364 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



different years in the nature and amount of the plankton, 

 at the same localities, no doubt depend upon the volume 

 and period of such invasions. They may depend also 

 upon other factors, such as the weather (temperature, 

 sunshine, rainfall, wind, &c.) at the time, and previously. 



The phyto-plankton which was so wide-spread in 

 July, 1909 and 1910, especially round Mull and the 

 Small Isles, seems in the last couple of summers, and 

 especially in August, 1912, to have become pushed back 

 or restricted to the more land-locked waters by an unusual 

 invasion of oceanic forms. Unfortunately, our observa- 

 tions this year were a month later than in 1907 to 1910, 

 and it is impossible to say how much of the change 

 which we have recorded must be ascribed to the natural 

 decrease of phyto-plankton and increase of zoo-plankton 

 as the season advanced. But even if some allowance be 

 made for that, we think there can be no doubt from our 

 hauls in the sea to the north of Mull that this summer 

 there was an unusual influx* of characteristically 

 Atlantic organisms, such as the Copepods Metridia lucens 

 and Candacia armata, the Siphonophore Cupulita sarsi, 

 and the pelagic Tunicate Doliolum tritonis. 



Metridia lucens is an inhabitant of the oceanic 



waters of the North Atlantic which occasionally is 



carried in shoals into coastal areas such as the Irish Sea, 



Loch Fyne and the Minch. Candacia armata is also a 



North Atlantic form captured on various occasions off the 



south and south-west of Ireland, and has been recorded 



rarely from the Outer Hebrides, the Irish Sea and the 



Clyde Sea-Area. Both these Copepods indicate the 



presence of "Atlantic Drift" water. 



* Perhaps in the British Seas generally, as we have evidence of an 

 unusual invasion of the English Channel and southern part of the 

 Irish Sea by Atlantic Siphonophora in 1912. Numbers of Physalia 

 and Velella were found cast up on the shores of South Wales and the 

 South of England in March and April, and we have found Muggiaea 

 atlantica in Cardigan and Carnarvon Bays in September. 



