REPORT OF COMMISSIONERS OF INLAND FISHERIES. 55 



fish. But in the case of flounders, it seems to be always' true that 

 the optic nerve growing out to form the eye that is later to migrate 

 over to the other side always passes above the other in the optic 

 chiasma. The only exception to this is in the case of reversed 

 flounders in which the relation of the nerves in the chiasma conforms 

 to that of the species and does not deviate with the exceptional 

 reversal. The case seems to be analogous to that of some of the 

 snails in which it is possible to trace the asymmetry back to the 

 eight-celled stage of the embryo, except that here, at the present 

 time at least, it is not possible to demonstrate the asymmetery at 

 nearly so early a stage. 



It is the necessary implication of the Lamarckian hypothesis that 

 the adaptative modifications acquired through "use and disuse'^ 

 must appear in, and, originally at least, have their source in, that 

 stage in the development of the individual which is affected by the 

 change of environment; the "use and disuse" of an organ or part 

 would not be called into play in any other stages, and so could not 

 directly produce modifications in them. Thus, in the case of flat- 

 fishes, the change to a bottom existence takes place after the free- 

 swimming stage has been assumed. Their modifications mvist be 

 adaptations to conditions of life first encountered in that stage and 

 can not be referred back for their origin to any earlier stage or to 

 the germ. Of course we must allow that the potentiality of pro- 

 ducing the modifications of the late stages must be present in the 

 earlier stages and in the germ, though there is no apparent reason 

 for assuming that the modifications themselves are projected back 

 to any earlier stage than that at which they are called out by the 

 reaction to the environment. No germinal modifications arising 

 in the egg itself is demanded in this case, for it encounters no new 

 conditions because the eggs of all flat-fishes (with one exception) 

 are pelagic and, therefore, subject to conditions which, as far as we 

 can see, are not different from those of many other fishes. Lamarckian 

 theories, then, as applied to the flat-fishes, must be considered to 

 imply that the modifications found in the adult have been superposed 



