62 



GENERAL PRINCIPLES OF ZOOLOGY. 



interstices of which are filled with other material (interfilar sub- 

 stance, enchylema, ground substance). The dispute lies especially 

 around the question whether this framework is formed of threads 

 and trabeculae or whether the appearance is not formed by small 

 chambers, bounded by fine partition-walls (foam structure of 

 protoplasm). 



Movement of Protoplasm. Movement expresses itself first in 

 changes of form of the whole body amoeboid movement and 



secondly in the change of position 

 of the small granules in the interior 

 of the protoplasm streaming of 

 granules. Examples of amoeboid 

 movement (fig. 16) are chiefly the 

 movements of many Protozoa, and 

 of the colorless blood-cells (leuco- 

 cytes) of multicellular animals; 

 here the protoplasmic body sends 

 out coarser and finer processes, 

 which may be again withdrawn, 

 serving for locomotion and hence 

 called pseudopodia or false feet. 

 The streaming of granules can be 

 observed in the interior of the cell- 

 body, as well as in the pseudopodia 

 (After extending from this. The pseudo- 



^fan Tyiav pvpri v, p qft fl T1p a . | n u p 

 podia may evei 



at the limits of visibility with our 

 strongest magnifications (fig. 17), yet in them it can still be 

 observed that the granules wander hither and thither like people 

 on a promenade, simultaneously centripetally and centrifugally, 

 some with greater, others with less speed. And yet the granules 

 are only passively moved by the protoplasm, for if we feed the 

 creature with some pigment granules, like finely-pulverized car- 

 mine, these granules show the same remarkable streaming. Indeed 

 nothing better illustrates the great complexity in the structure 

 of protoplasm than these extremely complicated phenomena of 

 motion in such narrow limits as pseudopodia in general. 



Irritability of Protoplasm. That amoeboid movements and 

 streaming of granules can be induced, brought to a standstill, and 

 modified by mechanical, chemical, and thermal stimuli, is a sure 

 proof of the irritability of protoplasm. Most important are the 

 thermal stimuli; if the surrounding medium rise above the 



FIG. 16. Amoeba proteus. 



Leidy.) efc, ectosarc; en, entosarc ; 

 cv, contractile vacuole ; w, nucleus ; 



^ fo 



