May it not be that closure of the gill-chamber by the opercular (=gular) fold, retardation of limb development, expansion of the lips, growth of parallel rows of horny teeth, and other correlated features that make a tadpole, were brought about as an adaptation of the primitive Anuran larva to a swift-stream habitat, and that this "basic patent" then later served to admit the tadpoles of descendant types to an alga-scraping habit in quiet water as well? The tadpole, as a unique larval type among vertebrates, bears the hallmarks of an abrupt adaptive shift, such as might have occurred within the limits of a single family, and it seems difficult to imagine the enclosed branchial chamber, the tooth-rows, and lips of a familiar tadpole as having evolved without some kind of suctorial function along the way. SUMMARY The Anura probably originated among temnospondylous labyrinthodonts, through a line represented approximately by _Eugyrinus_, _Amphibamus_, and the Triassic frog _Protobatrachus_, as shown by Watson, Piveteau and others. The known Paleozoic lepospondyls do not show clear indications of a relationship with Urodela, but _Lysorophus_ may well be on the ancestral stem of the Apoda. Between Urodela and Anura there are numerous resemblances which seem to indicate direct relationship through a common stock: (1) a similar reduction of dermal bones of the skull and expansion of palatal vacuities; (2) movable basipterygoid articulation in primitive members of both orders; (3) an operculum formed in the otic capsule, with opercularis muscle; (4) many details of cranial development, cranial muscles, and thigh muscles, especially between _Ascaphus_ and the Urodela, as shown by Pusey and Noble; (5) essentially similar manner of vertebral development, quite consistent with derivation of both orders from Temnospondyli; (6) presence in the larva of _Leiopelma_ of a salamander-like gular fold, four limbs, and no suggestion of modification from a tadpole (Stephenson). LITERATURE CITED Broom, R. 1918. Observations on the genus _Lysorophus_ Cope. Ann. Mag. Nat. Hist., (9)2:232-239. Bystrow, A. P. 1938. Dvinosaurus als neotenische Form der Stegocephalen. Acta Zool., 19:209-295. Case, E. C. 1935. Description of a collection of associated skeletons of _Trimerorhachis_. Contrib. Mus. Pal. Univ. Michigan, 4:227-274. Cope, E. D. 1889. The Batrachia of North America. Bull. U. S. Nat. Mus., 34:1-525. de Beer, G. R. 1937. The development of the vertebrate skull. Pp. xxiii + 552. Oxford, Clarendon Press. de Villiers, C. G. S. 1934. Studies of the cranial anatomy of _Ascaphus truei_ Stejneger, the American "Liopelmid." Bull. Mus. Comp. Zool., 77:1-38. Emelianov, S. W. 1936. Die Morphologie der Tetrapodenrippen. Zool. Jahrb. (Anat.), 62:173-274. Francis, E. T. B. 1934. The anatomy of the salamander. Pp. xxxi + 381. Oxford, Clarendon Press. Gamble, D. L.