THE EYES. 301 



around any objects they may meet with, and so moor- 

 ing the animal. That contact stimulates the tentacle 

 to grasping I infer from the frequency with which I 

 see one or more inserted into the central orifice of 

 their own umbrella, and bent round the edige. The 

 tips, probably, accidentally get in, in roving about, 

 when the touch of the edge stimulates the filament to 

 bend tightly round it. 



Midway between each pair of tentacles, and thus 

 quadrating the circle at four other points, the mar- 

 ginal canal carries on^ts exterior side a little swelling, 

 within the cavity of which are contained half a dozen 

 or more minute granules, in which I could not detect 

 any motion. Its cavity is isolated from the course of 

 the canal, which can be traced independently. (See 

 fig. 4). And close to this bulb, on each side, project- 

 ing from the interior of the canal, but sessile thereon, 

 is a globular capsule furnished with a narrow waved 

 veil or membrane hanging from its interior surface, 

 and formed apparently of the same substance as the 

 canal, but containing in its centre a spherule, trans- 

 parent, colourless, and of high refracting power — a 

 crystalline lens, in fact (Fig. 5). The vesicle which 

 carries this spherule is furnished with a very minute 

 tubercle, projecting from its edge towards the interior 

 of the animal. 



These vesicles, of which there are eight altogether, 

 I should without hesitation have set down as visual 

 organs, but for the weight of authority which has 

 pronounced them organs of hearing. Mr. Busk, how- 

 ever, in his memoir on a species of Thcmmcmtias 

 (Trans. Micr. Soc. 1850, p. 22 j, has given what ap- 



D 2 



