432 ANIMAL LIFE-HISTORIES 



these early stages the turbot and brill are rapacious, and feed 

 on other fishes smaller than themselves. They might capture 

 such prey when lying like the adult at the bottom, but in 

 summer time the young of other kinds of fishes are much more 

 plentiful in the open water and near the surface than at the 

 bottom. In the aquarium at Plymouth the young turbot have 

 been fed on pieces of dead fish, but both they and the brill 

 much prefer living prey, and when kept with other young fish, 

 such as flounders, speedily devour them or choke themselves 

 in the attempt." Later on these little creatures settle down to 

 a life on the sea-floor, and lose the swim-bladder, which is not 



required by a ground- 

 fish. The left side of 

 the body, which is kept 

 uppermost (fig. 957), 

 is strongly pigmented, 

 while the other side is 

 pale. Some of the 

 points in this life-his- 

 tory are good instances 

 of recapitulation, lead- 

 ing to the conclusion 



Fig- 957. Turbot (Rhombus maximus) 



that the asymmetrical 



flat-fishes are descended from symmetrical forms in which a 

 swim -bladder was present. While in Turbot and Brill both 

 eyes are on the left side of the body, the right side being kept 

 next the sea-bottom, the reverse is the case in most of our edible 

 flat-fishes, such as Plaice, Flounder, Dab, Halibut, Sole, and 

 Lemon Sole. 



Allusion has already been made to the spawning habits 

 of the Salmon (Salmo salar). Shoals of these fishes ascend 

 rivers in spring for the purpose of laying their eggs, which 

 event takes place in the autumn. Development is a very slow 

 process, for it is three or four months before the young hatch 

 out. They are then only about 2 - 5 of an inch long, and a large 

 yolk-sac projects from the under side of the body (fig. 958). 

 In the second year of life the young salmon, known in this 

 stage as " parr ", descend to the sea, apparently returning every 

 year to their native river for the purpose of spawning. Several 

 years elapse before the adult characteristics are fully acquired, 



