224 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Results of the Second Generation. 



The second generation of trout (Table V) were descended from Lot 

 B, 1901. This lot included offspring from parents both of which had 

 the right nerve dorsal in the chiasma. The condition of the crossing 

 in the more remote ancestors is unknown, but from the results of the 

 first generation and of the control lot, it may safely be assumed that 

 they were about equally divided between rights and lefts. 



The trout used for the second generation were small and immature. 

 Consequently the number of eggs produced was small, and the number 

 of young hatched proportionately smaller than in ordinary lots. Six 

 females and nine males were used. The eggs of three of the females 

 were divided into two lots each, making nine lots in all. The young 

 trout were taken soon after hatching and fixed, as before, in Kleinen- 

 berg's picro-sulphuric solution. 



TABLE VI. 



In these nine lots there were 335 specimens, of which 1G5 were 

 rights and 170 were lefts. These 335 trout can be divided into two 

 groups according to their parentage. Group A includes those whose 

 parents were both lefts ; Group B, those whose parents were both rights. 

 The results are summarized in Table VI. 



The excess of lefts in Group A at first thought seems significant, but 

 is doubtless due to the smallness of the lot (coinpare the result given 

 by Lot 2 a, 1903). This lot gave the same proportion (75 per cent 

 lefts to 25 per cent rights) which might be expected were this a case of 

 dominance under Mendel's Law, but the number of young is so small 

 as to make the chances of error very great. Not only the small number 

 included in Group A throws doubt on the significance of the result, 

 but also the results of the larger group (B). In this latter group there 

 are 251 individuals, of which 129 or 51 per cent are rights. We are 

 dealing here with individuals whose parents and grandparents were 

 rights, and yet the result is practical equality of rights and lefts. 



When discussing the results of the first generation, the writer stated 

 that if Mendelism applied to this dimorphism, the case must be one of 



