412 PROF. TH. W. BNGELMANN. 



imbibition of important quantities of water between inotagmata 

 and inotagma groups. The motility, as already shown, increases 

 or diminishes with the quantity of this water. 



The preceding observations afford a first step only towards 

 explaining protoplasmic movement, in so far as they allow the 

 many different forms under which it appears and the changes 

 which it undergoes as a result of all kinds of influences, to be 

 referred to a single process, which itself requires further 

 explanation — the changes of form of inotagmata. 



Let us detail at least some of the most important cases in 

 this connection. 



1. Formation of Spheres by Naked Protoplasm on 

 Excitation. 



This clearly must follow from the simultaneous assumption 

 of a spherical form by inotagmata, in so far as therewith the 

 surface attraction which they exert over one another, and thus 

 the cohesion of the entire mass, must be equally observable 

 everywhere and in all directions. 



A good proof of the correctness of the latter conclusion 

 exists in the sudden assumption of a spherical form by the air- 

 bubbles in the protoplasm of Arcella upon electrical excita- 

 tion. As in so doing the volume of the air-bubbles under- 

 goes hardly any diminution, it is evident that the assumption 

 of the spherical form cannot be a consequence merely of a con- 

 traction of the peripheral layer of the protoplasm, as is often 

 thought. The force with which this approximation to the 

 spherical form is brought about depends essentially upon the 

 force with which the inotagmata change their form, and upon 

 the average amount of the cohesion of the protoplasm ; and as 

 the latter decreases as the amouut of imbibition water increases, 

 the force must, as a general rule, decrease as the amount of 

 the water increases. As a matter of fact, in very thin fluid 

 protoplasm, e.g. many plasmodia, the force of gravity is suffi- 

 cient to prevent the drawing together to form a sphere. 



The formation of varicosities, the retraction or fusion with 

 one another of fibre-like or flattened processes (pseudopodia 



