0)1 the Nervous System of Actinia. 77 



but to cause the light to stimulate a rudimentary nervous system to 

 act in a reflex manner on the muscular system, which is highly 

 developed. The Actinia, therefore, may feel the light by means of 

 the transparent histological elements when they are separate and 

 constitute integral portions of the ectoderm ; but this sensation 

 will be intensified when the three kinds of cells are placed in such 

 order as has been observed in the chromatophores. 



The evolution of an eye, which can distinguish outlines, shadows, 

 and colours, probably took the path which is thus faintly indicated 

 in the Actinia, which doubtless has an appreciation of the difference 

 between light and darkness. 



V. On the Nerves of the base of Actinia mesembryanthemum. 



A large specimen of a pale green variety from the Mediterranean 

 ■was examined. 



The base being free and expanded, a rapid incision cut out a 

 triangular piece comprehending the ectothelium, the muscular layers, 

 and the mucous endothelium. The apex of the triangle reached the 

 centre of the base of the Actinia, and the base of the triangle, which 

 was covered, corresponded with the basal margin of the animal. 



Sections were made parallel with the original aspect of the base 

 of the Actinia, and then some others at right angles. 



The histological elements were studied separately and compared, 

 so that the following tissues could be distinguished readily : — 



1. A fibrous-looking tissue like ordinary white fibrous tissue 

 with dark nuclei, to which the muscular fibres are attached and 

 from which they originate. 



2. A dense layer of muscular fibres, or rather fibrils, which 

 originates at right angles to the fibre of the fibrous tissue. Each 

 fibril is refractile and nucleated. Each is separate from its neigh- 

 bours, and lies in the midst of granules and small cells which 

 contain granules, all being highly refractile. In some places the 

 fibrils are gathered together in masses, so as to leave areolae between 

 them. 



3. Large muscular fibres in contact laterally, so as to form a 

 thin layer. Each fibre is long, broad, has several pale elongate 

 nuclei and a distinct lateral dark line. There are no striae. 



4. The elements of the endothelium and ectothelium, which, as 

 they do not bear on the immediate subject, will be described in a 

 future memoir. 



The ol>ject of the investigation being to discover some trace of 

 a nervous system, which was presupposed to resemble somewhat 

 the traces observed below the chromatophores, the necessity of 

 becoming familiar with the fibrous and muscular tissues, so as to 

 decide what was not muscle and fibre, is apparent. 



G 2 



