^§ 55, 56. 



THE ACALEPHAE. 



61 



which encloses between its two lamellae numerous aerial canals, is said to 

 be of a calcareous nature.'-^ 



All these discs 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, loc. cit. p. 176, and Lesson, loc. 

 cit. VI. XII. fig. 3 ; also, Duperrcy, loc. cit. No. 

 7, fig. 3. 



1 Was:ener (MuUer^s Arch. 1847, p. 183, Taf. 

 VIII. fig. 4, 5) has described the peculiar baii'- 

 like productions on the sides of Beroe and Cydippe. 

 They have, near their free extremity, a multitude 

 of pedunculate small buttons, inserted on a clavate 

 swelling. 



1 Wagner (Icon. zoot. Tab. XXXIH. fig. 8, 

 10, 11, A. B. C. and Ueber den Bau der Pelagia 

 noctiluca, 1841. ; also, in fFiegmann's Archiv 

 1841. Th. I. p. 39) has found in Pelagia noctiluca 

 that the ncttUng cajjsules are situated among the 

 pigment cells beneath the epithelium of the disc. 

 According to this author, Oceania, which has feeble 

 nettling powers, has these capsules only upon the 

 marginal filaments. 



Ehrenberg {fViesmann's Archiv 1841, Th. I. 

 p. 71, Taf. III.) has failed to find these organs upon 

 the non-nettling disc of Cyanea capillata, although 

 they are found among their prehensile ch'ri, which 

 have irritating power. 



With these, as with the hooked organs of Hydra, 

 he thought the capsule was detached before the fil- 

 ament. Will (Horte tergest. pp. 62, 65) did not 

 find these organs in Cephea, except on the tenta- 

 cles of the genital organs ; and in Polyxenia only 

 on the marginal filaments. Kolliker (Beitrage, 

 loc. cit. p. 41) has seen them also about the gen- 

 itals of Chrysaora and Aequorea. 



The Siphonophora have only the prehensile fila- 

 ments covered with them. Thus in Stephanomia, 

 according to Milne Edwards (Ann. d. Sc. Nat. 

 XVI. p. 223, PI. VIII. fig. 9), they cover the whole 

 surface of these last ; while in Physophora, Diph- 

 yes and Ersaea, they exist only upon their en- 

 larged portions, according to Pfiilippi (3IuUer's 

 Arch. 1843, p. 62, Taf. V. fig. 9), and Will (loc. 

 cit. p. 79, 81, Taf. II. fig. 23-25). * 



2 Siebold (Beiti-ilge zur Naturgesch. der wirbel- 

 losen Tliiere, 1839, p. 10, 91, Taf. II. fig. 39) ; also, 

 Ehrenberg (Ucber die Acalephen 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. d. Sc. Nat. 

 XVI. p. 215), and Will (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 appearance, 

 and which contains a delicate, viscous filament. 

 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. — Ed. 



6 



