636 NATURAL SCIENCE. oct.. 



when it is 2 cm. in length, and yet it is larger, when first hatched, than the newly- 

 hatched turbot. All other genera whose larval stages have been described 

 resemble Pleuronectcs in their development and differ from Rhombus, excluding, of 

 course, the so-called Plagusin, which has a peculiarity of itsown. I cannot understand, 

 therefore, what is the similarity in development between furbotand flounder to which 

 Professor Giard alludes. I equally fail to understand how any Pleuronectida: can 

 be distinguished from the rest as having a gradual metamorphosis or palingenetic 

 development, since in that respect they all agree. Every Pleuronectid is hatched 

 as a perfectly symmetrical larva swimming vertically in the sea, and only acquires 

 the peculiarities of the adult after a gradual metamorphosis, in which one eye passes 

 from its original position to a new position on the opposite side of the head. 



If Professor Giard has discovered a true Pleuronectid which is hatched in the- 

 asymmetrical condition, he should say so ; and I should be the first to admit that 

 he had made a most remarkable and interesting discovery. It is, of course, true 

 that there is another mode of metamorphosis among Pleuronectidae besides that 

 which occurs in the majority of genera such as Rhombus and Phiironectes. This other 

 mode is that described by Steenstrup and Agassiz in P/(7oj(5/(;^ in which genus the eye 

 passes through the base of the dorsal fin to reach the opposite side of the head. 

 But surely the Professor would not assert that this mode is less palingenetic than 

 the other ? It is possible, indeed, that the early development of the dorsal fin is a 

 cenogenetic character, but the phylogenetic history is repeated in the bilaterally 

 symmetrical larva and the gradual torsion of the eyes in Plagiisia as in other 

 Pleuronectida}. 



I am not concerned to reply to Professor Giard's remarks about the abundance of 

 ambicolorate specimens in which no other abnormality is present. I need only say 

 that I am perfectly aware of their comparative commonness, and the point is not in 

 dispute between us. 



We come now to Professor Giard's reply to my criticism of his assumption that 

 the abnormal turbot he described must have swum in a vertical position. 



Neither in his original note nor in his reply to my article has the Professor 

 asserted that he ever saw an abnormal turbot, of adult size, swimming vertically in 

 the water ; he has simply said that his specimen demit luiger in that position. 

 He asserts he had the testimony of Day and Mcintosh in support of that opinion, 

 but this statement is not strictly accurate. As I stated in my previous article, I have 

 failed to find a particle of direct evidence, a single recorded observation, to prove that 

 abnormal flat-fishes swim vertically. Day (loc. at.) says that double flat-fishes " are 

 seen to swim vertically and to be more frequently found near the surface of the 

 water than those \vhich progress in a normal manner." But he does not say he has 

 seen this himself, nor mention anyone who has seen it. As for Professor Mcintosh, he 

 has not in either of the works cited by Professor Giard, namely," Marine Invertebrates 

 and Fishes of St. Andrew's," and the memoir on the "Development of Teleostean 

 Fishes," made any statement at all in reference to the position in swimming of mon- 

 strous adult specimens of flat-fishes of the same kind as Professor Giard's turbot. I 

 am considering now abnormal monstrous specimens of adult size, not larva? at a stage 

 of metamorphosis, which are, of course, normal. As there are no recorded observa- 

 tions as to the mode of swimming of the monstrous adult specimens, certainly none 

 cited by Professor Giard, I could not, and did not, assert that such observations 

 were erroneous. 



The Professor's method of controversy seems to me lamentably disingenuous. 

 He assumes that his monstrous turbot swam vertically, and I pointed out that there 

 was no evidence to prove this ; yet he now maintains that he had the testimony of 

 Day and Mcintosh to rely upon, although, as I have shown above, neither of those 

 authorities gives any evidence. My remark, " this is an error of observation," 

 referred to a perfectly distinct and separate question, namely, the position, in 

 swimming, of normal larval specimens whose metamorphosis is in normal progress. 

 Professor Giard, in his original note, stated that Professor Mcintosh had described 

 " un individu normal de 9 millimetres de long sur 7 millimetres de large, dont I'a-il 

 droit etait dejd arrive sur la crete du dos, et qui nageait encore dans la position 

 verticale." I replied that the assertion of its swimming in a vertical position was 



