ENTOMOLOGY

240 SANITARY ENTOMOLOGYthe larvre that issue therefrom. During the past summer the larvreemerging from ten masses of Tabanus phaenops eggs were counted. Thenumber per mass ranged from 156 to 885, giving an average of 281 + permass. Larvre from fifteen masses of Tabanus punctifer eggs were counted.The range was found to be from 159 to 701 larvre,-an average of 866 +per mass. However, this method of arriving at the number of eggs permass was very inaccurate in the case of Tabanus pwnctifer, as practicallyall these egg masses were, to a greater or less extent, parasitized, andin several of the masses a large per cent of the eggs failed to hatch.Larva! from a series of five unidentified Tabanus egg masses collectednear Alturas, California, were also counted. Here the range was from826 to 890,-an average of 509 + per mass, with no parasitism.Mitzmain records that the number of eggs per mass of Tabanusstriatus in the Philippines varies from 270 to 425. He observed theoviposition under cage conditions and found that the eggs were depositedat the exact rate of 10 per minute.References in literature to the incubation period are extremely scarce.King gives the period for Tabanus kingi as about 5 days, and for TabOJnlUspar as 5 to 6 days. These species occur in the Egyptian Sudan. Neavehrives the incubation period of Tabanus cora:c in Southern Nyasaland asabout 5 days. Mitzmain determined the period for Tabanus striatus inthe Philippines to be from 8 to 5 days.In my own experience in the Sierra Nevada Mountains, I have foundthat the eggs of Tabanus phaenops under laboratory conditions hatch infrom 6 to 7 days, while those of Tabanus punctifer require 14 days. However,in one case, a mass of T. punctifer eggs, after being kept a few daysin the laboratory, was placed outdoors in the sun, with the result thattIle incubation period was sllortened to 11 days. No doubt if the masshad been kept in the open from the time of oviposition a still shorterincubation period would have been recorded. The eggs of the unidentifiedspecies collected near Alturas, California, hatched in from 7 to 8 daysunder laboratory conditions.Usually most of the eggs in a mass hatch at about the same time, butin the case of Tabanus pltaenops I have found straggling larvre emergingseveral hours after the majority of the larvre were in the water at thebottom of the incubation vial.LARV./EIn arranging for the incubation of Tabanus eggs I am accustomed touse a large glass vial with water in the bottom. The egg mass is thensuspended in the vial over the water, usually by placing the stem orleaf, to which the mass is attached, against the side of the vial, and press-