MONSTROSITIES IN FISH. 



225 



we occasionally get what is termed a " monstrosity," 

 in which a flat-fish has its eyes one on each side 

 this being a reversion to the ancestral type. During 

 the earliest stages of all flat-fish within the egg they 

 are like ordinary fishes ; as they develop, one eye 

 may be seen gradually turning round to the same 



Fig. 155- 



The Brill (Rhombus Icevis). 



side as the fixed one, and in this way we have a 

 flat-fish, modified to swim and rest on one side, and 

 perfectly adapted to live under what seem the most 

 singular conditions we can imagine of any animal ! 

 The skull partakes of the same embryological modifi- 

 cation, being symmetrical when the fish is in the 

 e gg> an d gradually changing to an unsymmetrical 

 state as the fish gets older. Some of the flat-fish 

 attain a great size, especially the halibut, turbot, 

 and brill ; whilst others, as the little dab (Platessa 



Q 



