196 PROFESSOR E. RAY LANKESTER. 
in the development of Limnocodium which I am about to 
describe, corresponding as it does in a measure to the 
missing stage in the Geryonia series, must not be judged 
by reference to a scheme of Trachomedusan development 
supposed to be already ascertained—for such a scheme does 
not really exist upon any proper basis. Rather, it appears 
the Limnocodium embryo may throw light on the im- 
perfectly-known Geryonia development, and give credibility 
to the important observations of Haeckel, which have been 
too lightly dismissed by Fol and Metschnikoff. 
I was only able to observe Limnocodium embryos of three 
different ages, and those apparently very close to one another. 
I have already figured two of those embryos (this Journal, 
1880), and reproduce the woodcuts on the present occasion. 
The third embryo is figured in Plate XIII. 
Fie. 1.—Embryo of Limnocodium Sowerbii, 25th of an inch in diameter. 
A. Surface view of oral pole. 2B. Optical section of same specimen 
in a plane at right angles to the oro-apical axis. P¢. Per-radial ten- 
tacle. JZ. Preumbral lid. RC. Radial canal. S¢. Stomach. Ze. 
Ketoderm. G. Jelly of the disc. 
The youngest stage observed by me is shown in the woodcut 
fig. 1. At the tentacular pole is seen (a, L) a circular plate 
of small cells absolutely imperforate and closing in the “ sub- 
umbral cavity,” or “‘sub-umbrellar cavity ”—as is shown by 
the optical section of the next stage, which is but a little more 
advanced (fig. 28). This plate I call “ the preeumbral lid.” 
It is surrounded by the rudiments of eight tentacles—four 
of which (the per-radial tentacles) are somewhat larger 
than the other four. In neither of these specimens are 
