REPORT ON MOSQUITOES. 51 



cause they chance to lay hold of them, or whether they are covered with a 

 thin organic film which serves the larvae as food. 



I conclude from my studies that the mosquito larv?e seize and eat all small 

 particles that come in their way, and that to some extent from these particles 

 themselves, though mostly through vegetable and animal forms growing at- 

 tached thereto, they derive their chief sustenance. I am also of the belief that 

 there is no hope of exterminating the mosquitoes by attempting to destroy 

 their food suppl3% for while it may be possible that some breeding places may 

 be so rich in food material as to foster growth of larvae to a greater extent 

 than others, it is certain that practically all breeding places fui"nish enough 

 food to support myriads of mosquito larvae. 



The plants and animals which form such an important part of the food sup- 

 ply of the larvas are so small that a microscope is required either to discover 

 them or make out the details of their structure. They live in fresh water and 

 form a part of the lower orders of the vegetable and animal kingdoms. The 

 plants being grouped among the algae and the animals among the protozoa. 



Among the algae are distinguished these three classes : the diatoms, green 

 algae, and the blue-green algae. 



The diatoms are little unicellular, flowerless plants, which grow wherever 

 there is moisture. They can be distinguished by the naked eye, and they form 

 the brown slime that accumulates on the bottom of pools and on the stones, 

 sticks and grass that are in them. The diatoms have hard, quartz-like shells 

 of beautiful, graceful shapes, which are covered with delicate markings. From 

 their form the diatoms take their names, such as Navicula (little boat), Astcr- 

 ionella (little star), etc. The two other classes of algae form the pond scums, 

 which in the mass are somewhat repulsive to the sight and which many unin- 

 formed people regard as unhealthy. In reality they are to some e.xtent puri- 

 fying agents in the water in which they grow, and when looked at under the 

 microscope are very beautiful. 



The protozoa are microscopic, imicellular animals which, as a rule, lead 

 active lives in the waters in which they grow ; but there are a few forms which 

 remain attached to lilies, sticks, grass, etc., which are found in the water. 

 These forms are the ones most usually consumed by the mosquito larvae, and 

 possibly form a considerable part of their food supply; however, they are so 

 delicate and easily destroyed that there is very little chance of identifying them 

 after they are once inside the larva. 



Besides these things are the bits of fibre which are stripped by the mosquito 

 from the grass and other coarse plants that grow in the water. The mud 

 that I examined from certain salt marshes where mosquitoes breed proved to 

 be highly organic, but there appeared to be nothing in it peculiarly adapted 

 for larval food. However, the texture of this mud is such that it will retain 

 moisture for a long time, and it may be that for this reason the mosquito 

 deposits her eggs in it. 



Below I append the analyses of the contents of the alimentary canals of 

 certain larvae : 



Ciilcx pipicns — Larva from Metuchen, N. J. ; collected the 26th of May, 

 1903; examined the 7th of June, 1903. Larva No. i. Sand-grains, Amorphous 

 matter. Insect scales ; larva No. 2, Sand-grains, Amorphous matter. Insect 

 scales, Melosira. 



Cule.v sollicitans — Salt pond. Cape May, N. J. ; examined June 7th, 1903. 

 Larva No. i, almost wholly minute Naviculae; larva No. 2, the same. 



Sayreville — Examined on the 7th of June. Larva No. i. Amorphous matter, 

 Sand-grains, Oscillaria ; larva No. 2, Sand-grains, Oscillaria, Navicula, Cyclo- 

 tella. Insect scales. Amorphous matter. 



Sandy Hook — Examined 7th of June. Pupa : — Protococcus. 



Source unknown — Examined 7th of June, 1903. Larva No. i, Navicula, 

 Cyclotella, Oscillaria, Amorphous matter; larva No. 2, Navicula, Synedra 

 Oscillaria, Amorphous matter, Sand-grains. 



Source unknown — Bottle had been standing in the laboratory some time; 

 had dead Culex in it ; examined 8th of June. Larva No. i, Melosira, Oscillaria, 

 Closterium, Sand-grains, Vegetable fibres, many Culex scales. 



