274 Prof. P. M. Duncan on the 



tensifiecl when the three kinds o 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. 



Y. On the Nerves of the base of Actinia mesenibryanthemum. 



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 w r hite 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 neighbours, 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 object 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. 



I have not found any isolated fusiform cells amongst the tissues of the 

 base ; but under the endothelium, and also between the layers of muscular 

 fibres, there are structures which I feel disposed to believe must belong 

 to the nervous system. 1. They are in the position of nerves. 2. Their 

 structure is not that of muscle or fibre. 3. Their structure resembles, 

 in some instances, the plexiform tissues beneath the chromatophores. 



