62 The Advancing Poioers of Microscopic Definition. 



He also proceeds to observe that 



" An intermediate membrane (in these scales) has been described 

 by some observers, but this appears only the result of a deposit which 

 in most scales takes a more or less beaded form, and may combine 

 into a distinct layer of some kind. Dr. Pigott's ' beads ' are by no 

 means inconsistent with the existence of corrugations ; and the excla- 

 mation marks are probably true aspects with a particular focussing 

 and illumination, though few observers, who have taken much care in 

 the investigation, have for many years supposed them to afford an 

 accm-ate ami complete idea of structure. The extreme delicacy of the 

 Podura or Lepidocyrtus scale gives rise to so much difficulty, both of 

 observation and interpretation, that it is advisable to be guided by 

 analogy drawn from easier scales in its interpretation. This plan 

 was pursued by the writer (Mr. Slack), who traced what seemed to be 

 real beads in ordinary and easy butterfly scales, through more difficult 

 ones, up to those of Lepidocyrtus curcicollis. Mr. Mclntire took up 

 the question with great skill, and with an absence of prejudice some- 

 what remarkable in a discussion which has excited an unusual amount 

 of strong feeling ; and whatever ultimate conclusion may be reached, 

 his observations and beautiful sketches will have a permanent value.* 

 .... In scales of Polyxenus lagurus he found what was ' very 

 uncommon ' ; according to his observations, ' a deposit between the 

 membrane ' and the scale was a very solid structure. Most of his 

 endeavours to detect beaded deposits led him to think such appear- 

 ances were only ' ghosts ' ; and it is well known that false appearances 

 of beading are easily produced under certain conditions. Mr. 

 Mclntire's accoimt of his observations and experiments scarcely 

 warrants his conclusions, for he admits ' pigment granules ' in scales 

 such as Analthusla HorsfekUi, figured long since by Mr. De la Eue, 

 and in some others. Lieut. -Colonel Dr. J. J. Woodward, of the 

 U. S. Army, emi^loyed his well-known skill in photographing Podm-a 

 scales; and in a paper read before the Royal Microscopical Society 

 ' On the Coarser Degeeria Scale,' he says, ' I had no difficulty in 

 making out appearances, which, so far as I can gather from Dr. 

 Pigott's own descriptions and the published discussion of his views, 

 are substantially the same as those seen and shown by him .... 

 and even on the more minutely marked and difficult Lepidocyrtus 

 scale I have been able to develop appearances which seem to be sub- 

 stantially similar.'t Dr. Woodward did not, however (writes Mr. 

 Slack), pronounce any decided opinion as to the real structure, but 

 since this paper he has kindly forwarded to the Royal Microscopical 

 Society and to the writer, photographs of Degeeria domestica, beauti- 

 fully exhibiting a beaded appearance. In a communication to the 

 Royal Microscopical Society, read in May, 1871, Dr. Woodward 

 speaks of Mr. Joseph Beck having shown and left with him a fine 

 Podura slide, showing the noto of exclamation marks with remarkable 

 clearness, ' but immediately afterwards, with the same optical com- 

 bination and magnifying power, without any change in the cover 



* See 'Monthly Microscopical Journal,' January 1, 1871, &c. 

 t April No. of the ' Monthly Microscopical Journal,' 1871. 



