LIMNOCODIUM (CRASPEDACUSTEs) SOWERBII. 363 
conditions, which are highly specialised and developed in such 
forms as Cunina. 
In the first place the tentacle-roots of Cunina, instead of pass- 
ing centrifugally towards the margin of the disc, have rather a 
centripetal direction. This is simply due to the fact that the 
marginal ring and its tissues are so largely developed as to push 
the tentacle root towards the centre of the disc ; and is not a 
difference of a fundamental character. 
Further, the cartilage of the ring is much more largely de- 
veloped in Cunina than in the new Medusa, and acquires the im- 
portance of a well-marked skeletal ring, which it is only (as it 
were) beginning to assume in Limnocodium. The same spe-- 
cialisation of the nettle-ring and of the peronia is observable in 
Cunina as compared with Limnocodium, but does not invalidate 
the claim of the simpler structures found in the latter to re- 
cognition. 
It appears exceedingly probable that the Trachyline Medusae 
are the modified descendants of such simpler forms as the Lep- 
tomedusae, and if we search amongst the latter for conditions 
approaching those exhibited by the tentacle-roots and marginal 
ring so frequent among the former, the nearest case which we 
can find is that of the genus Laodice, one of the Thaumantidae 
of HaeckeFs system. Here the tentacles do not spring from the 
margin of the disc freely, but from the convex surface of the 
disc, the axis of the tentacle being prolonged as a root to join 
the wall of the marginal canal, which has a cartilaginoid cha- 
racter. Nevertheless, in Laodice the tentacles are hollow, and 
there does not appear to be any structure corresponding to peronia. 
From the consideration of the characters of the tentacles 
and marginal ring alone, I think that we should be led to the 
conclusion that Limnocodium is a representative of the Tracho- 
medusae in an early or archaic phrase of differentiation, already 
distinctively Trachomedusan, but not far advanced on that path. 
We have next to see what indications a closer examination of 
the marginal bodies (otocysts) may give us, and we shall find 
that they confirm very distinctly the conclusion already enunciated. 
Bevelopmerit oj the marginal bodies . — The marginal bodies of 
Limnocodium vary in number, as do the tentacles, according to 
the size of the specimens examined. I have seen as few as fifty 
in specimens measuring one third of an inch across the disc, and 
as many as 120 in larger specimens. Even in large specimens 
the marginal bodies are continually being developed, so that 
there is no difficulty in obtaining that opportunity for tracing 
the development^ which Professor Allman has stated to be 
desirable. 
The marginal bodies consist of a spherical refringent body 
