GREAT BRITAIN. 183 



pupil of the eyes, no longer makes a right angle with the 

 longitudinal axis. This movement of translation is soon 

 followed by a slight movement of rotation, so that when 

 the young fish is seen in profile, the eyes of the two sides 

 no longer appear in the same plane, that on the blind side 

 being now slightly above and in advance of that on the 

 coloured side. With increasing age the eye on the blind 

 side rises higher and higher towards the median longi- 

 tudinal line of the head. The back fin gradually extends 

 >wards the nostrils, and finds its way behind the eye 

 h has come from the blind side. The eye is trans- 

 ferred at such an early period that the bones of the skull 

 ire cartilaginous, and the transfer is carried out by a com- 

 )ined process of translation and rotation. In some cases 

 was observed to be transferred, as described by Malm, 

 >und the head by the snout, and in others to actually pass 

 irough the soft tissues of the head, and this divergence 

 appeared to be due solely to the generic differences in the 

 position of the dorsal fin. 



Some flat fishes have the eyes normally on the right side 

 of the body, others on the left, but reversed instances,, or 

 those in which the coloured side is on that which is, as a 

 rule, uncoloured, are not uncommon among most genera of 

 flat fishes. Such is very frequently observed in flounders, 

 these fishes, living close in shore, being more exposed to 

 the actions of currents than those genera which live in the 

 deep sea. In this way they become, in their very early 

 life, forced on to the side which is not the normal one. 

 Such variations are more commonly perceived in some 

 localities than in others, and will generally be found due 

 to local disturbing causes. Professor Agassiz kept young 

 flounders in glass vases raised high above the table, and 

 found that, notwithstanding the fact that here no dis- 



