396 



Professor W. C. Mclntosli 



[Feb. 1, 



Fig. 14. 



and stronger, and thus in many cases a parallelism exists between tbem 

 and the minute forms on which they prey, for the eggs rise on deposi- 

 tion towards the surface, where the helpless larvae (or newly hatched 

 young fishes) also often occur, and then they seek the lower regions of 

 the water as their size increases. 



There is much that is wonderful in such a life-history, especially 

 in the metamorphoses or changes of form undergone by many of our 



best fishes such as the flat fishes 

 (Pleuronectidae), which come out of the 

 egg just like a haddock or cod, with 

 an eye on each side, as in Fig. 2, yet 

 in after life have both eyes on the same 

 side. Nothing like this occurs in any 

 of the higher vertebrates. Gradually 

 during growth the body of the fish 

 increases in depth (Fig. 14), then the 

 right or left eye passes over (Fig. 15) 

 the ridge of the head to the opposite 

 side, while the creature, hitherto pela- 

 gic, sinks deeper in the water and 

 exhibits a tendency to lie on the side from which the eye has 

 passed, and which gradually loses its dark pigment so as to become 

 white.* It finally reaches the bottom, taking uj) its residence amongst 

 the sand or sandy mud, and lying with the two eyes and the coloured 

 side up, the white underneath. The mode by which the eye travels 

 round has been a fruitful source of discussion with scientific men, and 



Young " Witch " 



(Pleuronectes cynoglossus) 



in the third stasje, enlarcred. 



Fig. 15. 



Young " Witch " at a later stage, the left eye just appearing on the 

 ridge of the head, enlarged. 



amongst these the names of Steenstrup, Malm, Schiodte. and Alex. 

 Agassiz abroad, with Wyville Thomson and especially Traquair in 

 our own country, are well known. The fact is — two methods exist 

 in nature ; in the one the eye travels over the ridge of the head, as just 



* The tardy disappearance of tlie pigment in some forms is interesting. 



