In our absolute ignorance of the source from whence life came, we have no ground for assuming that it was a purely planetary product, or that its unknown potentialities are concerned with purely planetary ends. It would be as rash for the biologist to assume that life on earth can only point to generations of further life on earth as it would have been for some cosmic geologist to assume--before the appearance of life on earth--that geological forces must needs constitute all the activity which could take place on this planet. Since the germ of life appeared on earth, its history has been a history not only of gradual _self-adaptation_ to a known environment, but of gradual _discovery_ of an environment, always there, but unknown. What we call its primitive simple irritability was in fact a dim panæsthesia; a potential faculty, as yet unconscious of all the stimuli to which it had not yet learnt to respond. As these powers of sensation and of response have developed, they have gradually revealed to the living germ environments of which at first it could have no conception. It is probable, to begin with, that the only environment which the vast majority of our ancestors knew was simply hot water. For the greater part of the time during which life has existed on earth it would have been thought chimerical to suggest that we could live in anything else. It was a great day for us when an ancestor crawled up out of the slowly-cooling sea;--or say rather when a previously unsuspected capacity for directly breathing air gradually revealed the fact that we had for long been breathing air in the water;--and that we were living in the midst of a vastly extended environment,--the atmosphere of the earth. It was a great day again when another ancestor felt on his pigment-spot the solar ray;--or say rather when a previously unsuspected capacity for perceiving light revealed the fact that we had for long been acted upon by light as well as by heat; and that we were living in the midst of a vastly extended environment,--namely, the illumined Universe that stretches to the Milky Way. It was a great day when the first skate (if skate he were) felt an unknown virtue go out from him towards some worm or mudfish;--or say rather when a previously unsuspected capacity for electrical excitation demonstrated the fact that we had long been acted upon by electricity as well as by heat and by light; and that we were living in an inconceivable and limitless environment,--namely, an ether charged with infinite energy, overpassing and interpenetrating alike the last gulf of darkness and the extremest star. All this,--phrased perhaps in some other fashion,--all men admit as true. May we not then suppose that there are yet other environments, other interpretations, which a further awakening of faculty still subliminal is yet fated by its own nascent response to discover? Will it be alien to the past history of evolution if I add: It was a great day