SEA-NETTLES. 99 



those with a spiny skin (Echinodermata) as a second order 1 . They 

 were first described as a distinct class of animals by CUVIER in the 

 first edition of the Eegne Animal, under the name of Acalepha? 2 . 



The name of gelatinous animals is more appropriate to this class 

 than to some others of the Kadiates of CUVIER. The kinds most 

 generally known bear the name of Zeekwallen in Holland, [Quallen 

 in Germany, Squalders 3 or sea-jelly or sea-blubber in England.] 

 When thrown by the sea upon the strand, they lie 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 

 Casswpea) they were not discovered. Each of these threads lies 

 rolled up in a little oval vesicle or cell, from which, on pressure or 

 irritation 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 4 . Nevertheless an accomplished 



1 Radiaires mollasses, LAMARCK Syst. desanim. s. vertebres, 1801, pp. 341, 352, and 

 in his later works, Extrait du Cours de Zoologie sur les anim. s. v. 1812, and Hist. Nat. 

 des Anim. s. vert. 1815. 



2 CUVIER in his Tableau e"lementaire (1798) and in the tables at the end of the first 

 part of his Lecons d'Anat. c'omp. 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 Acalephce. 

 Here also he placed the Actiniae, which however in the second edition of his Eegne 

 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 uber muthmassliche Nessdorgane der Medusen, WIEGMANN u. ERICH- 

 SON Archiv. f. Naturg. 1841, I. s. 38 42 ; Ueber den Bau der Pelagia noctiluca. 

 Leipsig, 1841, fol. Icon. Zoot. Tab. xxxiu. Subsequently these parts were also inves- 

 tigated by EHRENBERG, PHILIPPI, WILL, MILNE EDWARDS &c. 



7 2 



