262 A. EARLAND ON RADIOLARIA. 



social Eacliolarians, in which the central capsule often contains ;c 

 single large oil globule, which may occupy a third of its diameter. 

 The oil globules are usually colourless and highly refractive, but 

 occasionally they are yellow, brown, rose-coloured, or even a deep 

 blood-red in colour. Physiologically they are of the greatest 

 importance. Firstly, they diminish the specific gravity of the 

 organism, thus neutralising the increase of the specific gravity 

 due to the growth of the skeleton. Secondly, they are probably 

 used as a reserve store of nutriment. In this latter respect 

 it may be noted that in the process of spore formation each 

 flagellate spore usually contains a fat granule. 



Intra-capsular Pigment Bodies. 



Most living Padiolarians have the central capsule coloured. 

 The colour is always due to the formation of definite pigment 

 granules, sometimes distributed evenly through the endoplasm, 

 sometimes aggregated in one spot. They vary in dimensions, but 

 are usually too small to be measured, appearing under even a 

 high power as fine dust. Their chemical constitution is unknown. 

 The commonest colours are yellow, red and brown ; violet and 

 blue are rare, green still rarer. Sometimes a definite tone of 

 colour obtains through the members of a whole group, and the 

 same colour is usually constant in individuals of a species. 



Intra-capsular Crystals. 



Crystals are frequently found in the central capsule, and are 

 of two kinds, small and large. The small or " spore crystals,"^^ 

 which are widely distributed among the Porulosa, are rod-like or 

 spindle-shaped bodies, consisting of an organic substance which 

 probably serves as a reserve of nutriment for the developing 

 spore, since each swarm spore often contains a crystal. The 

 large crystals, on the other hand, have only been observed in a 

 few of the social Radiolarians (Polycyttaria), and are probably to- 

 be regarded as excretory products. 



IXTRA-CAPSULAR CoNCRETIOXS. 



Concretions of diflferent shapes and constitution are found in 

 the endoplasm of a few Radiolaria. They are usually circular or 



