PAKKER: OPTIC CHIASMA IN TELEOSTS. 



223 



ference being never more than ten per cent, and that in the remaining 

 four (Menidia, Pomatomus, Tautogolabrus, and Gadus) this difference 

 does not exceed in any instance twenty per cent. The differences, more- 

 over, are not all in favor of one side ; in four species the excess is in left 

 nerves dorsal, and in six in right nerves. Summing all together, it 

 appears that in a total of one thousand the right nerve was dorsal 514 

 times, the left 486. Since in each of the ten species both conditions 

 are so abundantly represented and are often so nearly equal, one is 

 justified in concluding that neither nerve is characteristically dorsal, 



TABLE I. 



though there is a slight difference in favor of the right. This difference 

 is so slight, however, that it is probable that a larger numV)er of observa- 

 tions would give a still closer agreement in numbers, a state indicative 

 of the unimportance from a physiological standpoint of the dorsal or the 

 ventral position of a nerve at tlie chiasma.^ 



Since both types of nerve crossing were abundantly represented in 



1 Material supplied from the Biological Laboratory of the United States Fish 

 Commission, Woods Hole, Mass. 



2 A condition of approximate equality, essentially like that just pointed out, 

 has been. observed by F. H. Herrick ('96, p. 143) in the right or left occurrence of 

 the crushing claw of the common lobster and by Yerkes (:01, p. 424) in the enlarged 

 claw of tlie male fiddler crab. 



