a?HE GENERAL SIGNIFICANCE OF AMPHIMIXIS 331 



laying a hundred eggs in a single bud. How does it happen that 

 'the mutual influence of two different hereditary substances which 

 so powerfully promotes individual development ' can be here altogether 

 dispensed with 1 Only because it does not really exist, except in the 

 imagination of my opponents, still influenced by the old dynamic 

 theory of fertilization. 



But it may be asked, whence come the injurious results of 

 inbreeding, if not from the union of two nearly related germ-plasms ? 

 They certainly do arise from that cause, but it is not through 

 a 'formative stimulus,' too slight in this case, exercising a direct 

 formative chemical eflfect upon the two hereditary substances, but 

 through the indirect influences exerted by these too similar hereditary 

 contributions during the development of the new individual. Lest 

 it be imagined that I am tilting against windmills, I will refer to one 

 of the numerous examples of the evil eff'ects of inbreeding which 

 have been submitted to me as specially corroborative of the conception 

 of amphimixis as a 'formative stimulus' whose strength depends upon 

 the difierence between the germ-substances. The renowned breeder, 

 Nathusius, allowed the progeny of a sow of the large Yorkshire breed, 

 imported from England when with young, to x-eproduce by inbreeding 

 for three generations. The result was unfavourable, for the young- 

 were weakly in constitution and were not prolific. One of the last 

 female animals, for instance, when paired with its own uncle — 

 known to be fertile with sows of a different breed — produced a 

 litter of six, and a second litter of five weakly piglings. But when 

 Nathusius paired the same sow with a boar of a small black breed, 

 which boar had begotten seven to nine young when paired with sows 

 of his own breed, the sow of the large Yorkshire breed produced in the 

 first litter twenty-one and in the second eighteen piglings. 



How could this really remarkable difference in the fertility of the 

 sow in question be the result of a formative stimulus, exercised by the 

 sperm-cells of the unrelated boar upon the ova of the female animal ? 

 If the progeny of the sow had been more fertile than herself, then 

 we should have been at least logically justified in concluding that 

 this was the case, but it is not intelligible that the egg-cells of this 

 mother sow should be increased twice or three times because they 

 were fertilized by a new kind of sperm as they glided from the ovary. 

 The number of ova which are liberated from the ovary depends in the 

 first instance upon the number of mature ova contained in it; and 

 unless we are to make the highly improbable assumption that the 

 crossing with the strange boar had as an immediate result the 

 maturing of a large number of ova, we must look elsewhere than 



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