206 PART III. PHYSIOLOGY. [ 47 



47. The Spontaneous Movements may be conveniently 

 considered under the two heads of movements of protoplasm, and 

 movements of cellular members. 



A. Movements of Protoplasm. Under this head are included 

 such spontaneous movements as can be directly observed in the 

 protoplasm. The first to be noted is the streaming movement, 

 which can be frequently observed either in naked protoplasm (e.g. 

 plasrnodia of Myxomycetes), or in the protoplasm of ccenocytes 

 clothed by a cell-wall (e.g. hyphse of Fungi), or in that of cells 

 (e.g. leaf of Elodea and Vallisneria, internodal cells of Characeae, 

 root-hairs of Trianea bogotensis, hairs of the stamens of Trades- 

 cantia, etc.). The movement takes place in the more fluid por- 

 tion of the protoplasm, and is made evident by the granules of 

 various kinds which are carried along by the current. The 

 direction of the movement varies somewhat according to circum- 

 stances : the current travels in one direction, and this simple 

 longitudinal movement is all that can be observed in plasmodia 

 and in hyphse ; but in cells, owing to their shortness, it can be 

 observed to travel up one long side, across the end, and down the 

 other side ; and when the cytoplasm forms not merely a parietal 

 layer, but forms strands traversing the vacuole (e.g. Fig. 36 Z>), 

 currents can be observed in these strands also. 



The contractile vacuoles are small, more or less nearly spherical, 

 cavities which make their appearance in the protoplasm and 

 then suddenly disappear. In their relatively slow expansion 

 (diastole), they become filled with cell-sap, which is forced out 

 on the sudden contraction (systole). They have been exclusively 

 found in motile organisms, such as the Volvocineae, the plasmodia 

 of Myxomycetes, the zoospores of many Algae and of some Fungi. 



In the second place the protoplasmic movements which involve 

 locomotion have to be considered. The simplest case of this is the 

 amoeboid movement exhibited, among plants, by the zoospores of 

 the Myxomycetes and of some Algae, and by the naked masses of 

 protoplasm which constitute the plasmodia of the Myxomycetes. 

 There is here no specialised motile organ, but any part of the 

 protoplasm may be protruded as a pseudopodium into which the 

 remainder of the protoplasm gradually flows, and thus locomotion 

 of the whole is effected. 



The locomotory movements of most zoospores, of spermatozoids, 

 and of entire organisms such as Volvox, Pandorina, etc., is effected 

 by means of specialised motile organs, which are delicate proto- 



