SEA-FISHERIES LABORATORY. 355 



Pennatulid Virgularia is also common and forms a con- 

 stant food of various Gradidse. Many edible fishes 

 spawn here, Pleuronectids like the Plaice, Flounder and 

 Dab, and Gadoids such as the Cod, Haddock and Whiting. 

 During the spawning season ripe fish may always be taken 

 by trawling on the ground, and pelagic eggs in various 

 stages of development are found in plankton gatherings 

 made at the surface. Another spawning ground exists 

 further North, due East of the North end of the Isle of 

 Man. On the West side of the Isle of Man are grounds 

 due West of Dalby where other Pleuronectids, and 

 probably the Plaice also, spawn, and it is very probable, 

 though systematic surveys have not yet been made, that 

 similar spawning areas lie further South out from the 

 Lancashire and Welsh coasts. 



As we have already stated the Plaice emits its spawn 

 at the bottom of the sea and the eggs rise towards the 

 surface. Here their inshore migration begins. The 

 developing embryo while still within the egg capsule has 

 of course no power of movement of its own, and even after 

 it has hatched and is a pelagic organism its powers of 

 migration are extremely limited, so that its present move- 

 ments are determined entirely by the combined operation 

 of physical agents, waves, prevailing winds, tidal drift and 

 currents, and from a consideration of the working of these 

 factors the general course of the eggs and embryos from the 

 spawning grounds can be determined. 



The general drift of small objects floating at or near 

 the surface of the sea has been studied in the Irish Sea by 

 observing the movements of weighted bottles designed to 

 drift partially or wholly submerged. Two such series of 

 experiments have been made,* and their results shew that 

 the combined operation of the various agents indicated 

 ♦Lancashire Sea Fish. Laby. Eeports, 1895, p. 12, and 1898, p. 30. 



