268 Prof. P. M. Duncan on the 



nematocysts of the tentacles without the internal thread (PI. II. fig. 2). 

 These are placed side by side, and the external rounded end of each is 

 separated by a small space from the terminations of its neighbours. 

 These ends are free and are in contact with the water in which the 

 Actinia lives. The rods are cylinders, and are separated from each 

 other by a very delicate film of protoplasm, in which are numerous 

 dark opaque granules and a few flat simple colourless rounded cells 

 (PI. II. fig. 3). The inner ends are sffaped like the external, and 

 are embedded in the next layer of tissue. Each of these bodies is 

 a simple cell filled with a transparent fluid. When a thin film 

 of the surface of a chromatophore is removed and examined under a 

 ytg-inch, the bacilli may be observed to crowd together over a layer of 

 large refractile cells. The thin glass cover is generally sufficient to crush 

 down the bacilli, so that their sides may be seen as they rest in all kinds 

 of positions on the deeper cellular layer (PI. II. fig. 17). 



The bacilli are not found universally over the chromatophores, nor do 

 they invariably cover the layer of large refractile globular cells. 



It will be noticed, on examining excised portions which include two or 

 three chromatophores and their intermediate tissue, that not only are 

 they marked on their surface by foldings of their superficial tissue, but 

 that between them there are others which are microscopic. These last 

 rarely have bacilli. Moreover, in some parts of the margins of the chro- 

 matophores, other pigments are visible than the turquoise, and the red 

 often predominates ; the bacilli are not usually present there. 



Beneath the superficial layer of bacilli and their separating protoplasm, 

 which is faintly granular, there is some granular tissue with a few 

 small spherical cells containing granules, and the inner ends of the bacilli 

 are embedded therein (PI. II. fig. 3). 



This granular tissue is very thin, but it covers and dips down between 

 the large refractile cells, which form the next layer (PI. II. figs. 4, 13, 

 15, 16, 17). 



These cells are more or less spherical ; the cell-wall is very thin, and 

 the contents are transparent, colourless, and refractile. Some have a 

 pale grey tint, and one or more extremely faint nuclei are attached to the 

 inner surface of the cell-wall. The ovoid shape is occasionally seen. 



These large cells, which transmit light so readily, are universally found 

 on the chromatophores; and when there are bacilli upon them, the spherical 

 shape is common. 



At the margins of the chromatophores, and where the red pigment 

 commences, these refractile cells assume much larger dimensions and more 

 irregular shapes. These refractile cells are, as has already been noticed, 

 embedded in a tissue of granular and slightly cellular protoplasm, and 

 this occasionally is differentiated into some peculiar structures. 



Where there are no bacilli this granular tissue is increased in thickness 



