§^ 65, 66. 



THE ACALEPHAE. 



69 



CHAPTEK VIII. 



ORGANS OF SECRETION. 



*§ 65. 



The air-cavity of certain Siphonophora, which is surrounded by a dou- 

 ble meuibrane, ought probably to be regarded as an organ of secretion ; for, 

 according to many naturalists, the air contained could not have been de- 

 rived from without, and consequently was secreted by the sides of the 

 internal membrane.^'' 



CHAPTEK IX. 



ORaANS OP GENERATION. 



§66. 



Reproduction by fissuration and gemmation with the Acalephae has 

 been observed only in the youngest states of certain Medusae. '^^ But repro- 



cavity, belongs probably to the aquiferous system. 

 That which in Porpita has been taken for a mouth, 

 belongs probably, also, to the same system. I 

 would not, however, deny that another significa- 

 tion may be given to the so-called respiratory and 

 digestive organs of the Siphonophora. 



If one prefers, with Philippi, to regard the open- 

 ing between the tentacles of Physophora, yelella 

 and Porpita, as a mouth, then the cavity of these 

 tentacles should belong to the aquiferous system. 

 Moreover, these tentacles, as to their form and mo- 

 bility, remind one of the jjedicles of the Echino- 

 derms ; but it is remaLkable that they can absorb 

 food. 



Sars (Faun, littoral. Norveg. p. 34, 42, Tab. VI. 

 fig. 3, gg. and Tab. VII. fig. 3, e.) has observed m 

 the interior of the cartilaginous, natatory pieces of 

 the Physophoridae and Diphyidae, aquiferous 

 canals which are probably of a respiratory nature. 



Ho/lard, likewise, regards the hollow and tubuh- 

 form tentacles of Velella as aquiferous tubes, and 

 in this way, as the tentacular feet of the Echino- 

 derms, includes them in the aquiferous system. See 

 Ann. d. Sc. Nat. III. 1845, p. 250. 



1 Many naturaUsts entirely deny the presence of 

 openings in these aSrial cavities, and do not admit 

 that they are filled with gas. Thus Philippi 

 (Miiller's Arch. 1843, p. 63) affirms to have found 

 neither external opening nor air ui the pouch at 

 the end of the longitudinal canal of Physophora 

 te.trasticha. Olfers (Abhandl. d. Bed. Akad. 

 1831, p. 165) has not been able to find in Phyaalia 

 the oi)ening of the internal sac, said to be near the 

 one of the external sac. In fact, Bennett (I'roc. 

 Zool. Soc. London, 1837, p. 43 ; and Wiegmanii's 

 Arch. 1838, II. p. 332), with the same species. 



has not seen an opening of this cavity, and was 

 unable to force au- from it. Future researches 

 must determine if these pouches have not a respir- 

 atory function. 



1 See, upon this subject, the Embryology of these 

 animals, below. It is not yet demonstrated that 

 adult Acalephae reproduce by fissuration ; and 

 although Mertens (M6m. d. I'Acad. de St. Peters- 

 burg, II. p. 494, PI. I. fig. 2-4, and p. 527) has 

 observed detached corpuscles from the body of 

 Cestum and Cydippe swim freely about, and rap- 

 idly enlarge, yet his observations are here lim- 

 ited. 



In the same way, Will (Horse tergest. p. 42) has 

 seen analogous bodies detached from Eucharis, 

 and has found in the water others supposed to be- 

 long to the Ctenophora, but has not traced their 

 fui'ther condition. 



Propagation by buds has also been found with 

 the Acalephs, through the excellent researches of 

 Sars (Fauna littoral. Norveg. p. 11, Tali. IV. fig. 

 8-12), for this observer has seen on the external 

 sm-face of the tubuliform stomach of Cytaeis octo- 

 punctata, and upon the four ovaries of Thauman- 

 tiasmiilticerrata,sma,U campanuliform Acale])hs 

 resembling their parent, in the process of develop- 

 ment, and which were finally detached. In the 

 genus Agalmopsis which is allied to Agalma, 

 Sars has observed (Ibid. p. 38, Tab. VI. fig. 14-17) 

 campanuliform bodies sprout out between the pre- 

 hensile filaments and the tubuliform stomach, and 

 which were finally detached, swimming freely like 

 the Discophora. Accoriling to Sars, also (Ihid. 

 p. 43, Tab. VU. fig. 11, b. 13, b. and 14), there is, 

 likewise, an analogous mode of propagation with 

 Diphyes.* 



* [ § 66, note 1.] See also Huxley (Ann. Nat. they multiply by germnatiou as well as by ova. 

 Hist. VI. p. 394), who has described the reproduc- See, also, Mailer's Arch. 1851, p. 3S0, Taf. XVU. 

 live processes of the Diphyidae, and shown that — Ed. 



