Gr. S. GtRAIIAM-SmITH 
459 
pipes about six inches in diameter, half buried vertically in the ground and 
filled with earth up to the ground level. After a day or two, when many 
eggs had been deposited, the top of the pipe was covered with butter 
muslin over which was placed an earthenware saucer. If, on subsequent 
inspection, there seemed to be insufficient food for the larvae more 
was added. The purpose of this procedure was to confine the larvae 
as much as possible, and to aid in coimting the numbers of the adults 
of the new generations as they emerged and were released from the 
pipes. Also the flies were prevented from laying more eggs on a 
given supply of food than it could nourish. 
The first eggs were noted on May 15, and eggs were deposited by 
this generation up to June 11, when only 43 flies remained alive. The 
flies which emerged from the winter pupae reached their greatest 
number on May 15 and after that time the number present gradually 
diminished until on June 16 only five remained of this, the parent, 
generation. The flies of the first generation developing from the 
eggs deposited in the pipes by the parent generation only commenced 
to emerge on June 17, so that the parent generation had almost died 
off before its descendants reached the adult stage. Flies of this 
generation continued to emerge up to July 21. The eggs first deposited 
by the parent generation produced flies in 32 days. 
According to Fabre the blow-fly lays about 300 eggs in one batch 
and therefore the first generation resulting from 100 parent females 
ought to have consisted, had adults matured from all the eggs deposited, 
of at least 30,000 individuals. The total number, which emerged under 
apparently most favourable conditions, was 2789. 
Lack of food for the larvae was not the cause of this theoretically 
very small number since the bodies of numerous guinea-pigs were 
provided, and as shown by other observations more than 1000 flies 
may be bred from a single body (p. 504). Competing larvae and damp 
may also be excluded. 
A glance at Chart 2 shows that in all the generations considerable 
numbers usually emerged about the same period, and the curve for 
the total number of flies present in consequence rises suddenly. 
In most cases it also falls suddenly within a few days owing to the 
very great mortality which occurs amongst the newly emerged flies. 
This mortality, whatever its cause, occurred regularly throughout 
the season and is probably one of the most important factors in limiting 
the numbers produced. The general causes of mortality are discussed 
in the next section. 
Parasitology vm 
30 
