SUN-ANIMALCULES. 
559 
are found to exist. When the surface water is too cold for surface Globigerinas, 
no Globigerina ooze is found below. Numerous species of Foraminifera, which 
live only at the bottom, and are never found 
at the surface, contribute a small percentage 
to the composition of the ooze, the bulk of 
which is, however, formed of organisms which 
have rained down from the surface. The 
deposits occurring in depths over two thousand 
five hundred fathoms do not contain calcareous 
matter. The rain of Foraminifera skeletons 
falls down from the surface as over the areas of 
lesser depth, but the shells are dissolved before 
they reach the bottom, apparently by the excess 
of carbonic acid in the deep zones of the ocean. 
Here the ooze is formed of red clay,—a material 
probably resulting from the disintegration of 
volcanic remains, pumice, etc., and almost devoid 
of organic traces. This deposit extends in its 
more or less unmixed condition over an area of about fifty-two millions of square 
miles, and is also present in varying proportions in Globigerina and other oozes. 
In from three to four thousand fathoms in the Eastern Indian Ocean and in part 
of the Central Pacific, over a total area of about two and a quarter millions 
of square miles, the deposit contains a large percentage of siliceous skeletons of 
Radiolaria, and is termed Radiolarian ooze. Beyond the northern and southern 
boundaries of the Globigerina ooze, in the Arctic and Antarctic Oceans the deposit 
consists of a fine, white, chalky-looking siliceous mud, with a green tinge in the 
shallower depths, mainly composed of the trustifies of Diatoms. 
The figured Polystomella, which belongs to the Nummulite group (so named 
because some of the species resemble coin - like discs), is cosmopolitan, ranging 
from the shore-zone to abyssal depths. Only the last convolution of the spiral 
series of chambers is visible, a section of the shell revealing one or two more 
coils completely invested by the outer; the radiating lines mark the divisions of 
the chambers, and on the last partition of the last chamber is seen a series of 
minute pores. The second figure shows the sarcode-body of a nearly related 
species, whose shell has been dissolved by acid; the nucleus (a) being visible in one 
of the segments. Nummulitic limestones which cover an immense tract, extending 
from the Pyrenees, along Southern Europe and North Africa, through Asia Minor 
to the Himalaya, are composed of the shells of an allied genus ( Nummulites ). 
As these rocks belong to the Tertiary epoch, and form some of the highest 
Himalayan peaks, they indicate how recently these mountains have been elevated. 
Sun- Animalcules,— Order Heliozoa. 
These animalcules are inhabitants of fresh water; their chief character¬ 
istic, and the one to which they owe their name, being the possession of long, 
slender, somewhat stiff pseudopods, which radiate from all parts of the spherical 
SARCODE BODY OF Polystomella AFTER SHELL 
HAS BEEN DISSOLVED IN ACID. «, Nucleus 
(200 diameters). 
