final causes, which have been sounded from the days of Spinoza to the present time; but there is a problem here which science can not leave in abeyance. The facts are undoubted, and the natural causes must be sought. The parts of the flowers are adapted to the forms and habits of the insects; the insects are adapted to the work of fertilizing the plants; the question is, How are these two things secured? The inquiry which has awakened general interest as to the development of species in the history of distinct orders such as orchids, insects, pigeons, and dogs, must strive to complete its work, by pressing on to this more complicated question concerning the adaptation of distinct organisms to influence and aid each other in the work of development. In what way science may deal with this question, and how far it may be able to advance in the search for an answer, it may be difficult to decide. For it is much easier to indicate the logical necessity for an advance, than to say in what manner the advance is to be accomplished. The one is a simple question of logical requirement; the other must be a matter of continued observation, and scientific inference. Whether science may yet discover an answer; or whether it may prove true at this point, as at other points already mentioned, that science has here reached clear marks of its own limits, must be left to the future, to be determined by those devoted to scientific research. As long, however, as this question of interdependence remains without a scientific explanation, it must be obvious that there are important facts which seem to imply some modification of the theory of descent, or evolution of species by means of selection, under the severe struggle for existence. Or, to put it from another point of view, nature has marvellously provided for mitigation of the struggle for existence, by contrivances providing both for vegetable and animal life; therefore the theory of the origin and development of life which depends chiefly on the struggle for existence must be adjusted to allow for a theory of the effects arising from the natural provision for obviating the struggle, and providing for a large increase of life. Quite beyond this, as a matter entirely distinct, is the question as to the primordial forms of existence in the history of plants and insects. As to this, science may be able to give very little testimony, as it is a question of the remote past, on which present facts may afford little evidence. Still, beyond these primordial forms, in a region which science can not enter, there lies the question of origin, of actual beginning, creation of life, as to the reality of which science can speak only indirectly by discovery of its own limits, in the terms of its _ultimatum_, nature has provided that such and such things shall be.