SEA-NETTLES. 99 
those with a spiny skin (Zchinodermata) as a second order’. They 
were first described as a distinct class of animals by CUVIER in the 
first edition of the Regne Animal, under the name of Acalephe?. 
The name of gelatinous animals is more appropriate to this class 
than to some others of the Radiates of Cuvier. The kinds most 
generally known bear the name of Zeekwallen in Holland, (Quallen 
in Germany, Squalders® or sea-jelly or sea-blubber in England.] 
When thrown by the sea upon the strand, they le motionless 
during the ebb; for they do not creep, but can only move in the 
water by contraction and expansion. 
The pungent and burning pain like that caused by stinging 
nettles, which many species inflict on being touched, was generally 
considered in former times to be the effect of a mucus secreted by 
the skin of these creatures. It is only since 1841, from WAGNER’s 
microscopic investigations, that minute threads situated on the 
surface of the skin have been recognised as connected with this 
phenomenon, since in Acalephes which cause no such pain (as in 
Casstopea) they were not discovered. Each of these threads lies 
rolled up in a little oval vesicle or cell, from which, on pressure or 
iritation of the skin, it is forced out by eversion; they are readily 
detached with the vesicle to which they are fixed by a tubercle, 
and are always present in the secreted mucus that produces a burn- 
ing pain. Yet the cause of this ought not to be considered as 
entirely mechanical; it is probable that some acrid fluid, secreted 
by the cells, adheres to the threads*. Nevertheless an accomplished 
* 
1 Radiaires mollasses, LAMARCK Syst. des anim. s. vertebres, 1801, pp. 341, 352, and 
in his later works, Hatrait du Cowrs de Zoologie sur les anim. s. v. 1812, and Hist. Nat. 
des Anim. s. vert, 1815. 
2 Cuvier in his Tableau élémentaire (1798) and in the tables at the end of the first 
part of his Legons dAnat. comp. had comprised all the animals, which he afterwards 
named radiated animals, in a single class, under the name of Zoophytes. Of this the 
Orties de Mer make the second order, which agrees with his later class of the Acalephe. 
Here also he placed the Actiniw, which however in the second edition of his Régne 
Animal he separated from it again, in order to unite them, as had already been done 
by others, with the Polyps. 
3 [Sir T. Browne’s Works edited by WiLKIns, Vol. Iv. p. 333, quoted by ForBEs 
Brit. Starf. p. 87.] 
4 R. WAGNER iiber muthmassliche Nesselorgane der Medusen, WIRGMANN u. ERicu- 
son Archiv. f. Naturg. 1841, I. s. 383—42; Ueber den Bau der Pelagia noctiluca. 
Leipsig, 1841, fol. Jcon. Zoot. Tab, xxx11I.—Subsequently these parts were also inves- 
tigated by EHRENBERG, PHILIpr1, WILL, MILNE Epwarps ke. 
(—2 
