302 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



varying from about 19 to 35 centimetres were marked 

 and liberated. In neither case was the condition of the 

 fish very satisfactory since they had been rather roughly 

 handled in the course of the trawling by which they had 

 been caught, but quite enough were liberated in a condi- 

 tion sound enough for the purpose designed. 



The summer migration may be considered first since 

 this is not shown in the chart on p. 301. Eighteen fish 

 are recorded : these were they returned during the months 

 of June, July, and August. The months of recapture 

 are indicated by the lines representing the hypothetical 

 paths pursued by the fishes caught. Continuous lines 

 represent the June-caught fish, broken lines those caught 

 in July, and lines and dots those re-captured in August. 

 The heavy lines are isotherms for the middle of the whole 

 period — August 15th. Chart VI shows these migrations. 



The number of fishes recaptured is, it is true, few, 

 but the nature of the migrations made are almost 

 precisely similar to those observed in the recaptures of 

 previous years in two experiments made on this ground 

 at about the same time. It is, therefore, quite justifiable 

 to conclude that these migration paths are not 

 " accidental " nor unusual ones, but really represent 

 those followed by plaice living on this fishing ground at 

 this time of year. There were a few other fishes returned 

 during the same months, but the place of recapture of 

 these was uncertain, and they are not included in the 

 chart. 



The latter shows clearly that the migration paths 

 are, in the main, perpendicular to the direction of the 

 isothermal lines; they cross the latter, very generally by 

 the shortest routes. It is true that the paths are not 

 exactly transverse to the isotherms, but the latter have 

 been drawn for the middle of August. It is quite likely 



