192 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



At the spawning season the eggs and milt are shed, 

 and drift about in the sea. Fertilisation then takes place 

 as described above. 



The eggs of all the flat fishes, and of most round 

 fishes (the cod, haddock, whiting, gurnard, sprat, &c.) 

 float near the surface of the sea. The eggs of the skate, 

 rays and dogfishes, herring, and some other fishes (which 

 are not used as food) sink to the bottom, and pass through 

 their development there. 



The average number of eggs spawned by a single 

 female fish in the course of one season are : — 



In the Turbot ... 

 „ Cod 

 „ Sole ... 





8,600,000 



4,500,000 



570,000 



,, Haddock 





450,000 



„ Plaice ... 

 ,, Whiting 

 „ Herring... 



,, Skates, rays a 

 dozen or 1 



300,000 



120,000 



31,000 



nd dogfishes, about a 

 sss in the season. 



Third Day. 

 The Mussel. 



The structure of the musse 1. — The 

 mouth and stomach ; the gills ; the mantle ; the foot or 

 " tongue " ; the byssus or " weed." 



The feeding of the musse 1. — The mussel 

 feeds " by suction." Its food consists of exceedingly 

 small animals and plants that float about in the water. 

 The water containing this food is sucked into the cavity 

 of the shell and the food is then taken into the mouth. 



The mussel breathes by means of its gills. When the 

 gill is examined under the microscope it is seen to consist 



