5 6 4 
THE LOWEST ANIMALS. 
Pyrocystis (magnified 100 diameters). 
enable one to see the time by a watch, at a distance of a foot or more. A few 
organisms swimming or floating about in plenty of sea-room in a tumbler of water, 
will not become luminous unless the water be 
shaken about, but when crowded together, they 
become diffusely luminous, owing to mutual 
jostling and irritation. The luminosity in an 
individual sphere, which should be inspected with 
a lens, may appear as a sudden, generally diffused 
flash, followed by darkness or by less intense 
light, or again, in the form of brilliant points of 
light. The name of the organism, which belongs 
to the flagellated infusorians, is Noctiluca. The 
body forms a peach-shaped cyst, about one-fiftieth 
of an inch in diameter, and with a tough mem¬ 
branous wall. A groove on the surface sinks at 
one end into a funnel leading into the interior. 
From the interior of the funnel there arises a large transversely striated flagellum, 
or proboscis, by means of which the animal swims, and there is also in the 
same place a fine wliip-like flagellum. At the apex of 
the funnel there is a mass of sarcode, which extends 
itself as a wide-meshed, highly-vacuolated network, to 
the inner wall of the cyst, where it forms a thin layer, 
whence the phosphorescence emanates. Noctiluca 
multiplies by dividing into two, or by becoming 
encysted, after drawing in its flagella, and breaking 
up into numerous ciliated helmet-shaped “ swarm- 
spores.” Frequently two organisms fuse into one which 
may then divide up into spores. Noctiluca is found 
only in waters near land, the related forms met with 
in the open ocean belonging to the genus Pyrocystis. 
In one of the species of the latter the body is spherical, 
about one-thirtieth of an inch in diameter, and without 
the big flagellum. The phosphorescence, which in each 
individual chiefly emanates from the nucleus, is dis¬ 
played on the ocean surface on calm nights in the 
Tropics. Prof. Butschli regards this species as an 
encysted or resting phase of the common form- 
Noctiluca occasionally swarms in such abundance as to 
give in daytime a reddish or yellowish hue to the 
surface. When the sea is rough, the organisms are 
dashed below the surface, and do not form a sufficiently 
continuous layer to give rise to much luminosity, and 
when the wind is off shore they are blown out to sea. 
Among the Flagellata are included certain parasitic organisms, which, owing 
to their being immersed in nutrient fluids, are not compelled to seek further for 
food, and do not possess flagella. The Gregarina, living in the intestine of the 
MUSSEL-ANIMALCULE (Stylo)iychici 
mytilus) under surface. 
a, Mouth : b, Contractile vacuole ; 
c, Nucleus. (Magnified 150 
diameters.) 
