THE LIVING SUBSTANCE. 



87 



[91] The true nature and mode of formation of cell walls seem 

 to be that they are but pellicular modifications of the continuous 

 substance of masses into plates, or membranes, which are as 

 readily formed internally as externally ; that they do not differ 

 either in origin or constitution from other internal and external 

 physiological pellicles or ectosarcal formations ; that they are, 

 in short, not substance dividers nor substance isolators, but 

 substance structures, substance differentiators, ajid differentiations, 

 substance organs; and finally, that they belong primarily to the 

 mass and but secondarily to cells. 



[92] We can no longer regard these formations as having for 

 the living substance the value of a prison wall. We must rather 

 look upon them as substance strengtheners ; as devices for 

 securing a qualified independence for areas which yet maintain 

 absolute physical and physiological continuity. They limit to 

 some extent the areas surrounding centres of control distributed 

 through the mass. By such "centres" I mean the nuclei, which 

 would seem to control the supply and the use of specific 

 environment of the substance as such. 



The pellicular membrane which surrounds cells is no better 

 reason for thinking of these cell areas as isolated, independent, 

 reproductions of the original unit, than is the nuclear membrane 

 for calling that organ an intra-plasmic cell. 



[93] Notwithstanding this reasoning, Metazoan develop- 

 ment may still remain to our thought a multiplication of cells, 

 but must cease to be to it, as of old, that multiplication of 

 morphological units which Huxley preached. // is rather sub- 

 division of the substance, with or zvithoiit growth of mass, than 

 a reproduction of the first egg cell. Cell division is mass differ- 

 entiation ; that is its true meaning, — making it one with all 

 the host of substance ojganizations of the elements of the living 

 substance for physiological finction. 



Passing in review in the light of all my facts those colonial 

 and compound organizations of living substance found in both 

 Protozoa and Metazoa, it becomes evident that so long as there 

 is between the units composing it, a protoplasmic connection, 

 even the most delicate, a whole colony must be conceded the 

 value of a morphological unit, and each so-called cell, or unit, of 



