THE MEDUSZ. 137 
The bodies of the meduse dilate and contract alternately. 
This double movement is the chief means by which they move. 
This was observed by the ancients, who compared it to the action 
of respiration in the human chest; hence their popular name of 
Sea-lungs. When they journey, their convex part is always fore- 
most, and their course slightly oblique. If, while they are thus 
swimming, they be touched ever so slightly, the umbrella con- 
tracts, the tentacles are folded, and the timid creatures sink into the 
depths. A careful examination of the marginal portions of the 
acalephz has discovered the presence of visual and auditory organs. 
M. Kolliker announced the existence of the first in his “ Océanie.” 
M. Gegenbauer has since found them in other classes (A/zzostoma, 
Pelagia), and he also perceived the presence of the second organs. 
The eyes consist of two small hemispherical masses—which are 
coloured and full of cells, in which are half-buried little crystalline 
globules—the exposed part of which is perfectly uncovered. The 
auditory apparatus is attached to these organs; it is composed of 
small vessels full of liquid. So nature produces eyes without eye- 
lashes or eyelids, and ears without openings. 
But the marvel of marvels is the process of the reproduction of 
these vagabond tenants of the waves. Ata certain time of year the 
medusz are full of eggs of most brilliant colours, suspended in large 
festoons over their floating bodies. These eggs are very small. 
In some species they appear hooked on to the body of the medusa, 
and do not detach themselves until they reach their full develop- 
ment. The larvae produced from these eggs do not bear the 
slightest resemblance to their mother. They are long, worm-like 
forms, thicker at one end, like microscopical leeches ; and they have 
scarcely-perceptible vibratory cils, whose movements are by no 
means slow. At a further stage of development they are found 
transformed into polypes with eight tentacles. This embryo medusa 
~-a truly wonderful creature—rejoices in the power of reproducing 
itself, by buds and shoots growing on the surface of its body, and 
also by filaments which sprout from it here and there. Thusa 
single individual may become, in a little time, a large colony. 
The polype in this process undergoes a remarkable transformation. 
It folds itself upon itself; its body becomes jointed, and appears 
