THE ECTOPLASM 



postulated for these activities in free-living Amoebae. 

 But even were there only one accepted theory of the 

 cause of amoeboid movement in free-living Amoebae, there 

 would still remain the necessity to prove that such a theory 

 could apply to white blood cells in the blood-stream of 

 warm-blooded animals. It would be more advantageous 

 further to study the white blood-cells themselves. Since 

 amoeboid movement and capacity for engulfing solid par- 

 ticles reside in the ectoplasm,^ the study of primary im- 

 portance for the elucidation of these phenomena exhibited 

 by human white blood-cells relates to the ectoplasm of the 

 various types of these cells and to each of them in their 

 different physiological states in health and in disease. 



This cursory review dealing mostly with vertebrate 

 tissue-cells by no means pretends at exhaustion. Tho- 

 roughly to treat the subject of ecto-endoplasmic differentia- 

 tion as found in cells of multi-cellular animals would 

 demand a volume in itself. But the review shows that 

 from sponges to man tissue-cells exhibit ecto-endoplasmic 

 differentiation; that the ectoplasm gives rise to processes 

 which interlock with other cells; that the ectoplasm may be 

 cast off to form inter-cellular substance; that it enters 

 largely into the formation of contractile cells (muscles) ; that 

 it is the conductive material par excellence of nerve-cells and 

 that cells, as amoeboid blood cells, in their locomotor 

 capacity indicate ectoplasmic action. 



Ecto-endoplasmic differentiation is by no means confined 

 to the tissue-cells of multicellular animals. Very early in 

 the history of the study of Protozoa, it was recognized that 

 in these unicellular organisms the superficial cytoplasm is 

 marked off structurally from the interior. Indeed, nowhere 

 else in the animal kingdom is the ectoplasm so sharply 

 defined by so rich and various sculpture. 



^ Metschnikoff on amoeboid cells of sponges, iSjg. 



87 



