Lateness, then, in the average age of reproduction appears to be the principle underlying longevity. There does not appear at first sight to be much connection between such distinct and apparently disconnected phenomena as 1, the orderly normal progress of development; 2, atavism and the resumption of feral characteristics; 3, the more ordinary resemblance _inter se_ of nearer relatives; 4, the benefit of an occasional cross, and the usual sterility of hybrids; 5, the unconsciousness with which alike bodily development and ordinary physiological functions proceed, so long as they are normal; 6, the ordinary non-inheritance, but occasional inheritance of mutilations; 7, the fact that puberty indicates the approach of maturity; 8, the phenomena of middle life and old age; 9, the principle underlying longevity. These phenomena have no conceivable bearing on one another until heredity and memory are regarded as part of the same story. Identify these two things, and I know no phenomenon of heredity that does not immediately become infinitely more intelligible. Is it conceivable that a theory which harmonises so many facts hitherto regarded as without either connection or explanation should not deserve at any rate consideration from those who profess to take an interest in biology? It is not as though the theory were unknown, or had been condemned by our leading men of science. Professor Ray Lankester introduced it to English readers in an appreciative notice of Professor Hering's address, which appeared in _Nature_, July 18, 1876. He wrote to the _Athenaeum_, March 24, 1884, and claimed credit for having done so, but I do not believe he has ever said more in public about it than what I have here referred to. Mr. Romanes did indeed try to crush it in _Nature_, January 27, 1881, but in 1883, in his "Mental Evolution in Animals," he adopted its main conclusion without acknowledgment. The _Athenaeum_, to my unbounded surprise, called him to task for this (March 1, 1884), and since that time he has given the Heringian theory a sufficiently wide berth. Mr. Wallace showed himself favourably enough disposed towards the view that heredity and memory are part of the same story when he reviewed my book "Life and Habit" in _Nature_, March 27, 1879, but he has never since betrayed any sign of being aware that such a theory existed. Mr. Herbert Spencer wrote to the _Athenaeum_ (April 5, 1884), and claimed the theory for himself, but, in spite of his doing this, he has never, that I have seen, referred to the matter again. I have dealt sufficiently with his claim in my book, "Luck or Cunning." {43} Lastly, Professor Hering himself has never that I know of touched his own theory since the single short address read in 1870, and translated by me in 1881. Every one, even its originator, except myself, seems afraid to open his mouth about it. Of course the inference suggests itself that other people have more sense than I have.