24 



8 and 10. Around this dilatation, an agglomeration of glandular 

 cells takes place, causing a considerable thickening of the walls of the 

 canal at that part. This dilatation eventually forms the cavity of the 

 bulb, and is prolonged thence into the tube of the tentacle. The 

 lower surface of these incipient bulbs is from the first thickly beset 

 with filiferous vesicles (fig. 8, c). The ovaries or reproductive glands 

 are four in number, and in all the specimens (not a great many) exa- 

 mined by me in the mature state, these bodies contained ova in vari- 

 ous stages of development (figs. 4, 5). On the margin of the disk and 

 between the tentacles are placed minute bodies or organs, to which I 

 am more particularly desirous of directing attention, as it appears to 

 me that considerable obscurity rests upon their true nature, and 

 much confusion in what is said about them by different observers. 

 One of these organs in the form they more usually assume, is shown 

 in fig. 12, and other modifications of form in figs. 13, 14. They con- 

 sist of a perfectly transparent, homogeneous, outer envelope of consi- 

 derable thickness ; within this is contained a cyst or cysts filled with 

 a transparent fluid, and containing also a spherical, highly refractive 

 corpuscle. Where there is more than one of these corpuscles, and 

 they sometimes amount to nine, each is usually contained in a dis- 

 tinct secondary cavity or cyst (fig. 13). The cavity of the outer cell 

 or cyst, exterior to the smaller or inner cyst which contains the re- 

 fractive corpuscle, is occupied by a fine granular material, in which 

 an indistinctly fibrous, radiating appearance may sometimes be de- 

 tected. Sometimes within the inner cyst may be seen, besides the 

 large spherical corpuscle, other small unequal sized spherules, as 

 shown in fig. 14. 



Under polarized light the spherical corpuscle exhibits a well-de- 

 fined black cross (fig. 15), an appearance which may probably be 

 taken to indicate a greater density in the centre, gradually and uni- 

 formly diminishing towards the circumference. This structure would 

 seem to bear a close resemblance to that of the crystalline lens, and 

 the body in fact may be regarded as closely similar in form and 

 structure to the crystalline lens of fishes. These marginal bodies 

 consequently should be regarded as visual organs, and not as auditory 

 capsules, as they have hitherto, I believe, been usually considered. 



The substance of the umbrella is indistinctly cellular. That of 

 the subumbrella is composed for the most part of a muscular expan- 

 sion, lined internally by a delicate membrane, and between these 

 layers the four gastric canals appear to run. The velum also is com- 

 posed of very distinct muscular fibres. All these muscular fibres are 



