40 THE ENTOMOLOGIST. 



exhaustive examination of the relations between red and yellow : 



a development as unexpected as discouraging, coming as it did at 

 a time when I fancied mj^self to be pretty well acquainted with 

 the phenomena of the red pigment. At this time my articles 

 were already in course of publication in the * Entomologist ' ; and 

 not knowing what modifications in views already foreshadowed 

 might be necessitated by this new departure, I inserted, — in 

 order to guard myself somewhat, — the footnote on p. 186 as to 

 the " after phenomenon," confining it, however, to the case of 

 hydrochloric acid ; at the last moment, before this was published, 

 I obtained further results, which led me to add, " and other 

 acids." We will now consider the question in detail. 



Three, and only three, explanations seemed possible, of this 

 reversion to the original red : it might be a time effect pure and 

 simple : it might be due to washing with water ; or to washing 

 with alcohol. 



I first made a set of experiments with Z.filipendulce — 

 A. & B. Wings were exposed to HCl for one hour. 



C. Similar exposure for two hours. 



D. Similar exposure for one week. 



In each case a parallel experiment was made with HNO3 in 

 order to determine whether the reversion phenomenon was or 

 was not confined to specimens originally transformed by HCl.* 



The wings, at the expiration of their periods of exposure, 

 were respectively treated as follows : — 



A. By merely washing with distilled water a large part of 

 the red returned there and then in the HCl specimen. The 

 HNO3 specimen remained immovably yellow. 



B. Washed as above, then with alcohol, and finally left 

 standing in alcohol. 



C. Simply washed as with A., and with the same result. 

 The HCl specimen recovered its red ; the HNO3 remained 

 yellow. But on examining these A., B. and C. (HCl) speci- 

 mens after a lapse of 24 hours, I found that they were again 

 yellow; and at the end of a week still yellow (C. orange). But 

 on washing again with water the red was partly restored. 



All the HNO3 specimens had retained their yellow from 

 first to last. 



D. The HCl specimen (after one week's exposure to acid) , 

 was at once restored to red by simple washing. 



The HNO3 specimen remained immovably yellow. 



A., B. (or C.) and D. HCl specimens, after having regained 

 their red, as above related, were left alone for a week. At the 

 end of that time they were still the full red. 



The HNO3 specimens of course had retained their yellow. 



* This whole set of experiments was made in the same mode aa usual, viz., by 

 treating wings gummed on to watch-glasses. 



(To be continued.) 



