( 24 ) 

 CORKESPONDENCE. 



BUTTEBFLY ScALES. 



To the Editor of the '■Muntlihj Microscopical Journal' 



Brussels, November 22, 1871. 



Sir, — I think it is most important for everyone that he should be 

 able to see through the microscope all that is to be seen, and nothing 

 else. 



Having for some months jiast made a constant use of the parabo- 

 loid with immersion objectives of Koss and of Hartnack (^V*^ Ross, 

 Nos. 9 and 11 of Hartnack), and studied the scales of many butterflies 

 and moths of European, Chinese, and Brazilian origin, I have been 

 struck by the elegance of the beaded appearance those objects 

 presented, 



I may thus entirely confirm Mr, S. J. Mclntire's views : tJiose 

 scales have almost all of them a headed appearance, perfectly defined ; 

 biit where I differ totally with this most distinguished Fellow of the 

 Eoyal Microscopical Society is when he asserts in his paper " On the 

 Minute Structure of the Scales of Certain Insects," read the 9th Nov., 

 1870, " that those beads have no real existence as beads, but are due 

 to the interference of the rays of light by corrugated membranes ; that 

 they are, in fact, (jhost-heads." 



Reasoning upon this hypothesis, it is not at all wonderful that 

 Mr. Mclntire should have attributed his failures, when " he wished 

 but could not call into existence those almost palpahle heads," as he calls 

 them himself, so distinctly they are visible, " to a predisposition of his 

 mind, and to the want of that necessary adroitness in manipulating 

 which everyone knows very well is not always at one's own command." 



Be that as it may, it must be admitted that his whole reasoning on 

 the matter in hand shows very well that there exists a very serious 

 difficulty of making a proper use of high-power objectives, and of 

 selecting that kind of illumination which is best adapted to the nature 

 of the object which is to be seen, and in particular which is wanted to 

 show the beaded appearance of the scales of the wings of insects. 



But all those reasonings seem not to me to be conclusive. One 

 assertion alone, if it were justified by facts, would be very serious ; it 

 is that these beads disappear altogether without leaving any traces or 

 remains whatever, when the scale is crushed. 



I should beg Mr. Mclntire to reconsider this his last assertion, 

 because I am positive that the beads subsist as distinct and isolated 

 things after the scale has been crushed ; but it may happen that 

 the scales which he has seen were partially so crushed as to leave in 

 the parts which were crushed no remains at all. Then, but then 

 only, the assertion of Mr. Mclntire seems very Avell justified by facts, 

 but in that it is no conclusion at all. 



Now for what I have observed, and the mode of illumination 1 

 have made use of. 



