E. E. Atkin and A. Bacot 
485 
series and not with those in some other experiments in which the con¬ 
ditions or media differed. 
With regard to the hatching of eggs, much preliminary work was 
done by Bacot in Sierra Leone which is fully detailed in his rejmrt 
(1916), but for the benefit of those who have not had any opportunity 
of perusing it, the main facts may be briefly recapitulated as follows: 
The eggs of Stegomyia fasciata are small black spindle-shaped objects 
of 0-630 to 0-650 mm. in length, by about 0-160 mm. in width if of 
average size. The shell, which is highly chitinized, is covered with a 
delicate cellular reticulation and from the central area of a large number, 
if not of all, the cell spaces rise small rounded bosses, which sections of 
the egg show to be gelatinous, and not merely the bulgings of the chitin 
wall of the egg. The eggs are deposited by the females singly, either 
on the water surface or the wet margins of objects in or surrounding 
the water surface; no doubt capillary action is responsible for the 
stranding of many eggs. Incubation is complete after a period of 30 
to 50 hours according to the temperature, and Bacot states that it is 
necessary that the surface of the egg be kept moist while incubation is 
in progress. McGregor (1916) seems also to have experienced this 
necessity. After incubation the eggs now containing living larvae may 
be dried and remain dry for many months, without losing their vitality. 
Hatching on immersion, after incubation and drying, is generally erratic, 
a few eggs or a number may hatch within a few minutes; some will 
take hours, while others will remain dormant under water for days, 
weeks, and even months, and yet eventually yield healthy lar\-ae. 
The quantity of water in which the eggs are immersed makes no 
appreciable difference, nor does the age of the female, or whether the 
eggs were of a late or early batch. Changing the water in which the 
eggs were laid had no effect when the fresh water was from the same 
source and of the same temperature, but a fall in the temperature of 
the water in which the eggs were lying, exposure to cool air for a few 
minutes followed by reimmersion in the same water acted as a stimulus 
to the hatching of a varied percentage of the dormant eggs. The effect 
of cooling, however, seldom caused more than a small percentage of 
the dormant eggs to hatch and sometimes had no effect. The immersion 
of incubated eggs before they had been allowed to dry and others of the 
same batch after drying, gave divergent results^. 
* Although we have not yet followed this point up by planned e.xperiments we have 
some reasons for supposing that the divergence may he due to hacterial action, during 
or immediately following incubation. 
32—2 
