PLATE 9. 



Proboscis of Blow-fly. 



(See also Plate 8.) 



A B 



Magnification... 105. 220. 



Objective Swift's 1" Achromat. Swift's \" Achromat. 



Eye-piece Swift's No. 3x7. 



Extension ... 20". 10". 



Condenser ... Watson's Universal, Universal. N.A. 1.0. 



front lens removed. 



Illuminant ... Incandescent gas. 



Light Filter ... Saturated solution of copper acetate. 



Plate Imperial Special Rapid Ortho. 



The proboscis of Blow-fly is a very favourite test object for low- 

 power objectives. It must be mounted quite flat, and examined with 

 a f or 1 cone of critical light. Under these conditions the spirals on 

 the suctorial tubes should be clearly defined, and the fine hairs round 

 its margin shown distinctly and without blurring. 



Photos. W. B. R. [To follow Plate 8 and page 80. 



