72 



THE ACALEPHAE. 



^70. 



of procreation, the females of some Discophora are easily distinguished 

 from the males by the numerous pouches of their tentacles, and in which 

 -eggs and newly -hatched young are carried for a short time/^'' 



§70. 



As yet, the development of a few only of the Acalephae has been traced. 

 It is attended by a remarkable metamorphosis. 



After the usual segmentation of the vitellus, ovoid embryos resembling 

 infusoria are developed ; these turn freely on their axis, and swim about in 

 the water by means of ciliated epithelium.'^* Shoi-tly after, they become 

 attached by the anterior extremity to some object. Upon the opposite free 

 extremity tentacles appear, and between them the mouth. The animal has 

 then the form of a Polyp. ^-^ It is during this period that the young ani- 

 mal reproduces by gemmation,'^^^ and sometimes by ix&ns,veT^Q fissuratioii. 

 This last mode occurs in the following remarkable manner : 



The polyp-like animal increases in length, and its body divides trans- 

 versely into many segments. Around each of these segments eight bifid 

 processes are developed ; after this, each segment is successively separated 

 from before to behind, and they float about for a time as eight-rayed Aca- 

 lephae, but soon attain, however, their adult condition.'^ 



■seen genital organs of the same form between th"; 

 tentacles of A^almopsis ; but he found at the same 

 time (loc. cit. p. 38, 43), in the campanuliform individ- 

 uals produced from buds, testicles with Agalmopsis, 

 -and ovaries with Diphyes. It may therefore be 

 justly supposed that these various Siphonophora 

 are compound, sexless individuals, which, lilie the 

 Hydrina and Sertularina, reproduce by alternation 

 of generation, — that is, by buds, — individuals 

 having sex. 



l'^ Medusa aurita and Cyanea capil/ata ; see 

 Ehrenberg, Abhandl. &c. loc. cit. Taf. III. fig. 1, 

 2, Taf. VIII. fig. 1 ; also, Sars in WiegmanrVs 

 Arch. 1841, I. p. 19. 



1 The development and metamorphosis of Me- 

 dusa aurita ?i\v\ of Cyanea capiLlata have been 

 observed by Siebnld (Beiträge lue. cit. p. 21, Taf. 

 I. II. ; and Froriep's neue Not. No. 166, 1838, p. 

 177) i and by Sars {fViegmann''s Arch. 1841, I. p. 

 19, Taf. I.-IV.). In the first stage of development 

 <see Ehrenberg, Abhandl. &c. loc. cit. Taf. VIII. 

 fig. 15-18 ; also, Siebold, Beiträge loc. cit. Taf. I. 

 fig. 17-19 ; and Sars, fViegmann's Arch. loc. cit. 

 Taf. I. fig. 1-6), these infusoria-like Medusae have 

 been regarded by Baer as the larva (^Meckefs 

 Deutsches Arch. VIII. 1823, p. 389). 



2 Siebold, Beiträge loc. cit. p. 29, Taf. I. fig. 

 25-33, Taf. II. fig. 04 ; and Sars, fViegmann^s 

 Arch. loc. cit. Taf. I. fig. 7-31. During my last 

 ■visit at Trieste (autumn of 1847), I convinced 

 myself that the young of Cephea ffagneri are 

 •developed wholly like those of Medusae, by passing 

 from infusoria-like forms to polypoid young ani- 

 mals.* 



8 The reproduction of the polyp-form Medusae 

 by bud» has been observed by Sars in Cyanea 



"'"""!*" He has also seen them develop pedi- 

 cies iiom the enu of which new individuals would 

 appear, which resembled Polyps. See fViegmann's 

 Arch. loc. cit. p. 26, Taf. I. fig. 37, 41, 42, 38, 39, 40. 

 4 These young Medusae, whilst composed of rings, 

 have been taken for a new genus (Scyphistotna) o{ 

 Polyps by Sars (Isis. 1833, p. 222, Taf. X. fig. 2). 

 Steenstrup (Ueber d. Generationswechsel, p. 17) 

 has regarded them as nurses of the Medusae. At 

 a latter jjeriod, when the rings have been separated 

 and have acquired the bifid prolongations, Sar^ 

 (Isis. 1833, p. 224, Taf. X. fig. 4 ; and Beskrivei- 

 ser, &c., p. 16, PI. III.) has described them as a 

 new species of Medusae (Strobila octoradiata). 

 But lately he has perceived that they are the young 

 of Medusa aurita {WiegmaniVs Arch. 1837, I. 

 p. 406) ; it did not occur to him, however, that these 

 young constitute, very probably, the genus Ephyra 

 of Eschscholtx (see Wiegmann''s Arch. 1841, Th. 

 I. p. 10). It will probably be discovered that 

 many small campanulate or discoid Medusae 

 are only the young of other Acalephae; for it is very 

 likely that they all undergo a sunilar metamorpho- 

 sis. It may also prove that many naked Polyps 

 are only transitionary forms of known species of 

 Acalephae. In this connection the observation of 

 Dujardin (Comp. rend. 1843, p. 1132) deserves 

 the attention of naturalists. In tracing the devel- 

 opment of on^ of the Discophora allied to Oceania, 

 he observed that ihis animal in its early condition 

 8ei)arated from a corallum resembling that of Syn- 

 coryne, and was of a form quite like an Eleuthe- 

 ria. However various these develo])ing forms may 

 be, that one must be regarded as the real one 

 which exists during the development of the testi- 

 cles and ovaries. t 



• [ § 70, note 2.] See, also, for recent researches 

 on the development of Cephea, Ecker, Bericht üb. 

 die Verhandl. d. naturf. Qesellsch. in Basel. VIII. 

 1849, p. 51 i Busch, Beobachtungen üb. die Anat. 

 Ac. Berlin, 1851, p. 30 ; and Frantzius, in Sie- 



bold and Kölliker'a ZeiUch. f. Zool. IV. p. 118, 

 June, 1852. — Ed. 



t [ § 70, note 4.] In regard to the development 

 of the Acalephae, it may be mentioned that recent 

 researches, few as they are, have verified some 



