f a
mouth leading to a short digestive cavity, and having close beside it
a filament, by means of which it probably moves about. The sphere is
filled with protoplasm, in which there is a nucleus and one or more
gaps, or "vacuoles." Such is nearly all the structure that can be
discerned with the aid of the microscope in this simple organism.

Nevertheless, this lowly form is the chief cause of that diffused
phosphorescence which is sometimes seen over a wide extent of the
ocean. How innumerable the individuals belonging to this species must
therefore be, may be left to the imagination. Probably the Noctiluca
is not rivalled in this respect even by miscroscopic unicellular algae
which compose the "red snow."

By filtering sea-water containing Noctilucae its light can be
concentrated, and it has been found that a few teaspoonfuls will then
yield light enough to enable one to read holding a book at the
ordinary distance from the eyes--about ten inches.

A singular and highly remarkable case of diffused marine
phosphorescence was observed by Nordenskioeld during his voyage to
Greenland in 1883. One dark night, when the weather was calm and the
sea smooth, his vessel was steaming across a narrow inlet called the
Igaliko Fjord, when the sea was suddenly observed to be illumined in
the rear of the vessel by a broad but sharply-defined band of light,
which had a uniform, somewhat golden sheen, quite unlike the ordinary
bluish-green phosphorescence of the sea. The latter kind of light was
distinctly visible at the same time in the wake of the vessel. Though
the steamer was going at the rate of from five to six miles an hour,
the remarkable sheet of light got nearer and nearer. When quite close,
it appeared as if the vessel were sailing in a sea of fire or molten
metal. In the course of an hour the light passed on ahead, and
ultimately it disappeared in the remote horizon. The nature of this
phenomenon Nordenskioeld is unable to explain; and unfortunately he had
not the opportunity of examining it with the spectroscope.

If we come now to consider the more partial phosphorescence of the
sea, we find that it is due to animals belonging to almost every group
of marine forms--to Echinoderms, or creatures of the sea-urchin and
star-fish type, to Annelid worm, to Medusidae, or jelly-fish, as they
are popularly called, including the "great domes" and the "silvery
disks" of the passage above quoted from Professor Martin Duncan, to
T