2 Transactions of the V'ZT.i^j^^'t^^l^^' 



markings, and corrected his former statements, in -wliich he dis- 

 tinctly asserts his behef that the scale is a corrugated structure, if 

 he believed them to have any real existence as spherules. But, on 

 the contrary, the latest expression of opinion by that authority 

 which I heard him give, was to the effect that no alteration had 

 taken place in his views with regard to the structure of the scale of 

 Lepidocyrtiis (Podura scale). 



In making some notes, as a necessary supplement to the short 

 paper I have already communicated on the scale-bearing Podurae, J 

 may be permitted, perhaps, to state, with some diffidence, the objec- 

 tions which seem in my mind to militate against the new theories : 

 I say theories because I have heard two urged. The most formidable 

 objection to the " bead-like spherule " theory seems to me to be the 

 fact, that all through the scales of insects, whether Lepidopterous 

 or Coleopterous, so far as my knowledge extends, the markings are 

 due to corrugations or wrinklings of one or both membranes of the 

 scales. Now, if this plan of structure holds good so extensively in 

 the Lepidoi^tera, Coleoptera, and Dij^fera, as I believe it does, I 

 cannot help asking, " Why should not the same plan affect the 

 Thysanura ? " I think I shall presently be able to show, by com- 

 parisons, that it does, with certain modifications. The other theory 

 is founded on the optical illusion of rows of beads which is often 

 observable when two Lepidopterous scales of known striated struc- 

 ture lie across each other at any angle. A similar appearance and 

 its cause is alluded to by IMr. Beck in his book on the Microscope, 

 in treating of the scale of Leinsma Saecharina. It also is often seen, 

 but I believe it is equally illusive, in solitary scales of certain 

 foreign Lepidojotera, &c., where the strong longitudinal costoe are 

 crossed at right angles by transverse corrugations. The theory 

 which is advanced is to the effect, that the elongated " heads," or 

 "note of exclamation" markings of the Podura scale, are due to 

 striae on opposite sides of the scale, crossing each other at an angle 

 of about 17"^. Against it I would only urge one objection, namely, 

 that supposing this to be the true solution of the question, we ought 

 to see the elongated beads forming patterns with regard to each 

 other either of squares or rhombs ; but they do not, as a glance at 

 any of the scales the structure of which is disputed, will, I think, 

 convince most observers. Therefore I am unable to accept this 

 theory as containing the whole truth and its explanation. 



Now what analogy is there between the scales of the Tlujsanura, 

 especially Podura scales, and the scales of other insects ? 



If we compare the scales of Lepisma Saecharina, the British 

 species, with the species of Leiyisma lately alluded to in ' The 

 Student ' by Dr. Mann (as introduced from the East Indies into 

 Natal, where its destructiveness is a great nuisance) — some specimens 

 of which species I believe found their way from Bombay to the 



