14 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
“ Archiv. f. Naturgeschichte,” 1851, b. i.; McCrady, 
“ Descriptions of Oceania, etc.,” “ Proceedings of the 
Elliot Society of Natural History,” vol. 1, 1859; 
L. Agassiz, “Contributions to the Acaliphe of 
North America,” “Memoirs of the American 
Academy of Arts and Sciences,” vol. iil, 1860, 
vol. iv., 1862; Leuckart, “Archiv. f. Naturge- 
schichte,” Jahrg. 38, b. 11, 1872; Hensen, “ Studien 
tiber das Gehororgan der Decapoden,” “ Zeitchr. i. 
wiss. Zool.,” bd. xiii., 1863 ; Semper, “ Reisebericht,” 
“ Zeitschr. f. wiss. Zool.,” bd. xiii. vol. xiv.; Claus, 
“Bemerkungen iiber Clenophoren und Medusen,” 
“Zeitschr. f£. wiss. Zool.,’ bd. xiv., 1864; Allman, 
“Note on the Structure of Certain Hydroid 
Meduse,” “Brit. Assoc. Rep.,” 1867; Fritz Miiller, 
“ Polypen und Quallen von 8S. Catherina,” “ Archiv. 
f. Naturgesch.,” Jahrg. 25, bd. 1, 1859; also “ Ueber 
die Rand-blaischen der Hydroidquallen,” “ Archiv. 
f. Anatomie und Physiologie,” 1852; Haeckel, 
“Beitrige zur Naturgesch. der Hydromedusen,” 
1865; Eimer, “Zoologische Untersuchungen,” Wiirz- 
burg, “ Verhandlungen der Phys.-med. Gesellschaft,” 
N.F. vi. bd., 1874. 
The most important of these memoirs for us to 
consider are the two last. I shall subsequently 
consider the work of Dr. Eimer, which up to this 
date was of a purely physiological character. Pro- 
fessor Haeckel, who made his microscopical obser- 
vations chiefly upon the Geryonidee, described the 
nervous elements as forming a continuous circle all 
round the margin of the umbrella, following the 
course of the radial or nutrient tubes throughout 
