546 ME. H. M. KYLE OK NASAL 



The other structures in connection with the mouth vary little 

 in the different specimens. In all, the jaws of the upper (eyed) 

 side are quite bare, whilst those of the lower (blind) side display 

 strong series of chisel-shaped teeth (fig. 3, t.m.). The mandibular 

 and maxillary " breathing-valves " * are strongly developed 

 (fig. 4, h.v.), and the only appreciable difi"erence is seen in the 

 length of the gill-filaments. These are very long in all specimens, 

 exceeding the usual length found in the Heterosomata, but are 

 slightly longer in the divergent specimen than in the others. 

 Although dissections of four of the specimens were not made, it 

 is most probable that in other characters of the head and body 

 all five are alike, since by analogy I find in the Plaice and 

 Flounder, in which the internal structure differs little, that what 

 important differences there are may be seen externally. 



The question then presents itself whether the single specimen 

 of Gynoglossus is entitled to be taken as the type of a new 

 species. It is possible, indeed, that such a species really exists, 

 because if this peculiar combination of characters occurs in one 

 individual, there is no reason why it should not occur in many 

 others. On the other hand, it is possible that this individual 

 may be quite unique, and that the accessory portion of the 

 lateral line and the increased length of the gill-filaments may 

 have arisen after the perforation of the roof of the mouth in the 

 life-history of it alone ; but this does not seem very probable. 

 The lateral line in other forms is developed at a very early stage, 

 and if an accessory branch is present, we should imagine that it 

 would arise about the same time as the main portions. Hence 

 the perforation of the roof of the mouth must have appeared in 

 the earlier stages of life ; and, if so, is possibly inherited — that is 

 to say, a distinct species may exist whose characters are fairly 

 constant and reappear in the offspring. It is possible again that 

 we have here only the beginning or the foreshadowing of a new 

 species. If we reason from the principle of Natural Selection, 

 we may conclude that the possession of a naso-pharyngeal 

 communication would result in great advantage to a fish living 

 in the sand. Or we may say, with Dohrnf, that the change in 



* Owen, R. : ' Anatomy of Vertebrates,' vol. i. p. 413. — Dahlgren, W. : " The 

 Maxillary and Mandibular Breathing-vahes of Teleostean Fishes," Zool. Bull. 

 Boston, 1898. Smitt, F. A. : ' Scandinavian Fishes,' p. 263. 



t Dohrn, A. : ' Das Princip des Functionswecbsels.' Leipzig, 1874. 



