EEPORT ON THE RADIOLARIA. Cxli 



The vibratile movement of the swarm-spores is the result of active sinuous oscillation 

 of the single or multiple flagellum, and is not essentially different from that of ordinary 

 flagellate Infusoria (see note A). Of the active swimming of mature Radiolaria, only 

 that form is known which is vertical in direction and causes the sinking and rising in 

 the sea-water. This is probably, for the most part (perhaps exclusively), due to 

 increase or diminution in the specific gravity, which is perhaps brought about by the 

 retraction or protrusion of the pseudopodia ; slow, oscillating, sinuous motions of these 

 organs have been directly observed to take place (though very slowly) in suspended 

 living Radiolaria. The most important hydrostatic organ is probably the calymma, by 

 the contraction of which the specific gravity is increased, while it is diminished by its 

 expansion ; the contraction is probably brought about by active contraction of the 

 sarcodictyum, and is connected with exosmosis, while the expansion is probably due to 

 the elasticity of the calymma and the inception of water by endosmosis. In the 

 Acanthometra (96) the peculiar myophriscs 'appear to be charged with the duty 

 of distending the gelatinous envelope, and thus diminishing the specific gravity ; the 

 latter increases again when the myophriscs are relaxed, and the calymma contracts by 

 virtue of its own elasticity (see note B). The slow creeping locomotion exhibited by 

 Radiolaria on a glass slide under the microscope, does not differ from that of the 

 Thalamophora (Monothalamia and Polythalamia), but can only occur normally when the 

 animal accidentally comes into contact with a solid surface or sinks to the bottom of the 

 sea. Whether this actually occurs periodically is not known (see note C). The slow 

 or gliding locomotion exhibited by creeping Monozoa on a glass slide is due to muscle- 

 like contractions of bundles of pseudopodia, just as in the case of the social central 

 capsules of Polyzoa, which live together in the same ccenobium and are able to move 

 within their common calymma sometimes centrifugally to its surface, sometimes towards 

 the centre where they aggregate into a roundish mass (see note D). 



A. Begarding the movement of the flagella in mature swarm-spores compare L. N". 22, p. 375; 

 L. N. 26, pp. 31, 35; L. K 41, p. 452, and L. K 52, p. 170. 



B. On the active vertical swimming movements of mature Eadiolaria, especially the cause of 

 sinking and rising, see L. N. 16, p. 134; L. N. 41, p. 443, and L. K 52, pp. 97-102. 



C. On the active horizontal creeping movements of mature Eadiolaria on a firm ground, compare 

 L. N. 12, p. 10, and L. N. 16, pp. 132-134. 



D. Eegarding the motion of social central capsules within the same ccenobium and the changes 

 thus brought about in the structure of the calymma, see L. N. 16, pp. 119-127, and L. K 52, 

 pp. 75-82. 



221. Contraction. Motions, which are due to the contraction of individual portions 

 and cause changes in volume or form, have been partly already spoken of under the 

 head of locomotion ( 220) and are partly connected with other functions. Examples 

 may be seen in the contraction of the central capsule and of the calymma. A certain 



