EGG.

COLOR. Birds' eggs may be said to be normally chalky white, but in a great number of groups they are colored. The color may be a uniform tint over the whole surface, or a tint with markings; or simply dots, spots, streaks, or blotches of one or more hues on an otherwise colorless shell. These colors exude from uterine glands in the form of pigment-corpuscles deposited with the forming shell, and stain 'its deeper as well as its more external 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 exist. This matter was studied by H. C. Sorby by the methods of spectrum analysis described by him in the Proceedings of the Zoological Society of London for 1875. He learned that the coloring matters in egg-shells are connected with hæmoglobin and the bile-pigments, and are definite physiological products. He reported seven of these products as follows:

(1) Oörhodeine. The most important of the colors, present in almost all eggs, which gives an effect when alone of brownish red. The spectroscope shows so close a similiarity between this and the product of the decomposition of the red corpuscles of the blood as to make it probable that they are physiologically identical, and derived from the same source. Such red-brown eggs as those of the grouse are mainly tinted by this material.

(2) Oöcyan. A fine blue.

(3) Banded Oöcyan. Also a fine blue, but giving a different spectrum. A chemical similarity is apparent between the two oöcyans and the pigments of the bile, and they must be regarded as derived by separate physiological processes from the same source.

(4) Yellow Oöxanthine. Clear yellow; unstable and liable to fade.

(5) Rufous Oöxanthine. Reddish yellow. (6) A substance giving narrow absorptionbands in the red. Probably brown.

(7) Lichenoxanthine. A brick-red substance, apparently identical with a coloring matter common in plants, especially in lichens and fungi.

The mixture of these pigments in various ways gives the varied colors observed in eggshells. Thus the nightingale's egg has been shown to be colored with a mixture of oörhodeine and oocyan; while all the varying greens and blues so common as ground-tints are due to varying mixtures of oöcyan with oöxanthine, and such are likely to fade or to change color when long exposed to the light.

An interesting feature in this connection is that not only the state of health, but the state of mind of a bird, may affect the colors of its eggs, as Hewitson long ago recorded.

THEORIES OF COLOR-MARKINGS ON EGGS. The reason for the many and various colorings of birds' eggs has been a favorite field of speculation, and many ingenious theories have 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

TYPES OF EGGS OF WATER AND GAME BIRDS.

1. Pintail duck. 2. Petrel, stormy. 3. Darter. 4. Rail, Virginian. 5. Night-heron. 6. Partridge, Gambel's. 7.

EGG.

that birds' eggs are examples of protective mimicry in color, as the result of natural selection. Impartial examination shows, however, that only in a minority of cases does the theory of adaptive coloration seem to be adequate and not open to serious interference from other explanations or contradictions: such favorable cases are those of the nightjars, game birds, shore birds, coots, and some other ground-builders making scanty nests, whose eggs certainly do closely simulate the beach, or leaves, or marsh-grass upon which they lie. They are certainly very difficult to see, especially for human eyes; but most of the despoilers of birds' nests are not human, but brute foes which, for the most part, depend less upon their eyes than upon their noses to discover 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 mentioned 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 coloration" 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. Many 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 specific or tribal likeness which universally characterizes the eggs of birds.

UTILIZATION OF BIRDS' EGGS. Eggs being intended not only for the production of new beings, but for their nutrition during the embryonic period, mainly consist of a store of highly nutritious material, which is as good food for other animals as for the young birds. Hence all eggs may be called edible, though some are so impregnated with a fishy or musky flavor or odor as to be unpalatable 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 EGG 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 islands of the Pacific eggs of gregarious sea-fowl are gathered by thousands, for the purpose of making from them commercial albumen; but this industry is diminishing by reason of the steady depletion of the numbers of the sea-fowl thus disturbed and robbed. making of collections of egg-shells for scientific museums, and still more for the satisfaction of private curiosity and ambition, has long been an industry in which much money is annually expended, rare eggs often commanding very high prices, the few eggs remaining of the extinct great auk (q.v.) being worth at present more than $2000 each. Lastly it is to be mentioned

The

13.

10. Coot. 11. Dove. Zenaida. 12. Ptarmigan, willow. Kildeer (plover). 14. Bittern, American. 15. Tern, arctic.

eggs and fledglings form an important part of the food of many other animals.

MAMMALIAN EGGS. The eggs of all the mammals except the monotremes (q.v.) are minute globules (that of human beings being only about of an inch in diameter) containing little yolk, which pass through all their stages of development within the body of the mother. (See EMBRYOLOGY.) The two groups of monotremes, the duckbills and echidnas (qq.v.), however, are ovoviviparous, that is, they produce eggs which are voided from the mother and developed outside her body. These eggs are very much larger than those of other mammals, because they must carry a comparatively large amount of yolk-food. Those of the duckbill, two in number annually, are globular, about threefourths of an inch in diameter, and have a tough yellow calcareous shell; they are deposited in a soft nest in the animal's burrow and hatch there. The echidna produces one egg a year, one-half to three-quarters of an inch in diameter, and covered with a leathery envelope (keratin), which is placed as soon as voided in a mammary pouch and there completes its development.

Most

EGGS OF REPTILES AND AMPHIBIANS. reptiles are oviparous, laying eggs, either globular or oblong in shape, closely resembling birds' eggs in composition of yolk, albumen, and coverings, except that the shell is not calcareous, but of a tough, yellowish-white, parchment-like (coriaceous) material. "These are usually deposited in holes and left to hatch by the heat of the sun. In the [case of] the crocodiles they are deposited in a rough nest, and guarded by the mother. In all cases development has only progressed to a very early stage when the deposition of the eggs takes place, and it is only after a more or less prolonged period of incubation that the young, fully formed in every respect, emerge from the shell and shift for themselves." eggs are most numerous in the case of the turtles, numbering from 25 to 250, and are buried in the sand of sea-beaches and river-banks. Those of the fresh-water species are mostly nauseous, but the eggs of sea-turtles are excellent food, will keep fresh a long time, and are extensively gathered, the people of many tropical countries subsisting largely upon them in their season. They are also much fed upon by wild animals. Many lizards and serpents do not lay eggs, but are viviparous; but the pythons not only lay them, but incubate them within the circle of their coiled bodies.

These

THE EGGS OF THE AMPHIBIANS. These differ from eggs of reptiles in being small, numerous, having comparatively little food-yolk, and are usually laid in the water inclosed in gelatinous masses or cords. Sometimes they float or lie upon the bottom, or attached to submerged plants, or are laid under logs or stones; and in a few cases they are carried about by one or the other parent until they hatch, or the mother coils about them in an underground cell. They are devoured by some aquatic animals.

EGGS OF FISHES. The fishes may be broadly divided into 'cartilaginous' and 'bony,' which differ essentially in respect to their eggs. The cartilaginous fishes-sharks, rays, etc. (qq.v.)produce in each case only a few eggs, which are proportionately nearly as large as those of birds or reptiles, and which, like those, are inclosed in protective envelopes and contain much yolk and semi-liquid albumen. Some species are vivipa

rous.

In those which extrude their ova in a more

or less advanced stage of development each egg is covered by a dark-brown chitinous case, which most commonly is flat and four-cornered, with twisted filamentous appendages at the corners, by means of which it becomes attached to seaweeds and the like. These are the 'sea-purses' of fishermen.

The bony fishes mostly emit minute eggs, usually called 'spawn,' in vast quantities, a single sea-fish producing two or three hundred thousand in some cases. These are cast into the water and contribute a large part of the food-supply of aquatic creatures, nineteen-twentieths, probably, being quickly devoured. Some float at or near the surface; others sink to the bottom. Some fresh-water fishes, however, deposit their eggs in prepared nests, where they are guarded and attended until they hatch. (See NIDIFICATION.) This reduces the proportion of loss so greatly that comparatively few need be produced, and they are far larger, relatively, than in the other case. The eggs of such fishes as the shad, under the name of 'roe,' and of the sturgeon (caviar), enter largely into the list of human comestibles.

EGGS OF INSECTS. Eggs and their deposition among the insects present a great variety of interesting phenomena, of which only a sketch may be given here. In many cases in this class the eggs are so carefully placed as to insure the survival of almost every one, and in proportion as the precautions are complete the number periodically laid is diminished; in fact, in nearly all cases, except in the Hymenoptera, each egg, or else a group of eggs, is within a strong shell or capsule.

Bees, wasps, and ants lay relatively large, elliptical, shell-less eggs, usually each by itself, in the cells of their combs or burrows, placing with them food for the expected larvæ (honey, beebread, palsied spiders, etc.). Other insects place them within or upon the bodies of other insects, as is the habit of the parasite ichneumons and chalcidids; or insert them into plant-tissues and wood, as do the gall-flies, sawflies, etc. Many flies produce living larvæ, and others retain their eggs until nearly mature. The bottle-shaped eggs of mosquitoes stick together in a sort of cake or raft that floats on the surface of water; those of the midges are imbedded in jelly, which swells in the water and sticks to a support; the buffalognats glue theirs in large patches to submerged rocks. The snipe-flies, gadflies, and some others put their eggs on dried branches overhanging the water, sometimes in large pear-shaped masses to which several females contribute, and many others force theirs into the ground or into decaying wood or dung, carrion meat, or wounds, as is the case with. house-flies, flesh-flies, syrphusflies, etc.; while the bots attach theirs to animal hairs, where they may be licked off and develop in the stomach of their host. It is clearly impossible to carry this particular description through the list. One of the longest as well as most entertaining chapters in the admirable Introduction to Entomology, by Kirby and Spence, is filled with such details. An excellent summary has been made by Carpenter as follows: "The outer form of insects' eggs is exceedingly variable. Very many-as those of beetles, grasshoppers, and flies-are elongate, like the cockroach's. The eggs of some moths are globular, while those of butterflies, and especially those of