[24] The cultures were begun in 1884 and are still continued (March 6, 1902), still multiplying as abundantly as at the outset. I reckon that there are on an average five generations in a year, which means about eighty generations in sixteen years. 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 effect 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 effects 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 difference 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 reproduce 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.