CYTOMORPHOSIS 39 



a cell has begun to develop in one direction it cannot start 

 out to develop in any other direction. In the higher animals, 

 on the contrary, we find a relatively large egg which has become 

 large through the storing up in it of yolk or nutritive material. 

 The developing ovum can nourish itself for a long time from 

 this yolk. In this type of development we encounter not 

 larvae but embryos which are characterized thereby that they 

 contain many cells of the embryonic or undifferentiated type. 

 These cells assume definite groupings to form the rudiments 

 or anlages of the various organs. So that we may say that 

 the anatomical development progresses without there being 

 a corresponding alteration in the structure of the single cells. 

 Thus we observe in the human embryo the stomach, or other 

 organ, which shows the essential characteristics of its total 

 form and of its relations to other parts of the body, and yet 

 consists of cells not differentiated. In my opinion we are 

 justified in regarding the embryonic development as a con- 

 trivance to make the postponement of a cytomorphosis pos- 

 sible, in order that the total number of cells available for 

 differentiation shall be larger. Of the great importance of 

 the number of cells we can get some notion by considering the 

 cortex of the brain. The number of pyramidal cells in the 

 cerebral cortex of man is over 4,000,000,000. This number 

 is not astonishing; a cubic millimeter of blood contains be- 

 tween four and five million corpuscles. 



The purpose of differentiation is known. Every living 

 cell certainly carries on all the essential functions of life. In 

 the higher organisms we encounter a division of labor. 

 Each organ takes over as its special task one or another 

 function, which the organ performs to the advantage of the 

 whole. These functions are not new; they are always such 

 as are common to the living substance in general, and in 



