CHAP. VIIL] WHEN DO OYSTERS BECOME REPRODUCTIVE ? 339 



size represents the oyster as it appears when three months 

 old. The other sizes are drawn at the ages of five, eight, 

 and twelve months respectively. Oysters are usually four 

 years old before they are sent to the 

 London market. At the age of five years 

 the oyster is, I think, in its prime ; and 

 some of our most intelligent fishermen 

 think its average duration of life to be 

 ten years. 



In these days of oyster -farming the 

 time at which the oyster becomes reproductive may be easily 

 fixed, and it will no doubt be found to vary in different 

 localities. At some places it becomes saleable chiefly, how- 

 ever, for fattening in the course of two years ; at other 

 places it is three or four years before it becomes a saleable 

 commodity ; but on the average it will be quite safe to as- 

 sume that at four years the oyster is both ripe for sale and 

 able for the reproduction of its kind. Let us hope that the 

 breeders will take care to have at least one brood from each 

 batch before they offer any for sale. Oyster-farmers should 

 keep before them the folly of the salmon -fishers, who kill 

 their grilse i.e. the virgin fish before they have an oppor- 

 tunity of perpetuating their race. 



Another point on which naturalists differ is as to the 

 quantity of spawn from each oyster. Some enumerate the 

 young by thousands, others by millions. It is certain enough 

 that the number of young is prodigious so great, in fact, as 

 to prevent their all being contained in the parent shell at one 

 time ; but I do not believe that an oyster yields its young 

 " in millions" perhaps half a million is on the average the 

 amount of spat which each oyster can "brew" in one season. 

 I have examined oyster-spawn (taken direct from the oyster) 

 by means of a powerful microscope, and find it to be a liquid 

 of some little consistency, in which the young oysters, like 



