of the Fishery Board for Scotland. 



295 



Petersen, as far as I understand him, does not attempt to account for 

 the difference in size of the first year fry except as the result of unequal 

 growth, although the group-series indicated upon some of his tables are 

 quite as marked as those I have instanced from St Andrew's Bay. 



He finds that the plaice in Danish waters has a spawning period from 

 November till April inclusive, with a maximum in the heart of the winter ; 

 but he takes the age of his fry from the month of March, though he 

 mentions that ' the birth-time for the great mass of plaice ' is in the 

 heart of winter. 



From a spawning period of January to May we were able to date the 

 mean-sized fish from March, a month which corresponds with that 

 selected by Petersen in spite of the different spawning period, so that, by 

 this fortunate coincidence, his results, as regards age, may be compared 

 with those given above. 



The great majority of his fry caught at Frederickshaven reach \ inch 

 in May, \\ inch in July, and 2 inches in September, results closely similar 

 to mine. It is important to note that, although he reports a spawning 

 period starting two months before that on the East Coast of Scotland, yet 

 the young fry only commence to appear at the same date as those here (May). 

 To explain this anomaly he has to assume that the November eggs actu- 

 ally take six months (November — May) to hatch and develop to the post- 

 larval stage, when they resort to the sandy shallows. Such an immense 

 retardation of development by low temperature from a duration of about 

 two months (hatching ten days, development during pelagic period six 

 weeks) to one of six months is scarcely likely ! If the spawning really 

 takes place to any extent in November and early December, it would pro- 

 bably be a less rash hypothesis to assume, until definite information is 

 obtained, that this is more or less exceptional, and that the young of that 

 date never grow to post-larval forms, but perish during their migration, 

 or earlier. 



It will be noticed that the same objection applies, to a lesser extent, to 

 the eggs laid in January and February ; but in this case we have not to 

 assume such an enormous retardation of growth. It is well known that a 

 low temperature will lengthen the period of incubation to eighteen or 

 twenty days, and a like retardation in the larval period, from six to about 

 ten or twelve weeks, would bring the period of inshore migration, even of 

 the mid-January brood, well into May. 



Upon somewhat the same lines as the recent work of Petersen, I have 

 gone over the only available statistics of the capture of plaice on the East 

 Coast. These were taken by the 'Garland,' and the measurements of 

 those captured in 1891 and 1892 appear in the Fishery Board Reports. 



The principle upon which the curves are plotted is obvious upon an 

 inspection of Diagram I. and II., and they have been given here only to 

 point out the fact that the number of fish captured do not form one 

 complete curve, but fall into a succession of secondary groups, which, 

 considering everything, are remarkably pronounced. 



The measurements were not taken for this purpose, and are so widely 

 approximated in the 1892 series that they are quite useless. Even in the 

 1891 series there are approximations of an inch or more which greatly 

 vitiate the results ; and when we remember that the observations were 

 made promiscuously throughout the months, it is remarkable that there 

 should be left any trace of recurring groups. Lastly, we find that the 

 various hauls were made quite indiscriminately throughout the various 

 stations, the number of hauls in each station in no way corresponding for 

 each month ; and we have also taken no account of the steady migrations 

 of the plaice which are known to take place in the Firth and in St 

 Andrew's Bay. 



