144 
G. HERBERT FOWLER. 
well expanded. The whitish-yellow colour of the specimens is 
to be attributed merely to preservation in alcohol. 
The animal is flattened in shape, and almost medusiform ; it 
appears to be free-swimming (? crawling), for the aboral 
ectoderm is entirely similar to that of the oral surface, and 
shows no trace of attachment, past or future, to any foreign 
body. From the biconvex shape, it follows that there is no 
true body wall (mauerblatt, colonna), but the animal is divisible 
into oral and aboral surfaces. Of these, the oral surface is 
beset irregularly with what I shall term pseudo-tentacles, since 
neither in number, position, nor structure can they be regarded 
as homologous with true tentacles (fig. 1). In the expanded 
specimen (fig. 2) fourteen true tentacles surround the stomo- 
dseum, and peripherally to them are seen the earliest buds 
of the pseudo-tentacles ; but in retracted specimens (fig. 3) the 
true tentacles, together with the stomodaeum, are drawn 
downwards and outwards into the coelenteron. From the 
regularity and symmetry with which this is effected in both 
cases, it is evidently the normal mode of retraction, and is not 
due to death struggles or alcoholic contortion. 
The aboral surface is covered by a single layer of columnar 
ectodermal cells, which are shortest at the centre of the disc, 
and lengthen towards the circumference, at which the two 
surfaces meet in an acute angle. The oral surface is histo- 
logically identical with the aboral, but bears the pseudo-tenta- 
cles scattered irregularly over its surface to within a short 
distance of the bases of the true tentacles. The point at 
which the pseudo-tentacles cease marks the boundary of that 
part of the oral disc which is drawn inwards and downwards 
in retraction by the action of the sphincter muscle. 
The pseudo-tentacles, three stages in the growth of which 
are shown in fig. 4, arise each as a simple hollow outgrowth 
from the coelenteron, in which all three body-layers take part 
(fig. 9). The bud extends laterally over the surface into three 
or four “ roots,’’ and is continued upwards as a free, finger-like 
process (fig. 4). The cavity is nearly obliterated by the 
presence of great numbers of zooxantliellae. The ectoderm on 
