126 PROFESSOR B, RAY LANKESTER, 
surface of the endoderm by circular apertures (Plate IX, 
fig. 4) corresponding each to a ripe secretion cell. 
The nuclei of the ripe secretion cells are less defined than those 
of the younger cells, and IL am inclined to think that they undergo 
atrophy, and that the whole secretion cell, when its chemical 
metamorphosis is complete, is passed into the gastric cavity. I 
am also led to believe that this takes place periodically by the 
following observation. 
Whilst in some specimens of Limnocodium studied by me the 
oral gastric endoderm presented uniformly the appearance repre- 
sented in Plate IX, fig. 3, yet in another batch of specimens it 
had uniformly a very different appearance, which is drawn in 
Plate IX, fig. 6. In this case all the sites which in the former 
example were occupied by large-sized secretion cells are empty 
(7). The framework (d) remains, and projecting into the empty 
spaces, as though destined in their turn to occupy them, are small 
secretion cells (0). 
I can only interpret these appearances on the supposition that 
the large cells are shed when ripe, and that the next generation 
grow out into the spaces left, whilst a third generation is de- 
veloped from the scattered cells, with at present little protoplasm, 
and merely indicated by the nuclei (a). And, further, it seems 
that the ripening and shedding of the secretion cells must take 
place in the whole of the oral gastric endoderm simultaneously. 
It is possible that a periodicity of this kind may be inherent 
in the growth and development of these cells. It is also exceed- 
ingly likely that the simultaneous clearing off of all the ripe 
secretion cells is due to some special act of the Medusa. It is 
likely that the act of feeding, of seizing prey, such as Entomo- 
straca (on which the Medusa was frequently seen to feed), would 
be the determining cause of the clearing out of the secretion 
cells. 
This hypothesis is borne out by some further facts, to be related 
below. 
Whether it be accepted or not, it is clear that we have a copious 
secretion produced by the oral-gastric endoderm, and it is in the 
highest degree probable that this secretion has the action of a 
ferment or of a solvent upon the larger food masses taken into 
its gastric tube by Limnocodium. 
A modification of the endoderm, not unlike this of the oral- 
gastric region of Limnocodium, is described by Claus in Cha- 
rybdaa marsupialis, that most interesting of all Meduse. In 
his admirable memoir on Charybdeea (‘ Arbeiten des Zoolog. 
Instituts zu Wien,’ 1878) Claus gives, in his plate iv, figs. 36 
and 37, drawings of endoderm from the oral portion of the 
gastric tube, closely resembling that figured by me im 
