358 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the plankton at a definite time and place — the periodic 

 reproduction of the Balanus causes the nauplii to appear 

 in the plankton at a certain time. 



Many other swarms of neritic, and especially mero- 

 planktonic, forms (such as crab zoeas and fish eggs) are 

 similarly due to the succession of stages in the life- 

 history; but oh the other hand, swarms of oceanic forms 

 may be due to immigrations caused by unusual hydro- 

 graphic or " weather " conditions. It does not seem 

 possible, as yet, to determine the effect of the various 

 factors — e.g., life-history and environmental conditions 

 in producing and terminating the great maxima, such as 

 that of the Diatoms in spring. But we have given some 

 evidence in favour of the view that increase in sunlight 

 rather than any rise in sea-temperature precedes the vernal 

 maximum of phyto-plankton. 



The most populous zone in the sea is below the 

 surface, but above 10 faths. The weighted net, ranging 

 down to about 10 faths., usually gives larger hauls thaa 

 the surface ones used at the same time. The organisms 

 in this zone no doubt rise and fall to some extent as a 

 result of weather conditions. Copepoda swarm on 

 occasions at the surface, and on other occasions are more 

 abundant a few fathoms below the surface. Diatoms, 

 when present in abundance in spring, are sometimes 

 found in increasing ratio from the surface down to 

 20 faths. 



Certain organisms seem to be frequently distributed 

 in shoals. This is, of course, normally the case with 

 many larval forms, but is also common with, for example, 

 Calanus, Anornalocera, Temora, and probably Micro- 

 calanus. We have referred above to certain large shoals 

 of Calanus, and to an occasion when an unusual quantity 

 of tish eggs was obtained from one spot. 



