13 





Egg.— The female lays her eggs (fig. 4) on the surface of the water 

 or on the sides of the container at or just above the water line. The 

 eggs do not adhere one to the other to form the compact boat-shaped 

 masses characteristic of Gulex (fig. 5), but lie on their sides more or 

 less isolated, though frequently grouped into clumps. At the moment 

 of laying the eggs are of a cream color but rapidly become jet black; 

 they are somewhat cigar shaped with one end slightly broader and 

 more bluntly rounded than the 

 other. They measure on an aver- 

 age about 0.55 mm. in length and 

 0.16 mm. in width at the broadest 

 part. Under the microscope the 

 apparently cylindrical egg is seen to 

 be slightly flattened "on one side. 

 The eggs are most commonly laid 

 during the night or early morning, 

 but they may be laid at any time during the 24 hours. The total 

 number of eggs laid varies, the average being about 65 to 70; the 

 maximum recorded is 144. " 



The act of ovipositing appears to greatly exhaust the mosquito, so 

 that it may fall on the surface of the water and die immediately after 

 even the first egg laying. There are numerous exceptions, however, 



and ' the act may be re- 



AY 



Fig. 



4.— Eggs o£ Stegomyia calopus (after 

 Stephens & Christopher, 1904).- 



w 



Fig. 5.— Eggraft and eggs of Culex (after Stephens & 

 .Christopher, 1904). 



peated several times and 

 the mosquito survive for 

 some time after. 



If laid on the surface of 

 the water the egg floats, 

 being supported by the 

 surface film. Disturbance 

 of the water surface may 

 cause the egg to become wet and sink to the bottom, but this does not 

 prevent its hatching out into the larva. The egg shows marked powers 

 of resistance to unfavorable influences. Thus it may be kept dry for 

 from two or three to six and one-half months b and still retain its 

 vitality and hatch out when put back into the water. Eeed and 

 Carroll c have shown that freezing does not destroy its vitality. The 

 egg probably plays the leading r61e in the hibernation of this mosquito. 

 Under the most favorable conditions as to temperature (30° C. 

 (86° F.) and over) eggs hatch out in about 36 hours after they are laid, 

 but with a lowering of the temperature this period becomes progress- 

 ively longer until 20° C. (68° F.) is reached, below which they will 

 not hatch at all. 



aMaEchoux and Simond, 1906b. 6 Francis, 1907. «Eeed and Carroll, 1901. 



