HISTOLOGY OF CERTAIN SPECIES OF CORALLINACE. 201 
lina vermicula is covered with very regular and small polygonal spaces. Each space is 
separated by a narrow raised border from its neighbours; and the surface within the 
border is more or less depressed and has a central opening. Тһе border and depressed 
surfaces aré of carbonate of lime; and the first represents the junction of the outer cells of 
_ the cellular tissue of the frond at the outside, and each of the depressed surfaces consists 
of the carbonate of lime in the cell-wall of a collapsed superficial cell. Where there was 
no carbonate of lime in the central spot there was perfect cell-wall; and this disappears 
during desiccation. But the filament, long and slightly oblique, arose from this central 
spot, and therefore was much narrower than the whole cell from which it sprang, and was 
continuous. (Plate XXVI. fig. 17.) 
In some parts of a specimen the minute dot-like space uncovered by carbonate of lime 
is not central, but close to the edge of the polygonal area; so that the filament did not 
arise invariably centrally, but often at one end; and it appears to be oblique. The 
polygonal spaces moreover differ in size, and some are more elongate than others; so 
that the distribution of the filamentous growth is not perfectly uniform. ‘Towards the 
end of the frond the calcareous element does not predominate as it does elsewhere; and 
the green tint of the cells which are not affected by the mineral is very distinct. 
On decalcifying specimens it is observed that the calcareous matter is granular, and 
that it is between the cells, in the cell-wall, and also within the cell to a certain extent- 
The inside of the frond is eminently cellular, and consists of series of long tubes and of 
compressed globes of carbonate of lime with faint central hollows placed longitudinally 
andradially. Beyond them is the outer coating of polygonal cells, which are intruded 
on by carbonate of lime—on their sides perfectly, but on their distal and proximal ends 
imperfectly, so аз to leave some cell-wall in those situations. (Plate XX VI. figs. 15-17.) 
Corallina tridens, when dry, has its surface covered with minute pits separated by 
ridges so as to assume a polygonal shape; and at the bottom of them, even in very old 
specimens, а dry slender filament may be seen projecting from a central part where there 
is no carbonate of lime. The spaces between the projecting ridges (or the pits) are pro- 
duced by the collapse of the cell-contents during drying, and form part of the free ends 
of the external layer of cells, Each cell corresponding to a pit was infiltrated with car- 
bonate of lime (except а minute central spot) during life. A very delicate cell-membrane 
covered the pits and ridges, and was continuous with the filaments also; this will be 
noticed further on as the analogue of the superficial epidermic layer of the British 
Corallines. Relics of this membrane are seen in dried specimens. It contained green 
colouring matter ; and where it has been abraded the carbonate of lime of the underlying 
cells is glistening and white. 
The filiform processes are very numerous in the living specimens, and forma complete 
down on the surface. They arise by a kind of neck-like constriction from the most 
external cells (those of the pits) of the frond, and are wider at their distal end, being 
otherwise cylindrical. They give origin at their remote end to two neck-like processes, 
which subdivide rapidly, and end in long club-shaped cells ; so that the original filament 
produces four others. "They are all tense with fluid and with marked distinct and nume- 
Tous globular granules, more or less tinted green. (Plate XXVI. figs. 10-13.) 
