LARRABEE. — THE OPTIC CIIIASMA OF TELEOSTS. 225 



alternative dominance, and the suppositional grounds were stated on 

 which that claim might be based. In discussing the group which in- 

 cluded the young of trout both of which were rights, it was stated 

 that both parents must be heterozygotes. Assuming this to be the 

 case, it would follow that of the rights produced in the so-called first 

 generation, one half would be pure and the other half heterozygous, 

 i. e., rights having the left condition recessive. According to the laws 

 of chance, out of a considerable number of these rights, there would 

 be one chance out of three of obtaining a " pure " right. Among the 

 parents of Group B there were four females and six males. Applying 

 the law of chance stated above, it is improbable that out of ten speci- 

 mens not one should prove to be a "pure " right, — an animal which 

 would give at least 75 per cent of right offspring. These results lead 

 inevitably to the conclusion that the Mendelian principles of heredity 

 do not apply to the dimorphism of the chiasmata of the trout, thus 

 confirming the doubts caused by the results of the first generation. 



The trout in Group B, whose parents and grandparents were 

 rights, afford a basis for comparison with the results to be expected 

 from another theory of heredity, namely, the one advanced by Galton 

 ("89). According to this theory, the parents contribute one half the 

 hereditary influences, the grandparents one quarter, the great-grand- 

 parents one eighth, and so on. 



In Group B there were 251 individuals, whose parents and grand- 

 parents were rights. According to the law of Galton, the influence of 

 these more immediate ancestors would be 75 per cent. The remoter 

 ancestors would probably be divided about equally between rights and 

 lefts. This would increase the influence of the rights to 87| per cent. 

 Of the 251 trout, then, about S~^ per cent, or 219 individuals, should 

 have the right nerve dorsal. Actually there were 51 per cent, or 129 

 rights. Such a discrepancy as this between the calculated and observed 

 results clearly indicates the inapplicability of Galton's Law, 



The results of selective breeding in the trout clearly indicate that 

 neither dimorphic condition is a racial character. All the trout came 

 from the same locality, and although bred to the second generation, no 

 effect of selection on the dimorphism was evident, unless possibly a 

 tendency to make the two conditions more nearly equal. 



The Results of Selected Matixgs in the Codfish 

 (Gad us morrhua L.). 



The results obtained from the codfish have little significance in 

 themselves, but they serve to confirm the conclusions drawn from the 

 study of the brook trout. 



VOL. XLII. — 15 



