On the Nervous System of Actinia. 71 



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 ^V-iuch, 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 bacilh, so that their sides may be seen as they rest in all kinds 

 of positions on the deeper cellular layer (PI. LXIX., Fig. 17). 



The bacilh 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 super- 

 ficial tissue, but that between them there are others which are 

 microscopic. These last rarely have bacilli. Moreover, in some 

 parts of the margins (?f the chromatophores, other pigments are 

 visible than the turquoise, and the red often predominates ; the 

 bacilh are not usually present there. 



Beneath the superficial layer of bacilh 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 imbedded therein (PI. LXIX., 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. LXIX., 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-waU. 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 pig- 

 ment commences, these refractile cells assume much larger dimen- 

 sions and more irregular shapes. These refractile cells are, as has 

 already been noticed, imbedded 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 and becomes superficial ; moreover the granules then con- 

 tribute to the colour of the chromatophore, and probably they 

 always do so to a certain degree. 



The refractile ceUs are not invariably confined to the layer above 

 the so-called cones of Piotteken, although they are often thus limited 

 in their position, especially if there are bacilli covering them. In 



