16 
be carried oil almost equally by all the spiracles. In 
the case of moth and butterfly caterpillars these air- 
pores are eighteen in number, and placed one on each 
side of the 1st segment behind the head, and of the 4th 
to the 11th segment inclusive; but in the case of two¬ 
winged flies the majority of the larvse have only two 
spiracles, which are situated at the extremity of the 
body. 
If, when the insects are in an active state, the spiracles 
or breatliing-pores are choked by any means which pre¬ 
vent air entering the creature, it dies : how far it suffers 
from fluid in which it may be partially lying gaining 
entrance to the system through the tubes, we do not 
know, but practically the effects appear to be very in¬ 
jurious to such kinds as have many spiracles. 
The exact method by which heavy or long-continued 
rainfall clears off insect pests by fields’ full, which we 
have no other means of getting rid of, is an important 
practical matter, and we need to know much more about 
it relatively to the possibility of supplying ourselves 
artificially with a similar kind of remedy, and applying, 
on an extended scale, the methods now found serviceable 
in many gardens. 
Year by year we see the recurrence of the same 
reports regarding various insects. The Turnip Fly, or 
Beet Fly, or whichever it may be, was very injurious till 
the rain washed it off, or started the plant, or in some 
way put an end to its ravages. Now, if we look at the 
.great amount of injury we suffer from overplus of rain 
in some years and deficiency in others, it appears well 
worth consideration whether a more extended plan of 
field cisterns and drainage of water into them, both 
from fields and roofage, might not be of service. The 
average yield of water per year from a roof 15 ft. 
by 20 ft. (that is, a roof covering an area of ground of 
that measurement), from a mean rainfall of 25 in., is 
calculated at 3900 gallons. Deducting 20 per cent, for 
loss on a tiled roof, or 10 per cent, (which is above the 
amount lost) on a slated one, this would give a yield 
