202 ` MAJOR-GEN. NELSON AND PROF. DUNCAN ON THE 
Corallina tuna, a bright green succulent Coralline, resembling Corallina opuntia 
in its habit, bas its broad joints covered with a down of crowded and articulated fila- 
ments. Тһе filaments are of several kinds. Some are simple long club-shaped cells; 
others are of the same shape at their base, but become compound by giving forth cells | 
from the free end ; and many, after having had these secondary cells developed, have 
others growing from them. All the cells are narrow at their origin, cylindrical, and 
largest at the end. (Plate XXVI. figs. 1-3.) 
The surface of the joints of the frond is covered with a very minute areolation. Each 
minute area has its limiting ridges, and is regularly hexagonal, the ridge between the 
areas having a fine line on it. Each area is the top of a cell; and the ridge represents 
the intercellular space and the cell-walls also: it is caleareous. The calcareous deposit 
does not transgress over the front of the outside cells (those forming the areas) as it does 
in the Corallines already mentioned; so that almost all the area is semitransparent in 
dried specimens. But there is a little calcification of the outer wall nevertheless, except 
near the centre whence the filiform appendage of the cell arises; for the wall has a 
vitreous appearance. (Plate XXVI. figs. 4-6.) 
Тһе green colour of some of the dried joints is partly due to the preservation of an 
external superficial cell-membrane which covered all the calcareous cells, and which, 
as in the other Corallines, is a kind of lateral expansion of the base of the filiform pro- 
cesses, and is seen in Corallina tridens (see page 201). Іп the dried specimens the pro- 
cesses may be just traced, their proximal ends lying in the hollow of the area. Тһе 
hollowing of the area depends upon collapse of the cell during desiccation. 
"This Coralline is only caleareous externally ; for within there are ramose masses of great 
elongated simple cells, forming trunks near the articulation, and very fine branchiets 
near the underside of the outer expansion of the joints of the frond. Hence, on removing 
the film of caleareous cell-matter which forms the outside of the joint, these ramifications 
become visible. (Plate XXVI. figs. 1, 2, 9.) à; 
On decaleifying a dry specimen, the paucity of the carbonate of lime in the frond 
becomes evident; for the ridges between the polygonal external cells are then seen to be 
mainly composed of true cell-wall: hence the mineral is mainly within that structure, 
and not much between the cells. There has been a deposition within the cells; for the 
relics of the cytioplasm are seen in some crowded up in a mass. The cells themselves look 
crumpled more or less, so as to give the appearance of raphides within them. 
On the edge of a frond, in a decalcified specimen, the bases of the filiform processes 
could be seen, and a perfect process also. The cell-wall of the processes is well 
developed, and has glandular markings and slight prominences on it. (Plate XXVI. 
fig. 8.) 
The ramose cellular structure within the joints is very remarkable ; some of it consists 
of huge long cells constricted here and there, and of smaller cells with neck-shaped 
processes terminating in round bottle-shaped ends, which underlie the external layer of 
polygonal cells. (Plate XXVI. fig. 9.) ; | 
These species may be taken as the types which explain the external construction of 
the Corallines, and, to a certain extent, their internal configuration. They are all rapid 
