68 On the Nervous System of Actinia. 



science by Homard and Haime. So far as they bear on the 

 nervous system, the result of his researches may be stated as 

 follows : — " The bourses marginales " (chromatophores) are un- 

 doubtedly organs of sense, and, indeed, compound eyes. They are 

 pyriform diverticula of the body-wall, standing between the tentacles 

 and the outer margin of the peristome ; they are constructed after 

 the fashion of a retina, and the following layers of structure may be 

 distinguished in them : — 1, externally a cuticular layer broken up 

 into " bacilli " by numerous pore-canals ; 2, a layer of strongly 

 refractile spherules, which may be regarded as lenses ; 3, cones — 

 hollow, strongly refractile, transversely striated cylinders or prisms 

 rounded at the ends; these have hitherto been confounded with 

 urticating capsules (nematocysts) : at the exterior end of each cone 

 there is generally one lens, and sometimes two or three may stand 

 in the interspaces; 4, a granular fibrous layer occupying the 

 interspaces between the cones ; 5, a layer which is deeply stained 

 by carmine, and contains numerous extremely fine fibres and spindle- 

 shaped cells, probably nerve fibres and cells ; 6, the muscular layer ; 

 7, the endothelium, which bounds the perigastric cavity. 



Actinia mesembryanthemum was the species examined, and the 

 diagram (PL LXIX., Fig. 15) will explain the relative position of 

 the layers, 



Kotteken could not determine the position of the pigment of the 

 chromatophores from the alcoholized specimens. An examination of 

 the minute anatomy of the tentacles of Actinia cereus, Ellis and 

 Solander, determined that the refractile spherules and large cones 

 were to be found on the tips of these organs. 



Dana,* in his popular work on Corals and Coral Islands, appears 

 to accej)t the statements quoted above. He states that " they some- 

 times possess rudimentary eyes "; and elsewhere, " they have 

 crystalline lenses and a short optic nerve." He then observes : — 

 " Yet Actiniae are not known to have a proper nervous system ; 

 their optic nerves, where they exist, are apparently isolated, and 

 not connected with a nervous ring such as exists in the higher 

 Kadiate animals," 



II, A Description of the Morphology of the Chromatophores. 



During the summer of 1871 the author of this communication 

 was examining into the minute anatomy of Actinia mesembry- 

 anthemum, and had the advantage of possessing living specimens. 

 Havmg satisfied himself of the general correctness of Eotteken's 

 admirable work, he relinquished the inquiry until 1873, when he 

 resumed it. 



Everyone who has endeavoured to anatomize one of the Actinia 



* 'Corals and Coral Islauda,' by James D. Dana, LL.D., 1872, pp. 39, 41. 



