STRUCTURE OF THE MEDUS&. is 
present in the Medusz is one which has long 
occupied the more or less arduous labours of many 
naturalists. The question attracted so much in- 
vestigation on account of its being one of unusual 
interest in biology. Nerve-tissue had been clearly 
shown to occur in all animals higher in the zoolo- 
gical scale than the Medusz, so that it was of much 
importance to ascertain whether or not the first 
occurrence of this tissue was to be met with in 
this class. But, notwithstanding the diligent appli- 
cation of so much skilled labour, up to the time 
when my own researches began there had been so 
little agreement in the results obtained by the 
numerous investigators, that Professor Huxley— 
himself one of the greatest authorities upon the 
group—thus defined the position of the matter in his 
“Classification of Animals” (p. 22): “ No nervous 
system has yet been discovered in any of these 
animals.” 
The following is a list of the more impor- 
tant researches on this topic up to the time 
which I have just named:—Ehrenberg, “Die 
Acalephen des rothen Meeres und der Organismvs 
der Medusen der Ostsee,” Berlin, 1836 ; Kolliker, 
“Ueber die Randkorper der Quallen, Polypen und 
Strahlthiere,’ Froriep’s neue Notizen, bd. xxv., 
1843; Von Beneden, “Mémoire sur les Campanu- 
laires de la cdte d’Ostende,” “ Mémoires de 
Académie de Bruxelles,’ vol. xvi, 1848; Desor, 
“Sur la Génération Medusipare des Polypes 
hydraires,” “Annales d. Science. Natur. Zool.,” ser. iii. 
t. xii. p. 204; Krohn, “ Ueber Podocoryna carnea,” 
2 
