OBJECTIONS TO THE THEORY OF NATURAL SELECTION 189 



in still-existing Cetaceans, lead us onward to the enormous plates 

 of baleen in the Greenland whale. Nor is there the least reason to 

 doubt that each step in this scale might have been as serviceable 

 to certain ancient Cetaceans, with the functions of the parts 

 slowly changing during the progress of development, as are the 

 gradations in the beaks of the different existing members of the 

 duck-family. We should bear in mind that each species of duck 

 is subjected to a severe struggle for existence, and that the struc- 

 ture of every part of its frame must be well adapted to its con- 

 ditions of life. 



The Pleuronectidae, or Flat-fish, are remarkable for their asym- 

 metrical bodies. They rest on one side — in the greater number 

 of species on the left, but in some on the right side; and occasion- 

 ally 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 color, 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 colored. 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 while 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 flattened and asymmetrical structure 

 for their habits of life, is manifest from several species, such as 

 soles, flounders, etc., being extremely common. The chief ad- 

 vantages thus gained seem to be protection from their enemies, 

 and facility for freeding 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 pin- 

 guis, 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 toward the other side of the head could 

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



