104 TOILERS IN THE SEA. 



as universally scattered, not only in tropical regions, 

 but to the North and South Poles, where their limit 

 has not yet been found amongst the eternal ice, in 

 which their skeletons are imbedded. The richest 

 development of forms, and the greatest number of 

 species, undoubtedly occur between the tropics, whilst 

 the frigid zones exhibit great masses of individuals, 

 in but comparatively few genera and species. "The 

 surface of the open ocean seems everywhere, at a 

 certain distance from the coast at least, to be peopled 

 by crowds of living Radiolaria." Thomson and 

 Murray were convinced, as one of the results of their 

 experience, that " these animals exist at all depths 

 of the ocean, and that there are large numbers of 

 true deep-se species which are never found on the 

 surface or at slight depths." It has been admitted 

 'that the great majority of species, which have hitherto 

 been observed, have been obtained from the bottom 

 of the deep sea, and more than half of all the species 

 have been derived from the pure Radiolarian ooze, 

 which forms the bed of the Central Pacific, at depths 

 of from 2,000 to 4,000 fathoms. 



The Geological Distribution of Radiolaria is also 

 remarkable, since they are found in all the more 

 important groups of the sedimentary rocks of the 

 earth's crust. The great majority belong to the 

 Cainozoic or Tertiary period, and, in fact, to its 

 middle portion, the Miocene period. To this period 



