90 
The Queensland Naturalist. 
Nov., 1928- 
remained so throughout life, lie had recently discovered 
that at least one change of sex occurred in the life of 
every rock oyster. The great majority, if not all, func- 
tioned first as males, and later as females. Possibly a 
recurring change of sex occurred throughout life. An 
oyster might spawn when 12 months old, or even younger, 
and the female might eject upwards of a million eggs at 
each spawning period. The wastage that took place be- 
tween the ejection of the eggs and the attachment of the 
oyster as spat was enormous, and it was well that it was 
so, for a calculation made by Professor Brooks, an Ameri- 
can investigator, had shown that if all the eggs of oysters 
were to be fertilised, and were to live and grow to matur- 
ity, they would fill an entire bay in a single season, while 
the fifth generation of descendants from a single female 
would make more than eight worlds as large as the earth,, 
even if each female spawned but once. 
'Within a few hours after fertilisation, the embryo 
oyster, a naked cluster of cells about one-five-lmndredth 
of an inch in diameter, began to swim about. Within two* 
clays it developed shells, and then began to feed. During 
the whole of the first te 11 days of its existence it was 
swimming continually from the surface of the water to 
the bottom, and, although for its size it was a relatively 
strong swimmer, it was nevertheless carried hither and 
thither by currents, and was at the mercy of wind and 
tide. During the later stages of its larval life, the oyster 
developed a foot, by means of which it was able to crawl 
about and extricate itself from minute debris which would 
otherwise overwhelm it. Having indissolubly attached its 
shell to an object in the water, its swimming organ and 
foot were absorbed within a day or two, and the oyster 
could never again move about, 
“Oyster cultivation in Queensland,” continued Mr 
Roughley, “has for the last 40 or 50 years been confined 
almost solely to the gathering of young oysters from 
areas where they grow but slowly and transferring them 
to beds, usually prepared by top-dressing heavily with 
dead shells, where a more rapid growth takes place. And 
this has for many years proved to be most wasteful of 
results. Oysters lying in contact with the bottom are 
at the mercy of numerous pests which frequently take 
toll of very large numbers. If the industry is to thrive, 
these pests must be combated, and this can readily be 
done by keeping the oysters off the bottom. The most 
efficient means of doing this is by the use of wire netting 
