204. MAJOR-GEN. NELSON AND PROF. DUNCAN ОМ THE 
acid, the glycerine being used after washing as the medium. A polarizing apparatus is 
necessary. (Plate XXVII. figs. 1—9.) 
Let the acid solution act slowly and for some time if the internal structures are to be 
examined; but if the delicate film of tissue which covers the frond is to be shown, а 
rapid development of gas-bubbles is rather an advantage; for it is tolerably certain to 
happen that some bubbles escape and blow out this tissue so that it can be examined. 
Young specimens should be obtained; for experience and observation prove that 
minute Gasteropoda browse over the Corallines, and destroy much of the superficial cell- 
growth before it is much infiltrated with the carbonate of lime. 
The surface of the frond of the Coralline, and also of the little basal expansion from 
which it rises, is covered with an exceedingly delicate cell-membrane (Plate XXVII. 
fig. 3). This is usually demonstrable after the action of dilute hydrochloric acid upon 
the frond; for the bubbles of gas escaping, separate it from the cellular mass of the 
plant which it covers. It resembles a beautiful pavement epithelium; its broad and 
shallow polygonal cells usually, but not always, touch by thin walls, and the whole is 
colourless. When seen in section in semi-decalcified specimens, the cells are observed 
to overlap those below, and, whilst covering the intercellular space, to be in organic 
connexion with the distal ends of the cells of the mass. No calcareous element enters 
into the composition of this superficial structure. Here and there an additional cell is 
seen on the free surface and covering one of those polygonal in shape; and near the 
joints, in some rare instances, the polygonal cell gives rise to a thread-like cell of about 
the length of 1 of the breadth of the joint (Plate XXVII. fig. 2). In some forms from 
Port Natal, which greatly resemble Corallina monile, Elis, the surface-membrane 
extends from joint to joint, covering the articulation and its elongate cells. "This ex- 
ternal tissue gives no evidence of containing carbonate of lime; but the cells have 
minute refractive dots in them. Finally, it is thickest at the free end of the joints of 
the frond, and there often exhibits rather tall cells, united together by a structureless 
protoplasm. | 
Beneath this superficial tissue are the terminal cells of the mass of the frond ; and they 
are continuous with long rows more deeply seated. Each of these terminal cells is ofa 
light green, and it succeeds a series which, gradually becoming darker with depth, assume 
a port-wine colour. "The cell-wall is stout, a portion of it being perfectly transparent 
even in old specimens. "This transparent portion forms either part or the whole of the 
distal end of the cell ; and nearly all the rest is opaque. On decalcifying, it is found that 
the cell-wall, especially at the sides of the cell, and not at the ends, is incomplete here 
and there, as was noticed in the Velobesie by Rosanoff. There appears to be a pos- 
sibility of connexion between the sides of contiguous cells. That this is a normal con- 
dition is probable from the small number of the pores; for did the incomplete condition 
depend on the removal of raphidic masses of carbonate of lime, there would be more of 
the pore-like markings, and their position would be irregular *. 
* A careful examination proves that some markings on the longitudinal sides of the cell-walls of Corallines, 
already noticed, from Bermuda, are spots of excessively thin cell-wall. They are circular in outline, very few in 
nabor, and transmit light more readily than the rest of the tissue ; they are, then, not absolute pores, but are p 
like, and are the seat of a very thin and diaphanous membrane. 
