The Black-hacks of the Bass. 51 



More than this we shall probably never be able to settle. 

 One can hardly imagine that the earlier ornithologists were 

 altogether wrong in their identification ; yet, unfortunately 

 it cannot, I think, be said that they have left behind them 

 any conclusive evidence on the point.^ At same time, I see 

 no good reason why a pair or two of Great Black-backs 

 should not in those days have resorted to the Bass for the 

 purpose of rearing their young. An odd pair may even have 

 occasionally done so since, but to my mind this is unlikely. 

 My experience has led me to form the opinion that the Great 

 Black-back is a winter visitor to the ''Forth," while the 

 Lesser Black-back is as essentially a summer visitor. 



IX. On -the Distribution of the Pelagic Organisms in 

 Scottish Lakes. By James Murray. 



(Read 23rd January 1905.) 



The survey of the Scottish lochs is now so nearly com- 

 pleted, that it is possible to review the more important 

 facts in the distribution of the organisms which constitute 

 the plankton. For districts not visited by the Lake Survey, 

 information as to the Crustacea is supplied by the numerous 

 observations of Dr Scott (1 and 2) on the lochs of the 

 mainland and islands; while Messrs West (4) have done 

 valuable work on the phytoplankton of the Highlands and 

 the Outer Hebrides. Mr Scourfield (5) has also studied 

 the Entomostraca of part of the central Highlands, and has 

 examined many collections sent by us from other districts. 



The plankton of lakes does not at first sight appear to 

 offer a very promising subject for the study of geographical 

 distribution, as it is known to be of a nearly uniform 

 character over vast areas. As stated by Dr C. Wesenberg- 

 Lund (6) in a paper read before the Eoyal Society of 

 Edinburgh on 23rd January 1905, "freshwater plankton 

 is very homogeneous from Pole to Pole " ; " the plankton 



1 The somewhat parallel case of the alleged former nesting of the Common 

 Gull {L. canus) at St Abb's will no doubt occur to some. The existence 

 for generations of a large colony of L. fuscus on the Fame Isles may, perhaps, 

 also be noted. 



