THE DISCOPHOKES, OE LAEGE MEDUSAE. 
123 
change the very foam into u sparkles of sea-fire.” * The Me- 
dusa represented in our plate (. Pelagia cyanella) is eminently 
phosphorescent. We owe some of the best observations we 
possess on the subject to Spallanzani, who had the opportunity 
of studying a luminous species of Discophore on the coast of 
Sicily, and has given us in his “ Travels ” an interesting 
account of the results which he obtained. He found that the 
light was intermittent, sometimes continuing for a quarter of 
an hour, h^lf an hour, or more, and then being suddenly ex- 
tinguished, and not reappearing for a considerable interval. 
He was led to believe that the phosphorescence was manifested 
strongly only so long as the Medusa oscillated uninterruptedly, 
and faded when it passed into a state of rest. He also ascer- 
tained that the light was more vivid during the contraction 
than during the expansion of the disc, and that the principal 
seat of it was the edge of the swimming-bell and the large 
tentacles. This localisation of the phosphorescence has been 
noticed in many of the hydroid medusiform zooids. In one 
species the light kindles in the central proboscis alone, and re- 
sembles a little lamp suspended in a crystal globe. Amongst 
the fixed polypites the phosphorescence is fitful in its mani- 
festations ; they kindle their lights when irritated, and quench 
them when left to themselves. Of the mode in which the 
luminosity is produced, and its precise relation to the economy 
of the animal, we know little or nothing. 
The development of the Discophore is the next point which 
claims our attention; and though the remarkable series of 
facts first brought to light by the independent researches of Sars 
and Daly ell has become so familiar as to have lost much of 
its marvellous hue, the real interest of it is still fresh as ever ; it 
still reads like a romance to the uninitiated, while the naturalist 
has, perhaps, hardly fathomed its full significance. As I have 
mentioned, there is some variation in the course of develop- 
ment. I propose to follow the line which may be regarded as 
normal and characteristic of the tribe, and in doing so to take 
special note of the parallelism between the history of the Dis- 
cophore and of the Hydroid, and also of the points of divergence. 
The Medusa, then, as we have seen it, is fully equipped for 
the discharge of the reproductive function ; and at the proper 
season the laden ovaries yield up their contents, and the 
^embryos make their way from the generative chamber through 
the digestive cavity and its oral opening, and lodge themselves 
{how it is hard to say) amongst the ample folds of the tenta- 
* The phrase is Nathaniel Hawthorne’s, who had the keenest eye for all the 
aspects of nature, and who thus describes the phosphorescence, which he 
had witnessed from the deck of a steamer off the American coast. 
