276 A. EARL AND ON RADIOLARIA. 



to the ca23sule membrane. In shape they agree with the extra- 

 capsular xanthellpe ; but their size is greater, averaging -01 to 

 •03 mm. They are probably a distinct species of Alga. 



The Radiolaria have other sources of nutriment besides the 

 xanthelloe and their by-products, for the amount of food 

 extracted from the surrounding water by means of their 

 pseudo-podia must be large. Diatoms, infusoria, foraminifera, 

 and particles of decaying animal and vegetable matter, are seized 

 l.)y the pseudopodia and conveyed to the sarcodictyum and thence 

 to the sarcomatrix, there to be assimilated. The insoluble portions, 

 such as the diatom valves and calcareous shells of foraminifera, 

 are often to be found here in large numbers. They are eventually 

 removed by the streaming of the sarcode. 



Currents in the sarcode body, commonly known as streaming 

 of the protoplasm, are continuous throughout the life of the 

 Radiolaria. They are, as a rule, only visible owing to the 

 motion thereby imparted to solid particles of matter imbedded 

 in the sarcode, but sometimes the plasma itself may be seen to 

 circulate. The currents are only visible under exceptional 

 circumstances within the central capsule, although we may 

 presume that the sarcode here is also in continual motion. They 

 may be readily observed in the pseudopodia, and can be followed 

 through the sarcodictyum and sarcoplegma to the sarcomatrix, 

 and thence occasionally through the openings in the capsule 

 membrane to the central capsule. The flow of the current is 

 radial in direction, and sometimes the same pseudopodial thread 

 shows reverse currents on its opposite sides. The rapidity of 

 the currents varies greatly. They must be of great importance 

 in the economy of the animal, not only for the inception of 

 food and dispersal of waste products, but also for locomotion and 

 perception. 



The powers of motion in the mature Radiolarian, as opposed to 

 the free-swimming zoospore, are very limited. It is practically 

 certain that they float freely suspended in the water either near 

 the surface or at definite zones of depth. This is due to the 

 equilibrium existing between the organism and the surrounding 

 water. The increase of specific gravity due to the formation of 

 the skeleton is counterbalanced by the secretion of oil and fat 

 globules, and perhaps also by the formation of alveoles in the 

 sarcode. The radial spines and the pseudopodia radiating in all 



