173 



PROCEEDINGS OF THE SOCIETY. 



AN OEDINARY MEETING 



OF THE Society was held at No. 20 Hanover Square, W., 

 ON Wednesday, December 20th, 191(j, Mr. E. Heron-Allen, 

 F.L.S. F.Gr.S, ETC., President, in the Chair. 



The President having announced that Mr. Rousselet had donated 

 to the Society a SHdiug Stage of his own design, a Stage- Vice by Ross, 

 and a complete series of the papers on the Rotifera and kindred subjects 

 which he had communicated to this and other Societies, a vote of thanks 

 was accorded by acclamation. 



Mr. A. Bacot, F.E.S., contributed a note on " The Effect of the 

 Presence of Bacteria or Yeasts on the Hatching of the Eggs of Steijomyia 

 fasciata (The Yellow Fever Mosquito)," which may be summarized 

 as follows : — 



The eggs of Stegomyia fasciata are small, dark, spindle-shaped objects 

 of G to • 7 mm. in length, having a strong chitinous shell. The bosses 

 with which the shell is studded are not structural excrescences of the 

 shell but thickenings of or pockets in a delicate outer envelope. 

 Sections of the eggs, both before and after extrusion from the body of 

 the female, show that the substance forming the bosses is stained by 

 ha^matoxylin ; most probably it is of a gelatinous nature. The eggs 

 are laid singly, either on tiie surface of the water (usually so close to its 

 margin as to become stranded by capillary action) or on the wet margin 

 itself. Moist conditions after laying seem to be essential to incubation, 

 which takes a period of thirty or forty hours, by which time the larvae 

 are fully developed within the egg. 



In this stage the eggs retain their vitality, when dry, for long 

 periods, four or five months being usual, while under exceptional 

 conditions a small percentage may survive and hatch after a period of 

 twelve months. When dry eggs are immersed in water the hatching of 

 a given batch is frequently distributed over a considerable period of 

 time ; this is especially apt to occur if the water has a low organic 

 content. Under such conditions hatching may be delayed for weeks or 

 }nonths, in two instances eggs hatched after five mouth's immersion. 



Certain stimuli cause dormant eggs to respond by hatching. A fall 

 of temperature of 6° to 10° F. will usually cause a percentage of these 



