on the Obliquity of Flounders. 363 



bony cranium there is a single orbit, entirely surrounded by 

 bone, containing the upper eye only ; the lower eye lies outside 

 the orbit, and is protected above by the bones which form its 

 lower margin. These bones are always found to be the frontals 

 and prefrontals belonging to the eye side ; and as the lower eye 

 lies uuder these, it is evident that it is in the usual position with 

 reference to the forehead of its own side. The upper eye, which 

 from its position may be regarded as having belonged to the 

 blind side, and which will be shown to have been seated on the 

 blind side at an earlier stage, lies within the orbit, whose lower 

 border consists of the above-mentioned " partition •" its upper 

 margin is composed of the frontal and prefrontal bones of the 

 blind side. " From this it directly follows that the eye of the 

 blind side has come round to the (inner) side of the frontal bones 

 of the blind side, v/hich is turned towards the middle line, instead 

 of lying at the outer (now upturned) side/' 



The partition between the eyes, instead of being formed equally 

 from the right and left frontals and prefrontals, is formed only 

 by those of the eye side, right or left, or at most with the addi- 

 tion of a small plate from the frontal bone of the blind side ; 

 whilst the remainder of the bone-mass formed by the frontal 

 and prefrontal of the blind side surrounds the lower or upturned 

 margin of the eye, forming the margin of the orbit next the 

 dorsal line. " There is thus an unmistakeable encompassing of 

 the parts, which apparently goes beyond all rule — nay, even be- 

 yond all analogy ; for usually when parts with definite relations 

 to one another change place, forwards or backwards, upwards or 

 downwards, inwards or outwards, in an organism, the associated 

 parts are moved more or less in the same direction, so that the 

 relative position of the parts remains in the main unchanged." 

 To this rule the different relations which the upper eye in the 

 Flounder bears to its frontal bones forms an exception, which 

 can only be accounted for by a moving round of the parts upon 

 one another. The hitherto received explanation, that the abnor- 

 mal position of the Flounder's eyes is clue simply to a greater or 

 less degree of torsion of the whole head upon the axis of the 

 body, or of a part of the head upon the axis of the head, must 

 therefore be regarded as insufficient, since this position could 

 not have been attained without an actual removal of parts of the 

 head. In many forms the eyes lie close to one another, and the 

 partition between them is quite narrow ; while in others the par- 

 tition is even twice as broad as the diameter of the eye. Some- 

 times the upper eye lies before the lower, and sometimes behind 

 it — in some cases so far behind it as to seem to rest on the 

 back of the head or the nape of the neck. Notwithstanding all 

 these varieties in position, the relations of the upper eye to the 



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