10 Transactions of the 



Though I do not feel satisfied that Dr. Pigott is correct in 

 speaking of the basic membrane of a Podura scale, above and below 

 which he says beads he in chains, I yet think what he sees has 

 some foundation ; and it is our business, in the absence of experi- 

 ence with his aplanatic searcher, to ascertain if what he shows us 

 bears any analogy to, or is conflicting with, ascertained structure in 

 other scales. If the latter, no amount of optical knowledge on his 

 part would convince me he is right; and, on the other hand, if 

 analogous appearances have been seen in similar structures before, 

 I shall be prepared to accept his views, subject to correction. 



Now, it is clear to my mind that Dr. Pigott's discovery as 

 regards the scale of Lepidoeijrtus curvicollis admits of one or other 

 of two interpretations : — either the appearances he sees are caused 

 by pigment granules in the membranes, identical with those seen in 

 the scales of insects generally, but which have never yet been as- 

 serted, so far as 1 know, to exist in Podura scales, or he sees " ghost- 

 beads," which are always the result of some surface inequality, such 

 as minute corrugations of the membrane or membranes, the exist- 

 ence of which minute corrugations in the scale of Curvicollis has 

 likewise never yet been suspected. And, whichever interpretation 

 be finally accepted, I for one admit that a step is gained, and Dr. 

 Pigott can claim the credit of being the first to notice it. 



This result places me in a position to view with favour the 

 method by which he has obtained the appearance. Another consi- 

 deration is, that it is highly improbable that the lens Dr. Pigott 

 has used in the investigation is the only exponent of the truth, 

 such as it is. (I think he admitted something to this efiect at the 

 October meeting.) Can I then test the value of this method of 

 examination by means of the apparatus I have by me ? 



I have endeavoured to obtain upon L. curvicollis the same re- 

 sults as he does, and on two occasions was approximately successful. 

 JMy process was as follows. The lamp was on my left, and about 

 ten inches from the microscope which had the achromatic condenser 

 (Powell and Lealand) on, and the smallest aperture of the diaphragm 

 accurately centered. The muTor was adjusted a little to the right 

 of the axis of the microscope, so that only enough hght to illuminate 

 without flare passed up through the lenses, and the illuminating 

 beam consisted of rays rendered parallel. It seemed to be indis- 

 pensable that the few large scales (for it was only a few in which I 

 thought I saw it) should lie in exactly a horizontal direction, with 

 the shafts pointing to the left of the field of view. The scale of 

 Degeeria domestica (or Seira domestica, for Sir J. Lubbock has 

 recently given the insect a new name) showed the same, or very 

 nearly the same, still more strongly. I went through the whole of 

 the Podura and Lepisma scales and saw beads abundant every- 

 where. Although I had seen the most of these beads before, it was 



