in his experiments on echinoderms, found that "the characteristics of the hybrid offspring depend directly on the relative degrees of maturity of the sexual products". Professor Ewart's experiments on rabbits pointed to a similar conclusion. The condition of the soma and changes in Habitat also
^ haves been usually supposed to cause variations but it is questionable whether these become impressed on the germ-cells in such a way as to be transmissible to the next generation.
With regard to intersub-crossing and inter-breeding Professor Ewart's conclusion was "that intersub-crossing though a direct cause of retro-gressive variation, is only an indirect cause of progressive variation, while inter-breeding (in-and-in breeding) at the right moment is a cause of progressive variations". And after discussing the swamping effects of inter-crossing he claims to have shown "(1).that progress in a single direction is probably often due to new varieties swamping old, it may be long established varieties; and (2) that sexual varieties may be sufficiently exclusive to flourish side by side in the same area, and eventually (partly owing to their aloofness, i.e., to differential mating) give rise to severalsexual new species".
