﻿EXPERIMENTS IN MALARIAL TRANSMISSION. 519 



be enemies of the mosquito larvae, so that when masses of algae containing large 

 numbers of mosquito eggs were placed in the water, the insects could develop 

 without menace from this source. However, it is probable that a limited number 

 of the larvae and pupae fell a prey to the tiny water beetles and their larvae, which 

 co\ild not all be removed from the water owing to the fact that many of them 

 burrowed in the mud when the pond was disturbed. One or two dragon-fly larvae 

 were left in the water and they reached maturity. They were seen to capture 

 some of the hundreds of Myzomyia ludlowii Theob., and Culeao rnicroannulutus 

 Theob., which emerged, but their quota must have been very insignificant, since 

 they were small damsel-flies and not the larger and more voracious Libellulince. 



One of the most satisfactory methods of collecting the adult mosquitoes for 

 experiment was to permit a large number of the larva to pupate under the net 

 among the algae and, within a day of the time for their emerging as adults, to 

 collect as many as needed with a scoop net. They were then placed in a jar of salt 

 water and covered ; the next morning all of the adults would be found, they having 

 emerged during the previous evening. 



Man.}' attempts were made to raise these mosquito'es in confinement, 

 but I succeeded only after numerous trials. Under ordinary conditions 

 evaporation is so rapid that water must be added each day ; this so disturbs 

 the larvae that they do not thrive well, especially when an attempt is made 

 thoroughly to mix the water at the time of its 'addition. Another detri- 

 mental feature is the amount of reflection of light from the sides of the 

 vessel. Thermometric tests show that the air just above the water con- 

 tained in a 10-liter porcelain evaporating dish is from 5° to 7° C. above 

 that of the outside. In 20-liter cylindrical glass vessels of 35 to 40 

 centimeters height it is from 8° to 10° C. Direct sunlight does not 

 detrimentally affect the larvae and pupae, but the adults die within fifteen 

 to twenty minutes when so exposed, so that those emerging under such 

 conditions in a covered vessel never reach the stage where they can fly. 

 Those not killed directly by the sunlight become so thoroughly soaked 

 by the moisture collecting on the sides of the vessel that they soon die. 

 It is possible, by using a large porcelain evaporating dish and shading 

 a portion of it with a black cloth under Avhite, to keep the temperature 

 down 2° or 3°, but even under such conditions great vigilance and a 

 repeated change in the position of the vessel to a shady place for an hour 

 or so and then back into the sunshine, is necessary. 



LIFE HISTORY OF MYZOMYIA LUDLOWII THEOB. 



The egg. — One and eight-tenths millimeters in length and 0.95 millimeter at 

 its widest point including the air-cells, it being slightly wider than deep. The egg 

 (PI. I, figs. 1 and 2) is nearly jet black, the surface being covered with an 

 iridescent, reticulated film which separates when the egg dries. It is blunt canoe- 

 shaped, the lower surface strongly convex, the upper concave lengthwise. At 

 each end is a small, round, lighter area having 7 to 8 tiny black dots within its 

 circumference. A rim of air-cells extends around the entire upper part and at 

 each side near the top and midway between the extremities occupying nearly one- 

 half the length is an arrangement of air-cells which extends from the top halfway 

 down the side of the egg (PI. I, fig. 2). These cells run dorso-ventrally, each one 

 widening downward. 



