AUTOMATIC MOVEMENTS 507 



changes involved, is very obsoin^e. Such phenomena are roughly 

 classed together under the name of automatism, or automatic 

 movement. 



We have seen that certain plants at particular times emit 

 from their body small masses of naked protoplasm which are 

 furnished with a varying number of long filaments. These 

 filaments, which are protoplasmic, are ordinarily in a state of 

 active vibration, causing currents in the water in which they 

 live, which float them quickly from place to place. Such free- 

 Svvimming cells include the zoospores of the Algss and the 

 antherozoids of these and higher plants. The movement is 

 brought about in the absence of any external stimulation, though 

 the cells are capable of receiving such impulses. The cause 

 of the movement is probably the contraction of each side of the 

 filament, or cilium, alternately, or of the part of the cell just at 

 its point of attachment. The impulse leading to the movement 

 must be sought in some decomposition originating in the 

 protoplasm itself, and not excited by any stimulus from without. 

 The phenomenon is often spoken of as dlia/ry m,otion. 



Of a somewhat similar character is the curious creeping 

 movement of the Myxomycetous fungi. Each of the zoospores 

 of these organisms consists of a mass of naked protoplasm 

 which makes its way over the surface of its substratum by 

 putting out blunt processes of its own substance, known as 

 pseudopodda. These are protrusions of the ectoplasm, and the 

 more fluid eudoplasm is in some way drawn into them, so that 

 the rest of the cell follows the movement of the pseudopodium. 

 Which part of the operation really corresponds to the act of 

 contraction is disputed, but it seems probable that it is the 

 second, and that the first protrusion is of the nature rather of 

 relaxation. In either case, however, the movement is indepen- 

 dent of any external stimulation. 



The Diatom,s, which we have seen to form a sub-class of the 

 Algae, are capable of a curious gliding movement, which enables 

 them to make their way with some rapidity through the water 

 in which they live ; they also are found to do this in the absence of 

 any apparent stimulus ; the Oscillatoriee, which are filamentous 

 algae anchored to a substratum by one end of the filament, are 

 also in constant wavy motion to and fro ; a movement the 

 mechanism of which is still unexplained, and which possibly 

 resembles that of the diatoms. These are instances of the same 

 automatism, the protoplasm in all probability originating the 

 movement and carrying it out. 



