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A NOTE ON THE PERIOD DURING WHICH THE 
EGGS OF STEGOMYIA F ASCI AT A (AEDES CALO- 
PUS) FROM SIERRA LEONE STOCK RETAIN THEIR 
VITALITY IN A HUMID TEMPERATURE 1 . 
By A. BACOT, F.E.S. 
(.Entomologist to the Lister Institute.) 
It is well known that the eggs of the above-named mosquito remain 
viable when out of water for many months. Various workers, among 
whom may be named Theobald, Newstead, Francis and Mitchell, 
record varying periods up to nine months’ duration. 
Howard, Dyar and Knab (1912) state that with some species of 
Aedes the eggs may remain dormant over a year. It does not seem to 
be so generally recognised, however, that the eggs when immersed in 
water may remain dormant. Marchoux, Salimbeni and Simond (1903), 
and Dupree, according to Mitchell (1907), were acquainted with the 
fact. The French investigators record a period of 70 days and Mitchell 
one of over a year. I think, G-oeldi, as quoted by Howard, Dyar and 
Knab (1912), must have encountered the phenomenon but he considered 
the dormant eggs to be dead, at least it is in this light that I view his 
statement that submerged eggs perish. Bacot (1916) showed that 
immersed eggs may remain dormant for five months. It is apparently 
essential to the retention of vitality under conditions of drought and 
dormancy, when submerged, that the eggs shall have been incubated, 
development within the egg having proceeded up to the stage of the 
larva being ready for immediate hatching. 
1 Since this Note went to press a batch of some 2000 or 3000 eggs of this mosquito, 
laid during April 1916, was tested after 15 months’ storage. The eggs had been laid on filter 
paper and were placed in a wax card jar kept in the cool room (ca. 9° C.) of the Lister 
Institute. All the eggs were placed in a pan of tap water; a few hatched within 24 hours, 
and others responded later to the stimulus of the addition of a little B. coli culture to 
the water. Twenty adults were reared. 
