blentz (ante) photographed the spectrum of the fluorescent light from solutions of luciferesceine and of the emitted light of the fire-fly itself, and showed that the spectra are almost complementary, and that the fluorescent spectrum does not appear on the plates of the emitted light of the insect, although these plates were sensitive to the wave-lengths embraced in the fluorescent spectrum. In any event the intensity of the fluorescence of the material in a single insect would be too slight to have any appreciable effect in modifying the color of the emitted light. (See Coblentz (5a)). In fact it seems probable from the work of Tappeiner and Iodlbauer (") that if the substance should actually fluoresce in the bodies of the insects, it would kill them. Pigments and other substances showing fluorescence are not uncc mmon in animals; Stübel (63) has claimed that all animal tissues exhibit fluorescence when exposed to ultraviolet light, while Arndt (private communication) states that he has observed the presence in most insects of substances which are fluorescent under the influence of the X-rays. Personally, the writer is inclined to regard the fluorescence simply as an incidental property dependent on the structure of some compound frequently met with in insects of this nature, much as Jordan (328) regards the fluorescent pigment of Bacillus fluorescens liquefaciens. Dr. Coblentz finds that these fluorescent extracts exert a strong+ rotation on polarized light. 5. BIOLOGIC RELATIONS OF THE PHENOMENA. There has been a good deal of discussion as to the significance of the photogenic functions for the forms possessing it. There are four recent papers of considerable importance in this connection. Galloway (22) [Galloway and Welch (23)] has observed the use of "phosphorescence" as a mating adaptation in an Odontosyllid, Odontosyllis Enopla Verrill, this apparently being the first instance in which the relation between this function and the reproductive life of the organism has been definitely established. McDermott (51) has confirmed the old and frequently over-looked observation of OstenSacken (5) that the photogenic function plays an important part in the mating of Photinus pyralis, and has extended the observation to a few other species of Lampyridae. Mast (45) has confirmed this result as applied to Photinus ardens, and brought out the bearing of the phenomenon on the problems of phototaxis and orientation. Lund (41, 42) has made observations on Odontosyllids, Lampyrids, and Elaterids, which tend to support the observations recorded in the above-mentioned papers. An extended study of the relation of the photogenic function to the reproductive life of a large number of species of Lampyridae of different genera would be of great interest, especially as the females of a great many of the species of this family are unknown, while in some other instances, the females alone are known. A number of observations of the relations between size of eyes, length and complexity of antennae, and the development of the photogenic function in the sexes have been made, the extreme of which appears to be reached in forms like Phengodes laticollis, where the male is winged, has very large eyes, large, plumose antennae and is non-luminous, while the female is intensely luminous from a large number of photogenic organs, is entirely apterous, has very small eyes, and only rudimentary antennae. The reported luminosity of midges (Chironomus) has long been a matter of curiosity and speculation. It has at last been proven by Issatschenko (30)—as was previously suspected that the light emission in these insects is due to bacterial infection, apparently pathogenic. This strongly recalls Giard's observation (25) of the pathogenic relation of a species of photogenic microorganism to Talitrus. It may also have a confirmatory value toward the explanation offered by Distant (10) of the alleged luminosity of Fulgora. In view of the known propensity of owls to hide during the day in hollow trees, and the frequent infection of such trees by photogenic molds, etc., it seems that a similar explanation might be advanced for the occasional instances in which these birds have been reported to be luminous, such as those cited by Dobbs and Moffatt (1), and Purdy (58a). A number of observers have, at various times, reported the luminosity of various species of earth-worms. Walter (") attributes this property to the secretion of certain glands in the skin of the worm, which is of interest when considered with the studies of Galloway (22, 23) on the related marine Odontosyllids, and those of Kutschera (38) on Acholoe; in this latter instance the luminosity appears to have a defensive function. So far as marine forms in general are concerned, the photogenic function appears to have a variety of uses, its significance to a given organism depending on the method of life of the species. Alcock (1) brings out this variation in the use of the function in marine organisms very well. Nutting (55) has also had a very interesting paper on this phase of the subject. With the increasing knowledge of the existence of light-giving structures in numbers of species of fish, cephalopods, crustanceans, and many lower forms, the views as to the use of such organs to their possessors are gradually broadening, and the conception of the conditions of life in the depths of the sea becoming more and more definite and interesting. Several studies of the structure and development of the luminous organs in various fish have been made, perhaps the most interesting and complete of which are those of Greene (27) and Gatti (24); neither of these papers can be conveniently quoted here, but both are important. It seems to the author that the question of the relation of the photogenic function to the lives of the creatures possessing it has not had the attention it deserves. Reliable and definite observations are scattered, and sometimes conflicting, and there is much ground that has not been covered that would form an inviting field for some extremely interesting biologic studies. Moore (53) has made the interesting observation that certain luminous marine organisms show a diurnal periodicity of lightemission, even when kept in complete darkness for several days; this periodicity shows itself by the appearance of light at approximately the same time in the evening and its cessation at about dawn, even though the creatures are kept away from light during the whole time of observation. CONCLUSION. We can not say now what possibilities lie before us in the discovery of the "secret of the firefly," particularly as to the kind of "oil" he uses in his little lamp. Perhaps it will be discovered and turned to practical account. The emitted light of the firefly is far from being a good light for general illumination, in spite of its high luminous efficiency, on account of the very limited range of color effects possible under it. A single firefly has been variously estimated to give from (Coblentz,5a) to ʊ (Langley and Very,) of a candle power, so we would need quite a high "firefly power" to light our homes. and streets by biophotogenic light. There are still many gaps in our knowledge of this interesting subject, in spite of the large amount of work that has already been done, but one by one we hope to close these up and discover the secret of the cheapest form of light: REFERENCES TO THE LITERATURE. 1 Alcock, A., "A Naturalist in Indian Seas," Lond., 1902. 2 Barber, H. S., Proc. Ent. Soc. Wash., 1908, vol. 9, pp. 41-43. Da Coblentz, W. W., "A Physical Study of the Firefly." Publication No. 164, Carnegie Inst., Wash., Coblentz, W. W., Canad. Entomol., 1911, vol. 43, pp. 355-360; Physikal. 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Ztg., 1898, vol. 22, p. 58. 61a Singh and Maulik, Nature, Lond., 1911, vol. 88, p. 111. 62 Steche, O., Ztschrft. wissensch. Zool., 1909, vol. 93, pp. 349-408. 63 Stübel, H., Ach. f. d. ges. Physiol., 1911, vol. 142, pp. 1-14. 64 Tappeiner, H. v., Ber. d. deut. Chem. Gesellsch., 1903, vol. 36, pp. 3035-3038, and Iodlbauer, Arch klin. Med., 1905, vol. 82, pp. 520-546, and other papers. 66 Thomas, R. H., Nature, Lond., 1902, vol. 65, p. 223. 66 Townsend, A. B., Amer. Nat., 1904, vol. 38, pp. 127-151. 67 Trautz, Ztschr. physikal. Chem., 1905, vol. 53, pp. 1-111. 68 Turner, Psyche, 1882, vol. 3, p. 309. 69 Walter, A., Trav. Soc. Nat., St. Ptrsbrg., 1909, vol. 40 (Livr. 1 C. R.), pp. 136-137. 70 Watasé, S., Biologic Lectures, Woods Hole, Mass., 1898, pp. 177-192. ORGANIC EVOLUTION: DARWINIAN AND DE VRIESIAN. By N. C. MACNAMARA, F. R. C. S., Fellow of the Royal College of Surgeons of England, and also of the Royal College of Surgeons of Ireland; Fellow of the Calcutta University. The term "organic evolution" implies that existing organisms are children of the past and the parents of the future. As biologists we hold that this order of things is the result of natural processes of growth and change working throughout past ages; in fact, that existing plants and animals are the lineal descendants of ancestors on the whole somewhat simpler in organization, and that these are derived from still simpler forms, and so backward to pre-Cambrian geological periods, when we have reason to believe that living organic matter first came into existence on the earth. Of one thing we may be sure, which is that evolution, according to the above definition, depends on the fact that the living substance which constitutes the essential part of organisms on the one hand is capable of passing its form and functions on to its descendants, and on the other hand possesses an organic changefulness which we call variability.1 Organic evolution implies a definite structural arrangement and combination of an aggregate of elements into a form which constitutes a unit or cell; one or it may be a mass of these units form the body of an organism. This form of matter is known as protoplasm or the basis-substance of life, because the complete series of phenomena which collectively we call life are manifested through the instrumentality of this kind of matter." The protoplasm of living cells, among its other constituents, invariably contains a chemical compound known as protein, a wonderfully complex substance. For instance, the protein which exists in our red blood cells is said to be composed of molecules having a chemical formula of C600 H960 N154FeO179, whereas the formula of water is H2O. And just as the peculiar properties of water are given to it by the 1 Heredity, by J. Arthur Thomson, p. 12, London, J. Murray, 1908. 2 These phenomena include the power possessed by living protoplasms of replacing its worn-out elements from surrounding materials without changing its form or functions, of reproducing its like, of respiring, and by chemical action of forming enzymes; it is also capable of being modified by external and internal forces in such a way as to become a transformer of energy into psychical and other processes. |