264 Transactions of the 



ture, as with polarized light, though, if we disregard the appearances 

 produced by other methods of observation and illumination, which 

 furnish a better clue to the real structure, ivithout marked chro- 

 matic effects, we shall be in constant danger of accepting illusory 

 appearances. 



To the terms " ribs," " cross-bars," at first sight there may ap- 

 pear some objection ; but when the figures are examined where the 

 rib and its attachments are seen together stripped from the scale 

 (Fig. 2), the terms seem to me less objectionable than " corruga- 

 tions" " folds," or " striae." Now, Mr. Slack sees in the ribs " only 

 corrugations or wrinkles" in the butterfly scales, and I think Mr. 

 Mclntire and others prefer these terms to " ribs" ; hence it is with dif- 

 fidence the fonner are employed, for terms used to convey appearances 

 under the microscope are seldom quite satisfactory. Mr. Slack says, 

 " the beads more or less distinct, or coalescent, as the case may be, 

 I take to be formed by exudations, in drops, from the membranes, 

 consolidating, so far as they do consolidate, in a definite form."* 

 This view appears open to considerable doubt, though a kind of com- 

 promise of different theories and contrary to the one adopted in this 

 article, which is perhaps more advanced in particulars than sug- 

 gested by my friend Dr. Woodward in the recent pages of the 

 ' Monthly Microscopical Journal,' No. XXYIII., p. 158, or than 

 pointed out by that careful observer Mr. Mclntire. The inner mem- 

 brane appears slightly extensible, the ribs can be compressed out of 

 shape in some scales, and in none did they appear to me hollow, as 

 Dr. Bowerbank suggests : a communication through the quill to the 

 inner surfaces is suspected to exist in all scales, and in relation with 

 the membranes of the wing or dermic support. 



Whether the butterfly would show any change in the general 

 colouring of the wing, by the transmission of feeble electric shocks 

 through the living insect, is doubtful, though perhaps worth an 

 experiment It will be seen that I am disposed to give to these 

 flattened bladder-like bodies some function, higher than is usually 

 supposed, though the transition from hairs " protective " and 

 " ornamental " is so gradual towards their own varied shape and 

 substance, that they ajjpear more naturally to accord with those 

 ordinary dermic structures. Possibly they may be expended tegu- 

 mentary organs, which passed their active phase in the chrysalis 

 state, and merely preserved a common attachment upon emerging 

 from this condition. Mr. Mclntire points out t the moment they 

 become external appendages they cease to grow ; yet does it follow 

 that all changes in the material within the membranes of a semi-solid 

 greasy nature are checked, or are not kejit in a normal condition 

 for the benefit of the scale ? To some alteration in this material 



♦ ' Student; No. 1, p. 54. t ' M. M. Journal,' No. XXV., p. 6. 



