CXXXii THE VOYAGE OF H.M.S. CHALLENGER. 



which in the absence of sunlight are able to evolve oxygen by the aid of the phosphoresence of 

 other abyssal animals. Since the PH^EODAEIA are, for the most part, dwellers in the deep-sea, and 

 since the voluminous phaeodium must be of great physiological importance, a positive solution of 

 this hypothetical question would be of no small interest (compare 89). 



206. Respiration. The respiration of the Radiolaria is animal in nature, since all 

 Protista of this class, like all other true Rhizopoda, take in oxygen and give off carbon 

 dioxide. Probably this process goes on continuously and is tolerably active, as may be 

 inferred from the fact that Radiolaria cannot be kept for long in small vessels of sea- 

 water unless either they contain numerous Xanthellse or the water is well aerated. The 

 oxygen is obtained from two sources, either from the surrounding water or from the 

 enclosed Xanthellse, which in sunlight evolve considerable quantities of this gas. 

 Correspondingly, the carbon dioxide which is formed during the process of oxidation of 

 the Radiolaria is either given up to the surrounding water or to the inquiline Xanthellae, 

 which utilise it for their own sustenance ( 204, 205). 



The significance of the symbiotic Xanthellaj for the respiration of the enclosing liadiolaria may 

 be shown experimentally in the following way. If two Polycyttarian colonies of equal size, both of 

 which contain numerous Xanthellse, be placed in equal quantities of filtered sea-water in sealed 

 glass tubes, and if one tube be placed in the dark the. other in the light, the colony in the former 

 rapidly perishes, but not that in the latter ; the Xanthellce excrete only under the influence of 

 sunlight the oxygen necessary for the life of the Eadiolarian (compare Patrick Geddes, L. N. 42, 

 p. 304). 



207. Circulation. In the protoplasm of all Radiolaria, both inside and outside the 

 central capsule, slow currents may be recognised which fall under the general term 

 circulation, and have already been compared to the cyclosis in the interior of animal 

 and vegetable cells, as well as to the sarcode streams in the body of other Rhizopoda. 

 These plasmatic currents or "plasmorrheumata" probably continue throughout the whole 

 life of the Radiolaria, and are of fundamental importance for the performance of their 

 vital functions. They depend upon slow displacements of the molecules of the plasma 

 (plastidules or micellae) and cause a uniform distribution of the absorbed nutriment and a 

 certain equalisation of the metastasis. Furthermore they are of great importance also in 

 the inception of nutriment, the formation of the skeleton, locomotion, &c. Sometimes 

 the circulation is directly perceptible in the plasma itself ; but usually it is only visible 

 owing to the presence of granules (sarcogranula), which are suspended in the plasma in 

 larger or smaller numbers. The movements of these granules are usually regarded as 

 passive, due to the active displacement of the molecules of the plasma. Although the 

 intracapsular protoplasm is in communication with the extracapsular through the 

 openings in the capsule membrane, nevertheless the currents exhibit certain differences 



