m 



THE ACALEPHAE. 



§eo. 



their body, button and tongue-like organs, which, as they are connected 

 with neighboring ganglia, may well be regarded as organs of sense. 



Their essential structure is a membranous capsule, containing a clear 

 liquid, in which are suspended crystalline corpuscles. 



These organs, having sometimes a red pigment, have been taken for eyes ; 

 but, as most of them are without pigment, and as the crystalline corpuscles 

 behave in acid like the Otolites of the higher animals, they have more 

 recently been better designated as organs of hearing. 



The eight marginal, tongue-like bodies, found upon the disc of Medusa 

 aurita^ have been regarded as eyes.^^^ The sole fact for the support of this 

 opinion is the presence of pigment; for the small hexagonal crystals, irreg- 

 ularly scattered in the interior of these bodies, would scarcely allow them 

 to refi'act the light like a crystalline lens. 



The Ctenophora have only a single organ of this nature, and which is 

 situated near the ganglion at the posterior end of the body. It has been 

 regarded both as an eye and as an organ of hearing. <-^ 



With many Discophora, these organs appear as pale-yellow, or even 

 colorless marginal corpuscles, having more or less calcareous bodies.*"'^ 



It is yet doubtful whether the otolites of the Acalephae perform the same 

 movements as those of the acephalous and gasteropod moUusca.'^^ 



1 These marginal corpuscles, already observed in 

 the Medusae by Gaede (Beitrage zur Anat. u. 

 Phvs. der Medusen, 1816, p. 18, 28), and by Rosen- 

 thal (Zeitsch. f. Physiol. Bd. I. Hit. 2, 1825, p. 326), 

 were first described as eyes by Ehrenberg. See 

 Muller\^ Arch. 1834, p. 571, and Abhandl. d. Berl. 

 Akad. 1835, p. 190, Taf. IV. V. 



2 Milne Edwards has called this body, in Lesu- 

 euria vitrea and Beroe Forskalii, " Organe ocu- 

 liforme " (Ann. d. So. Nat. loc. cit. p. 206, 211, 

 PI. IV. fig. 1, k. and PI. V. fig. 4, i.). According 

 to Will (JProriep^s ncue Not. No. 599, p. 67, and 

 Horas tergest. p. 45, Taf. I. fig. 2, 4, 20, b.), the red 

 pigment of these organs is entirely wanting in 

 Beroe, Eucharis and Cydippe, while the hexago- 

 nal calcareous corpuscles are very numerous — a 

 fact leading him to conclude that these organs are 

 auditory vesicles. 



3 According to Wagner (TTeber den Bau, &c., 

 and Icon. zoot. Tab. XXXIII. fig. 31, g. 23, c. and 

 25), these corpuscles are pale-yellow in Pelagia 

 noctiluca, and colorless in Oceania, Cassiopea 

 and Aurelia. In Cephea, Will has observed only 

 pale-yellow corpuscles, fiUed with crystals. And, 

 according to him (loc. cit. p. 64, 68), the colorless 

 pedunculated marginal vesicles of Polijxenia leu- 

 nostyla contain, each only a single round otoUte, 

 while those of Cytaeis polystyla contain numbers, 

 colorless or yellow, and of ii-regular forms. He 

 has also observed (loc. cit. p. 72, Taf. II. fig 9, 

 10) that in Geryonia the number of these otolites 

 varies from one to nine. Milne Edwards (Ann. 



d. Sc. Nat. XVI. p. 196, PI. f. e.) has observed 

 upon the margin of the disc of Aequorea violacea 

 vesicles containing two or three spherical corpus- 

 cles, and which, probably, are auditory organs. 

 According to Sars (Wiegmann's Arch. 1841, Th. 

 1. p. 14, fig. 60), and IFill (loc. cit. p. 75, Taf. II. 

 fig. 21, A. B.), these marginal corpuscles are found 

 upon young Medusae belonging to Ephyra. 



i Will has never observed with the Otolites of 

 Acalephae similar movements to those of moUusca. 

 Kolliker (Froriep^s neue Not. No. 534, p. 82) has 

 observed vibratile cUia upon the inner surface of 

 the marginal corpuscles of Pelagia, Cassiopea, 

 Rhizostomum and Oceania, which are pja'iform, 

 and contain many calcareous crystals. In the 

 pedunculated vesicles of Geryonia, which contain 

 only a single crystal, these cilia are absent. In 

 none of the Sledusae has he found collections of 

 pigment, and in Oceania (nov. spec.) only he has 

 observed a mass of brown pigment cells upon the 

 external and superior surface of the base of these 

 corpuscles ; in the centre he perceived a round 

 transparent body, and upon the upper surface a 

 circular opening, so that the whole closely resem- 

 bles an eye, there being, moreover, a kind of pupil- 

 lary opening, and the traces of an optic nerve from 

 a ganglion. 



According to the observations of Frey and 

 Leuckart (Beitr. &c. p. 39), the group of otolites 

 contained in the auditory organ of a Cydippe per- 

 form oscillatory movements, due evidently to vibra- 

 tile ciUa situated on the auditive capsule.* 



* [ § 560, note 4.] The organs of sense of the Aca- 

 lephae liave been the objects of much study of late, 

 and to Agassiz we are indebted for the most minute 

 researches on these obscure points. He has shown 

 the eye-specks to be undoubted organs of sense, 

 from their connection with the nervous system. 

 With the naked-eyed Medusae, ^e regards them 

 light-perceiving instead of auditory organs. In 

 regard to the single organ found with the Cteno- 

 phora, and which Frey and Leuckart have re- 



cently declared to be of an auditory nature, he 

 remarks : " I am inclined to consider this organ, or 

 this speck, as somethmg similar to the central col- 

 ored speck which occurs in the middle of the disc 

 in Discoid Medusae, and which is particularly dis- 

 tinct in young animals soon after they have been 

 detached from the polyp-like stem on which they 

 grew, as a remnant of the connection which exists 

 between the mother-stem and its progeny in those 

 Medusae which multiply by alternate generations." 



