The frog: an introduction to anatomy, histology, and embryology . hese latter appear as small round bodies,each presenting a black half and a white half. If a number of hens eggs were broken into a basin, carebeing taken not to rupture the yolks, a mass would be producedsimilar to frogs spawn: the yellow yolks corresponding to thefrogs eggs, and the whites or albuminous investments of theyolks to the gelatinous matrix of the spawn. And just as thechicken is formed from the yolk, and not from the white of ahens egg, so also is the frog developed from the egg and notfrom the gelatinous investmen
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The frog: an introduction to anatomy, histology, and embryology . hese latter appear as small round bodies, each presenting a black half and a white half. If a number of hens eggs were broken into a basin, carebeing taken not to rupture the yolks, a mass would be producedsimilar to frogs spawn: the yellow yolks corresponding to thefrogs eggs, and the whites or albuminous investments of theyolks to the gelatinous matrix of the spawn. And just as thechicken is formed from the yolk, and not from the white of ahens egg, so also is the frog developed from the egg and notfrom the gelatinous investment. The frogs eggs, laid in this way and fertilised by the sperma-tozoa shed over them by the male, begin to develop at once.Each egg is at first spherical, but in about a week becomes ovoidin 1 hape, and tlion rapidly increases in length. By the tenthday it is divided by slight constrictions into head, body, and-taU. The whole animal becomes fish-like in appearance, thetail growing rapidly : two pairs of branching tufts, the external 100 DEVELOPMENT OF THE FROG. a .3 2s a „-, 3 g Ho o 5Hxl-O £tS 8 g DEVELOPMENT OF THE FROG 101 gills, followed shortly by a third pair, grow out from the sidesof the neck, and in about a fortnight from the time of laying ofthe eggs the young tadpoles make their way out of the gelatinousmass of the spawn, and swim freely in the water. At the time of hatching the tadpole has no mouth, and isdependent for food on granules of food yolk which are containedin large numbers in the egg, and at the expense of which all theearlier processes of development are effected. A horseshoe-shaped sucker is present on the under siu-face of the head, bywhich the tadpole is enabled to attach itself to weeds or otherobjects in the water. A few days after hatching the mouth appears, bordered by apair of horny jaws, and fringed with fleshy lips piovided withhorny papillis. The alimentary canal which has hitherto beenwide and short, now rapidly increases in length, becomi