J^^r- THE EVOLUTION OF FLAT-FISH. 357 



members of the Societe de Biologic to this question four months ago, 

 two large monstrous turbots have been noted to me, one at St. Vaast 

 la Hougue, the other at Le Croisic, by colleagues who only 

 occasionally visit the sea. 



Double specimens constitute an anomaly entirely distinct from 

 the preceding, much less profound, and much more frequent, since 

 they are to be found among all kinds of flat-fishes. It is almost 

 impossible to visit the fish markets in the French seaports without 

 finding one or several specimens. Among the turbot, double speci- 

 mens, or at least more or less spotted examples, must have been so 

 abundant at a certain time, or in certain localities, that, as I have 

 formerly remarked, our earlier ichthyologists (Daubenton, Bonnaterre, 

 Lacepede) considered the piebald coloration of the under side as a 

 specific character of Rhombus maximus. 



Among the flounders at Wimereux the average of individuals 

 completely double is about three per cent., but it would be much 

 higher if we included in our statistics the individuals merely piebald. 

 Malm has already recorded this frequency of specimens coloured on 

 the under side, and he attributed it to the fact that, as the flounders 

 lived near the mouth of rivers, in water continually agitated, their 

 young were unable to hold themselves constantly on one side or the 

 other. 



After having definitely established the distinction between the 

 two anomalies (ist, the arrest of development ; 2nd, the colouring of 

 the blind side), I found it insufficient to limit myself to the statement, 

 as my friend Pouchet has done recently, that it is very frequent to 

 find several anomalies on the same specimen.^ Indeed, if it is ordinarily 

 thus, it is because a first deviation in the development often entails 

 in consequence other modifications. I have, therefore, tried logically 

 to make the second anomaly subordinate to the first, and it is in 

 consequence of this that I have been led to speak of observations 

 well known and easily to be duplicated, at least in many cases, in the 

 metamorphosis of the Pleuronectids. 



I said that the turbot of which I speak " must have swum 

 [devait nager) in a vertical position, and must have rested rarely on its 

 right side." I am not in the habit of affirming what I have not seen for 

 myself, and, what is more, I had the testimony of two such experienced 

 ichthyologists as Day and Macintosh in support of my opinion. 

 Cunningham merely denies this evidence with the unnecessary 

 remark: "this is simply an error of observation." Now, on what 

 facts does Cunningham base this contradiction of his predecessors ? 

 On the observation of a double plaice (not monstrous), and even 

 imperfectly double, since the posterior three-fourths of the lower side 

 are coloured in the same way as the.upper, the anterior fourth being 



1 G. Pouchet, Remarque sur deux turbots a face nadirale pigmentee. Societe 

 de Biologic, 5 mars 1892, p. 200. 



