10 THE PHENOMENA OF LIFE 



envelope. In their relation to the life of the cell they are certainly hardly 

 second in importance to the cytoplasm itself, and thus Beale is fully justified 

 in comprising both under the term "germinal matter." The nuclei control 

 the nutrition of the cell, and probably initiate the process of subdivision. If 

 a cell be mechanically divided so that a portion of it possesses the nucleus 

 while other portions have no nucleus, that portion containing the nucleus will 

 live and develop while the parts without nucleus soon die. Concerning this 

 interesting question of the relation of the nuclei and cytoplasm in the cells, 

 Schafer summarizes as follows: "There are cells and unicellular organisms 

 both animal and vegetable, in which no reticular structure can be made out, 

 and these may be formed of hyaloplasm alone. In that case, this must be 

 looked upon as the essential part of protoplasm. So far as ameboid phenom- 

 ena are concerned it is certainly so; but whether the chemical changes which 

 occur in many cells are effected by this or by spongioplasm is another matter." 



Protoplasmic nuclei are highly differentiated chemically as well as func- 

 tionally. They contain special structures which react in a characteristic 

 chemical way to staining solutions, and to other chemical treatment. This 

 differential structure is emphasized in Chapter II. There the morphological 

 changes through which the nuclei pass in cell multiplication are given in 

 greater detail. It is the study of these changes that supplies the basis of fact 

 for many of our present conceptions of the physiological importance of 

 nuclei. 



Differentiation and Growth of Organized Protoplasm. The detail of cellu- 

 lar division of protoplasm is more fully given in Chapter II. The morphologi- 

 cal fact to which attention is called here is that as we proceed upward in the 

 scale of life from the unicellular organisms, another phenomenon is exhibited 

 in the life history of the higher forms, namely, that of development. The 

 one-celled ameba comes into being derived from a previous ameba; it mani- 

 fests the properties and performs the functions of its life which have been 

 already enumerated. In the higher organisms it is different. Each, indeed, 

 begins as a single cell, but the cells which result from division and subdivision 

 do not form so many independent organisms but adhere in one differentiated 

 community which ultimately forms the complex but co-ordinated whole, in 

 man the human body. 



Thus from the ovum or germ cell which forms the starting-point of an 

 individual animal during development, there is rapidly formed a number of 

 tissues each characterized by its own type of structure, the whole laid down in 

 an orderly manner to form the complicated individual. In the unfolding 

 of this individual growth process, the developing ovum soon forms a complete 

 membrane of cells called the blastoderm, and this speedily differentiates into 

 two and then into three layers, chiefly from the rapid proliferation of the cells 

 of the first single layer. These layers, figure 10, are called the Epiblast, the 

 Mesoblast, and the Hypoblast. In the further development of the animal 



