174 MISCELLANEOUS OBJECTIONS TO THE [CHAP. Vtt 



That the Pleuronectidoe are admirably adapted by their flattened 

 and asymmetrical structure for their habits of life, is manifest 

 from several species, such as soles, flounders, &c., being extremely 

 common. The chief advantages thus gained seem to be protection 

 from their enemies, and facility for feeding on the ground. The 

 different members, however, of the family present, as Schiodte 

 remarks, "a long series of forms exhibiting a gradual transition 

 from Hippoglossus pinguis, which does not in any considerable 

 degree alter the shape in which it leaves the ovum, to the soles, 

 which are entirely thrown to one side." 



Mr. Mivart has taken up this case, and remarks that a sudden 

 spontaneous transformation in the position of the eyes is hardly 

 conceivable, in which I quite agree with him. He then adds : " if 

 the transit was gradual, then how such transit of one eye a minute 

 fraction of the journey towards the other side of the head could 

 benefit the individual is, indeed, far from clear. It seems, even, 

 that such an incipient transformation must rather have been 

 injurious." But he might have found an answer to this objection 

 in the excellent observations published in 1867 by Malm. The 

 Pleuronectidse, whilst very young and still symmetrical, with their 

 eyes standing on opposite sides of the head, cannot long retain a 

 vertical position, owing to the excessive depth of their bodies, the 

 small size of their lateral fins, and to their being destitute of a 

 swimbladder. Hence soon growing tired, they fall to the bottom 

 on one side. Whilst thus at rest they often twist, as Malm 

 observed, the lower eye upwards, to see above them ; and they do 

 this so vigorously that the eye is pressed hard against the upper 

 part of the orbit. The forehead between the eyes consequently 

 becomes, as could be plainly seen, temporarily contracted in 

 breadth. On one occasion Malm saw a young fish raise and 

 depress the lower eye through an angular distance of about seventy 

 degrees. 



We should remember that the skull at this early age is cartila- 

 ginous and flexible, so that it readily yields to muscular action. 

 It is also known with the higher animals, even after early youth, 

 that the skull yields and is altered in shape, if the skin or muscles 

 be permanently contracted through disease or some accident. 

 With long-eared rabbits, if one ear lops forwards and downwards, 

 its weight drags forward all the bones of the skull on the same 

 side, of which I have given a figure. Malm states that the newly- 

 hatched young of perches, salmon, and several other symmetrical 

 fishes, have the habit of occasionally resting on one side at the 

 bottom; and he has observed that they often then strain their 

 lower eyes so as to look upwards; and their skulls are thus 

 rendered rather crooked. These fishes, however, are soon able to 

 hold themselves in a vertical position, and no permanent eflect is 



