The development of the anuran tympanic membrane during larval involution has presented many interesting problems. The earlier work, however, was concerned entirely with a determination of its histological structure. Thus, Moldenhauer (1878) sketched and described the conditions found in Rana esculenta and Rana temporaria, while more recently, Tokura ('25) worked out the fibrous construction of the dermal layers in Rana nigromaculata, a variety of Rana esculenta. The writer ('28), after working out the normal transformation of integument into normal tympanic membrane,l was able to show that the integument which normally develops into tympanic membrane is not peculiarly specific f o r membrane formation as compared with various body integuments. I n other words, potential tympanic membrane integument transplanted to the back and side failed to develop tympanic membrane structures during larval involution. Conversely, back and side integument transplanted do the tympanic membrane region always underwent histological transformations resulting in membrane formations during metamorphosis.
'The term tympaiiic membrane or membrane as used here aiid throughout the present paper refers oiily to the integumentary portion of the membrane aiid is not meaiit to include the lamiiia propria or internal epithclial layers.