108 



By the 21st May 1916, fifteen egg-rafts were found in A, the arti- 

 ficial stocking of the ponds being therefore unnecessary, but no rafts 

 appeared in B till 15th June. The preference shown by the mosquitos 

 for the iron trough and tin bath may have been due to the higher 

 temperature of the water in these, or to their positions allowing them 

 to be found more easily. The porcelain trough was never popular. 



The May and June rafts were evidently laid by the hibernating 

 adults of the jjrevious autumn, since subsequent eggs were not produced 

 abundantly till the middle of July, when a spell of very warm, moist 

 weather resulted in an abundant supply, which continued as long as 

 the same type of weather lasted till the middle of August. 



The deposition of rafts had been noted at about 5 a.m., but prolonged 

 observation showed that the majority were laid between 9.30 p.m. and 

 12 p.m., very few between 12 p.m. and 4 a.m., and some between 

 4 a.m. and 6 a.m. With the advance of the season, fewer were laid 

 in the morning hours. Numerous imagines were always found 

 hovering over the ponds at a height of about 6 feet in the evenings, 

 when damp heat greatly conduced to the deposition of the egg-rafts. 



Although larvae of Culex grow more quickly in a good culture of 

 Chlaniydomonas, yet Daphnia also flourish well on this diet, to the 

 detriment of the mosquito larvae, and this fact perhaps accounts for 

 the more frequent occurrence of Culex in the fairly clean water of 

 rain -barrels and drinlving troughs, when they might have been expected 

 to prefer a more stagnant habitat. 



The act of deposition of the egg-rafts takes about 15-20 minutes. 

 The females, which fly away after oviposition, appear to be perfectly 

 vigorous, and are probably capable of depositing more than one 

 raft in the course of the season. 



Bacot (A.). A Note on the Period during which the Eggs of Stego- 

 myia fasciata [Aedes calojtus) from Sierra Leone Stock retain their 

 Vitality in a Humid Temperature. — Separate from Parasitology, 

 Cambridge, x, no. 2, 22nd January 1918, pp. 280-283. 



The fact that the eggs of the mosquito, Stegomyia fasciata, remain 

 viable for many months when out of water has been recorded by 

 several authors. 



With a view to ascertaining whether eggs stored out of water, but 

 in a humid atmosphere, retain their viability, the author experimented 

 on a large number of ova from Freetown. These, laid on filter paper, 

 were placed in a waxed card jar and kept in an unused ice chest in a 

 cool cellar having a bricked floor, and showing a very even range of 

 conditions, with a high percentage of humidity. Immersion tests 

 begun 7 months after laying showed that the eggs hatched readily, 

 not" more than 10-20 per cent, of the larvae failing to emerge. Those 

 tested 9 months after laying also hatched readily. After 10 months, 

 there was a very noticeable rise in the percentage of failures to hatch. 

 After 1 1 months, probably not more than 5 per cent, of those immersed 

 yielded larvae, though these hatched within an hour of immersion. 

 Tested after 12 months, only 5 larvae emerged from about 600 eggs, 

 and then not until 5 or 6 hours after immersion, and all these lived to 

 pupate. From a batch of 1,000 eggs immersed after 13 months, a 



