SEA-FISHERIES LABORATORY. 203 



A female edible crab becomes mature for tlie first 

 time, and produces spawn, when it "is about five inches 

 broad. 



Kate at which the Shrimp Breeds. — 

 The shrimp produces on the average about 5,000 eggs. If 

 there were no destruction in the sea, and all these eggs 

 developed into young shrimps, then starting with a single 

 pair of shrimps — 



one male shrimp ) * , 



. . - 1st generation, 

 one female shrimp j 



The female spawns 5,000 eggs, which develop into 



4000 females > , 

 , „ „^ , [ 2nd generation. 



and 1000 males ) b 



At the next spawning each of these 4,000 females will 

 spawn 5,000 eggs, that is 4000x5000 = 20,000,000, and 

 they will develop into 



16,000,000 females i n 



, _ n , - 3rd generation. 



and 4,000,000 males j & 



At the next spawning again each of these 16,000,000 

 females will spawn 5,000 eggs, that is 16,000,000 x 5000 

 = 80,000,000,000, and these will develop into 



64,000,000,000 females ) AA , 

 , . ™~ ~~~ ™~ , ' 4th generation, 



and 16,000,000,000 males ) & 



Thus if we start with two shrimps, and imagine that they 

 only breed once in their lifetime, and that all the eggs 

 come to maturity, then in the fourth generation we shall 

 have 80,000 millions of shrimps, and at the fifth genera- 

 tion there would be spawned 320 billions of eggs. 



