YOUNG STAGES OF LIMNOCODIUM AND GERYONIA. 197 
there any indications of the marginal bodies (tentaculocysts) 
nor of avelum. Within the sub-umbral cavity—which is 
capacious—we find the manubrium provided at its extremity 
Fig. 2.—Embryo of Limnocodium Sowerbii, a very little more advanced, 
A, Surface lateral view. &. Optical section of the same specimen in 
a plane including the oro-apical axis. P¢. Per-radial tentacles. Z, 
Preumbral lid. UC. Sub-umbrella cavity. Mz. Manubrium. RC. 
Radial canal. #e. Ectoderm. G. Jelly-like substance of the disc: 
with a mouth, which thus opens into the closed space of the 
sub-umbrella. The cavity of the manubrium (stomach) can 
be readily traced by optical sections and followed to the four 
radial canals which run along the adumbral wall of the 
umbrella—that which it is proper to call “‘ umbrella” being 
the lateral wall of the sub-umbral cavity. 
There is no indication at this stage of the sub-umbral 
cavity having been formed by an invagination, the orifice. of 
which has closed up; and although it, or its representative, 
may thus form by invagination and become closed up in the 
gonophores and modified Medusz of some Hydromeduse, | 
see no reason to doubt that it has formed in Limnocodium, 
as it does in Hydractinia, namely, by a splitting in the thick- 
ened ectoderm (Ed. Van Beneden). The comparison of 
the development of the directly developing Meduse with 
that of the variously modified Medusz of hydroid colonies 
will, I cannot doubt, furnish an explanation of the pheno- 
mena which are observed in both series. 
If we now pass to the later stage which is represented in 
Pl. XIII, we find that although the young animal is but very 
little larger in size, and has still. only eight tentacles, yet 
certain changes of importance have occurred. 
