272 Prof. P. M. Duncan on the 



nuclei. It is intimately associated with the surrounding cell-structures, 

 but they may be separated by accident or compression. Here and 

 there the structure enlarges and a ganglion-like cell is seen (Plate II. 

 fig. 22). 



I have traced this structure almost across the whole field of the micro- 

 scope in some sections. 



It appears that this portion of the nervous system of Actinia (namely, 

 the fusiform and spherical cells with fibrils and the plexiform structure) 

 is distinct histologically from the fibrillar and cellular structures amidst 

 the Haimean and Eotteken bodies. These structures are connective and 

 developing ; but it must be remembered that it is possible for both series 

 to come in contact in the midst of the layers of granular cells which 

 underlie the Eotteken bodies. 



IV. Examination into the Physiological Relation between the Chroma- 

 tophores, the Nerves, and Light, 



The question arises, Are these nerves of special sense ? MM. Schneider 

 and Eotteken answer that the small portion of the nervous arrangement 

 they described, i. e. the fusiform bodies and their fibrils, are optic nerves. 

 They are satisfied with the physical arrangement of the bacilli, Haimean 

 and E/otteken bodies, and the nature of the colouring-matter imitating 

 that of an organ of vision. 



The discovery of the anastomosing fibrils and the plexiform arrangement 

 favour this theory ; but there are reasons to be considered which throw 

 much doubt on the views of the distinguished investigators. All Actinia 

 have not chromatophores, and closely allied genera may or may not 

 have them. Thus, amongst the Actinia with smooth tentacles, there is 

 a group with non-retractile and another with retractile tentacles : 

 amongst those with non-retractile arms are the genera Anemonia and 

 Eumenides without chromatophores, and Oomactis and Ceratactis with 

 them ; amongst the Actinia with retractile tentacles are Actinia with, 

 and Paractis without, chromatophores. 



Amongst the tubercular division, the genus Phymactis has chromato- 

 phores, but its close ally Cereus has them not. 



"Whatever may be the value of this classification of the Actinia, it is 

 quite evident that to group together those with and without chromato- 

 phores in separate divisions would be the reverse of producing a natural 

 arrangement. It is therefore difficult to believe that these ornaments, 

 with something resembling an optical arrangement, can be the seat of 

 special sensation. 



MM. Eotteken and Schneider have observed the large refractile 

 Haimean bodies in the tentacles, and, as will be noticed further on, 

 I have found them of enormous size in the peristome. 



They are surrounded in those places, but not covered, with pigment- 

 cells and granules, and are situated jnst beneath the nematocyst layer in 



