124 PROFESSOR E. RAY LANKESTER, 
acid are stained with picro-carmine and examined under the 
highest powers of the microscope by means of teazing and sec- 
tions. ‘The meshwork of ameeboid cells in which intra-cellular 
digestion takes place is seen to be confined to the four proximal 
angles of the gastric tube. 
Endoderm of radial canals.—The endoderm suddenly changes 
its character at the commencement of the radial canals (see 
Plate IX, fig. 8 w), and in these continuations of the gastric 
chamber, instead of a network, we find closely-set nuclei, the cell 
areas not distinctly marked off from one another and the proto- 
plasm free from granulations. ‘These cells as seen in the living 
condition are ciliated. 
The nuclei are precisely similar in form and size to those of 
the gastric tube, and take up the carmine staining in a way 
which is characteristic of the endoderm nuclei in general (see 
Plate). 
Doiodern of the ring-canal.—I have in my former paper on 
Limnocodium (this Journal, July, 1880) described and figured 
(Plate XXX, fig. 6) the modification of the endoderm cells on 
the abumbral wall of the marginal ring-canal. The cells of the 
adumbral wall are like those of the ring-canals. The cells of 
the abumbral wall are modified by the deposit of block-like 
masses of a dense substance within them, which usually obscure 
the nuclei. These cells also have a remarkably angular and 
irregular form. They form the representative in Limnocodium 
of the cartilaginous marginal ring of Trachymeduse, and are 
drawn out into lobes which are continuous with the roots of the 
tentacles. The endoderm of the gonads (genital pouches) has 
a similar structure to that of the abumbral wall of the ring- 
canal. 
Endoderm of the gonads.—A portion of this part of the endo- 
derm is drawn in Plate IX, fig. 9. It quite closely resembles 
that of the abumbral wall of the ring-canal. The block-like 
deposits within the cells and the dark colour which the whole 
layer had assumed under the influence of osmic acid were suffi- 
cient to obscure the nuclei, which accordingly are not seen in 
the drawing. 
Endoderm of the middle third of the gastric tube.—This is 
represented in Plate X, figs. 1 and 2. Over a comparatively 
small area the cells present a uniform hexagonal pavement when 
viewed from their free surface (Plate X, fig. 2). The nuclei 
have the same size and character as in the other endoderm cells, 
but the cell substance is small in quantity and of a homogeneous 
appearance. Here and there in this and in other parts of the 
gastric tube, nematocysts are scattered in considerable numbers, 
They sometimes are embedded in the endoderm (g g) so as to 
