EGG. 677 EGG. Color. Birds' eggs may lip saiil to bo noi- nially chalky whito. l)Ut in a great number of groups they are colored. The color may be a uniform tint over the whole surface, or a tint with marking; or simply dots, spots, streaks, or blotches of one or mon' hues on an otherwise colorless shell. These colors exude from uterine glands in the form of pignient-corpuselos depos- ited with the fonniiig shell, and stain its deep- er as well as its more e.xtornal layers. Many of the variations in tint of the spots are thus due simply to their being overlaid by more or less transparent material, but certain real colors e.xist. This matter was studied by H. t'. Sorby by the methods of spectrum analysis described by him in the Proccedinqs of the Zoolofiical >S'o- cicti/ of Loudon for 1875. He learned that the coloring matters in egg-shells are connected with ha'niaglobin and the bilc-]iigments, and are def- inite ])hysii)logi<-al products. He reported seven of these products as follows: ( 1 ) Oiirhodeine. The most important of the colors, present in almost all eggs, which gives an effect when alone of brownish red. The spec- troscope sliows so close a similiarity between this and the product of the decomposition of the red corpuscles of the blood as to make it jnobalde that they are physiologically identical, and de- rived from the same source. Such red-brown «ggs as those of the grouse are mainly tinted by this material. (2) Oiiri/an. A fine blue. (3) Bonded Oocjian. Also a fine blue, but giv- ing a dilTerent spectrum. A chemical similarity is apparent between the two owyans and the pig- ments of the bile, and they must be regarde(i as derived by separate physiological processes from the same source. (4) Yi'lloir Onxrtnthine. Clear yellow: unsta- ble and liable to fade. (.5) Ittifous Ooxanthinr. Reddish yellow. (6) .1 siil)Stance ijirinf/ nrirrow absorption- hands in the red. Probably brown. (7) Lichenoxanthine. A brick-red substance, apparently identical with a coloring matter com- mon in plants, especially in lichens and fungi. The mixture of those pigments in various ways gives the varied colors observed in egg- shells. Thus the nightingale's egg has been sho«Ti to be colored with a mixture of orirhodeine and oiicyan: while all the varying greens and blues so common as groiuid-tints are due to vary- ing mixtures of oiicyan with ooxanthine, and such are likely to fade or to change color when long exposed to the light. An intercstini; feature in this connection is that not only the state of health, but the state of mind of a bird, may eflfect the colors of its eggs, as Hewitson long ago recorded. Theobie.s of Colok-.M.rkixgs ox Eggs. The reason for the many and various colorings of birds' eggs has been a favorite field of speculation, and many iiigvuiims theories liave been constructed to explain the matter, from the pious musings of Sir Thomas Browne to the present day. The most important thesis is that advanced by Wallace and enlarged by Poulton, who attempt to show TYPEH OF EOOS OF WATER ASU GAME BIRDS. 1. Pintail (lui'k. 2. Petrel, stormy. 3. liart«T. 4. Rail, Virpnnian. .'>. Mgrht-hpron. 6. Partrldtfi*. (JambePH. 7. Fhttlarope, WIIhmiV)*. s. UiIs. whit**. '.». Sandpli»'r. spotted. 10. Toot. 11. l>ove. Zfiiaiila. 1'2. I'ranni^an. willow. i:j. Kilde«r (plover). 14. Bittvru, American. 15. Tern, arctic. tliat birds' eggs are examples of protective mim- icry in color, as the result of natural selection. Impartial examination shows, however, that only in a minority of cases doei^ the theory of adap- tive coloration seem to be adequate and not oi)en to serious interference from other explanations or contradictions: such favoral)le cases are those of the nightjars, game birds, shore l)irds, coots, and some other ground-builders making scanty nests, whose eggs certainly do closely sinuilate the beach, or leaves, or marsh-grass upon which they lie. They are certainly very dillieult to see, especially for human eyes; but most of the de- spoilers of birds' nests are not htunan. but brute foes which, for the most part, dejiend less upon their eyes than upon their noses to <liscover what they seek, and most of which go about by night rather than by day. Against such foes color is of small importance among the factors of safety. It is quite probable that in the cases above men- tioned the inconspicuous coloring of the eggs is of some consequence, and may be the result in some degree of natural selection : but these cases are only a small part of the whole array of bird life, and 'protective mimicry' certainly fails as yet to account for the coloring of birds' eggs as a whole. It is much more likely that this phenomenon falls under the theory of 'recognition' colors. JIanv facts go to show that birds recognize their own eggs, and the supposition is reasonable that the tints and markings, if they serve any useful purpose at all, serve that of identification by their owners. This would account for the fact that eggs laid in dark holes are usually white; and it would explain the individual variation within the limits of specifie or tribal likeness which universally characterizes the eggs of birds. Vtilization- of BiEns' Eggs. Eggs being in- tended not only for the production of new beings, hut for their nutrition during the enibryonic period, mainly consist of a store of highly nutri- tious material, which is as good food for other animals as for the young birds. Hence all eggs may be called edible, though sonic are so im- pregnated with a fishy or musky flavor or odor as to be impalatable to civilized mankind. The vast use made of the eggs of domestic fowls as food and in the arts is elucidated in another article (see Ego as a Food), but attention may be called here to the fact that in many parts of . the world the gathering of the eggs of birds, mainly sea-birds, which nest in vast communities, is a regular industry furnishing an important part of the food of the local population. This is especially true of high northern regions. In some of the i.slands of the Pacific eggs of gre- garious sea-fowl are gathered by thousands, fur . the purpose of making from theni coiiinu'rcial albumen; but this industry is diminishing by reason of the steady depletion of the numbers of the sea-fowl thus disturbed and robbed. The making of collections of egg-shells for scientific museums, and still more for the satisfaction of private curiosity and ambition, has long bwn an industry in which much money is annually ex- pended, rare eggs often commanding very high prices, the fe-sv eggs remaining of the extinct great auk (q.v. ) lieing worth at jircsent more than .S'^OOO each. Lastly it is to be mentioned that in the season when birds are breeding their eggs and fledglings form an important part of the food of many other animals.
