HABITS OF MARINE ANIMALS 153 



animal and vegetable life known as protozoa and 

 protophyta, of which diatoms are the most important. 

 Protozoa and protophyta each consist of but a single 

 cell, and are among the lowest forms of life to be found 

 in the sea. 



The seal feeds on the cod, the cod on the whiting, 

 the whiting on the sprat, the sprat on the copepod 

 (a minute form of crustacean always present in the sea), 

 and the copepod on protozoa and diatoms. 



Again the ray devours the plaice, the plaice devours 

 the worm, and the worm feeds on various low forms of 

 marine life, which exist on diatoms, and so protozoa 

 and diatoms are the ultimate food producers. 



How comes it that diatoms can meet the immense 

 demands that must be made upon them, since each 

 of these consist of but a single vegetable cell, not the 

 size of a pin's head ? It has been calculated that a 

 diatom, dividing in two, as it usually does five times in 

 a day, would at the end of a month, if no destruction 

 occurred, form a mass a million times as big as the sun. 



Thus we see that diatoms and other microscopic 

 plants constitute the pastures of the sea upon which 

 everything, including man, ultimately feeds. 



Now life in the sea may be conveniently divided 

 into three great divisions. Firstly, fishes and some 

 crustaceans which roam from end to end of the ocean ; 

 secondly, the life which lives on the bottom, such as the 

 sea-weeds, sponges, shell-fishes, star-fishes, and the 

 fish that are of sedentary habits ; and, lastly, the life 



