CHAPTER XXV 

 PHENOMENA AND PRINCIPLES OF BREEDING 



Kinds of reproduction. In the simplest forms of animal life 

 reproduction is by self-division, the separating parts being (nor- 

 mally) equally developed. As the scale of life ascends and organ- 

 isms become larger and more complex, division into equal parts 

 becomes detrimental or impossible, and the organism at maturity 

 reproduces by a series of divisions, at each of which there is thrown 

 off from the parent body a part such as that body itself was at an 

 earlier stage of development. Still higher in the scale, with life 

 and its functions growing more complex, reproduction takes place 

 only when the elementary bodies from two mature bodies unite at 

 (or very near) the time of separation from the parent organisms. 

 With the evolution of the sexual from the asexual method of re- 

 production we are not here concerned. Such facts as the funda- 

 mental similarity of the forms of reproduction and the necessity 

 of the higher organisms for diverse parentage, which gave rise to 

 sex, are elementary in the study of the principles of breeding. 



Likeness in asexual reproduction. In the self -division of 

 simple animal forms the maxim of the breeder " Like produces 

 like " is, according to our observation, exacdy applicable. The or- 

 ganism resolves itself into like and equal parts. In forms a ..little 

 higher up, the organism resolves itself into parts unequal in size 

 and development, the larger and more advanced part producing a 

 succession of smaller parts without change in itself, then dying, 

 the others (such as survive) growing to maturity and producing 

 and perishing in the same manner. 



Relations of body and germ. The higher we go in the scale 

 of life, and the more complex the structure of the animal becomes, 

 the greater the difference, both in size and appearance, between 

 the fully developed organism and the part which separates from 

 it in reproduction, until in creatures which reproduce sexually the 

 germs are (as compared with the body) very minute and of the 



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