THE BIOLOGY OF THE CELL SURFACE 



appearance of the rays. These rays thus indicate structure 

 in the cytoplasm or at least the capacity of the cytoplasm 

 to form structures. 



So far I have dealt with the cytoplasm, the ground- 

 substance outside of the nucleus. I should remind the 

 reader that I consider the nucleus likewise as differentiated 

 ground-substance. The formation of intra-nuclear spindles 

 just referred to, the origin of centrosomes from nuclei, 

 sometimes described, can be interpreted on the same basis 

 as the formations in the cytoplasm. Nucleus and nuclear 

 constituents are themselves conceived as expressions of the 

 capacity of the ground-substance to form structures. 



In its other derivative, the ectoplasm, the ground-sub- 

 stance likewise exhibits capacity for structural formations. 

 Indeed, ectoplasmic structure in many cells, e.g., Protozoa, 

 is a diagnostic characteristic. I wish to consider this 

 peripheral ground-substance as it appears in animal cells. 

 But first I must discuss the question of the cell-membrane, 

 because it has obfuscated a proper appreciation of that part 

 of the cell beneath the membrane, the ectoplasm. 



The cell-membrane, like many another cell-structure, is a 

 perennial subject for debate. The majority opinion is that 

 cells are invested with membranes but the minority is as 

 insistent that a membrane is neither present nor necessary. 

 Of those in the camp of the majority, some hold that the 

 cell-membrane is an endogenous structure, a living thing 

 built by the cell; whilst others deny its life, considering it a 

 sort of excretion; and still others assert that it is a formation 

 induced by the cell's external medium. Opponents of the 

 membrane's existence declare that since the cell-substance 

 is in the colloid state, it is unnecessary to postulate the 

 presence of a membrane: the mere boundary of the colloidal 

 system is sufficient to preserve the cell's integrity. Accord- 

 ing to them the cell is somewhat like a drop of oil in water; 

 just as the surface of the oil keeps the oil intact, so does the 



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