62 



GENERAL PIUNCIPLES OF ZOOLOOT. 



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

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

 around the question whether this framework is formed of threads 

 aud trabecular or whether the appearance is not formed by small 

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

 protojjlasm). 



Movement of Protoplasm. — Movement expresses itself first in 

 changes of form of the whole body — amosboid movement — and 



secondly in the change of position 

 of the small granules in the interior 

 of tlie protop)lasm — streaming of 

 granules. Examples of amoeboid 

 movement (fig. 10) 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 jirocesses, 

 which may Ije again withdrawn, 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 j^seudopodia 

 Fig, k. ~ Amreha pmtniK. (After extending from this. The pseudo- 



Leidy.) c/r, ectosarc : en, entcsarc ; i ■ . „ v xi j. i 



CD, contractile vacuole; A, nucleus i podia may even be SO fine as to be 

 j\^ food-vacuoies, ,^(. ^j^g jj^^j^g ^,f visibility with our 



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

 observed that the granules wander hither and thither like peop)le 

 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 arno^lioid movements and 

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

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

 proof of the irrital)ility of protoplasm. jMost important are the 

 thermal stimuli; if the surrounding medium rise above the 



