Explanation of Plates. 183 



about the position it occupies when the direct penetration is nearly 

 completed, but on the leaf instead of in it. Magnified x 3. 



The photographs on PI. XI show the terebra of one of my actual 

 flies X 25. I have found it impossible to mount for photography 

 the terebra with the two blades in natural opposition. Here they 

 are somewhat slid apart, with this advantage, as it happens, that 

 the two saws are not advanced to precisely the same place in each : 

 in one it is fully advanced, in the other somewhat withdrawn, 

 and their actual movement in cutting is alternately from one position 

 to the other, the one advancing as the other retreats. The other 

 photograph, from a specimen not taken by me, shows the terebra 

 separated into its four constituents, two guides or supports and two 

 saws — a condition to which they are only too easily reduced in 

 mounting. 



Plate XII shows the further enlargements of the extremity and 

 margin of the terebra, for which I am indebted to Mr. Morice. 



It seemed desirable in order that my notes should be capable of 

 being easily understood that I should i^resent some figures. For 

 this purpose, I have in some degree improved the diagrams I made 

 at the time, but they remain only crude diagrams, useful, I hope, 

 to give greater clearness to my descriptions of what I saw, but 

 not to be in any way trusted outside this object.* In the first 

 place I wish to describe movement; this is, of course, quite 

 absent from the diagrams. But, further, to make them simple, 

 I have used a photograph of one blade only of the terebra. In the 

 absence of movement, this is unimportant; some day, perhaps, 

 some one may secure a cinematographic film of the whole operation. 



The diagrams are magnified about 18 diameters. 



PI. XIII, figs. 1, 2, 3, and 4, attempt to show the progress of the 

 terebra into the substance of the leaf immediately below the upper 

 cuticle and practically at right angles to the margin of the leaf. 

 The whole incision so made is just so much wider than the width of 

 the terebra, as the tip of the saw curls round the end of the guide and 

 so cuts a fraction beyond its margin. 



Direct movement into the leaf ceasing, the terebra then moves 

 forward as shown in 



Fig. 5, until it reaches the position shown in 



Fig. 6, .when the pocket is completed. After a short rest the 

 laying of the eggs begins. 



PL XIV, fig. 7. At tills early stage a strip of the margin of the egg 



* For example I show the pocket, so far as cut, as a blank, but, 

 in fact, the cuticle returns to its position, and the appearance is 

 almost the same when the pouch is formed as it was before. 



