198 PROFESSOR E, RAY LANKESTER,. 
In the first place, as seen in Pl. XIII, fig. 1, the pre- 
umbral lid is now perforate, A minute opening has appeared 
at its centre (0). 
The preumbral lid does not, however, as might be ex- 
pected, proceed to develop into the velum.! On the contrary, 
the velum is already present as a distinct, highly muscular 
fold, rising from the inner border of the ring which carries 
the eight tentacles (Pl. XIII, fig. 1a). Its movements 
are very active and constant, consisting in an alternation of 
undulations of contraction and expansion—the latter move- 
ment causing it to completely close in and hide the pre- 
umbral lid, whilst its free margins come into contact centrally, 
as seen in Pl. XIII, fig. 4. and fig. 5. In Pl. XIII, fig. 3, the 
tentacular pole of the young Limnocodium is shown with 
the velum completely expanded and its free margin brought 
into such close contact at the centre of the tentacular area 
that its existence is not at first suspected. Suddenly, 
whilst this condition is under observation, the velum is seen 
to roll back centrifugally and to expose the preumbral lid, 
as shown in Pl. XIII, fig. 1. 
It is necessary to state that there is no confusion here of 
the true oral surface of the manubrium with the preumbral 
lid. By causing the specimen to roll over, or by deeper 
focussing, the manubrium, with its mouth, can be brought 
into view lying at some distance below the perforated pre- 
umbral lid within the sub-umbral cavity—just as it was 
seen in the earlier stage (woodcut, fig. 2B). 
Besides the velum and the perforation in the preeumbral 
lid, the tentaculocysts (marginal bodies) have now com- 
menced to develop. Two are present—one a little more 
advanced in development than the other—and are seen in 
Pl. XIII, figs. 1 and 2, o¢., and in fig. 6. An endodermal 
axis and an ectodermal cortex are present, but the secondary 
investing capsule, or velar canal, is not yet indicated. 
Besides the movements of the velum there are very active 
and sudden movements of the whole umbrella, and also 
slower movements of contraction and expansion, which 
give to the embryo the irregular outline depicted in the 
plate. At the stage now under description, striated mus- 
cular fibres can be detected in the wall of the umbrella 
(Pl. XIII, fig. 2 ee). The radial canals are large and give 
evidence of ciliation of their lining cells. 
1 The distinction between preumbral lid and velum—which develops 
later than the lid itself and from its periphery—is borne out by Metschni- 
koff’s observations on Geryonia, 
