The common frog . lled branchial arches. The eggs are hatchedtowards the end of April, and the tadpole emergesin the stage represented at Fig. 3, 1. It has a rela-tively large head, a rounded body, and a long tail, bylateral undulations of which the little creature swimsabout. From behind the head, on each side, jut forthexternal branchiae as a small plume-like structure, butno limbs are visible. As the tadpole grows, the external plumose gillsat first greatly enlarge (Fig. 3, 2 and 2a), but after-wards become gradually absorbed, and are succeededby short gill filaments, which are developed al
The common frog . lled branchial arches. The eggs are hatchedtowards the end of April, and the tadpole emergesin the stage represented at Fig. 3, 1. It has a rela-tively large head, a rounded body, and a long tail, bylateral undulations of which the little creature swimsabout. From behind the head, on each side, jut forthexternal branchiae as a small plume-like structure, butno limbs are visible. As the tadpole grows, the external plumose gillsat first greatly enlarge (Fig. 3, 2 and 2a), but after-wards become gradually absorbed, and are succeededby short gill filaments, which are developed alongeach of the branchial arches. These latter filaments 1 Gills (or branchise) are delicate processes of skin richly suppliedwith minute blood-vessels, wherein the blood becomes exposed to thepurifying action of the air dissolved in the water. II.] THE COMMON FROG. 17 do not appear externally, and indeed a membrane,termed the operculum (Fig. 2, op), is developedfrom the front of each series of branchial apertures,. Tig in different stages of development, from those just hatched(i) till the adult form is ailamed (S). and which, extending backwards by degrees, ul-timately covers over and conceals them. Little by little the limbs bud forth and grow,the hind ones being the first visible because the i8 THE COMMON FROG. [chap. fore limbs are for a time concealed by the opercularmembrane. As the legs grow, the tail becomesabsorbed (Fig. 3, 7), not falling off, as some gills also disappear, and the branchial aperturesclose, that on the right side first becoming obsoleteby adherence of the operculum to the skin of the body. As the gills diminish and cease to serve the pur-poses of respiration, lungs at the same time becomedeveloped in an inverse ratio, and the tadpoles ab-solutely require to come to the surface to breathe. The process, from the hatching to the acquisitionof the miniature form of the adult, may be accele-rated or retarded by elevation or depressio
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
