of the Actinice and Corals. 



439 



law of the origin and increase of the calcareous lamellas must 

 be adopted. Nevertheless it is important that we see, in the 

 Rugosttj that the numerous calcareous lamella exhibit not only 

 bilateral symmetry, but, as in the Octactinise, a distinction of 

 back and belly. We cannot, however, at present define the 

 dorsal and ventral surfaces. 



The investigations of M. Eotteken have been extended to 

 the whole histology and anatomy of the Hexactinise, and have 

 brought to light numerous new facts. 



In the first place, he has found that the whole of them 

 possess an annular canal which closely surrounds the mouth. 

 This must not be confounded with the apertures of the septa, 

 which occur frequently but not regularly, and which were 

 discovered by Hollard. By this annular canal the Actiniae 

 approach the Medusae more closely than has hitherto been 

 supposed. 



He has also discovered that the so-called " bourses margi- 

 nales " (Hollard) are undoubtedly organs of sense. Fig. 4. 

 and, indeed, compound eyes. These organs 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 allow the following layers to be distin- 

 guished in them (fig, 4) : — 1, externally a cuticular 

 layer which is broken up into bacilli by numerous 

 pore-canals ; 2, a layer of strongly refractive sphe- 

 rules, which may be regarded as lenses ; 3, cones, 

 consisting of hollow, strongly refractive, ti-ans- 

 versely striated cylinders or prisms rounded at the 

 ends, which have probably hitherto been confounded 

 with urticating capsules : at the exterior end of 

 each cone there is generally one lens, sometimes 

 even two or three other lenses may stand in the 

 interspaces ; 4, a granular fibrous layer, which also 

 occupies the interspaces of the cones ; 5, a layer 

 which is deeply coloured by carmine, and contains 

 numerous extremely fine fibres and spindle-shaped 

 cells, probably nerve-fibres and cells; 6, the mus- 

 cular layer ; 7, the endothelium. These observa- 

 tions were made on Actinia mesemhryanthemum^ Gosse. Only 

 spirit-specimens were at command, so that nothing can be 

 stated upon various points, such as the position of the pigment 

 which these eyes have during life. M. Rotteken has found 

 the same cones and lenses in the tips of the tentacles of Ac- 

 tinia cereus, Ellis & Sol. ; and he believes that their difi'usion 

 among the Actinia is very general. 





mmm 



