On the Nervous System of Actinia. 75 



grey film with definite branches, and the whole has few granules 

 here and there and a very few 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-Hke cell is seen (PL LXIX., Fig. 22). 



I have traced this structure almost across the whole field of 

 the microscope in some sections. 



It appears that this portion of the nervous system of Actinia 

 (namely, the fusiform and spherical cells with fibrils and the plexi- 

 form 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 remem- 

 bered 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 

 Chromatophores, 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 Eotteken 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 con- 

 sidered 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 Comactis 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 

 chromatophores, 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 

 chromatophores in separate divisions would be the reverse of pro- 

 ducing a natural arrangement. It is therefore difiicult to believe 

 that these ornaments, with something resembling an optical arrange- 

 ment, can be the seat of special sensation. 



MM. Eotteken and Schneider have observed the large refractile 



VOL. XII. G 



