PARKER: OPTIC CHIASMA IN TELEOSTS, 



231 



sinistral specimen, and Pleuronectes flesus, also dextral, has been re- 

 ported by the same authority (:00, p. 339) as represented in different 

 localities by from five to thirty-six per cent of sinistral individuals. In 

 American waters three such species are known : the halibut of the 

 Atlantic and Pacific coasts, and the bastard halibut and starry flounder 

 of the California coast. The halibut is typically a dextral species and, 

 like Pleuronectes platessa, is only rarely represented by sinistral in- 

 dividuals. The bastard halibut, according to Jordan and Evermami 

 ('96-00, p. 2625), is almost as frequently dextral as sinistral, and the 

 starry flounder, a dextral species, is said by the same authorities 



TABLE IV. 



{'96-00, p. 2G07) to be frequently sinistral. If now the determina- 

 tions as to which optic nerve shall be dorsal at the chiasma and as to 

 which eye shall subsequently migrate are dependent phenomena, it 

 follows that in those species in which the left eye migrates in some 

 individuals and the right one in others, there should be found two 

 corresponding types of nerve crossings. In ascertaining whether such 

 is the case or not, I examined specimens of the three American species 

 mentioned ; the results of this examination are given in Table IV. 



1 Atypical individuals are indicated by italic numerals. 



2 Material supplied in part by the United States Commission of Fish and 

 Fisheries. 



