176 



REPRODUCTION 



With the exception of the great group of insects, spiders 

 and the higher vertebrates and a few others, most of the 

 dominant classes of animals 

 live in or on the water, and 

 amongst them as a rule the 

 females shed their eggs into 

 the surrounding aqueous me- 

 dium, and the males standing 

 by shed their spermatozoa 

 near the eggs. In many cases 

 the eggs and the spermatozoa 

 exist in simply incredible 

 numbers. Amongst the fishes 

 the female turbot will pro- 

 duce annually 9,000,000 eggs, 

 the cod 6,000,000, the flounder 

 1,400,000, the sole* 570,000, 

 the haddock 450,000, the 

 plaice 300,000, whilst the 

 herring has to be content 

 with comparatively few, its 

 meagre total reaching only 

 31,000. The spermatozoa must 

 be produced in numbers that 

 are even far greater, for it is 

 rare to find an unfertilized egg 

 in the sea ; and yet many sper- 

 matozoa must miss their goal. 

 The reflection that if the stock 

 of cod remains about constant — 

 as indeed it does — only two out 

 of 6,000,000 eggs attain maturity, 

 almost paralyses imagination as 

 to the destructive forces at work. 



The amazing fecundity of cer- 

 tain animals and the paucity of 

 offspring of others is an apparent 



paradox. Whilst a turbot mil ^^^: ^f- ^- f ^5^^"^' ScylUum 



J „„„„^^^ „ ,., camcula Keduced. From Day. 



produce 9,000,000 eggs, of which 5. Egg-case opened to show young 



presumably only two survive — or embryo with yolk-sac. 



