THELACEROS RHIZOPHORM. 555 
of the tentacles was in a very much better condition than that 
of any other part of the specimen. The sections showed that 
the tentacle is covered by a strong radial ectodermic muscle 
layer. This is arranged in irregular folds lying over processes 
of the mesoglea, and occasionally an island of muscular fibres 
is enclosed in the mesoglea. So that, to use the terminology 
of Hertwig, the radial muscles of the tentacles are partly 
ectodermic, partly mesodermal. On the oral disc this muscular 
layer is still better marked, and more of it has become enclosed 
in the mesoglea. Some of the radial fibres of the tentacle in 
the region of a protuberance swing round to form a single 
layer of ectodermic muscular fibres running from the base 
to the extremity of the protuberance. In the section figured 
the pleated muscular layer of the tentacle passes into the single 
layer, as the protuberance and the individual fibres, instead of 
appearing in transverse section, appear in oblique or longi- 
tudinal section. 
There is a well-marked ectodermal nervous layer which is 
continued into the protuberance. The ectodermal epithelium 
is full of thread-cells, and these are hardly more numerous on 
the epithelium of the protuberances. The ciliated cells of the 
epithelium were not evident: there remained of them only 
occasional nuclei; but the outer edge of the whole tentacle 
was thickly covered with the débris of cilia. 
On the oral disc, between the base of the tentacles and the 
oral aperture, are a number of minute protuberances (fig. 5). 
They are hollow, and several of them open into each exocele 
and into each endocele. Some of them were distinctly com- 
pound and resembled the protuberances on the tentacles. It 
seems probable that they are rudimentary tentacles, but 
whether they are incipient or vestigial it is impossible to say. 
Certainly they are much smaller than the marginal tentacles, 
but it would be a matter of great difficulty to frame a definition 
of tentacle which would exclude them. 
The Stomodzeum.—tThis was in a very bad state of pre- 
servation, but it was possible to make out the presence of a 
thick longitudinal, ectodermal, muscular layer. No trace of 
