degrees, more and more perfectly led the bees to sweep equal spheres at a given distance from each other in a double layer, and to build up and excavate the wax along the planes of intersection; the bees, of course, no more knowing that they swept their spheres at one particular distance from each other, than they know what are the several angles of the hexagonal prisms and of the basal rhombic plates; the motive power of the process of natural selection having been the construction of cells of due strength and of the proper size and shape for the larvæ, this being effected with the greatest possible economy of labor and wax; that individual swarm which thus made the best cells with least labor, and least waste of honey in the secretion of wax, having succeeded best, and having transmitted their newly acquired economical instincts to new swarms, which in their turn will have had the best chance of succeeding in the struggle for existence."[6] And further, of instinct in general: "It will be universally admitted that instincts are as important as corporeal structures for the welfare of each species, under its present conditions of life. Under changed conditions of life, it is at least possible that slight modifications of instinct might be profitable to a species; and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that was profitable. It is thus, as I believe, that all the most complex and wonderful instincts have originated. As modifications of corporeal structure arise from, and are increased by, use or habit, and are diminished or lost by disuse, so I do not doubt it has been with instincts"; though Darwin adds: "But I believe that the effects of habit are in many cases of subordinate importance to the effects of the natural selection of what may be called spontaneous variations of instincts; that is, of variations produced by the same unknown causes which produce slight deviations of bodily structure." However, "No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous slight, yet profitable, variations."[7] And of habit as connected with heredity, Darwin writes: "Changed habits produce an inherited effect, as in the period of the flowering of plants when transported from one climate to another. With animals the increased use or disuse of parts has had a more marked influence.... No breeder doubts how strong is the tendency to inheritance; that like produces like is his fundamental belief; doubts have been thrown on this principle only by theoretical writers.... If strange and rare deviations of structure are really inherited, less strange and commoner deviations may be freely admitted to be inheritable. Perhaps the correct way of viewing the whole subject would be to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly.... If it could be shown that our domestic varieties manifested a strong tendency to reversion—that is, to lose their acquired characters whilst kept under the same conditions, and whilst kept in a considerable body, so that free intercrossing might check, by blending together, any slight deviations in their structure, in such case I grant that we could deduce nothing from domestic varieties in regard to species. But there is not a shadow of evidence in favor of this view; to assert that we could not breed our cart and race horses, long and short horned cattle, and poultry of various breeds, and esculent vegetables, for an unlimited number of generations, would be opposed to all experience."[8] Darwin recognizes, in instinct, the possibility for the play of a certain amount of imitation, as also of intelligence and experience,[9] though denying to these the range attributed to them by Wallace. And summing up his theory in the essay given by Romanes, he writes: "It may not be logical, but to my imagination it is far more satisfactory, to look at the young cuckoo ejecting his foster brothers, ants making slaves, the larvæ of the ichneumidæ feeding within the live bodies of their prey, cats playing with mice, otters and cormorants with living fish, not as instincts specially given by the Creator, but as very small parts of one general law leading to the advancement of all organic bodies—Multiply, Vary, let the strongest Live and the weakest Die."

It will thus be seen that Darwin, while confessing a disability to account for the origin of Instinct,—beginning with some form of instinct as already existent, just as he begins with life as already existent,—does advance some perfectly definite views as to the probable origins of instincts,—namely, preservation, in the struggle for existence, of numerous slight but profitable variations. The assertion of the inadequacy of habit to account for the origin of more complex instincts, as in the case of the hive-bees, when compared with the subsequent explanation, in the same connection, of the rise of these very instincts partly by habit acquired from experience and imitation, partly by accidental modifications of simpler instincts, both taken advantage of by natural selection,—would seem to limit the term "habit," as here used, to modes of action acquired during the life of the individual; this interpretation of the word being confirmed by the additional phrase "in one generation." But here, as everywhere in Darwin's work, an unknown quantity appears—namely, the cause of variation; i.e. of the differences, or tendency to differ, of offspring, from the parental type.

In "The Descent of Man," published twelve years later than "The Origin of Species," and "The Variation of Plants and Animals under Domestication," which appeared yet three years later, Darwin's views on instinct and habit are still further elaborated, and a definition of the relation of these to reason, pleasure, pain, and the moral sense, attempted. In Vol. I. of the former work, Darwin devotes two chapters to these subjects. Instinct he calls, pages 116-122, "inherited habit"; and on page 168 he says: "But as love, sympathy, and self-command became strengthened by habit, and as the power of reasoning becomes clearer, so that man can value justly the judgments of his fellows, he will feel himself impelled, apart from any transitory pleasure or pain, to certain lines of conduct." Here, I take it, the word "habit" cannot be interpreted as referring to one generation of men, but to the race as a whole, a general continuity being thus ascribed to the inheritance of mental characteristics, and the important concept of progress as adaptation acquired. In contrasting reason with instinct, Darwin thinks that instinct and intelligence do not, as Cuvier maintained, stand in inverse ratio to each other, but that a high degree of intelligence is compatible with complex instincts—as in the case of the beaver; "yet it is not improbable that there is a certain amount of interference between the development of free intelligence and of instinct,—which latter implies some inherited modification of the brain. Little is known