TRANSACTIONS OF THE SECTIONS. 75 
ture from the rest of the stomach, To this portion of the stomach Dr. Allman gave 
the name of cardiac cavity. 
Ov a line with the continuation of the cardiac into the great cavity arises the intes- 
tine from the upper part of the latter, and from the angle between the cardiac cavity 
and intestine the parietes of the stomach are prolonged into the great cavity obliquely 
across the pyloric orifice. By this arrangement the ventricular opening of the intes- 
tine is much contracted, and the prolongation of the walls appearing to act as a pyloric 
valve, will, under the influence of some vital stimulus, cause the alimentary matter to 
be retained in the stomach till fitted for passing into the intestine ; and when the 
contents of the stomach have undergone the necessary change and passed the pylorus, 
the same contrivance will probably prevent any regurgitation. 
Two distinct groups of muscles may be detected in Plumatella repens; one which 
cotresponds with the anterior set of retractor muscles described by Dr. Farre in the 
Ascidian Zoophytes of the sea; and another analogous to the opercular muscles of 
this anatomist. These last muscles are peculiar and may be divided into two sets. 
The first consists of a set of irregularly disposed fibres which arise from the inner side 
of the internal tunic, commencing all round at the part where this tunic becomes 
united, near the orifice of the cell, with the external, and thence extending for some 
distance down the walls of the cell, From these points of origin fibres pass nearly 
horizontally inwards, and are inserted into the permanently invaginated portion of 
the internal tunic. The second set consists of a series of distinct muscular fasciculi, 
longer and stronger than the former; below which they arise’also from the internal 
tunic, at regular intervals around the circumference of the cell, and in a plane per- 
pendicular to its axis, and thence radiating inwards, are inserted into the opposed 
surface of the reflected tunic. 
Of the structure of the ova of Plumatella, Dr. Allman gave the following account :— 
The ova will be found to consist, as in those of Alcyonella, of a central disc, in- 
closing the embryonic matter, and of a rim which surrounds the disc, and from which 
it differs considerably in structure. The disc is formed of two membranes, each of 
which is composed of a single layer of minute vessels. These membranes differ from 
each other in the size of the component vesicles, and as there is but a single layer of 
vesicles in each, one face of the disc must consequently be thinner than the other. 
Both faces are concave on one side and convex on the other, and the concave sides 
being opposed and the edges united, a closed space is thus formed, which is filled by 
an immense number of minute whitish globules floating in a gelatinous fluid, and which 
are afterwards to be developed into the perfect zoophyte. The walls of the disc are 
of a horny elastic texture, of a deep brown colour, and when emptied of their con- 
tents, are found to possess some degree of transparency. Immediately surrounding 
the disc is the rim, equally wide all round, composed of two laminz, united by their 
convex edges, and thence diverging to embrace the disc, which they overlap for a 
short distance. They inclose a cellular structure, the cells of which are irregular 
in form and arrangement. The rim is nearly colourless and transparent, and of a 
harder and more brittle texture than the disc. 
Besides the bodies just described, others may frequently be observed closely re- 
sembling them in form, but never attached to the sides of the tube. These last bodies 
also differ from the mature ova, in their want of colour and in the softness of their 
texture, being easily broken down under the needle. That they are ova in an imma- 
ture state there can be no doubt, their want of colour and softness of texture, and the 
fact of their never being found attached to the sides of the tube, being the only cir- 
cumstances in which they appear to differ from the bodies which have been already 
described. These characters they would appear to retain till they have acquired their 
full size. Whether the attachment of the ovum to the sides of the tube be an invari- 
able epoch in its history, it is not easy to determine ; many which differ in nothing 
from the attached ova, are found to float freely in the fluid which immediately sur- 
rounds the body of the polype ; and Dr. Allman has been unable to determine whether 
at any subsequent period they became fixed. The adhesion of the ovum to the sides of 
the tube is effected by an extra vascular unorganized substance resembling a varnish, 
transparent and brittle, and which is interposed between the thin face of the ovum 
and the parietes of the tube. Whether this uniting substance is poured out by the 
ovum itself, or secreted by the sides of the cell, or by some other part of the animal, 
