498 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the adjustment of the object-glass is correct ; tho effect (fig. 88) produced 

 on each side of the exact focus; and tho way (fig. 89) in which the 

 markings individually divide when all tho adjustments are correct, and 

 when tho focus is altered the least possible amount only each way. 



Figs. 90 and 91 show tho two appearances on one and the other sido 

 of tho best focus when tho adjustment is incorrect ; fig. 92 showing tho 

 appoarance of the same at its best focus. 



Villi on the Scales of Butterflies and Moths.— Dr. G. W. Royston- 

 Pigott considers * that the resolution of theso difficult objects is a capi- 

 tal introduction to the study of the minute structure of disease germs, 

 and he can consequently strongly commend it to the attention of micro- 

 scopists who have neglected this department of natural history. 



Many of the villi in butterfly and moth scales are pawn-shaped, 

 possessing a base and a spherical summit. This form was the first one 

 discovered, with oxceeding difficulty, on the scales of the Eed Admiral 

 butterfly. The scales of Amathusia Horsfeldii gave clearer indications, 

 but their extreme delicacy permits of no pressure being applied, as it 

 flattens and distorts them. After seven years' prosecution of the re- 

 search he was rewarded with finding an entirely new vein, which has 

 proved very rich in material, in motLs of the Zygoena tribe. Occasion- 

 ally they are seen to lie flat upon the basic membrane, and to be con- 

 nected by cross ramifications, interlacing in an extraordinary manner. 

 At other times the bases of the villi are ciliated, forming reticulations, 

 resembling ancient hieroglyphics or archaic writing. Their thickness 

 varies from 1/60,000 to 1/120,000 in., and their length is sometimes 

 prodigious. 



The villi principally observed at present take the following forms : — 

 i. Beaded villi ; ii. Embossed villi ; iii. Pillar villi ; iv. Ciliated 

 villi ; v. Connected villi ; vi. Banana or Bunched villi ; vii. Spinous 

 villi ; and viii. Tall villi. 



Out of about 400 preparations (dry mounts) of scales obtained from 

 all parts of the world, the author selects a few which with good object- 

 glasses give, he considers, some startling results. Only a brief abstract 

 is, however, given of the appearances. 



Mr. T. F. Smith considers f that some of the appearances described 

 in the paper are due to the villi being seen out of focus. In his view 

 they are in between the two membranes of which the scales are com- 

 posed, their use being to keep the two surfaces of the scale -apart, 

 and they are longer or shorter according to whether the surfaces are 

 more or less rounded. He had seen some of the appearances, but only 

 by taking too deep a focus. " As for the beading, he had never seen it, 

 and he was strongly inclined to the belief that it arose from Dr. Pigott's 

 methods being in some way at fault. He believed from what he had 

 read that Dr. Pigott worked with a very small aperture, and if any one 

 wanted to produce false appearances they could not go a better way to 

 work ; by using the lowest aperture of the condenser the same effects 

 could be produced. With regard to Dr. Pigott's test rings, he knew 

 that appearance perfectly well ; but it was again a false effect due to tho 

 results of using too small an aperture." 



Mr. Smith also shows J that " some very respectable beads " may be 



* Journ. Quek. Micr. Club, iii. (18S8) pp. 205-7. 



t Ibid., pp. 234-5. t Ibid., p. 204. 



