muscular fibres, which spread out on 
each side at the junction of the radial with the circular canal. 
The velum is of moderate width, and the extreme margin of 
the umbrella is thickened and festooned, and loaded with 
brownish-yellow pigment cells. 
^^The attachment of the tentacles is peculiar. Instead of 
being free continuations of the umbrella margin, they are given 
off from the outer surface of the umbrella at points a little 
above the margin. Prom each of these points, however, a ridge 
may be traced centrifugally as far as the thickened umbrella 
margin ; this is caused by the proximate portion of the tentacle 
being here adnate to the outer surface of the umbrella. It 
holds exactly the position of the mantelspangen or peronia, 
so well developed in the whole of the Narcomedusse of Haeckel, 
and occurring also in some genera of his Trachomedusse. Its 
structure, however, differs from that of the true peronia, which 
are merely lines of thread-cells marking the path travelled over 
by the tentacle as the insertion of this moved in the course of 
metamorphosis from the margin of the umbrella to a point at 
some distance above it, while in Limnocodium the ridges are 
direct continuations of the tentacles whose structure they retain. 
They become narrower as they approach the margin. 
^^The number of the tentacles is very large in adult speci- 
mens. The four tentacles which correspond to the directions of 
