THE CHROMOSOME COMPLEX OF CULEX PIPIENS. 291 
pared for them in the garden of Ladywood. Mr. MacDougalTs 
permission having been obtained, a hunt over his nursery 
gardens revealed the secret of the non-appearance of rafts 
on the Ladywood ponds. A large disused iron bath, elliptical 
in form (36 in. X 26 in. X by 11£ in.), and containing stagnant 
water, was swarming with larvae and pupae of every age 
which were evidently supplying hibernating imagines. This 
discovery was made too late in the year to be utilised for the 
further production of rafts — but it showed that the situation 
was a good one — the former experiments having possibly 
failed because of the smallness of the troughs, and because 
they were more or less concealed by the surrounding grass. 
Early in 1916, thanks to the kindness of Mr. MacDougall, 
four ponds, A, B, C, and D respectively, were prepared : 
One (A), a large circular iron trough, diameter 30 in., greatest 
depth 24 in. ; another (B), a wooden tub, 25 in. in diameter, 
depth 16 in. ; the third (C) was the bath already selected by the 
gnats in 1915 ; the fourth (D), a rectangular porcelain sink, 
20 in. X 14 in. X 10 in. 
The first two, A and B, were situated side by side, being 
protected on the north by shrubs, and on the east by a wall. 
The iron trough (A) was exposed to all the sunshine of 
morning, afternoon, and evening; the wooden one (B), being 
nearer the wall, was more shaded. Both, however, were 
quite unhidden by vegetation. The tinned iron bath (C) was 
surrounded on three sides by glass-houses, and exposed on 
the southern side; the fourth (D) was placed in the uncut 
grass of an open space. 
On May 21st, 1916, fifteen egg-rafts were discovered in A 
— there was thus no necessity to stock the ponds. No rafts 
appeared on the water in the wooden pond until June 15th. 
The preference shown by the gnats for the iron trough, and 
for the tin bath, may be due to the higher temperature of 
the water of these, or to the fact that they were in a more 
exposed situation, and consequently more easily found. The 
porcelain trough has never been popular, comparatively few 
rafts being forthcoming. 
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