ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 199 



interior of the body of the insect, and not in a pui'ely mechanical 

 manner, as contended for by Prof. Weismann. 



Colour is influenced not only by air and light, but also by heat 

 and cold and the wetness or dryness of the atmosphere, the season, 

 and the character of the country. Dr. Hagen distinguishes colours 

 as optical and natural. The former are produced by interference 

 in two different ways : either by thin superposed lamellee, or by 

 many very fine lines or small impressions in very near juxtaposition. 

 There must be present at least two superposed lamellae to j)roduce 

 colours by interference. There cannot be more than four layers 

 in the wings and scales, which show principally such colours in 

 insects — two external ones belonging to the cuticula, and two internal 

 ones belonging to the hypodermis. The naked wings of Diptera and 

 Neuroptera often show beautiful interference colours. The scales of 

 jEntimus and other Curculionidae are well known for their brilliancy, 

 and it is interesting to remark that when dry scales are examined 

 with the Microscope, many are found partly injured, which give 

 in different places different colours, according to the number of layers 

 which remain, the elytra of some Chrysomelina and other beetles 

 with iridescent colours probably belonging to the same category. 



Secondly, interference colours are produced by many very fine 

 lines or striae in very near juxtaposition. 



Perhaps in the colour-changing butterflies natural colours are 

 combined with optical colours, or perhaps interference colours pro- 

 duced by superposed lamellee are combined with those produced by 

 fine stri^. It will be necessary to deprive the wings of their natural 

 colours by bleaching, and then to make the microscopical examina- 

 tion. Dr. Hagen has begun experiments for this purpose. The wings 

 of Apatura clytie, a variety of A. ilia, are pale yellow in the colour- 

 changing part ; the wings of Euplcea siiperha are velvety black above, 

 the black changing into violet in the colour-changing part. Both 

 wings put in eau de javelle began to grow pale after an hour. The 

 paleness began first in the colour-changing part of E. sujperha, and 

 was less visible in the much lighter coloured wings of A. clytie. 

 After one hour and a half the whole colour-changing part of both 

 species was entirely hyaline. The not-colour-changing parts were 

 very little affected, and in A. clytie the light-brown spots were nearly 

 intact. Both wings had lost entirely the change of colours. The 

 microscopical examinations showed that the scales of the colour- 

 changing parts were very much affected. The scales were hyaline, 

 nearly visible ; the longitudinal striee less sharp, the transversal ones 

 even more affected, and mostly obliterated. In some places, in the 

 middle of the colour-changing part, the scales had disappeared, and 

 only their stems were left. On the other hand, the scales of the not- 

 colour-changing parts were nearly unchanged, and both kinds of the 

 striae as sharp as before. The under side of the wings does not change 

 colour at all, nevertheless, the parts corresponding to those iridescent 

 ones of the upper side were affected as much and in the same manner 

 as the scales of the upper side. From the beginning of the bleaching 

 process both sides made the same progress in becoming hyaline. 



Now the striae of the scales, though they had been much affected 



