slight differences of colour between allied species), cessation of selection is likely to be very soon assisted by a failure in the force of heredity; seeing that such newly added characters will not be so strongly inherited as are the more ancient characters distinctive of higher taxonomic groups. "Let us now turn to Weismann's view of degeneration. First of all, he has omitted to perceive that 'panmixia' alone (if unassisted either by reversed selection or an inherent diminishing of the force of heredity) cannot reduce a functionless organ to the condition of a _rudiment_. Therefore he everywhere represents panmixia (or the mere _cessation_ of selection) as of itself sufficient to cause degeneration, say from 100 to 5, instead of from 100 to 90 or 80, which, for the reasons above given, appeared (and still appears) to me about the most that this principle can accomplish, so long as the original force of heredity continues unimpaired. No doubt we have here what must be regarded as a mere oversight on the part of Professor Weismann; but the oversight is rendered remarkable by the fact that he _does_ invoke the aid of reversed selection _in order to explain the final disappearance of a rudiment_. Yet it is self-evident that the reversal of selection must be much more active during the initial than during the final stages of degeneration, seeing that, _ex hypothesi_, the greater the degree of reduction which has been attained the less must be the detriment arising from any useless expenditure of nutrition, &c.