3534 THE LOWEST ANIMALS 



Pacific, over areas comprising in all about fifty millions of square miles, the ocean 

 bed is formed of Globigerina ooze. Chalk is mainly composed of the skeletons of 

 Globigerinidce, coccoliths, etc., and, in fact, resembles Globigerina ooze. 



The question whether the Globigerinidce, which make up the bulk of the 

 ooze, live at the bottom as well as at the surface, has given rise to much discus- 

 sion. Dr. Murray has come to the conclusion that pelagic species do not live near 

 the ocean floor. His opinion is partly based on the fact that the area of Glo- 

 bigerina ooze coincides with the area of surface temperature at which Globigerinas 

 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 

 SARCODE BODY OK Polystomella AFTER probably resulting from the disintegration of 

 SHELI, HAS BEEN DISSOLVED IN ACID. volcanic remains, pumice, etc. , and almost devoid 



a. Nucleus (200 diameters). 



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 Radio- 

 laria, and is termed Radiolarian ooze. Beyond the northern and southern bound- 

 aries 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 Himalayas, 



