PROTOPLASMIC MOVEMENT. 377 



of many Myxomycetes, and in the protoplasm of numerous 

 vegetable cells. Special vacuoles filled with fluid in which 

 such movements take place are by no means always or even 

 frequently to be discovered. The whole plasma appears rather 

 to have little more cohesion than a thin fluid at such spots. 

 At the surface of very thin protoplasmic threads the extent to 

 which the granules move is greater than in the more hyaline 

 axis. Such fibres, moreover, very easily flow together, forming 

 " sheets " like ordinary mucous threads, while the hyaline layer 

 surrounding protoplasmic masses does not readily do so. 



That the flowing together does not, or at least does not 

 always, depend only upon the prior cohesive power of the sub- 

 stance is well shown in that the pseudopodia of difi'erent 

 individual E-hizopods,^ as well as the processes of plasmodia 

 belonging to diff'erent species ^ never fuse with one another. 



Doubtless the above-cited diff'erences in cohesive power de- 

 pend essentially upon the diff'erences in the amount of imbi- 

 bition-water, which is shown by the refractive index varying 

 in direct proportion to the amount of cohesion. These diff'er- 

 ences in cohesive power are also artificially produced along 

 with corresponding changes of volume and refracting power by 

 means which cause swelling or shrinking. In mobile granular 

 protoplasm a separation of the fluid in the form of small droplets 

 frequently takes place — vacuole- formation. The proto- 

 plasm may in consequence acquire a frothy appearance. 



In resting protoplasm the form of the vacuoles is for the 

 most part perfectly globular. During movement they may 

 be much drawn out, but always return to their globular 

 form. 



This also holds good for the form of the gas-bubbles^ 

 which have been observed in some instances in protoplasm. 



* Max Schultze, 'Das Protoplasma der Hhizopoden und der PflanzenzelleD,' 

 p. 25, 1S63. 



^ Cieiikowsky, " Zur Eutwickelungsgeschichte der Myxomyceten," 'Jahrb. 

 f. wissensch. Bot.,' iii, p. 335, 1863 ; de Bary, ' Die Mycetozoen,' 2 Aufl., 

 p. 40, 1864. 



^ Th. W. Engelmarn, " Beitrage z. Physiol, d. Protoplasma," 'Arch. f. d. 

 ges. Pliysiol.,' ii, p. 307, 1809; ' Zool. Anz.,' i, p. 152, 1878. 



