1324 THE STORY OF THE UNIVERSE 



plenty of fresh air, and they exhibit their characteris- 

 tic light; deprive them of one or the other and they 

 no longer shine. 



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 doubt- 

 less erroneous, to say that all the phosphorescence of 

 the se,a 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 accom- 

 plished 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 ob- 

 jects 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, 



