igS NATURAL SCIENCE. mav, 



among flounders taken from the sea.- The pigmentation in my 

 experiment may even, he suggests, be sufficiently explained as a 

 souvenir of the original bilaterally symmetrical condition. He mag- 

 nanimously mentions, however, that the individuals kept by me 

 under the ordinary conditions remained white on the blind side, 

 which is a fact that I stated, and he also adds that reversed speci- 

 mens must be rare at Plymouth, since I have not even anticipated 

 the objection, which is an erroneous inference. At Plymouth 

 reversed flounders are exceedingly common, almost as abundant as 

 normal specimens. It is true the objection did not occur to me, for 

 it is obvious that if inheritance in the flounder acted as Giard sup- 

 poses, there would be none but double flounders, since right-sided 

 and left-sided individuals are always breeding with one another. It 

 is remarkable that Giard does not perceive that his objection is 

 more applicable to his own explanation of the ambicoloured turbot. 



In conclusion, Giard reiterates his belief in his own theory, that 

 the asymmetry of the Pleuronectidae is due to the inequality of the 

 eyes in their pelagic larvae. This theory was announced in 1877, 

 a propos of Agassiz's researches. The kernel of the theory appears 

 to be contained in this sentence : — " From the moment when one eye 

 is stronger than the other there must be a rotation towards the more 

 feeble side, and a displacement of the (stronger) eye which can 

 see through the body on account of its transparency and slight 

 thickness : little by little selection reduces the amount of material 

 between the eye of the blind side and exterior objects," and so on. I 

 confess I do not understand Nature sufficiently to be able to appre- 

 ciate this theory. Transparent pelagic animals have sense organs, 

 especially eyes, according to Giard, of unequal size, but he does not 

 say why. As a matter of fact, the eyes in young flat-fishes are not 

 unequal in size — at least I have looked for any such inequality in 

 vain. It is true that Owen states that the optic nerve of one side 

 is thicker than the other in the halibut ; but I have recently dissected 

 the head of a halibut, and found no difference in thickness 

 between the two optic nerves. It seems to me that even if one eye 

 were larger than the other, this is no reason why it should move 

 out of its place ; and I imagine the mere transparency of the body 

 could not produce inequality in the size of the eyes. If I understand 

 Giard aright, the flat-fish lies on its side because its eyes are asym- 

 metrical, whereas it is obvious to other naturalists that the eyes are 

 asymmetrical because it lies on its side. 



It is not my purpose on the present occasion to set forth at 

 length the Views I agree with or hold on the subject I have dealt 

 with. I have intentionally devoted this opportunity to destructive 

 criticism. I have considered some examples of the loose and 



•* Giard evidently supposes that the abnormaUty of the eyes does not occur 

 in double flounders, since on the preceding page he states that it is confined to 

 the turbot. 



