21) 
Pennatulid Vzrgularia is also common and forms a con- 
stant food of various Gadide. 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 
* Laneashire Sea Fish. Laby. Reports, 1895, p. 12, and 1898, p. 30. 
