102 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



MID- WINTER INVASION OF NOCTILUCA AND 

 CTENOPHORA. 



By A. Scott, A.L.S 



On Tuesday, December 16th, 1919, Barrow Channel was 

 visited by an immense swarm of the Flagellate Noctiluca and 

 the Ctenophores Pleurobrachia and Beroe. The invasion was 

 sudden and short. Two days previously there was not the 

 slightest indication that these plankton organisms were in the 

 area. Two days later the many millions of Noctiluca and 

 millions of Pleurobrachia had vanished and left no trace that 

 anything unusual had occurred in the interval. 



The routine duties of the laboratory usually require one 

 or two visits to be made along the shore between tide marks 

 each week for general information and collecting useful material. 

 In the mussel fishing season the visits are more frequent. 

 A certain amount of supervision is needed to see that the 

 conditions of the concession for relaying mussels intended for 

 food are observed. One of these duty visits was made on 

 Sunday, December 14th, but nothing unusual was observed. 

 Next day there was a remarkably heavy fall of rain which 

 lasted for some hours. The rain was accompanied by a light 

 southerly wind, but the sea was almost smooth. Another 

 visit was made on December 16th, and attention was at once 

 drawn to the presence of great numbers of ctenophora that 

 had been stranded on the sandy mud flats during the ebb of 

 the early morning tide. The area (500 yards wide and about 

 1,000 yards long) between Roa Island and Foulney appeared 

 as if it had been thickly sprinkled with glass marbles. These 

 were Pleurobrachia. The distribution was fairly uniform, 

 but generally the numbers were distinctly greater on the 

 slopes of the little gutters which cut through the flat muddy 

 sand and act as drains. Mingled with the Pleurobrachia one 



