54 BASIS OF THE PEOBLEM 



61 inches long and weighing 54 pounds the ovaries contained 

 28,361,000 eggs ; a cod of 21 J pounds 6,652,000. The least 

 prolific of British food fishes is the herring, in which the number 

 of ovarian eggs varied from 21,000 to 47,000 in four specimens 

 examined.' * 



These vast numbers of eggs produced at any one time make 

 theoretically possible a prodigious rate of increase. It has been 

 calculated that a single cholera bacillus can give rise to sixteen 

 hundred trillion of bacilli in a day, forming a solid mass weighing 

 a hundred tons. ' Wallace quotes Kerner to the effect that 

 a common British weed (Sisymbrium sophia) often has three- 

 quarters of a million seeds ; if all grew to maturity for only three 

 years the whole of the land surface of the globe would not hold 

 them. An annual plant with only two seeds would be represented 

 by 1,048,576 in the twenty-first year. ... If all the progeny of 

 one oyster survived and multiplied, its great-great-grand-children 

 would number thirty-six with thirty-three noughts after it, and 

 the heap of the shells would be eight times the size of the world. 

 Huxley calculated that if the descendants of a single green-fly 

 all survived and multiplied they would, at the end of summer, 

 weigh down the population of China. The common house-fly 

 lays eggs in batches of 120 to 150 at a time, and may lay five or 

 six of these batches during its life of about three weeks in very 

 hot weather. At the end of summer, if all developed, and if 

 there were six generations, the progeny of a single pair, pressed 

 together into a solid mass, would occupy a space of something 

 like a quarter of a million cubic feet, allowing 200,000 flies to 

 a cubic foot.' 2 * There is no exception ', says Darwin, in a well- 

 known passage, ' to the rule that every organic being naturally 

 increases at so high a rate, that, if not destroyed, the earth would 

 soon be covered by the progeny of a single pair. Even slow- 

 breeding man has doubled in twenty years, and at this rate in 

 less than a thousand years there would literally not be standing 

 room for his progeny. Linnaeus has calculated that if an annual 

 plant produced only two seeds and there is no plant so un- 

 productive as this and their seedlings next year produced two, 

 and so on, then in twenty years there would be a million plants. 

 The elephant is reckoned the slowest breeder of all known animals, 



1 Bridge, Cambridge Natural History, vol. Fishes, p. 412. 2 Thomson, loc. 



cit., p. 82. 



