OBJECTIONS TO THE THEORY OF NATURAL SELECTION 191 



sides of the head are said to be somewhat dissimilar. Our great 

 authority on Fishes, Dr. Gunther, concludes his abstract of Malm's 

 paper, by remarking that "the author gives a very simple ex- 

 planation of the abnormal condition of the Pleuronectoids." 



We thus see that the first stages of the transit of the eye from 

 one side of the head to the other, which Mr. Mivart considers 

 would be injurious, may be attributed to the habit, no doubt 

 beneficial to the individual and to the species, of endeavoring to 

 look upward with both eyes, while resting on one side at the bot- 

 tom. We may also attribute to the inherited effects of use the 

 fact of the mouth in several kinds of flat-fish being bent toward 

 the lower surface, with the jawbones stronger and more effective 

 on this, the eyeless side of the head, than on the other, for the 

 sake, as Dr. Traquair supposes, of feeding with ease on the ground. 

 Disuse, on the other hand, will account for the less developed 

 condition of the whole inferior half of the body, including the 

 lateral fins; though Yarrel thinks that the reduced size of these 

 fins is advantageous to the fish, as " there is so much less room 

 for their action than with the larger fins above." Perhaps the 

 lesser number of teeth in the proportion of four to seven in the 

 upper halves of the two jaws of the plaice, to twenty-five to thirty 

 in the lower halves, may likewise be accounted for by disuse. From 

 the colorless state of the ventral surface of most fishes and of 

 many other animals, we may reasonably suppose that the ab- 

 sence of color in flat-fish on the side, whether it be the right or 

 left, which is undermost, is due to the exclusion of light. But it 

 cannot be supposed that the peculiar speckled appearance of the 

 upper side of the sole, so like the sandy bed of the sea, or the 

 power in some species, as recently shown by Pouchet, of changing 

 their color in accordance with the surrounding surface, or the 

 presence of bony tubercles on the upper side of the turbot, are 

 due to the action of the light. Here natural selection has probably 

 come into play, as well as in adapting the general shape of the 

 body of these fishes, and many other peculiarities, to their habits 

 of life. We should keep in mind, as I have before insisted, that 

 the inherited effects of the increased use of parts, and perhaps of 

 their disuse, will be strengthened by natural selection. For all 

 spontaneous variations in the right direction will thus be pre- 

 served; as will those individuals which inherit in the highest 

 degree the effects of the increased and beneficial use of any part. 

 How much to attribute in each particular case to the effects of 

 use, and how much to natural selection, it seems impossible to 

 decide. 



