Page:The New International Encyclopædia 1st ed. v. 06.djvu/780

* EGG. 678 EGG. IIammauax Eggs. The eggs of all the mam- mals except the monotremes (q.v.) are minute globules (that of lunuan beings being only about jjjf of an inch in diainetei) eoiitaining little yolk, which pass through all their stages of "development within the body of the mother. (See EiiiiRTOLoc.Y.) The two groups of mono- tremes, the duckbills and echidnas (qq.v.), how- ever, are ovoviviparous, that is, they produce eggs which are voided from the mother and de- veloped outside her body. These eggs are very much larger than those of other mannnals. becavise they nnist carry a comparatively large amount of yolk-food. Those of the duckbill, two in number aimually, are globular, about three- fourths of an inch in diameter, and have a tough white 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. Eggs ok Reptiles and Amphibians, ilost reptiles are oviparous, laying eggs, either globu- lar or oblong in shape, closely resembling birds' eggs in composition of yolk, albumen, and cov- erings, except that the shell is not calcareous, but of a tough, yellowish-white, parchment-like (cori- aceous) material. "These are usually deposited in holes and left to hatch by the lieat of the sun. In the [ease of] the crocodiles they are deposited in a rough nest, and guarded by the mother. In all eases development has only pro- gressed 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." These eggs are most numerous in the case of the tur- tles, numbering from 2.5 to 2.50, and are buried in the .sand of sea-beaches and river-banks. Those of the fresh-water species are niostl.v 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 7iot only lay them, but incubate them within the circle of their coiled bodies. 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 lloat or lie upon the bottom, or attached to submerged plants, or are laid under logs or stones; and in a few eases they are carried about by <me or the other parent imtil 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.) — prodice 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 mueh yolk and semi-liouid albumen. Some s|>ecies 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 ease, which most conuiHiidy is llal and four-cornered, with twisted tilanientous appendages at the corners, by means of which it becomes attached to sea- weeds and the like. These are the "sea-purses* of fishermen. The boiii/ fishes mostly emit minute eggs, usu- ally called 'spawn,' in vast (luantities, a single sea-fish producing two or three liundred thousand in some eases. These are east into the water and contribute a large jiart of the foodsupi)ly of aquatic creatures, nineleen-twentieths, prob- al)ly, being quickly devoured. Some tloat 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 NiuiFiCA- Tiox.) This reduces the proportion of loss so greatly that comparativ(dy few need be iiroduced. and they are far larger, relatively, tluui 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 Ix.sects. Eggs and their deposition among the insects present a great variety of in- teresting phenomena, of which only a sketch may be given liere. 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 numlier p<'- riodically 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, glob- ular, shell-less eggs, usxuilly each by itself, in the cells of their combs or burrows, placing with them food for the expected larvse (honey, bee- bread, palsied spiders, etc.). Other insects place them within or ujion the bodies of other insects, as is the habit of the parasitic ichneumons and chalcids: or else insert them into plant-tissues and wood, as do the gall-flies, sawflies, etc. ^lany flies produce living larvie, 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 ind>edded in jelly, which swells in the water and sticks to a support; the bulTalo- gnats glue theirs in large patches to submerged rocks. The snipe-llies. 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 nianv others force theirs into the ground or into de- caying wood or dung, carrion meat, or wounds, as is the ease will, house-flies, flesh-flies, syrphus- flics, etc.: while the bols attach theirs to animal liairs, where they may be licked off and develop in the stomach of their host. It is clearly im- possible to carry this particular description through the list. One of the longest as well as most entertaining chapters in the admirable Introduction to Enlomolofiii, by Kirby and Spence. is filled with such details. An excellent sunnnary has been made by Carpenter as follows: "The outer form of insects' eggs is exceedingly variable. Very many — as those of beetles, grass- hoppers, and flic< — are elongate, like the cock- roach's. The eggs of some moths are globular, while those of butterflies, and especially those of