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 ^\'atcr by means of ciliated epithelium/^' Shortly 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 ^e?rt/rta^io?«,'^' and sometimes by transy evsa Jissuration. 

 This last mode occurs in the ibllowing remarkable manner : 



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

 versely into many segments. Ai'ound 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 the 



tentacles of Agalmopsis ; but he found at the same 

 tiQie(l"C.cit.p.38,43), in the campanuUform 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, like the 

 Hydrina and Sertularina, reproduce by alternation 

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

 having sex. 



1'i Medusa aurita and Cyanea capiUata; see 

 Elireiibers:, Abhandl. &c. loc. cit. Taf. III. fig. 1, 

 2, Taf. VIII. fig. 1 ; also, Sars in Wiesmmin's 

 Arch. 1841, I. p. 19. 



1 The development and metamorphosis of Me- 

 dusa aurita and of Cyanea capillata have been 

 observed by Siebold (Beitrage loc. cit. p. 21, Taf. 

 I. II. ; and Froriep^s neue Not. No. 160, 1838, p. 

 177) ; and by Sars {Wiegmann''s Arch. 1841, 1, p. 

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

 (see Ekrenberg, Abhandl. &c. loc. cit. Taf. VIII. 

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

 fig. 17-19 ; and .Sars, Wiegmanr^s Arch. loc. cit. 

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

 been regarded by Baer as the larvse {Meckel's 

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



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

 25-33, Taf. II. fig. 34 ; and Sars, Wiegmann'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 fVagneri 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 buds has been observed by Sars in Cyanea 



capillata. He has also seen them develop pedi- 

 cles from the end of which new individuals would 

 appear, which resembled Polyps. See IViegmann'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 {Scyphistoma)ot 

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

 Steeiistrup (Ueber d. Generationswechsel, p. 17) 

 has regarded them as nui-ses of the Medusae. At 

 a latter period, when the rings have been separated 

 and have acquired the bifid prolongations, Sars 

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

 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 (fViegmann's Arch. 1837, I. 

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

 young constitute, very prol)ably, the genus Ephyra 

 of Eschscholtz (see fViegmann'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 similar 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 natm-alists. In tracing the devel- 

 opment of one of the Discophora allied to Oceania, 

 he observed that this animal in its early condition 

 separated from a corallum resembling that of Syn- 

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

 ria. However various these developing forms may 

 be, that one must be regarded as the real one 

 which exists during the development of the testi- 

 cles and ovaries.f 



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

 on the development of Cephea, Ecker, Bericht ub. 

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

 1849, p. 51 ; Busch, Beobachtungen Ob. die Anat. 

 &c. Berlin, 1851, p. 30 ; and Frauizius, in Sie- 



bold and Kijllikcr's Zeitsch. 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 



