36 HUMAN BIOLOGY 



comparative study of the nuclei in Protozoa shows that the 

 nucleus is not an original organ of the primordial cell, but 

 developed gradually in its history, and very probably long 

 before the evolution from the primordial form of Hfe, the 

 protocyte, of the first animal and vegetable cells had begun. 

 This would thus explain why mitosis is so similar in both. 

 The non-nucleated animal and vegetable cells are very 

 probably variant special survivals of descendants of the 

 protocyte. 



There was no superficial envelope for the protocyte such 

 as we find enclosing protozoan and protophytan organisms of 

 today. The superficial layer of its mass could have been 

 but what the superficial layer of molecules formed, molecules 

 kept in position by cohesive or molecular forces as the super- 

 ficial molecules of a drop of water or of mercury are fixed 

 in their position through the action of surface tension forces. 

 Such an envelope is found in many protozoan forms 

 (Amoeba, Pelomyxa, etc.) in Myxomycetes (the slime 

 moulds) and in leucocytes, and it is through decrease at 

 points on the surface of the tension there that ameboid 

 movement occurs. The envelope is thus so labile, physically, 

 that the cell can take in solid food particles and even other 

 organisms. This type of surface may, because of its general 

 occurrence, be considered as primordial. 



It had not differentiated so far as to constitute local 

 condensations in its interior in the form of granules, spherules 

 or chromidia. The protocyte would then be uniformly 

 homogeneous in a microscopic sense as it is in the plasmodia 

 of slime moulds and in the symplasms (Lohnis) of bacteria. 



The protocyte must, therefore, have been a simple undif- 

 ferentiated cytoplasmic structure, but because of its consti- 

 tution, with potentialities for chemical transformation 

 and for variations in structure which explain the origin 

 and development of the cellular organisms which have 

 evolved from it. It must have been very minute, much 

 smaller in volume than the cell of today which we can see 

 with the microscope. Fragmentation of it, physically or 

 mechanically engendered, must have been the method by 

 which it multiplied and descendant forms arose and carried 

 on life. 



