INTRODUCTION. 25 
three dimensions, those of medium size being the commonest; also, of very simple cells, 
either irregular in shape, or oblong or pyriform; and of small rounded and transparent 
globules, which form the innermost layer. 
“There are no cells in the external tegument which produce the colour of the 
polype. The white warts which project on the surface are made up of a mass of large, 
transparent and elongated vesicles. 
“The nematocysts, which form the most important part of the integument of the 
tentacules, are slender and cylindrical, one of their extremities being smaller than the other.’ 
They contain a thread regularly rolled up as a spiral, and which near the large end termi- 
nates in a straight and central portion. The thread when unrolled is about two tenths of 
a millimetre in length. The nematocysts are perpendicular to the tentacular surface, 
and their large end is the most external; the internal thread makes its exit by this 
extremity. 
“The terminal bulb’ of the tentacules is almost entirely composed of these filiferous 
capsules ; there are two other kinds in it unlike those just described, some larger and 
stouter, and others much narrower and more slender. ‘The first are elliptical, slightly 
attenuated at one of their ends, and they contain a thread rolled into a slack spiral. This 
thread shoots out from the small end of the cell. ‘The remaining nematocysts do not 
appear to have a proper cell-wall; they are cylindrical, slightly smaller at both ends, and 
very slender; they are formed by a filament very closely rolled into a dense spiral, which 
unrolls itself like the wires used in some elastic clothing. 
“The structure of the skin is the same over the whole surface of the polype. The 
nematocysts of the second size are the most common. A certain number of those of the 
largest size are found in the stomacho-buccal rim. he cilia are very distinct at this spot, 
and around the disc also, although they are very delicate; they are rare and feeble on 
other parts of the polype; they are very indistinct on the tentacules, and are wanting on 
the bulb. 
“2. The middle or muscular layer is formed by transverse and vertical fibres which 
are excessively slender and sparely distributed. Very thin oblique muscular fibres may 
be seen at the bases of the tentacules. 
“3. The internal membrane is formed by a layer of transparent cells tolerably adherent 
to each other, and by a layer of colour-bearing globules which are spherical or slightly 
oval in shape. 
“Tt is these cells which give the colour to the polype; they are filled with irregular- 
shaped grains, of a bright brown colour; they themselves are secreted in certain trans- 
parent vesicles, and present the greatest resemblance both in shape, colour, and structure 
to the globules which float free in the tentacular cavities of young sea-anemones. It is 
probable they have a corresponding function in their early age. Near the top of the 
1 Plate LI, fig. 1. 2 Plate II, fig. 3. 3 Plate II, fig. 6. 
4 
