198 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



rim we find that the smallest animals in the sea live on 

 the Diatoms. 

 Thus— 



The Cod feeds largely on Crabs, 

 The Crab „ „ „ Worms, 



The Worm „ „ ,, Diatoms. 



The Plaice feeds largely on Shellfish (mussels and 



cockles), 

 Shellfish „ „ „ Diatoms. 



The Herring and Mackerel feed largely on Copepods, 

 Copepods feed on Diatoms. 



So everything in the sea depends for its food on the 

 Diatoms or on other plants living in the sea. The 

 Diatoms and other plants feed on the carbonic acid in the 

 sea water and on substances containing nitrogen which 

 are washed down from the land into the sea. 



A number of pictures ivill be shown by the lantern on the 

 last afternoon of the first week oj the class. These pictures 

 will be explained, and they will illustrate the work of the first 

 week. 



Sixth Day. 



The structure of Fishes. 



Skates and Rays and Dogfishe s. — 

 These fishes differ in many ways from the round fishes 

 like the cod and haddock. Their bones are gristly, they 

 breed in a different manner, and their gills are different. 



The structure of a skat e. — Its brain and 

 nerves ; the ear ; the heart, stomach and intestine ; the 

 gills. 



