SEA-FISHERIES LABORATORY. 321 



mortality, there is the process of metamorphosis going on 

 whereby the nauplius changes into the " cypris " stage, 

 which settles down after a few weeks on the sea bottom as 

 a young barnacle. The hatching period is probably a 

 very short one and the nauplii are liberated from many 

 barnacles at the same time. Unless the plankton is 

 collected at the critical moment the swarming may there- 

 fore escape notice. A sample of plankton collected eight 

 years ago in Barrow Channel consisted almost wholly of 

 barnacle nauplii, and supplied us with enough material 

 for use in the fishermen's classes until the spring of 1910. 

 Although we have collected plankton every spring in the 

 same locality and during the same period as in 1902, we 

 have, so far, not again met with another swarm. 



In the first part of this lieport ('08, p. 186) we 

 recorded a definitely localised swarm of Crab Zoeas. 

 These are cases of mero-planktonic organisms where the 

 swarm is determined no doubt by the position and time 

 of reproduction of the Neritic adult; but holoplanktonic 

 and oceanic forms give equally good examples. 



On Plate A, figs. 1 and 2 show " uniform monotonic " 

 gatherings of the Dinoflagellate Ceratium tripos and of 

 Noctiluca miliaris — the two most abundant causes of 

 luminosity in the Irish Sea. Ceratium more usually 

 occurs in quantity in the open sea round the Isle of Man, 

 and Noctiluca along the coasts of Lancashire and North 

 Wales. Both occur in greatest abundance in late summer 

 or autumn. In September, '08, one of us found Noctiluca 

 so plentiful at Piel, in the Barrow Channel, that estima- 

 tions made by coHecting bottles of the water and counting 

 the Noctiluca showed that there were about 2,000,000 per 

 gallon present. 



The remaining two figures on Plate A show a mono- 

 tonic Diatom plankton (fig. 8), consisting, however, of a 



