Gatty Marine Laboratory^ St. Andrews. 551 



As formerly pointed out by Dr. J. H. Wilson and myself, 

 though stunted they are ripe; it may be that the same 

 explanation will suffice for the pearls, which occurred in 

 25 per cent, of them. It will thus be evident that pearls 

 appear in the common mussel much more frequently than in 

 the pearl-oyster, or, as a rule, in the freshwater pearl-mussel 

 {Margaritana maryaritifera) , but generally their lack of 

 lustre and beauty makes them of little value. 



In connexion with Dr. Lyster Jameson's views that the 

 eider duck and the scoter are the final hosts of the parasites 

 which form the nuclei of the pearls, it may be stated that 

 both occur in considerable numbers in the estuary of the 

 Eden and feed on the mussels. Moreover, the intestine of 

 the common scoter in St. Andrews Bay harbours large 

 numbers of these and other parasites, and thus is in contrast 

 with that of such forms as the guillemot and red-throated 

 diver — birds more purely piscivorous, and in which such 

 parasites are rare, though cestodes are common. It is 

 possible also that other species amongst the many birds 

 frequenting the mussel-beds, such as the oyster-catcher, 

 may be found to harbour the same parasite. 



Respecting Sir E. Home's statement that the ova of tlie 

 mussel form the nuclei of the pearls in the mantle, it has to be 

 mentioned that pearls are found in the males, where no ova 

 occur. 



2 The Effects of Marine Piscatorial Birds on the 

 Food-Fishes. 



It i-s often supposed that man in these days stands out 

 pre-eminently as the great destroyer of sea-fishes — by his 

 nets, trawls, and other apparatus; but, as shown in the 

 ' Resources of the Sea ' and in former " Notes," there are 

 other agencies which exist, and have existed for ages, wdiich, 

 in their persistent influences on the young stages or on the 

 adults of the fishes, place the efforts of man in a less 

 prominent position. This reflection has been suggested by 

 the captures of sea-birds in the nets for j)laice and cod in 

 St. Andrews Bay. These nets have been worked for more 

 than two years — at any rate for two seasons, viz. from 

 the middle of September to the middle of May, that is for 

 8 months each year. The majority of the birds captured 

 have been guillemots [Uria troile, L.), but divers, common 

 and velvet scoters, scaup-ducks, and razorbills are also 

 procured, the latter more rarely. Neither gulls nor gannets 

 have been obtained. Taking an average of 25 birds as a 



