THE RADIOLARIA 97 



temperature, cause contraction of the calymmal plasma. The pseudo- 

 podia are withdrawn, the vacuoles burst, and the animal descends 

 until the calmer zone enables it to reform its calymma and recharge 

 its vacuoles, upon which it ascends. No " contractile vacuoles " 

 are present, but their place is taken by these fluid-spaces in the 

 calymma. 



Food. The food of Thalassicolla consists of Copepods, Diatoms, 

 Infusoria, and probably also of Peridiniae. These organisms adhere 

 to the surface of the Radiolaria by contact with its sticky pseudo- 

 podia. They are subsequently enfolded by a plasmic web and 

 carried into the deeper part of the calymma. Here a digestive 

 vacuole is formed, and the ingested organism becomes converted 

 into a granular mass, which is disseminated, by division of the 

 digestive vacuole, throughout the ectoplasm. An accumulation of 

 debris may sometimes be found in the denser layer enveloping 

 the central capsule, and there is little doubt that the products of 

 digestion do not stop here but are carried into the endoplasm, for it 

 is known that a streaming movement occurs along the pseudopodia 

 that connect the inner and outer cytoplasm through pores in 

 the capsular wall. Once inside the capsule, the food material is 

 probably synthesised into the fatty or proteid masses that con- 

 stitute reserves. The endoplasmic globules of fat are usually 

 coloured with a pigment that varies according to the species of 

 Thalassicolla under consideration. The other reserves take a con- 

 cretionary form and recall starch grains in their stratified composi- 

 tion, though not in their reactions. They lie in vacuoles filled 

 with a proteid, and are still imperfectly known (Fig. 2, A, Cone.). 



Yellow Cells. The ingestion of solid food is, however, not 

 essential to the life of Thalassicolla for at least several months. If 

 kept in water that has been taken from the open sea and com- 

 pletely filtered, Thalassicolla will live for at least six months without 

 showing retrogressive changes beyond a shrinkage of calymmal 

 volume. Brandt, who has carried out experimental studies on 

 these organisms for many years, states (24) that if comparable 

 batches are maintained in such filtered water in darkness and in 

 light, the illuminated ones alone survive. He infers that Thalas- 

 sicolla under these conditions lives upon food which is in some way 

 elaborated under the influence of light ; and in point of fact such 

 a substance starch does exist in the ectoplasm. It occurs both 

 free in the capsular layer arid imbedded in the substance of certain 

 corpuscles which are scattered through the calymma and are 

 known as the "yellow cells." The significance of these cells or 

 " zooxanthellae " Is, in Brandt's view, a nutritive one. 



That these bodies are independent organisms living in association 

 with Thalassicolla and are not part of it was proved by Cienkowski (6). 

 They are spherical structures "015 mm. in diameter, and consist of 



