§§ 65, 66. 
THE ACALEPHAE. 69 
CHAPTER VIII. 
ORGANS OF SECRETION. 
§ 65. 
The air-cavity of certain Siphonophora, which is surrounded by a dou- 
ble membrane, 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.“ 
CHAPTER IX. 
ORGANS OF GENERATION. 
§ 66. 
Reproduction by fissuration and gemmation with the Acalephae has 
been observed only in the youngest states of certain Medusae.” But repro- 
has not seen an opening of this cavity, and was 
unable to force air from it. Future researches 
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 wutauies of Physophora, Velella 
and Porpita, as a mouth, then the sAvitv of these 
tentacles should belong to the aquiferous sysicu. 
Moreover, these tentacles, as to their form and mo- 
‘bility, remind one of the pedicles of the Echino-~ 
derms ;. but it is remarkable 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 in 
the interior of the cartilaginous, natatory pieces of 
the Physophoridae and Diphyidae, aquiferous 
canals which are probably of a respiratory nature. 
Hollard, likewise, regards the hollow and tubuli- 
form tentacles of Veledia 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. IIT. 1845, p. 250. ° 
1 Many naturalists entirely deny the presence of 
openings in these aérial 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 in the pouch at 
the end of the longitudinal canal of Physophora 
tetrasticha. Olfers (Abhandl. d. Berl. Akad. 
1831, p. 165) has not been able to find in Physalia 
the opening of the internal sac, said to be near the 
one of the external sac. In fact, Bennett (Proc. 
Zool. Soc. London, 1837, p. 43; and Wiegmann’s 
Arch. 1838, II. p. 332), with the same species, 
* (§ 66, note 1.] See also Hurley (Ann. Nat. 
Hist. VI. p. 394), who has described the reproduc- 
tive processes of the Diphyidae, and shown that 
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 (Mém. d. l’Acad. de St. Peters- 
burg, IT. p. 494, Pl. 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 (Hore 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 
fufther condition. 
Propagation by buds has also been found with 
the Acalephs, through the excellent researches of 
Sars (Fauna littoral. Norveg. p. 11, Tab. IV. fig. 
8-12), for this observer has seen on the external 
surface of the tubuliform stomach of Cytaeis octo- 
punctata, and upon the four ovaries of Thauman- 
tias multicerrata, small campanuliform Acalephs 
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 fil ts and the iform st h, and 
which were finally detached, swimming freely like 
the Discophora.' According to Sars, also (Ibid. 
p. 43, Tab. VII. fig. 11, b. 18, b. and 14), there is, 
likewise, an analogous mode of propigation with 
Diphyes.* 
they multiply by gemmation as well as by ova. 
See, also, Miudler’s Arch. 1851, p. 380, Taf. XVI. 
— Ep. 
