44 



G. F. HILL. 



extruded in the same manner. Three eggs were then laid close to and in front of the 

 first two, each one as it left the ovipositor being pressed firmly against those behind, 

 until the latter lay almost parallel to the twig. In this way three or four gradually 

 widening rows were laid, each slightly nearer vertical than the preceding one. Then 

 a second and similar tier was commenced on top of those already laid, the first row 

 of eggs of the second tier resting on the second or third row of the lower tier. Moving 

 her body slightly forward, the fly extended the lower tier two or three rows before 

 continuing the upper tier. In this way the operation was continued until the 

 mass had covered the lower side of the twig for a length of 30 mm., when the fly 

 moved forward a few millimetres and remained stationary until captured. The rate 

 of oviposition was about three eggs a minute, and at no time was the apex of the 

 abdomen brought under the thorax, as stated by writers dealing with extra- Australian 

 species. 



The Egg-mass. The size and shape of the egg-masses are very variable. As a 

 rule they are about 20-33 mm. long by about 2 mm. wide when deposited on slender 

 twigs or narrow blades of grass, or they may be more compact when laid on seed-heads 

 or other objects offering a wider base for the mass. The mass is invariably as wide 

 as the object upon which it rests and generally contains two layers of eggs. Some 

 of the masses, however, contain three layers of eggs and are proportionately shorter 

 and higher. Sometimes a second and even third mass is laid very near to or over- 

 lapping part of an earlier one, and small masses containing only a few score of eggs 

 are found near masses of average size. The number of eggs per mass probably 

 averages about 500, but much smaller and much larger masses, i.e., 250-700, are 

 found. At first the mass is creamy, but in the course of about 24 hours it changes 

 to light slate-purple, and gradually darkens with the development of the larvae. 

 There is a complete absence of the white chalkv substance used by some species as 

 an outer coating of the mass, and more often than not its general appearance is 

 distinctly rough and lacking finish. 



Fig. 1. Tabanus aprepes, Tayl., eggs. 



Fig. 2. T. aprepes, embryo 78 hours old. 



The Egg. The eggs measure 1 -60 mm. to 1-65 mm. in length, by 0-3 mm. in 

 width, and are variable in shape according to their position in the mass, but always 

 bluntly rounded at either end (fig. 1). The surface is smooth and glossy and, in 

 recently laid eggs, pearly white. The colour changes rapidly ; eggs that were laid at 

 1.50 p.m. on 16th April changed to grey by 5.15 p.m., to dark slate-purple by 

 9.30 a.m. on 18th, and hatched during the night of 22nd or early morning of 23rd. 

 Another batch of eggs which was laid at 4.30 p.m. on 2nd April changed to 

 dark slate-purple by 9.30 a.m. on 4th and hatched between 2 and 4 p.m. on 8th. 

 The egg period therefore was from six and a quarter days to seven days in the one 

 case and about six days in the other. 



For at least 24 hours before the young larvae hatch they are distinctly visible 

 through the clear, thin shell (fig. 2). During this period they are active, dark-banded 

 little creatures, with the head always directed outwards from the point of attachment 



