ON THE ORIGIN OF DEATH. II 5 



of the germ-plasm be accepted, there is no difficulty in 

 understanding why heredity should occur. Ancestors, 

 parent, and offspring are all a part of the same stuff. 



Now in regard to variation, and why it should occur. 

 Every individual is the result of the union of the male 

 and female germ-cells, and Weismann holds that the 

 minor characters are due to the manner in which these 

 cells are mixed. He assumes that these cells are of 

 the most complex molecular structure, so that when 

 they unite it is impossible that exactly the same arrange- 

 ment of the molecules should be repeated. Put a hand- 

 ful of currants into two loaves of bread, and after 

 baking see whether there is exactly the same number 

 and arrano-ement in the fifth slice of each. The chances 



O 



against this are enormous. 



All variations which occur in nature, — size and shape 

 of the features, organs, stature, color of skin or hair, 

 — depend on the molecular combinations formed in 

 the union of the two germ-cells. If a single germ-cell 

 should develop without so uniting with another, the 

 young would be the exact duplicate of its parent, for 

 it would be composed solely of the germ-material of 

 which its parent was composed. 



In essence the male and female germ-cells are identi- 

 cal. Each is potentially capable of producing an em- 

 bryo by itself, if the proper physical conditions could 

 be secured. Weismann says that if it were possible 

 to bring about the conjugation of two ova, fertilization 

 would be accomplished, and development pursue its nor- 

 mal course. Indeed, this, or something very similar, 

 has been done. Boveri succeeded in removing the 

 nucleus of an echinoid ovum, and then induced this 



