196 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



are so extremely abundant in the sea, that when they die 

 their dead shells fall to the bottom, and form a layer of 

 mud or ooze. 



The difference between an animal and a plant. 



Most animals have a very different appearance from 

 plants, but in the case of diatoms, and other small 

 creatures, it is quite impossible to tell by their appearance 

 whether they are animals or plants. The real difference 

 lies in the methods of feeding. 



An animal must live on food which is either alive, or 

 has been alive. So animals feed on the living or dead 

 bodies of other animals or plants. 



A plant lives on material which has never been alive 

 —on the carbonic acid and the substances containing 

 nitrogen, which are in the air or are dissolved in the sea- 

 water. 



Noctiluca. — Magnified about 70 dia. 



Noctiluca . — This is a small animal which is 

 always present in some parts of the Irish Sea during the 

 summer. It is sometimes so abundant as to colour the 

 water brown. It is simply a little round blob of jelly-like 

 material. It feeds on diatoms, and these will usually be 



