Recent reviews on thyroid function by E'leischmann ( '47), Goldsmith ( '49), and Lynn and Wachowski ('51) point up the fact that although the thyroid gland in other classes of vertebrates has been the object of extensive research, relatively little has been done on the gland in reptiles. Moreover, no experimental study on its embryonic function has yet been reported. Nevertheless, the normal developmental pattern of the gland has been worked out for several species, among them the lizards Lacerta agilis (de Meuron, 1886; Maurer, 1899; Eggert, '34) and L. uiviparna (Eggert, '34) ; Anguis fragilis (Prenant, 1896) ; S e p s chalcides (Dorello, '48) ; and Xphaerodactylus goniorhyrzchus (Walker, '51) ; the snake, Thamnophis radix (Harrison and Denning, '29) ; the alligator, AZZigator mississippiensis (Hammar, '37) ; and the turtles, Chrysemys @eta picta and C. picta m a r g k a t a (Shaner, '21) and Chelydra serperztina serperztinna (Dimond, ,52).

Epinephrine (E), norepinephrine (NE), tyramine (T) and nicotine were tested at various dosage levels on different atrial regions of the heart of the eastern painted turtle, Chrysemys picta picta (Schneider), and the median effective dose determined. The three phenethylamines acted according to the following pattern in their effect on rate increase, amplitude increase, and inhibition of tonus waves: E > NE > T, except for amplitude increase in the left atrium and tonus wave inhibition in both atria, where E and NE were equal. The right sino-atrium and left atrium differed in sensitivity to the drugs. The various responses, including treppe, are consonant with the theory of the release from the tissues of a potentiating substance and a depressing substance. Histological stains for chromaffin tissue, a possible source of potentiating substance, were negative, but a differentially stained type of cardiac muscle, a possible conducting tissue, is present in regions of the sinus venosus and both atria and at the base of the interatrial septum.