290 MISCELLANEOUS OBJECTIONS TO THE [Chap. 7H 



The Pleuronecticlae, or Flat-fish, are remarkable for 



their asymmetrical bodies. They rest on one side, — in 



the greater number of species on the left, but in some on 



the right side ; and occasionally reversed adult specimens 



occur. The lower, or resting-surface, resembles at first 



sight the ventral surface of an ordinary fish : it is of a 



white colour, less developed in many ways than the 



upper side, with the lateral fins often of smaller size. 



But the eyes offer the most remarkable peculiarity ; 



for they are both placed on the upper side of the head. 



During early youth, however, they stand opposite to 



each other, and the whole body is then symmetrical, 



with both sides equally coloured. Soon the eye proper 



to the lower side begins to glide slowly round the head 



to the upper side ; but does not pass right through the 



skull, as was formerly thought to be the case. It is 



obvious that unless the lower eye did thus travel round, 



it could not be used by the fish whilst lying in its 



habitual position on one side. The lower eye would, 



also, have been liable to be abraded by the sandy bottom. 



That the Pleuronectidae are admirably adapted by their 



llattened 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, winch are entirely 



thrown to one side." 



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



