HEREDITY. 



13 



absence of tail will be shown by the embryo at a stage, on 

 which the cooperation of the lacking gene would be necessary 

 for a growing out of the vertebral column, or in the case of the 

 rats, we can doubtless demonstrate the aberration at a stage 

 of the development, at which normally the lacking genes would 

 be necessary for a normal development of the internal ear. 

 The order in which an organism's characters are unfolded is 

 one of structural necessity, it is given in the combination of the 

 inherited factors present in the zygote and the non-inherited 

 factors of the environment. If a church- tower is constructed out 

 of materials donated by the parishoners, it matters not at all 



in what order these ma- 

 terials arrive. It may be 

 that thegilded weather- 

 vane and the tiles for 

 thereof areamongst the 

 first articles got toget- 

 her. First the stones 

 must be used for the 

 heavy foundations and 

 buttresses. Only after 

 the walls have reached 

 a certain height can the 

 lighter bricks be used 

 for the upper part. 

 Not before the walls 

 are ready can the 

 wooden super-struct- 

 ure be built, and the 

 tiles will have to wait 



Fi g- 1- until the steeple is 



Diagram to illustrate the effect of presence . *, 



or absence of some genes on the action of ready to receive them. 

 others, which modify the result of cooperation Jjj some circles we 

 of the first ones to the development. 



meet with the remark- 

 able question, whether the inherited or the environmental 

 factors in the development are the more important. Especially 



