Schröder. 1900. Henry H. Donaldson: Observations on the Wight and Lenght of the Central Nervous System and of the Legs, in Bull-Frogs of Different Sizes. Journ. of Comparative Neurology 8 (4), 314-335. 1898. Zeitschrift für Psychologie und Physiologie der Sinnesorgane 22: 389