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 

 barcode body op Polystometta after shell probably resulting from the disintegration of 



HAS BEEN DISSOLVED IN ACID. a. Nucleus -, . . . , , . , . . 



(200 diameters). 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 frustules 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 



