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



Chapter YIIL— ANIMAL FUNCTIONS. 



(§§ 218-225.) 



218. Motion. — In addition to the internal movements wliich appear generally in the 

 unicellular Radiolaria and have already been mentioned as plasmatic currents in treating 

 of the circulation (§§ 207—209), two different groups of external motor phenomena are 

 to be observed in this class : first, the contraction of individual parts, which brings about 

 modifications of form (§ 220), and secondly, voluntary or reflex locomotion of the whole 

 body (§ 220). These movements are partly due to changes in form of undifferentiated 

 plasmatic threads or sarcode filaments, partly to the actual contraction of differentiated 

 filaments which are comparable to muscle fibrlUse, and must therefore be distinguished 

 as myophanes. In addition to this, endosmose and exosmose probably play an important 

 part in some of the locomotive phenomena, but nothing is yet certainly known regarding 

 these osmotic processes. AVe are at present equally ignorant whether all the movements 

 of the Eadiolaria are simply reflex (direct consequences of irritation) or whether they 

 are in part truly spontaneous. 



219. Suspension. — From direct observation of living Eadiolaria, as well as from 

 deductive reasoning, based upon their morjahology (and especially their promorphology, 

 §S 17—50), the conclusion appears justified that aU Protista of this class in their normal 

 condition float suspended in the sea-water, either at the surface or at a definite depth. 

 A necessary condition of this hydrostatic suspension is that the specific gravity of the 

 Eadiolarian organism must be equal to, or but slightly greater than that of sea-water. 

 The increase in specific gravity brought about by the production of the siliceous skeleton, 

 is compensated by the lighter fatty globules, and partly perhaps by the calymma, 

 especially when the latter contains vacuoles or alveoles. The fluid or jelly contained in 

 the latter appears to be for the most part lighter than sea-water (containing no salt, or 

 only a very small quantity ?). But if the specific gravity of the whole body should 

 be generally (or perhaps always) slightly greater than that of sea-water, then the 

 organism would be prevented from sinking, partly by the increased friction, due to the 

 radiating pseud opodia and the radial spines usually present, and partly perhaps by 

 active (if only feeble) movements of the pseudopodia. 



220. Locomotio7i. — Active locomotion of the whole body, which is very probably to 

 be regarded as voluntary, occurs in the Eadiolaria in three different modes; (l) the 

 ■vdbratile movement of the flagellate swarm-spores ; (2) the swimming of the floating 

 organisms ; (3) the slow creeping of those which rest accidentally upon the bottom. 



