298 | | Royal Society :-— 
stinguished—one ovate, with the invaginated tube occupying the 
axis; the other fusiform, with the invaginated tube oblique. 
The deeper zone of the ectoderm consists of a very remarkable 
tissue, composed of peculiar membraneless cells, each of which is 
prolonged into a tail-like process, so that the cells assume a clavi- 
form shape. In most situations, where this tissue is developed, 
the processes from several such cells unite with one another, so as 
to form branching, somewhat botrylliform groups, whose common 
stalk can be followed into the fibrillated layer. The author is 
thus enabled so far to confirm the observations of Kleimenberg on 
cells of apparently the same significance in Hydra, In Myrvothela, 
however, these cells do not, as in Hydra, reach the surface. With 
the exception, apparently, of their condition in the transitory arms 
of the Actinula or locomotive embryo, they form everywhere a deep 
zone interposed between the muscular layer and the superficial 
layer of the ectoderm. This zone is designated by the author as 
the zone of claviform tissue. Though it is in intimate association 
with the fibrillated layer, the author did not succeed in tracing a 
direct continuity of the individual fibrille with the processes of 
the cells (as described by Kleinenberg in Hydra). 
The author adopts, as a probable hypothesis, the views of 
Kleinenberg respecting the caudate cells of Hydra, which he 
regards as representing a nervous system. While the deep layer of 
ectodermal cells in Myriothela would thus constitute a nervous 
layer, the superficial layer would represent an epidermis; and 
since recent researches justify us in regarding the ectoderm and 
endoderm of the Celenterata as respectively representing in a 
permanent condition the upper and lower leaf of the blastoderm 
in the development of the higher animals, we should thus find 
Myriothela offermg no exception to the general law, which derives 
both epidermic and nervous tissues from the upper leaf of the 
blastoderm. 
The structure of the tentacles is in the highest degree interesting. 
In their narrow stalk-like portion, the condition of the endoderm 
departs widely from that of this tissue in the tentacles of other 
marine hydroids ; for it presents no trace of the septate disposition 
so well marked in these. It is, on the contrary, composed of a 
layer of small cells loaded with opaque granules and surrounding 
a continuous wide axile cavity. 
__ dt is, however, in the terminal capitulum of tho tentacle that 
the structure of these organs departs most widely from any thing 
that has as yet been recognized in the tentacles of other hydroids. 
Here a very peculiar tissue is developed between the muscular 
layer and the proper ectoderm, where it takes the place of the 
zone of claviform tissue. It forms a thick hemispherical cap over 
the muscular lamella and endoderm of the tentacle, and is composed 
of closely applied exceedingly slender prisms, with their inner ends 
resting on the muscular lamella, to which the prisms are perpen- 
dicular, the whole structure forcibly suggesting the rod-like tissue 
associated with special sense-apparatus in higher animals. It. 
