106 PETER OKKELBERG 



olism in the germ cells might modify sex. The case is similar to 

 that of delayed fertilization in the frog which results in the 

 formation of an increased number of males. 



In fish cultures it is not rare to find an excess of males or of 

 females, Woltereck ('08) has reported various records made by 

 Thumm upon the sex ratio in fishes. In Jenynsia Uneata broods 

 were obtained of 68, 92, and 116 individuals without a single 

 female. A female of Cichlasoma nigrofasciatum three years old, 

 bred to a male one year old, gave a progeny of 800 individuals, 

 of which not fifty were females. A female of the same species 

 one year old, bred to a male two years old, (the same male as in 

 the first case), gave 400 young, of which over 300 were females. 

 To summarize: "aeltere starke Weibchen, verpaart mit jiingeren, 

 daher schwacheren Mannchen, brachten in Nachzucht vorwie- 

 gend Mannchen und umgekehrt." It was also found that in 

 viviparous 'Korpflingen' the percentages of males were higher in 

 the spring than later in the season, and that in the fall it was 

 often very low. This apparently corresponds with the results of 

 Riddle on pigeons, where also the percentage of males is greater 

 in the early part of the season. It does not seem possible that 

 the results obtained by Thumm in the cases above are due to 

 selective survival. 



6. General conclusions in regard to the problem of sex determina- 

 tion. In the case of the lamprey it has been seen that, in young 

 stages, a series of individuals may be arranged exhibiting all the 

 intermediate forms between apparently pure females and appar- 

 ently pure males. Pure in this sense is used to designate the 

 individuals which possess no visible characters which normally 

 distinguish the opposite sex. Out of the sex intermediates both 

 males and females develop, so that in the adult condition only 

 two kinds of individuals are found, functional males and females. 

 The designation of sex intermediates among the young is based 

 on the appearance in the germ gland of primary sex characters, 

 namely, oocytes and cell nests. The presence of oocyi^es in the 

 germ gland is unquestionably a female character, while the pres- 

 ence of cysts may indicate a juvenile condition or a male charac- 

 ter. The oocytes, in one case, and the well-developed cysts, in. 



