THE VITAL PROPERTIES OF THE CELL 69 



directions." Further, the rate of movement may vary in different 

 places, or it may gradually alter ; it may be so great that under 

 a powerful lens the granules appear to travel so fast that the eye 

 can scarcely follow them ; on the other hand, it may be so small 

 that the granules scarcely appear to change their place. 



The second kind of movement consists of a change of form in 

 the individual threads and in the network as a whole. As in 

 the Arncebd, processes are protruded and withdrawn from various 

 places, a mass of homogeneous protoplasm being first protruded, 

 into which the granular protoplasm flows later on. Occasionally, 

 when the streaming movements are very powerful, it appears as 

 though the granular endoplasm is pressed forcibly into the newly 

 formed processes. By this means the plasmodium can, like the 

 Amceba, crawl slowly along over a surface in a given direction; 

 new processes are continually being protruded from the one edge, 

 towards which the endoplasm chiefly streams, whilst others are 

 withdrawn from the opposite one. 



Gromia oviformis (Fig. 40) is a classical object amongst the 

 Reticularia, for the study of protoplasmic movements (see p. 29). 

 If the little organism has not been disturbed in any way, a large 

 number of long fine threads may be distinguished stretching out 

 from the protoplasm, which has made its way out of the capsule, 

 and spreading themselves out radially in every direction into the 

 water; here and there lateral branches are given off, and oc- 

 casionally all the threads are united together into a network by 

 such branches. Even the most delicate of these threads exhibit 

 movements. As Max Schultze (1. 29) aptly describes it, " a glid- 

 ing, a flowing of the granules which are imbedded in the threa' 

 substance," may be seen with a high power; ''they move alol^N 

 the thread, more or less quickly, either towards its periphery or 

 in the other direction ; frequently streams flowing in both direc- 

 tions may be seen at the same time even in the finest threads. 

 When granules are moving in opposite directions, they either 

 simply pass by each other, or else move round one another for a 

 time, until after a short pause they either both go on in their 

 original directions, or one takes the other along with it. All the 

 granules in a thread do not move along at the same rate ; hence 

 sometimes one may overtake another, either passing it or being 

 stopped by it." Many evidently pass along the outermost surface 

 of the thread, beyond which they can be plainly seen to pro- 

 ject. Frequently other larger masses of substance, such as spindle- 



