STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 211 



of 3 per cent, alcohol. As many as possible of the tadpoles that 

 died at the time of metamorphosis were preserved; and sections 

 were made of their gonads in the hope that it would be possible 

 to ascertain the sex of the individuals by this means. In very 

 few cases, however, were the gonads sufficiently developed to 

 make a definite determination of sex possible. 



The stunting of the individuals and the mortality at the time 

 of metamorphosis was much less evident where the eggs had 

 been fertilized in I per cent, alcohol; while in the other lots in 

 the series the tadpoles were as large and as vigorous as were 

 those in the control. In lots of tadpoles that have developed 

 from normally fertilized eggs under similar external conditions 

 there is always considerable variation in the size of the individuals 

 of the same age. Although, as a rule, most of the tadpoles are 

 of medium size, it not infrequently happens that a few giant in- 

 dividuals may be found that are nearly twice as large as the 

 smallest individuals in the lot. It is, therefore, only when the 

 majority of the individuals show marked deviations from the 

 usual size that one can safely attribute the change to the unusual 

 conditions to which the eggs have been subjected. 



2. THE INFLUENCE OF THE SPERMATOZOAN ON THE DETER- 

 MINATION OF SEX IN Bufo. 



In his latest contribution to the subject of sex-determination 

 Hertwig ('07) describes a series of experiments in which the eggs 

 of two different frogs were divided into six lots and fertilized with 

 sperm from six different males. The mortality in several of 

 these lots of eggs was very great, and there was no uniformity 

 in the sex ratios that were obtained. Some cultures gave over 

 90 per cent, of females; others produced an excess of males. In 

 spite of this lack of uniformity, Hertwig considers that the results 

 indicate that the male has some influence in determining sex 

 in Rana, although he is of the opinion that, as a rule, "die Eier 

 zur Zeit der Befruchtung sexuell in so hohem Grad determiniert 

 sind, dass der relativ geringe Einfluss des Samens gar nicht zur 

 Geltung kommen wurde." 



Morgan ('08) has suggested that, if there be a dimorphism of 

 the spermatozoa of amphibians that is associated with sex-de- 



