STRUCTURE OF THE MEDUSA. lo 



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 

 IVoni 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, wdiile 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 marc^inal 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 Medusfe is given by 

 Drs. Hertwig in their more recently published work 

 on the nervous system and sense-organs of the 

 Medusae, 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 marojinal rino- 

 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 



