29 



merely as minute rudimentary bulbs. It would seem, therefore, that 

 Prof. E. Forbes has considered the cavity of the bulb in certain 

 species, in which occasionally an active vibratory or rather rotatory 

 movement of irregular -sized particles is to be observed, as corre- 

 sponding to the so-termed auditory vesicle of Will, &c. That this is 

 not the case, however, is abundantly clear, and, though speaking with 

 much diffidence, owing to the want of observation in a sufficient 

 number of species, I am inclined to agree, I believe it is with Will, 

 in thinking that the rotatory movement above described (in the 

 naked-eyed Medusa at all events) is to be referred to the existence 

 of a sort of vortex or torcular at the point where the cavity of the 

 bulb joins the marginal canal. 



The true nature of these marginal bodies is still obscure ; but 

 from what has been noticed with respect to the intimate structure and 

 optical properties of the spherical body or bodies contained in those 

 of the naked-eyed class, it is not an improbable supposition, that 

 these little organs are visual and not auditory. Allowing also, as 

 can perhaps scarcely be denied, that the marginal vesicles above de- 

 scribed are homologous with the peculiar bodies regarded, I believe 

 by all, as the eyes of the covered-ej^ed species, this supposition would 

 appear to be much strengthened. 



I would here also call attention to the remarkable fact, that these 

 marginal vesicles in the Gymnophthalmata, where present, are almost 

 invariably, if not always, sessile (Polyxenia and perhaps Cytceis, ac- 

 cording to Will, offering an exception), and contain but one or but 

 few spherical corpuscles ; whilst in the Steganophthalmata, as also in 

 the Beroidw, they are always pedunculated, and filled, not with sphe- 

 rical lenses, but with a mass of crystals. The former class would, 

 therefore, seem to have the better eyes of the two. It is to be re- 

 marked with regard to the chemical constitution of these lenses, that, 

 although their solubility in dilute acid with effervescence appears to 

 be universally allowed, and consequently that they are of a calcareous 

 nature, yet that in the naked-eyed species at least, upon immersion 

 of the Medusa in spirit of wine, these spherules immediately become 

 opaque, as an optic lens in other cases would. 



The bean-shaped, granular, opaque substance, from which the pe- 

 duncle in the case of the Steganoplitlialmata springs or appears to 

 spring, may perhaps be regarded as homologous with the granular, 

 indistinctly fibrous mass, in which the internal cyst containing the 

 lens is partially imbedded in the other. 



