298 MEDICAL ENTOMOLOGY 



compact mass of eggs is built up, which, if examined with a lens, demon- 

 strates the precision with which the eggs are placed in reference to one 

 another. 



It is often possible to watch a female tabanid with a hand lens while 

 she is laying her eggs without disturbing her ; sometimes it is even 

 possible to break off the leaf or twig and to earn- her some distance to a 

 laboratory, where she will continue to lay her eggs. 



In Madras all the smaller species of Tabanus, as well as Chrysops 

 dispar and the two species of Haematopota referred to above, spread 

 their eggs out in one or more layers on blades of grass ; in some instances 

 they are moulded into the hollow of the blade right up to the tip (Plate 

 XLII, figs. 2, 11 and 12). Tabanus speciosus (Plate XL, fig. 2), 

 instead of forming a V-shaped mass as is usually the case with the 

 larger tabanids, lays its eggs in a round heap, which it then plasters over 

 with a chalk-like substance, almost completely covering the eggs. 



The eggs of all the smaller tabanids in Madras are torpedo-shaped, 

 while those of the larger species, such as albimedius, are sub-cylindrical 

 with tapering ends. The eggs of Tabanus bicallosus, a small species, 

 measures Tl mm. in length and '2 mm. in breadth, that of ditaeniatus is 

 about 1'2 mm. in length and also "2 mm. in breadth ; the eggs of albimedius, 

 a larger fly, measure 1*9 to 2 mm. in length and '4 mm. in breadth. 

 Most of the eggs of the smaller species are white when first laid, but 

 they soon become dark. Those of one species of Haematopota are dark 

 grey when deposited, while those of albimedius, striatus and liilaris are 

 brownish white. 



The egg masses of tabanids are often parasitized by small species of 

 hymenoptera which oviposit in them. Phanarus tabanhorus, Ashmead, 

 is common in the United States, where, according to Hart, it parasitizes 

 a large number of the egg masses of Tabanus at rat us. Telenomus 

 benefactor, Crawford, is another chalcid which parasitizes the eggs 

 of tabanids in the Soudan. In Madras a similar insect, which has 

 not been identified, regularly destroys large numbers of egg masses of 

 albimedius and striatus. A parasitized egg mass can be recognized by 

 the almost black colour which it assumes when the development of 

 the embryos of the hymenopteron is almost complete. 



In Madras the smaller species of Tabanidae always lay their eggs in 

 the afternoon, commencing about 4 p.m. ; Chrysops dispar has been 

 seen ovipositing as late as 7 p.m. The larger species, on the other hand, 

 lay their eggs any time during the day, but as a rule in the morning. 

 The larvae hatch out in from four to seven days after the eggs are laid ; 



