. Analysis of development. Embryology; Embryology. 632 Metamorphosis from the thyroid. This can be fractionated to yield two active iodized derivatives of tyrosine, namely di-iodo-tyrosine and thy- roxine. The latter, being far more active than the former in respect to thyroid-like proper- but fail to show any metamorphic changes even if kept for many times the normal larval period and until they exceed by far the maximum size for control larvae (Allen, '18; Hoskins and Hoskins, '19a). These re-. Fig. 217. The pattern of metamorphosis in the frog, Rana pipiens. The graph shows the growth of th
. Analysis of development. Embryology; Embryology. 632 Metamorphosis from the thyroid. This can be fractionated to yield two active iodized derivatives of tyrosine, namely di-iodo-tyrosine and thy- roxine. The latter, being far more active than the former in respect to thyroid-like proper- but fail to show any metamorphic changes even if kept for many times the normal larval period and until they exceed by far the maximum size for control larvae (Allen, '18; Hoskins and Hoskins, '19a). These re-. Fig. 217. The pattern of metamorphosis in the frog, Rana pipiens. The graph shows the growth of the hind legs (solid line) compared to that of the body (broken line). The scale on the ordinate is for hindleg length; the abscissa scale is given in days, counting the day of emergence of the forelegs as day 30. Metamorphic changes shown in sketches of tadpoles occur at times indicated. Metamorphosis begins with differential acceleration of hind leg growth. When the legs are about half grown the tissue in which the anal canal lies (anal canal piece, ) begins to be absorbed and completely disappears in two or three days. About this time an area of disintegration in the skin above the gills begins to develop, becoming clearly defined in a few days (skin window for the forelegs, ). When the forelegs emerge the stage of early metamorphosis (prometamorphosis) goes over into metamorphic climax when rapid morphological changes take place. The animal ceases to feed, the horny teeth and beaks (B) and the associated fleshy mouth parts are lost and the mouth widens in a few days to that characteristic of the frog. Tail resorption and eye growth proceed rapidly at this time. The last morphological altera- tion is that of the formation of the tympanum (T). (After Etkin, '32; Taylor and Kollros, '46.) ties on all test animals, is often discussed as though it were "the hormone" of the gland (Means, '48). In the absence of the thyroid gland, meta- morphosis fails to occ
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
