Nervous System of Actinia. 275 



The nervous structures are found to present three characteristic 

 shapes : 



1. A thin layer of muscular fibrils of the small and separate (see 

 2 above) kind, with well-defined dark nuclei in them, was examined. 

 The whole was very transparent and well defined under the y^-inch 

 objective. 



Underlying this layer, and extending on either side beyond it, so as 

 tp appear in one of the meshes between groups of these fibrils, was a 

 ramified pale grey tissue, which was less pervious to light than the mus- 

 cular fibrils (PL III. fig. 25). Swollen in one part and faintly granular 

 throughout, it had its margins very faintly visible. It was flat, and had 

 a definite resemblance to the widest portion of the plexus already men- 

 tioned. 



2. A large section of muscular tissue was examined. It consisted of 

 one layer of large muscular fibres (see 3 above) in close lateral contact. 

 Running obliquely over the layer was an irregular but continuous cord 

 ramifying here and there, the branches breaking up into fibrils. In one 

 part the cord was swollen (PI. III. figs. 26 & 27). A second ramification 

 passed from the opposite end of the field of the microscope and broke up 

 into ultimate fibrils, and in this structure there was a fusiform cell. 



Careful manipulation separated a portion of the upper cord from the 

 muscular fibres, but a part of it evidently dropped down amongst them. 



3. A layer of muscular fibres of the same kind as those just mentioned 

 was examined. It was marked, as usual, with the lateral dark lines and 

 pale elongated nuclei. 



Three long and irregular fibres passed more or less obliquely over the 

 muscular tissue (PI. III. figs. 28-30). They had distinct lateral or mar- 

 ginal lines, were swollen out in several places, and their texture was faintly 

 granular. 



I believe that these fibres were continuous with the fine ramifications 

 of the plexiform arrangement just described. 



4. Above the muscular layers, and under the folds of the endothelium, 

 I found an inosculating series of ramifications arising from a common 

 cord. It was situated upon the layer of muscular tissue, with small and 

 separate long fibrils. 



The structure was faintly granular, pale grey in colour, with faint 

 outlines, and was swollen in some places : it covered a considerable por- 

 tion of the field of the microscope; and portions of it had a close resem- 

 blance to the ramifying structure mentioned as having been observed 

 below the muscular layer (PL III. fig. 31). 



The multiplication, if it be justifiable, of these structural elements in 

 the other segments of the base which were not examined would give a 

 fair notion of the plexiform arrangement of the basal nervous tissue. I 

 presume that it consists of a reticulate structure beneath the endothelium, 

 which sends large branches between the vacuities of the most delicate 



VOL. XXII. T 



