STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 43 



to be influenced by possible normal variations in the sex ratio in 

 different lots of eggs. The two sets of eggs were fertilized by 

 sperm from different males also and there is the possibility, as 

 Morgan has suggested, that the male is responsible for sex-deter- 

 mination in amphibians. The last experiment was carried out in 

 the manner described in order to obtain as large a number as 

 possible of eggs that were fertilized normally at different tem- 

 peratures, since it is not safe to draw conclusions from the results 

 of experiments in which comparatively few individuals are used. 

 Another series of experiments will be made next spring which, 

 it is hoped, will determine definitely whether temperature can 

 influence sex in Bufo. An account of the experiments already 

 carried out is published in the hope that other investigators 

 working in the same field may consider the suggestion here 

 made as of sufficient value to warrant testing on any suitable 

 material with which they may be working. 



LITERATURE, 

 von Griesheim, A. 



'81 Ueber die Zahlenverhaltnisse der Geschlechter bei Rana fusca. Arch, fur 



die gesammte Phys., Bd. XXVI., 1881. 

 Hertwig, R. 



'05 Uber das Problem der sexuellen Differenzierung. Verhandl. der Deutsch. 



Zoo]. Gesellschaft, 1905. 

 '06 Weitere Untersuchungen iiber das Sexualitatsproblem. Verhandl. der 



Deutsch. Zool. Gesellschaft, 1906. 

 '07 Untersuchungen iiber das Sexualitatsproblem, III. Verhandl. der Deutsch. 



Zool. Gesellschaft, 1907. 

 King, Helen Dean 



'07 Food as a Factor in the Determination of Sex in Amphibians. Biol. Bulletin, 



Vol. XIII., 1907. 

 Morgan, T. H. 



'08 The Determination of Sex in Frogs. Amer. Naturalist, Vol. XLIL, 1908. 

 Pfliiger, E. 



'82 Ueber die das Geschlecht bestimmenden Ursachen und die Geschlechts- 

 verhaltnisse der Frosche. Arch, fur die gesammte Phys., Bd. XXIX., 1882. 

 Reed, T. E. 



'07 The Sex Cycle of the Germ Plasm. New York Medical Times, 1907. 

 Yung, E. 



'85 De 1' influence des Variations du milieu physio-chimique sur le developpement 



des animaux. Arch, des Sci. phys. et natur., t. XIV., 1885. 

 WISTAR INSTITUTE OF ANATOMY AND BIOLOGY, 

 PHILADELPHIA, PA. 



