278- A. EARLAND ON RADIOLARIA. 



great abundance of forms in the tropics cannot be due entirely 

 to the increase of temperature, for quite half of the Radiolaria 

 live normally at abyssal depths where the temperature remains 

 constantly just above the freezing point. The more favourable 

 conditions of life produced by the large supply of food obtainable 

 from the decaying animal and vegetable matter suspended in the 

 water, is probably answerable for the richness of the Kadiolarian 

 fauna in the tropics. 



Having no power of horizontal motion, the Kadiolaria are 

 entirely at the mercy of oceanic currents. Such cui-rents occur 

 not only at the surface, but also at all depths of the sea, and as 

 a result we find that a great many Kadiolaria, probably the 

 majority, have a very wide range of distribution. A large 

 number of species are practically cosmopolitan, being found in 

 all the great oceans. The class reaches its greatest development 

 in the Pacific, both as regards variety of species and individual 

 numbers. The only extensive areas of Kadiolarian ooze known 

 occur in the deepest portions of the central and northern Pacific, 

 and the dead shells form a considerable proportion of the 

 calcareous oozes and red clays from the shallower areas of this 

 ocean. 



The Kadiolaria do not appear to be confined to the surface 

 water, as was at one time believed, for the researches of the 

 Challenger and other expeditions have proved the existence of 

 a distinctly abyssal Kadiolarian fauna, connected with the pelagic 

 species by intermediate zones of life. It seems probable that 

 J70ung individuals inhabit deeper water than the adult form. 



The pelagic Kadiolaria float normally at or near the surface, 

 and probably never descend below thirty fathoms. At a certain 

 distance from the shore the surface of the ocean appears to 

 swarm with living Kadiolaria. In the tropics the crowd consists 

 of many different species, but in colder seas, the individuals, 

 though equally numerous, present less variety. The great bulk 

 of these pelagic Kadiolaria belong to the first and second legions, 

 the Porulosa. There are very few pelagic Osculosa, and these 

 belong principally to the third legion, the Nassellaria, as the 

 fourth Legion, the Ph^odaria, have very few representatives 

 among the pelagic forms. Pelagic Kadiolaria may usually be 

 distinguished by the more delicate and slender structure of their 

 .skeletons. The pores of the lattice shells are larger and the 



