This knowledge helps us to understand, then, the phenomenon of phosphorescence. It is visible only at night because in the full glare of day the greater light overpowers the lesser; it is visible at certain times and seasons because the conditions are such as to evoke it. And what is favorable for the lighting up of a single bacterium is favorable for all; hence the myriad multitudes of infinitesimal units, each set glowing with its tiny light, are sufficient in the sum total to put a whole ocean aflame. It would, of course, be presumptuous, and doubtless erroneous, to say that all the phosphorescence of the sea is due solely to photo-bacteria; it can only be asserted in the present state of our knowledge that they are certainly responsible for a great share of it. But this wonder of nature must now be regarded as yet another instance of the mighty results accomplished through the agency of the smallest of living things. THE JELLY-FISH AND OTHER HYDROZOA --P. MARTIN DUNCAN If anybody were asked to name the commonest objects on a sandy or pebbly seashore, the reply would be--sea-weed, crabs, limpets, a stranded jelly-fish, looking like so much blubber, and a sea-gull flying overhead. The first three things really belong to the shore; the bird is a visitor that is looking after food, and the large, turned-upside-down, basin-shaped, jelly-looking mass is a waif from the ocean. If one of these stranded jelly-fish is looked at, as it lies on the sand, its shape appears to be something like that of an umbrella without the stick. It is thick, however, and has some curious markings about its surface and inside. Even something like a fringe of thick hairs may be detected around the edge. On trying to take it up or turn it over, the fingers go into it, so readily does the animal tear; but on getting the umbrella on its back, the underneath part is seen to be made up, in the middle, of some projections slightly more solid than the rest of the body; and if put between them, the finger passes through a sort of tube into a cavity in the body, which is the stomach.