AMCEBA AND SOME ALLIES: PROTOZOA 281 



complicated substance without which life cannot exist. The 

 principal organ of the cell is the nucleus, composed of pro- 

 toplasm more dense than that which surrounds the nucleus. 

 Frequently zoologists distinguish the protoplasm of the 

 nucleus, nudeoplasm, from that of the cell-body or cytoplasm. 

 The nucleus is usually quite difficult to see unless the amoeba 

 is killed by chemicals and 



its protoplasm "fixed" and ^-,. ^|fcj 



stained. The cytoplasm is ^ : 9j^^^ 



finely granular all through, VSIflfli 



except for a thin layer on lii|Sfe:>....--;:"-'- N I.SSR! 



the surface, which is always /^ip-fSSSS^F'S-v;-;:? 4lS*l-/ 



clear and without granules. Sk ^^~ : ^^SS^S?Q' 



The granular part of the ^^S^ 



cytoplasm is called endo- 



plasm, and the non-granular 



sheath the ectoplasm. FlG - 14(X Amceba ' Much enlar ed 



During locomotion the < From Sedgwick and Wilson's General 

 . , , Biology) 



pseudopodia are first formed 



of the ectoplasm, the endoplasm following immediately and 

 continually in the same direction that the ectoplasm takes. 

 The method of locomotion in Amoeba, as stated by Professor 

 H. S. Jennings, of the University of Pennsylvania, is as 

 follows. " Locomotion in Amoeba is a process that may be 

 compared with rolling, the upper and lower surfaces contin- 

 ually interchanging positions. This is shown by observation 

 of the movements of particles attached to the outer surface 

 or imbedded in the ectosarc [ectoplasm] of the animal. Such 

 attached particles move forward on the upper surface and 

 over the anterior edge, remain quiet on the under surface 

 till the body of the amoeba has passed, then pass upward at 

 the posterior end, and forward on the upper surface again. 

 Single particles may thus be observed to make many com- 

 plete revolutions." 



