of the Fishery Board for Scotland. 189 



IV.— CONTRIBUTIONS TOWARDS THE NATURAL HISTORY 

 OF THE PLAICE (P. PL A TESSA L.). By H. M. K y le, 

 M.A., B.Sc, Exhibition Science Scholar, St. Andrews. (Plates 

 IX.-X.) 



CONTENTS. Page. 



Introduction, 189 



Average-Size at First-Maturity, 190 



Variability and the Method of Treating Variations, ..... 201 



The Various Forms of Variability. ........ 207 



I. Sex-Variability, 207 



II. Growth-Variability, 212 



III. Race-Variability, 220 



Conclusion . 237 



INTRODUCTION. 



The following pages contain the record of a portion of the work that 

 has been going on for some time, and was concerned with the variations 

 and variability of the plaice. It was at first proposed to collect and 

 examine material from various places over the whole area inhabited by 

 the plaice before publishing anything, but the w T ork threatened to grow 

 beyond all control, and it was thought advisable, for this as well as for 

 other reasons of expediency, to work through a small portion thoroughly, 

 so that the experience thereby gained might be of service to myself and 

 others in the further development of the work. 



The leading ideas contained in the present paper may be briefly stated. 

 In the science of the fisheries the great bugbear to the naturalist, placing 

 almost insuperable difficulties in the way of framing definite conclusions 

 with regard to anything whatsoever, has been the great range of variations 

 which everything — structure, size, rate of growth, spawning season, &c. — 

 displays. This difficulty has not been confined, as is well known, to 

 fisheries, but is common to every department of biology. The 

 presence of this variability accounts for much of the indefiniteness and 

 i n conclusiveness of the work of the past. Within recent years, however, 

 the prolonged endeavours of Galton and the stimulus given to the subject 

 by the brilliant work of Bateson and Pearson, have been successful in 

 establishing a method of treating variations and in founding thereby a 

 new school of thought. In fisheries, Heincke has been the first to 

 introduce the new method, and with it further original developments 

 more particularly suited to the work on fishes. The present paper dis- 

 plays the working of this method so far as the material was suited to it. 

 The various forms of variability and the problems in connection therewith 

 are discussed. Race-variability is shown to be distinct from sex and 

 growth variability ; their close relationship, however, is made evident, 

 and the various and diverse causes of race-variations are displayed. 

 Incidentally to the main body of the work, the material was found suit- 

 able to the discussion of a hitherto unsolved problem, and a method is 

 shown by which this problem, the average size at which the plaice 

 becomes ripe for the first time, may be solved. 



With the exception of the herring, there is no species concerning which 

 so much has been written as the plaice. A summary of this past litera- 

 ture has not been thought suited to the present instalment of the work, 



