112 HYDEOZOA. 



ages situated in the vicinity of the oesophagus, as well as in the oviferous 

 cavities. In short, he states the general distribution of the nervous 

 matter in the Medusiform Acalephse to be as follows : Four groups of 

 nervous ganglia are situated around the oesophagus in the oviferous 

 cavities close to the ovaria, which are in communication with as many 

 groups of tentacula. Upon the outer border of the disk, close to the 

 base of the marginal tentacles, is another series of nervous nodules, 

 interrupted at regular intervals by the eight brown- coloured corpuscles. 

 Lastly, there exists a series of isolated ganglionic masses, eight in num- 

 ber, situated at the bases of the supposed ocular organs, to which they 

 give off nervous filaments. 



(288.) The so-called ocular organs, named by Ehrenberg unhesitatingly 

 ft pedunculated eyes," present a very remarkable structure. Each " pe- 

 dunculated eye " is directed towards the dorsal aspect of the disk, and 

 has, situated beneath its lower surface, a minute sacculus of a yellowish 

 colour, but variable in its shape, wherein is contained a number of solid 

 crystals, clear as water, and which the action of acids proves to be com- 

 posed of carbonate of lime. 



(289.) Not only eyes, however, but ears also are conceded by modern 

 naturalists to these favoured occupants of the ocean. 



(290.) At the base of the marginal tentacula, or cirri, says Pro- 

 fessor Forbes*, there are present, in a great many of these animals, 

 coloured spots or bulbs ; and in some species these points are so strongly 

 coloured, that, from this circumstance and their magnitude, they indi- 

 cate the course of the animal when in motion, appearing like a circle 

 of gems in the water. When these bulbs are examined with the mi- 

 croscope, they are found to contain a small cavity, quite distinct from 

 any coloured matter that may be present ; the former is regarded by 

 modern naturalists as an otolithic vesicle) the latter as an ocellus, or 

 eye-spot. 



(291.) The otolithic vesicle, which, from analogy and its peculiar 

 structure, is considered as an organ of hearing, is a small spherical sac, 

 developed in the midst of the granular substance of the bulb, and con- 

 taining more or fewer minute vibrating bodies. Will has described 

 the otolithic vessel and its contents, as they are found in Geryonia, as 

 follows : " The auditory vesicles are seated in the course of the mar- 

 ginal circular vessel, in very uncertain number ; usually, however, one 

 at each side of the larger marginal cirri. They are round, measuring T \jth 

 of a line in diameter, and consist of a tolerably thick membrane ; they 

 contain from one to nine, and even more, round globules. If there is only 

 one, it is situated exactly in the centre of the vesicle ; but if there are 

 several, they are found lying together, either in two groups, or joined to 

 each other. I have never observed them move. Muriatic acid dissolves 

 them, and causes the vesicle to burst." The existence of similarly- 

 * Monograph on the British Naked-eyed Medusae. 



