STRUCTURE OF THE MEDUSZ. 15 
¢ 
their entire length, and proceeding also to the ten- 
tacles and marginal bodies. At the base of each 
tentacle there is a ganglionic swelling, and it is 
from these ganglionic swellings that the nerves just 
mentioned take their origin. The most conspicuous 
of these nerves are those that proceed to the radial 
canals and marginal bodies, while the least con- 
spicuous are those that proceed to the tentacles. 
Cells, as a rule, can only be observed in the gan- 
glionic swellings, where they appear as fusiform and 
distinctly nucleated bodies of great transparency 
and high refractive power. On the other hand, the 
nerves that emanate from the ganglia are composed 
of a delicate and transparent tissue, in which no 
cellular elements can be distinguished, but which is 
longitudinally striated in a manner very suggestive 
of fibrillation. Treatment with acetic acid, how- 
ever, brings out distinct nuclei in the case of the 
nerves that are situated in the marginal vesicles, 
while in those that accompany the radial canals 
ganglion-cells are sometimes met with. 
A brief sketch of the contents of these and other 
memoirs on the histology of the Medusze is given by 
Drs. Hertwig in their more recently published work 
on the nervous system and sense-organs of the 
Medusz, and these authors point to the important 
fact that before the appearance of Haeckel’s memoir, 
Leuckart was the only observer who spoke for the 
fibrillar character of the so-called marginal ring- 
nerve; so that in Haeckel’s researches on Geryonia, 
whereby both true ganglion-cells and true nerve- 
fibres were first demonstrated as occurring in the 
