390 ON THE NUMBER OF POLAR BODIES AND [VI. 



two polar bodies of the animal ^%g are not identical — although 

 externally they are extremely similar, and although they arise 

 in a precisely similar manner — I am even more inclined than 

 before to consider that the very various ' polar bodies ' of plants 

 possess very different meanings. 



But I do not feel justified in criticizing in detail the results 

 of botanical investigation. I must leave the decision of such 

 questions to botanists, and I only desire to state distinctly that 

 a ' reducing division ' of the nuclei of germ-cells must occur in 

 plants as well as in animals. 



V. Conclusions with regard to Heredity. 



The ideas developed in the preceding paragraphs lead to 

 remarkable conclusions with regard to the theory of heredity, 

 — conclusions which do not harmonize w^ith the ideas on this 

 subject which have been hitherto received. For if every ^gg 

 expels half the number of its ancestral germ-plasms during 

 maturation, the germ-cells of the same mother cannot contain 

 the same hereditary tendencies, unless of course we make the 

 supposition that corresponding ancestral germ-plasms are re- 

 tained by all eggs — a supposition which cannot be sustained. 

 For when we consider how numerous are the ancestral germ- 

 plasms which must be contained in each nucleus, and further 

 how improbable it is that the}?' are arranged in precisely the 

 same manner in all germ-cells, and finally how incredible it is 

 that the nuclear thread should always be divided in exactly the 

 same place to form corresponding loops or rods, — we are driven 

 to the conclusion that it is quite impossible for the 'reducing 

 division ' of the nucleus to take place in an identical manner in 

 all the germ-cells of a single ovary, so that the same ancestral 

 germ-plasms would always be removed in the polar bodies. 

 But if one group of ancestral germ-plasms is expelled from 

 one ^g%^ and a different group from another ^%g^ it follows that 

 no two eggs can be exactly alike as regards their contained 

 hereditary tendencies : they must all differ. In many cases the 

 differences will only be slight, that is, when the eggs contain 

 very similar combinations of ancestral germ-plasms. Under 

 other circumstances the differences will be very great, viz. 

 when the combinations of ancestral germ-plasms retained in 



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