1G8 A. A. C. ELIOT MERL1X OX THE FOOT OF THE HOUSE-FLY. 



point and the haft. When the hair is viewed in such a position as 

 to exhibit the full curve of the sickle, as in Figs. 5 and 6, the boss 

 cannot be made out, being then on the underside of the filament ; 

 it is only well seen when the hair is comparatively free from fluid, 

 and is observed somewhat edgeways, as in the first three figures. 



The lightly shaded portions of the diagrams represent the viscous 

 fluid as seen adhering to the filaments depicted, and show how 

 admirably they are adapted for the purpose they serve, the liquid 

 being disposed, not in rounded globules, but in the form of a thin, 

 flattened film held within or around the sickle, and frequently 

 extending beyond it, especially on the fore part of the pad, where 

 hairs with large films are commonly found, resembling Figs. 4 and 6. 



The protuberance may simply mark the position of the opening 

 through which the fluid exudes, our present optical means not 

 being sufficient to allow one to speak with absolute certainty ; but 

 some filaments examined have given the impression of being in 

 reality slightly cleft at this point, and possibly the opening may 

 be thus capable of considerable expansion under pressure, other- 

 wise the quantity of fluid required to make up a film Avould be 

 supplied very slowly. 



The surfaces of the films usually exhibit a roughened and 

 wrinkled appearance, to represent which no attempt has been 

 made in the annexed diagrams, which it is trusted may serve 

 to illustrate the features referred to. Although drawn at the 

 microscope with a power of 3,200 diameters, their actual scale 

 is much greater, being roughly about x 5,000. 



It appears to me that this observation is interesting, not only 

 on account of the further light shed on the true structure of the 

 object itself, but as proving what an increase in our knowledge of 

 even common and comparatively coarse organisations may be 

 confidently expected from each successive advance in the optical 

 efficiency of our lenses ; for here we have the case of a structural 

 detail which, although especially searched for, eluded notice with 

 an objective of N.A. 127, and yet immediately revealed itself 

 and became quite noticeable with an optical combination of 

 slightly superior resolving and defining power. 



Since observing the protuberance on the filament with the 

 apochromat, and being familiar with its exact position and 

 appearance, I have experienced no difficulty whatever in demon- 

 strating its presence with the older lens. 



Journ. Quekett Microscopical dub, So: 2, Vol. IX., No. 50, April 1905. 



