Replacement of the larval basement lamella by adult-type basement membrane in anuran skin during metamorphosis.

Ever since Gudernatsch (191. 3, 1914) proved that the mammalian thyroid gland contains an “ugerz~” which nil1 hasten metamorphosis when fed to amphibian larvae, biologists have been invtrstigating thcl mechanisms whereby the thyroid participates in controlling vertebrate development. Reviews by Allen ( 1938), Lynn and \I’achowski ( 1951 ), Etkin (1955), and Kollros (1959) should 1~ consulted for excellent discussions of earlier literature on amphibian metamorphosis. OUI concern in this paper will be the normal changes that transform the thin larval dermis of the frog Ranu pipiens into the thickened dermis of the adult. In particular, we will follon, tlw fntc of the larval hascment lamella (Kemp, 1959, 1960) and the development of the f)awmerit membrane of adult skin. The basement lamella in the tail of well-differentiated larvae of And@sto?ilu punctat~m, A. opacrm, Ram pipirns. and Xcnqxrs lnezjis (Weiss and Ferris, 1954a,b), and in the tail of ;I %-mm tadpole of Rann sylcaticcl (Kemp, 1959) contains “0 2 ” ortllogonall\~ aligned layers of collagenow filaments embedded in gronnh substance. Fibrillogenesis of these filaments proceeds ttstrwellularlv in the larva, beginning in Rann pipiens at Sh~~mwxv stage 18. As’ the larva grows, does the basement lamella reach a ‘constant thickness, or does it continue to thicken throughout larval lift (Weiss and Ferris, I954b)? Evidently deposition of new luycw contimws in tile head region of Runa pipiens, for 3 2 aligned lavers could he counted in the head skin of a 36-mm tadpole (Kemp, i9S9). What structural changes occur in the dermis of amphibian skin