THE society's NOTE-BOOKS. 203 



the adhesion is the result of the secretion of a viscid Uquid from 

 the underside of the foot. Careful observations by Mr. Hepworth 

 {Quarterly Journ. Micro. Set.) have led him to a conclusion whieh 

 seems in harmony ivith all the fads of the case — namely, that each 

 hair is a tube conveying a liquid from a glandular sacculus situated 

 in the tarsus, and that when the disc is applied to a surface, the 

 pouring forth of this liquid serves to make the adhesion perfect. 

 That this adhesion is not produced by atmospheric pressure alone 

 \% proved by the fact that the feet of files continue to hold on to the 

 interior of an exhausted receiver; whilst, on the other hand, 'that 

 the feet pour forth a secreted fluid, is evidenced by the marks left 

 by their attachmefit on a clean su?face of glass." Mr. Barrett (p. 201) 

 seems never to have heard of this. Dr. Carpenter continues : — 

 "Although when all the hairs have the strain put upon them 

 equally, the adhesion of their discs suffices to support the insect, 

 yet each row may be detached separated by the gradual raising of 

 the tarsus and pulvilli, as when we remove a piece of adhesive 

 plaster by lifting it from the edge or corners. Flies are often 

 found adherent to window-panes in the autumn, their reduced 

 strength not being sufficient to enable them to detach their tarsi." 



Hogg also says : — " The delicacy of the structure of these 

 hairs in the fly, the bend near this extremity, in each of which 

 supervenes an elastic membranous expansion, and from which a 

 very minute quantity of clear transparent fluid is emitted when the 

 fly is actively moving, explains its capacity for clinging to polished 

 surfaces." 



And, again, who has not read Rev. J. G. Wood's Cotjwioji 

 Objects of the Microscope ? This is what he says : — •" The organ 

 is seen under a very high power to be covered with hair-like 

 appendages, each having a little disc at the end, and probably 

 secreting some glutinous fluid which e?iables the creature to hold on to 

 perpendicular and smooth surfaces. Many of my readers will 

 doubtlessly have noticed the common fly towards the end of 

 autumn walking stiffly upon the walls and evidently detaching 

 each foot with great difficulty, age and infirmity having made the 

 insect unable to lift its feet with the requisite force." — F. C. Cox. 



I think the question of how the flies walk has been ventilated 

 before in our Note-Books. In addition to the authorities quoted 



