358 NATURAL SCIENCE. 



JULY, 



white. 2 But these specimens are very numerous ; all the fishermen 

 know them, and it is needless repetition to tell us that they lie 

 perfectly horizontally on the ground. In spite of this, Cunningham 

 remarks : " Giard assumes that double fishes swim vertically." What 

 I said was, that not the double but the monstrous specimen (which is very 

 different) swims vertically ; besides which, I do not affirm that 

 monstrous flat-fishes swim all their life vertically, but only that they 

 remain longer in that position than the others, and, in any case, long 

 enough to allow the influence of the light to act efficaciously on the 

 side ordinarily colourless. 



Cunningham tells us that he has made a series of careful experi- 

 ments to prove the direct action of the light on the skin of the under 

 side of the flounder. Obviously, I can only speak of those experi- 

 ments results of which he has published (ZoologiscJier Anzeiger, 1891), 

 and the method adopted in these does not seem to be satisfactory, for as 

 long as the young flounders were not covered by a net, the experi- 

 ment was not conclusive, and when they were held down by a net 

 (the meshes of which must have been extremely fine, since they 

 prevented the renewal of the water), the fishes died rapidly. This 

 experiment forcibly reminds one of that of the man in the fable, who, 

 wishing to habituate his ass to eat nothing, saw the animal die of 

 hunger at the very moment that his experiment seemed likely to 

 succeed. Cunningham tells us to-day what he had neglected to 

 mention in his previous paper, that "at Plymouth reversed flounders 

 are exceedingly common, almost as abundant as normal specimens," 

 and that he cannot see what disturbing influence this fact can have 

 on his own experiments. " It is obvious," says he, " that if inheritance 

 in the flounders acts as Giard supposes, there would be none but 

 double flounders, since right-sided and left-sided individuals are 

 always breeding with one another." This is an astonishing miscon- 

 ception of the laws which govern the products of cross-breeding 

 among animals. As all biologists know, the progeny obtained by 

 the union of two races cannot be intermediate between the two 

 progenitors, but resemble closely one or the other. For instance, 

 in a union between a female white mouse and a wild gray male, one 

 obtains constantly young, and some of whom are completely gray 

 others entirely white. Also, we know that a certain anatomical 

 character has a better chance of reappearing in the descendants 

 when it has disappeared more recently, and it is evident that a 

 right-sided flounder which can count a certain number of left-sided 

 individuals among its ancestors, will have a greater tendency to 

 acquire the colouring on its left side under the influence of the causes 

 which have determined in the race the possession of this colouring. 



2 The position of the eye and the terminating comb of the dorsal fin are not of 

 much signification in the plaice, where the eye is normally almost on the edge of 

 the head, and the dorsal fin terminates almost behind the eye. 



