148 Organisms from Eggs 



planting the anlage of a foreleg to different parts of 

 the body. No matter into which part of the body they 

 are transplanted the mesenchyme cells for the foreleg 

 will give rise to a foreleg only; even if they are trans- 

 planted into the spot from which the hindlegs grow out 

 under natural conditions. There is therefore nothing 

 to indicate "regulation." 



The same is true for the formation of the eye and 

 probably in general. We have to consider the forma- 

 tion of the various organs of the body as being due to 

 the development of specific cells in definite locations 

 in the organisms which will grow out into definite 

 organs no matter into which part of the organism they 

 are transplanted. It is at present unknown what 

 determines the formation of these specific anlagen. 

 They may lie dormant for a long time and then begin 

 to grow at definite periods of development. We shall 

 see later that we know more about the conditions which 

 cause them to grow. 



7. The fact that the egg, and probably every cell, 

 has a definite structure should determine the limits of 

 the divisibility of living matter. In most cases the 

 complete destruction of a cell means the cessation of 

 life phenomena. A brain or kidney which has been 

 ground to a pulp is no longer able to perform its func- 

 tions; yet we know that such pulps can still perform 

 some of the characteristic chemical processes of the 

 organ; e. g., the alcoholic fermentation characteristic 



