and an insect would inevitably remove the pollinia if it inserted its head into one of them. But he had not clung closely enough to his general principle. Darwin himself accepted

the correction of his inference as follows: "Delpino, with much sagacity, foresaw that some insect would be discovered" to remove the pollinia by entering the labellum by its large opening, and crawling out through one of the orifices near the anthers; "for he argued that if an insect were to insert its proboscis, as I had supposed, from the outside through one of the small orifices, the stigma would be liable to be fertilized by the plant's own pollen; and in this he did not believe, from having confidence in what I have often insisted on, namely, that all the contrivances for fertilization are arranged so that the stigma shall receive pollen from a distinct flower or plant. But these speculations are now superfluous; for, owing to the admirable observations of Dr. H. Müller, we know that Cypripedium calceolus, in a state of nature, is fertilized in the manner just described.”

Darwin's error in this case consisted in not considering one of the important elements of his principle of adaptation for cross-fertilization, namely, the importance, not only of

favoring cross-fertilization, but of protecting the stigma against self-fertilization. When this is considered, the direction in which the insect entered would appear much more important than comparative ease in getting at the nectar or proximity of the orifices to the stamens.

One of the most remarkable cases of oversight in Darwin's work occurred in connection with the Venus' Fly-trap. This plant is restricted to a very narrowly limited locality in North Carolina, and its organs are highly differentiated for the purpose of catching insects. Darwin could not reconcile the very limited range of so highly specialized an insectivorous plant with his general belief that the best adapted plants and animals spread over the earth and survive. In his discussion of Dionæa, (Venus' Fly-trap), he said, “It is a strange fact that Dionæa, which is one of the most beautifully adapted plants in the vegetable kingdom, should apparently be on the high road to extinction. This is all the more strange as the organs of Dionaea are more highly differentiated than those of Drosera." 1

All the studies of forty years had borne out the conviction that the adaptations of animals and plants to their environment were the result

1 Insectivorous Plants, p. 358.

of natural selection acting upon variations, and preserving those that conduced to the preservation of the species. Following this principle, it seemed almost self-evident that the more highly specialized the organs of a plant or animal are, and the more minutely adapted to its surroundings and mode of life they become, the more certain would the species be of continued existence and of success in the race of life. He never, so far as I know, recognized the inevitable consequence of extreme specialization. Had he pursued the deduction to the end, he must have recognized the fact that a high degree of specialization for a particular mode of life is the mess of pottage for which the birthright of the species has been surrendered.

Darwin was familiar with, and recognized the value of Agassiz's generalization that the progenitors of the greater animal and plant groups have been generalized forms. He himself deduced from his general theory the principle that the species of the larger genera, the wide ranging, much diffused, and common species vary most, that they are more closely related to each other, and that in this respect they more nearly resemble varieties than do the species of the smaller genera with restricted

distribution. It is clear that the wide range of a species, instead of depending on a high degree of specialization for any one environment, depends rather on the absence of it. He clearly recognized and pointed out the danger of extinction to a species of limited range, but nowhere recognized explicitly the connection, on the one hand, between a high degree of specialization for a particular environment or mode of life and restriction of the species to that particular environment, or the relation, on the other hand, between wide range over the earth and generalized characters which give some general advantage that would be useful under all or nearly all circumstances into which the species might be thrown.

He said: "If we ask ourselves why this or that species is rare, we answer that something is unfavorable in its conditions of life; but what that something is we can hardly ever tell.” He insisted that the improved and modified forms would crowd out and exterminate the less well adapted forms; but did not hit upon the truth that, the more beautifully adapted a species is to a definite locality and set of conditions, the less it is adapted to enter into a general competition for the possession of the

1 Origin of Species, pp. 42-44.

earth. Both Agassiz's empirical generalization that the progenitors of the principal plant and animal groups were generalized forms, and the deductive consequences of Darwin's own theory of natural selection would indicate that the highly differentiated forms are forever handicapped. They have a present advantage in having intensified their adaptation to a certain environment; but in the long run they are doomed because they have lost the power of adaptability to new conditions in direct proportion to their present gain.

It is curious that Darwin had before him, and mentioned in the same sentence, a case of each kind: Dionaea, with its extreme adaptations for insect catching, with only a single species in the genus, restricted to a very small locality, on the verge of extinction; and Drosera, with the same general advantage of catching insects, but with no extreme adaptations, with a vast number of species in the genus, distributed all but everywhere over the earth. It is as great a surprise that he did not see the connection between extreme specialization and extinction on the one hand, and general advantage and wide distribution on the other, as he says it was to him that Dionæa is on the verge of extinction. It is clearly inferable from