78 PETER OKKELBERG 



determining factors under normal conditions. In attempting to 

 explain how these factor operate, Witschi has adopted the inter- 

 pretation of Goldschmidt ('12) that the female is homogametic 

 with respect to sex (MFMF), while the male is heterogametic 

 (MFMF'). In these formulae the letters are ranked in value as 

 follows: F>M, F>F', and M>F'. Goldschmidt speaks of a 

 variation in values of the factors as Totenzgraden/ which may 

 be represented by figures; for example, M = 40, F = 60, etc. 

 It is assumed that these potencies may vary for different fertilized 

 eggs and that, in order that the resulting offspring may become 

 a male or a female which is free from the characters of the opposite 

 sex, the dominance of one sex tendency over the other must reach 

 a certain epistatic minimum. If it falls below this minimum, 

 intermediates are formed. 



Witschi found also, as had Pfiiiger, that different races of 

 frogs varied as to the number of intermediates produced. Races 

 of Rana temporaria from northern Germany (Konigsberg) and 

 from the Alps (Ursprungtal) differentiated early and only a few 

 or no intermediates were produced. In middle Europe (Utrecht, 

 Munich), however, intermediates were commonly formed. Wit- 

 schi designates these races as differentiated races and undiffer- 

 entiated races. 



Considerable space has been devoted to the results obtained 

 by Witschi, for it is about the only experimental evidence we 

 have that an external factor may influence the resulting sex of 

 the individual. There are other cases in which the sex of an indi- 

 vidual appears to be reversed by factors influencing the egg before 

 fertilization, such as overripeness of the eggs, overwork in repro- 

 duction, desiccation of the eggs before fertilization, etc. Some 

 of these cases will be discussed later. 



/, Discussion. It has not been found practicable to test sex 

 determination in the lamprey by experimental means, similar 

 to those employed in the case of the frog, because of the length 

 of the larval period and the difficulty, under laboratory condi- 

 tions, of rearing the larvae through the period of sex determination. 

 Witschi thinks that in the early phylogenetic history of the frogs 

 the germ cells were probably all of the same value as to sex and 



