$$ 55, 56. THE ACALEPHAE. 
61 
which encloses between its two lamellae numerous aérial canals, is said to 
be of a calcareous nature, ® 
All these dises have upon their surface markings of concentric rings and 
diverging rays. 
§ 55. 
The Acalephae are surrounded by a very delicate epidermis. Upon 
various portions of the body, and especially upon the arms, the tentacles, 
the prehensile filaments and the cirri, there exist cilia and peculiar net- 
tling and prehensile organs. In those species having active irritating prop- 
erties the nettling organs are situated in a mass under the epidermis.” 
§ 56. 
These nettling organs are generally composed of an oval capsule, con- 
taining a spiral filament which is thrown out from the slightest disturb- 
ance, and, together with its capsule, is detached from the skin.” 
In some species, there exist in place of these nettling organs others of a 
prehensile nature, consisting of an oval capsule in which is a stiff bristle. 
These last cause no burning sensation, but are the means by which these 
animals attach themselves to contiguous objects in a bur-like manner. 
They are situated, grouped in small masses, under the skin of most of the 
non-nettling Discophora, and their bristles project upon the cirri situated 
upon the border of the disc, upon the tentacles, the arms and the sexual 
organs.” 
2 Eschscholtz, lov. cit. p. 176, and Lesson, loc. 
cit. Pl. XII. fig. 3, also, Duperrey, loc. cit. No. 
1, fig. 3. 
1 Wagener (Miiller’s Arch. 1847, p. 183, Taf. 
VIII, fig. 4, 5) has described the peculiar hair- 
like productions on the sides of Berog and Cydippe. 
They have, near their free extremity, a multitude 
of pedunculate small buttons, inserted on a clavate 
swelling. 
1 Wagner (Icon. zoot. Tab. XXXIII. fig. 8, 
10, 11, A. B. C. and Ueber den Bau der Pelagia 
noctiluca, 1841.; also, in Wiegmann’s Archiv 
1841. Th. I. p. 39) has found in Pelagia noctiluca 
that the nettling capsules are situated among the 
pig cells t h the epitheli of the disc. 
According to this author, Oceania, which has feeble 
nettling powers, has these capsules only upon the 
marginal filaments. 
Ehrenberg (Wiegmann’s Archiv 1841, Th. I. 
p. 71, Taf. IIT.) has failed to find these organs upon 
the non-nettling disc of Cyanea captllata, although 
they are found among their prehensile cirri, which 
have irritating power. 
With these, as with the hooked organs of Hydra, 
he thought the capsule was detached before the fil- 
ament. Will (Hore tergest. pp. 62, 65) did not 
find these organs in Cephea, except on the tenta- 
cles of the genital organs ; and in Polyrenia only 
on the marginal filaments. Kélliker (Beitrage, 
loc. cit. p. 41) has seen them also about the gen-" 
itala of Chrysaora and Aequorea. 
° 
The Siphonophora have onty the prehensile fila- 
ments covered with them. Thus in Stephanomia, 
according to Milne Edwards (Ann. d. Sc. Nat. 
XVI. p. 223, Pl. VIII. fig. 9), they cover the whole 
surface of these last ; while in PAysophora, Diph- 
yes and Ersaea, they exist only upon then en- 
larged portions, according to Philippi (Muller’s 
Arch. 1843, p. 62, Taf. V. fig. 9), and Witz (loc. 
cit. p. 79, 81, Taf. IL. fig. 23-25). * 
2 Siebold (Beitrage zur Naturgeseh. der wirbel- 
losen Thiere, 1839, p. 10, 91, Taf. IL. fig. 39) ; also, 
Ehrenberg (Ueber die AcaJephen d. rothen Mee~ 
res, &c. &c., in the Abhandl. d. Berl. Akad. 1835, 
p. 205, Taf. IV-VIII.). He has compared these 
prehensile organs to suckers, 
According to Milne Edwards (Ann. a. Sc. Nat. 
XVI. p. 215), and Widi (loc. cit. p. 80, Taf. II. fig. 
24), they are found also upon the body of Beroe, 
and at the extremity of the prehensile filaments of 
Diphyes and Ersaea. 
According to Will, also (loc. cit. p. 51, Taf. I. 
fig. 19, A. B.), the prehensile filaments of the Cten 
ophora have two kinds of capsules; one, which 
upon the least touch bursts and discharges a liquid; 
the other, of a somewhat different appearana, 
and which contains a delicate, viscous filamem 
Similar filaments, he says, are found upon the 
warts on the body of Eucharis. 
® For these nettling organs and their intimate structure, see my note under § 27, note 1.— Ep. 
6 
