54 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



eggs of the right-handed species and those of the left-handed species 

 is shown by the fact that the eggs of most of the right-sided species 

 have no oil-globule, while the eggs of most of the left-sided species 

 have a single oil-globule. This applies to the Flounder family only, 

 and is not true of the Soles (Solidce). It is difficult to imagine that 

 the presence of the oil-globule has any reference to the external 

 conditions, since the eggs of all the species of flat-fishes (except those 

 of the Winter Flounders Pseudopleuronectes) are pelagic and, there- 

 fore, apparently at least, subject to similar sonditions. This appar- 

 ent relation between right and left-sidedness and the presence of the 

 oil-globule may, of course be a mere coincidence, 3^et the facts are 

 so striking that it does not seem to be doing violence to reasonable 

 inference if we believe that such a coincidence is a sio;nificant one 

 and based on a real difference in germinal structure. If this is true, 

 then the asymmetry of the fish must be inherent in the germ. 



There is another line of evidence, of much greater force, wJiich 

 seems to point unquestionably to the germ as the source of these 

 modifications. The relation of the optic nerves in the chiasma in 

 fishes has been studied by Prof. G. H. Parker. In the bony fishes 

 the optic nerves cross each other in the chiasma without any inter- 

 mingling of fibers. In the ordinary bony fishes it is apparently a 

 matter of chance whether the right or left nerve is above the other 

 in the chiasma. In 1,000 specimens of ten common species, 486 had 

 the left nerve uppermost and 514 the right nerve. In individual 

 species, similar figures hold true; for example in the haddock, 48 

 had the left nerve uppermost, and 52 the right nerve. In the 

 flounders, however, a different law holds true and the arrangement 

 of the nerves in the chiasma is not a matter of indifference. Of 

 flounders with eyes on the left side, 131 individuals, representing 

 nine species, all have the right nerve uppermost. Two hundred and 

 thirty dextral flounders, representing sixteen species, had the left 

 nerve uppermost. This is not true of the soles, however; in them 

 the arrangement of the chiasma is apparently a matter of chance as 

 in other bony fishes and has no relation with the asymmetry of the 



