THE MODES OF REPRODUCTION 17 



CHAPTER II 



THE MODES OF REPRODUCTION 



A NECESSARY preliminary to the study of heredity 

 is a consideration of the elementary facts of repro- 

 duction. We cannot understand heredity unless we 

 know the conditions in which it works. The modes 

 of reproduction in the animal and vegetable king- 

 doms are various ; there is a great difference between 

 the reproduction of one of the higher animals and 

 that of a bacillus which reproduces itself by simple 

 fission, or splitting; but in each and every case 

 heredity is observed. The child of a man is human, 

 the child of a bacillus bacillary. 



In the most primitive modes of reproduction there 

 is no problem of heredity. We have no difficulty 

 in understanding why the daughter bacilli should 

 resemble their mother. They are their mother — 

 subdivided. In the case of those plants, again, 

 which propagate by separation of integral portions 

 of their own person, there is similarly no problem. 

 The new individual is simply a separated and ex- 

 tended portion of the old. Looking at such cases 

 we understand how reproduction may be looked 

 upon as neither more nor less than growth beyond 

 the limits of the individual organism. The laws of 

 this growth and the circumstances which determine 

 the limits of the individual organism are certainly 

 worthy of study, but they do not directly concern 

 the student of heredity. Therefore, though we shall 

 have occasion later to refer to the simplest modes of 



