THE FUNCTIONS OF PROTOPLASM AND CELLS 



51 



division too. Cell division is described in Chap. 5, reproduction in 

 Chap. 14. 



Fig. 31. — Fibrillar structure of 

 cilium of Stylonychia. {From Del- 

 linger in Journal of Morphology.) 



I'lG. 30. - Locomotion in an amoeb;i with sevcM :il psoudopodia, which rest on the substratuni 

 only at their tips. (From Dellinger in Journal of Experimental Zoology.) 



Protoplasmic Movement. — One of the attributes of living organisms 

 usually distinguishing them from nonliving matter, is the power of 

 independent motion. Most animals at some stage in their existence, 

 many plants of the lower orders, and the 

 swarm spores of other low plants are 

 motile. Higher plants are not capable of 

 locomotion, but within their cells the 

 protoplasm may undergo movement. 



In many cells the protoplasm frequently travels as if in channels, 

 particle following particle, carrying plastids, food vacuoles, and cell 



inclusions along with it. When 

 an amoeba (a one-celled animal) 

 moves, it thrusts out one or more 

 lobelike processes, called pseudo- 

 podia. Then the body is pulled 

 forward or flows forward. Some- 

 times there is only one pseudo- 

 podium, and the amoeba just 

 flows along. In other kinds of 

 amoeba there are several pseudo- 

 podia at one time, and only their 

 tips touch the substratum, in 

 which case the animal may almost 

 be said to walk (Fig. 30). A 

 pseudopodium is extended appar- 

 ently because of a local increase 

 of viscosity in the outer layer of 

 protoplasm at some part of the 

 cell, carrying with it a slight contraction which forces the protoplasm else- 

 where to protrude; but how the change in viscosity is effected is not clear. 



Fig. 32. — Form of cilium during strokes; 

 forcible stroke at left, return stroke at right. 

 Numbers show successive positions, indicate 

 direction of movement. 



