122 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



dissecting microscope of moderate power by means of fine needles set in match- 

 sticks. One needle is inserted through the abdomen and held rigid; another 

 through the middle of the upper side of the thorax. The second needle is now 

 drawn forward, tearing apart the pupal envelope and carrying with it the anterior 

 part of the thorax with wings attached. The structure of the pupa with separate 

 envelopes for wings and legs in the lower Microlepidoptera renders this method 

 of procedure highly successful. The thorax may now be torn apart, allowing 

 the wings to float out flat. With a little experience, it is possible to remove 

 the wings in this manner without the displacement of either scales or cilia. The 

 wings thus removed from the pupa vary in length from L5 to 2 mm., being, 

 therefore, about one-half the length of the imaginal wings. 



The wings were examined with a simple lens to determine the general extent 

 of the color areas. For the more accurate observation of the positions and limits 

 of pigmented areas and individual scales pigmented, I have used a compound 

 miscroscope, 16 mm. objective, 4x eyepiece, giving a magnification of 60 diam- 

 eters. The observations were made almost entirely by reflected light and 

 under a cover glass. In the early stages, where the colors are very faint, I have 

 found black paper, as suggested by von Linden, very useful for a background. 

 Somewhat later, a pure white background is advantageous in the detection of 

 the first appearance of grayish tints. 



All of the wings were examined in .6 per cent NaCl solution, shortly after 

 removal from the pupa. Observations made thus are vastly more satisfactory 

 than when permanent mounts are employed. A number of the wings were, 

 however, transferred to absolute alcohol between pieces of glass to prevent 

 curling, and after about an hour embedded in Venetian turpentine made as 

 follows : 



Commercial Venice turpentine is mixed in a tall cylinder glass with an 

 equal volume of 95 per cent alcohol. The mixture is aflowed to stand in a warm 

 place for three or four weeks and then decanted. 



The mounting medium thus prepared is thin enough to flow easily and not 

 displace the deUcate cilia. However, the attendant darkening of the colors is a 

 disadvantage in comparing with adult specimens. 



I have found it possible to preserve all except the earliest stages without 

 the use of a mounting fluid, if the slide containing the wing under a cover glass is 

 immersed in absolute alcohol for a short period. Later the cover glass may be 

 closely appressed and fastened down around its edges. 



Both forewings in each specimen were examined; the two sets of observa- 

 tions thus serving as a check on one another. In the following descriptions, 

 reference is made to the forewings only. The hindwings are practically uni- 

 colorous, usually paler than the forewings, and reach their final development 

 somewhat in advance of the forewings. Their development yields no new 

 facts, merely confirming the results of earlier investigators upon the sequence 

 of colors. 



