210 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
In 1810 a paper was presented to the Royal Society of London 
by a man named McCartney, setting forth the causes of the light 
or phosphorescence of the sea. He goes over some of the older 
theories which had been advanced to account for the phenomenon. 
Some had thought that the light was due to “ putrefaction,” because 
it had been known that dead matter might become luminous. Others 
thought that the light of the sea was electric, because it was excited 
by “ friction.” Others thought that it was “ phosphoric,” that the 
element phosphorus was present in the sea, which phosphoresced 
as it does on a match. Others thought that the sea imbibed light 
which it afterwards gave off, much as will a phosphorescent mineral 
like calcium sulphide. 
Finally McCartney decided that the phosphorescence of the sea 
was due to animals living in it, and this is the correct explanation. 
Every phosphorescence of the sea is due to one or another form, 
usually microscopic, but many visible to the naked eye. I think few 
people realize how many luminescent organisms there are. If we 
examine the different groups of animals, we find that at least 40 
different orders contain one or more forms producing light, and at 
least two groups of plants are luminescent. The two plants which 
produce light are the fungi and the bacteria. All the phosphores- 
cence of wood is due to fungi, and all the phosphorescence of dead 
meat or fish in refrigerators, and other dead matter is due to bacteria. 
These luminous bacteria are very widespread and grow readily on 
an appropriate culture medium. 
Not only bacteria and fungi, but sponges, jellyfish, comb jellies, 
hydroids, sea pens, minute organisms in the water known as dino- 
flagellates and radiolaria, many kinds of marine worms and earth- 
worms, centipedes, brittle stars, several mollusks, many kinds of 
shrimp and crabs, and many kinds of cuttlefish or squid as well as 
true fish produce light. The number of luminescent species runs into 
the tens of thousands. 
In some squid (Watasenia) the ends of the tentacles contain 
luminous organs, and as the squid swims through the water, it waves 
these tentacles around and flashes them much as the firefly does. 
This form is found in Japan and is called “ hotaru ika,” or firefly 
squid. 
Another kind of squid (Heteroteuthis) from the Italian coast, 
throws out luminous secretion into the sea water. It lives in the 
depths of the sea, in perpetual darkness. The luminous secretion 
is manufactured in a gland corresponding to the ink sac that in 
surface squid produces the ink. According to the direction of evolu- 
tion this gland has produced the blackest known fluid in cuttlefish, 
or a fluid not only transparent but one shining with its own light in 
Heteroteuthis. It is startling enough to see a cuttlefish surround 
