^^ 59, 60. 



THE ACALEPHAE. 



63 



CHAPTER III, 



NERVOUS SYSTEM. 



§59. 



A nervous system has been found in many Acalephae. "With the Cteno- 

 phora the oesophagus is surrounded by a ring formed of eight ganglia/^* 

 and at the opposite extremity of the body there is a simple ganglion. Five 

 nervous filaments pass out from these ganglia, and along the sides of the 

 body are nervous fibres, which ultimately divide into delicate threads.® 



The tentacles of Medusae are supplied with nervous filaments which issue 

 from a ganglion situated at their base.® 



CHAPTER IV. 



ORGANS OF SENSE. 



§60. 



With many Acalephae, there are, upon the borders and extremities of 



1 These eight ganglia, which are connected 

 together by delicate cords, were first observed by 

 Grant (Trans. Zool. Soc. Lond. I. p. 10) in Cydip- 

 pe pileus. Compare, also, Wagner^ Icon. zoot. 

 Tab. XXXIII. fig. 37, A. B. From each of these 

 ganglia two nerves pass off to the side, while a 

 third, traversing the interior of the body, and hav- 

 ing two or three swellings, is finally distributed to 

 the intestine. Patterson (The Edin. new Philos. 

 Jour. XX. p. 26), and Forbes (Ann. of Nat. Hist. 

 1839, p. 145), have also observed the oesophageal 

 ring in Cudippe, but did not perceive the ganglia. 



2 Milne Edwards (Ann. des Sc. Nat. loc. cit. 

 p. 206, PI. IV. fig. 1) has observed at the poste- 

 rior extremity of the body of Lesueuria vitrea 

 (a new Beroid) a ganglionic body which sends 



* [ § 59, note 3.] The nervous system of the 

 Acalephae has been successfully studied Ijy Agassiz 

 upon several genera (Hippocrene, Tiaropsis, 

 Staurophora). His results are new, and different 

 from those of previous observers. I cannot do bet- 

 ter than to quote his words : " There is, unques- 

 tionably, a nervous system in Medusae, but this 

 nervous system does not form large central masses, 

 to which all the activity of the body is referred, or 

 from which it emanates. There is no regular com- 

 munication by nervous threads between the centre 

 and periphery and all intervening parts ; and the 

 nervous substance does not consist of heterogene- 

 ous elements, of nervous globules and nervous 

 threads, presenting the various states of complica- 

 tion and combination, and the internal structural 

 differences, which we notice in the vertebrated ani- 

 mals, or even in the Mollusca and Articulata." 



out in front four filaments ; and upon the sides of 

 this animal a nervous cord, from which pass off' 

 delicate branches at regular intervals. At the pos- 

 terior extremity of the body of Cydippe, Eiicha- 

 ris and Medea, fVill {Froriep's neue Notizen, 

 No. 599, 1843, p. 67, and Horse tergest. p. 44) has 

 likewise observed a round, yellowish ganglion, with 

 four prolongations, from which pass off twenty-five 

 or thirty nerves. 



3 Ehrenberg has found along the entire border 

 of the disc of Medusa aurita, and between each 

 two tactile filaments, a bifid nervous ganglion. He 

 affirms to have seen also two others similar, at the 

 base of each tentacle surrounding the genital organs. 

 See Abhandl. d. Berl. Akad. 1835, p. 203, Taf. IV. 

 fig. 1, x.; and MuUer^s Arch. 1834, p. 571.* 



" In Medusae the nervous system consists of a 

 simple cord, of a string of ovate cells, forming a 

 ring around the lower margin of the anunal (PI. V. 

 fig. 11, 2, 4, 5), extending from one eye-speck to 

 the other, following the circular chymiferous tube, 

 and also its vertical branches, round the upper 

 portion of which they form another circle. The 

 substance of this nervous system, however, is 

 throughout cellular, and strictly so, and the cells 

 are ovate. There is no appearance in any of its 

 parts of true fibres " (loc. cit. p. 232). That 

 this is the nervous system seems placed beyond all 

 controversy ; for, in a private letter, Agassiz has 

 informed me that in a new genus (Rhacostoma), 

 living on the shores of Massachusetts, he has seen 

 this system at night as an illuminated diagram. — 

 Ed. 



