[116] 



Selected IRotee from tbe Societi^'e 



sting of Wasp. — My idea of a well-mounted Wasp's Sting is 



this : — I St. — It should be in a natural position. 2nd. — It should 



show the poison bag and duct. 3rd.— The barbs must be extracted 



from the sheath. 4th. — It must be transparent enough to see the 



chitinous parts well, but yet not by any means so transparent as 



such slides are usually mounted. 



H. M. J. Underhill. 



Iridiscence of Fly's Wings.— I do not think Mr. Tuffen West's 



explanation of extreme thinness more than half accounts for the 



iridiscence of the wings of a fly. The colour is certainly not due 



to scales, as suggested by another member. Anyone who has 



blown soap-bubbles will remember that their iridiscence only 



appears in all its splendour when they are extremely thin ; when 



first blown, and when the film is (comparatively) thick, the 



iridiscence is slight. Now, these wings are thicker than the film of 



a soap-bubble ; consequently they ought not to be iridiscent. I 



have seen it stated, and from my own observation I beUeve that 



the statement is correct, that insects' wings are composed of two 



membranes. These may sometimes be partially separated, and 



when a wing is staified the staining fluid will get between the two 



membranes. Now, the fact that these two membranes touch one 



another is sufficient to produce iridiscence, just as " Newton's 



rings " are formed by two pieces of glass when they touch. That 



the colours are in more or less regular waves confirms this 



explanation. 



H. M. J. Underhill. 



Dermanyssus (PI. XIV., Figs. 7 — 9). — Can anyone suggest 

 what is the use of the most extraordinary second pair of legs ? 

 Are they for sexual purposes, and analogous to the palpi of 

 spiders ? In the ? specimen on the slide can be seen what I fancy 

 are the reproductive organs. The structure of the mouth is well 

 worth careful examination, and is best seen in the 9 specimen, and 

 also well shown in the drawing. The mouth is composed of a 

 lower lip, which I hardly know whether to call labium or mentum. 

 Just within this is a curious triangular membrane, which is very 

 difficult to see. Inside the mouth are two mandibles or chel?e, 

 with one moveable joint at the end, so as to form a pincer. This 



