of primary barriers on the distribution of species, as shown in the marked divergence of the faunas on the eastern and western slopes of the Cordillera. "We ought not," he remarks, "to expect any closer similarity between the organic beings on the opposite sides of great mountain ranges than on the opposite shores of the ocean, except for species which have been able to cross the barrier, whether of rock or salt water." (Ibid, pp. 326–7.)

I believe he was the first to draw attention to the paucity of insects on islands, and to establish the principle that the smaller the area, the less favorable it is for the development of insect life. (Ibid, p. 391.)

It is a fact of observation that islands predispose to the apterous condition among insects, a fact that is especially noticeable in Kerguelen's Land, as observed by Dr. Hooker, and particularly by our fellow member, Dr. Kidder. Darwin (Origin of Species, etc., p. 109,) first suggested the most plausible reason, viz: that the indiscriminate use of wings might prove injurious to an insular species by tempting it out to sea and to destruction, so that the loss of the power of flight is a positive advantage to the species. The argument against this explanation, viz: that insular species should be gifted with strong powers of flight to fortify themselves against being blown to sea in heavy gales, has little force, because either requirement may be fulfilled; and, in reality, where flight is absolutely necessary, as in the majority of Lepidoptera, and flowerfrequenting Coleoptera, the wing capacity, in insular species, is actually increased, or correlated with a diminution of bulk; whereas, in those less dependent on aërial progression, natural selection would decrease wing-power, and there would be just such a correlated increase of bulk as is generally the case.

The principle he laid down, that the accidental introduction of organic beings amongst others to whose interest they are hostile, may be a powerful means of keeping the latter in check, and of finally destroying them, finds vivid exemplification in insects, as I have shown in discussing those imported into this country.*

* Second Annual Rep. on the Insects of Missouri, 1879, pp. 8-13.

He gave reasons for the belief (now generally accepted) that the usual gaudy coloring of intertropical insects is not related either to the heat or light of those zones, but rather to the conditions of existence being generally favorable to life.-(Journal of Researches, etc., p. 381.) He has written on the Phosphorescence of Fire-flies, and on the habits of the larva of one of them-Lamphyris occidentalis. -(Ibid, pp. 29-30.) He discussed the food-habits of stercovorous beetles, with reference to the origination of a new habit and the power of adaptation to new conditions.—(Ibid, p. 490, note.)

At Port St. Julian, Patagonia, he found a species of Tabanus extremely common, and remarks: "We here have the puzzle that so frequently occurs in the case of mosquitoes-on the blood of what do these insects commonly feed? The guanaco is nearly the only warm-blooded quadruped, and is found in quite inconsiderable numbers compared with the multitude of flies." He has discussed the question of hibernation of insects, and shown that it is governed by the usual climate of a district, and not by absolute temperature. (Ibid, 98-9.) He gave the first true explanation of the springing power of the Elaterida when laid on their backs, showing how much depended on the elasticity of the sternal spine. (Ibid, p. 31.) He was the first, I believe, to record the exceptional powers of running and of making sound, in a butterfly, viz., Ageronia feronia of Brazil.

In his most famous work he lays stress particularly on the following facts and generalizations, for which he draws from insects: the individual differences in important characters; the remarkable manner in which individuals of the same brood often differ, dimorphism and trimorphism being only the extreme exaggeration of this fact; the difficulty of distinguishing between species and varieties; that geographical races are local forms completely fixed and isolated; that representative species are better distinguished from each other than local forms and sub-species; that the species of large genera vary more frequently than those of small genera, and that specific differences in the former are often exceedingly small;

that fecundity does not determine the rate of increase; that the struggle for life is most severe between species of the same genus; that secondary sexual characters are generally displayed in the same parts of the organization in which the species of the same genus differ from each other; that distinct species present analogous variations; that similar structures are often independently developed; the varying importance for classification of the same important organ in the same group of beings; that analogical or adaptive resemblances are misleading for classification; that the great frequency of mimicry among insects is associated with their small size and general defencelessness, as no species furnished with a sting, or other defensive property, is known to mimic other species; the importance of relative position or connection in homologous parts; the remarkable changes of structure effected during development; that adaptation to the conditions of life in the insect larva is just as perfect and beautiful as in the adult animal, and that, consequently, larvæ of different orders are often similar, and larvæ belonging to the same order often very dissimilar; that larval and pupal stages are acquired through adaptation, and not through inheritance; that rudimentary organs plainly declare their origin and meaning.

Finally he brought together a large body of interesting facts in entomology, bearing on the development and perpetuation of mimicry, and of secondary sexual characters-all more or less explicable by, and furnishing convincing argument for, the general theory of natural selection; while he freely acknowledged that he found among insects facts that seemed to be most fatal to the theory. This is especially the case in social insects where the colony contains neuters and sterile females which often differ widely in instinct and in structure from the sexual forms, and yet cannot propagate their kind. This is not the place to enter into a discussion of the subject, and I will simply remark that there are reasons for the belief that, in his candor, he has been led to exaggerate the difficulties in this case.

But Darwin's chief investigation into insect life were in its relations to plant life, and his work "On the Various Contrivances by which British and Foreign Orchids are Fertilized by Insects, and on the good effect of crossing," as also that on "Insectivorous Plants," are monuments of skill, industry, and lucid exposition.

Entomologists had often noticed the pollen masses of orchids. attached to the proboscis of various moths, and in commenting upon the fact had pronounced it "curious." Darwin in this, as in so many other cases, gave meaning to the curious, and brought light out of darkness.

Before his time we find frequent reference to the injury caused to plants by insects, and Sprengel, Gaertner, Herbert, and others had shown that insects were, also, in many cases, beneficial and even necessary to plants, the color, form, odor, secretions, and general structure of which have reference to their necessary insect pollinizers.

Yet their writings had produced but slight impression outside of a limited circle. It remained for Darwin to impress the world with a broader sense of the actual interrelation between the two, and to inspire a number of observers in this field, in all parts of the globe, who are now constantly adding to the rich store of facts we already possess on the subject. I need only refer to the work of Hooker, Bennet, Axell, Delpino, Hildebrand, H. Müller, and others abroad, and to that of Dr. Gray, and Mr. Wm. Trelease at home.

The importance of insects, as agents in cross-fertilization, was never properly appreciated till after Darwin's remarkable work on Primula, and his researches on Orchids, Linum, Lythrum, etc.

He established the principle that "nature abhors close fertilization," and though some less careful observers in this country— exaggerating the importance of their isolated and often inaccurate observations have opposed his views, the scientific world has been convinced alike by the force of his logic as by the eloquence of his innumerable facts.

We all know how paleontology has verified many of his anticipa

tions as to missing links being supplied with increased knowledge of the geological record, and in connection with his work on the fertilization of orchids, we have a remarkable instance of similar verification. The nectaries of Angræcum sesquipedale were found by him to sometimes reach 111⁄2 inches in length, with only the lowest 11⁄2 inches filled with nectar. He said "there must be moths with probosces capable of extension to a length of between 10 and II inches." In Nature for July 17, 1873, or some years later, Fritz Müller recorded, through his brother, Herman Müller, the finding of a Brazilian Sphingid having a length of proboscis of 0.25 meters, or between 10 and 11 inches.

I cannot do justice to Darwin's work on Insectivorous Plants within the time to which these remarks have been limited, nor without trenching on the ground to be covered by Prof. Ward. I must be content to remark, therefore, that he demonstrated the new and wonderful fact in physiology that many plants are capable of absorbing soluble matter from captured insects, and that they have special contrivances and sensibilities that facilitate the capture of their prey in other words, that plants actually capture and digest animal food; for the secretion of Drosera, and other insectivorous plants, with its ferment acid belonging to the acetic series, resembles the gastric juice of animals with its pepsin and hydrocloric acid. The fact of absorption demonstrated, it follows that the process would prove serviceable to plants growing in very poor soil, and that it would tend to be perfected by natural selection.

The pleasure Darwin took in observing the habits and ways of insects, and the simple and lucid manner in which he recorded his observations are frequently exemplified in his Journal of Researches, and his account of sundry Brazilian species on page 35, and following, may be consulted as an example.

In the same way that he has influenced all lines of thought and investigation, he has influenced entomology. We find everywhere, in his treatment of insects, the same acute perception, the same candor and impartiality, the same clearness of expression, the same