XLI 



Plusias being the best known ; reference may also be made to the strono- 

 metallic gloss in species of Morpho and in several Lycaenidae. In the Vanessa 

 pupae also it is doubtless simply a question of prismatic colour phenomena of 

 whose nature we are still ignorant and which have no relation to the direct 

 influence of light but which may be excited abnormally by abnormal disturbing 

 influence of light in so far as the susceptibility for it exists, as in the pupa of 

 Vanessa Urticae L. Disturbance of the natural course of development, there- 

 fore, is the cause in this case. This reacts on the colour of the pupae in 

 the presence of abnormal influence of light, in the same manner as may be 

 witnessed with respect to the colour and form in imagines resulting from 

 various influences, as indicated on page XIV stipra. The occasional appearance 

 of a pink colour under the same influences is doubtless to be interpreted in a 

 similar manner. 



The experiments in connection with influences of light have, therefore, 

 produced much confusion in the science of lepidopterology ; I hope to be able to 

 shed some light on the subject. It should be observed that a knowledge of the 

 phenomenon of colour evolution is closely associated with it. 



Fortwith to explain all the phenomena to be observed in this connection 

 would, indeed, be too great a task and more than could reasonably be expected. 

 The explanation of some, however, appears not impossible. 



The observations by Bordage indicate that in the normal condition Euploea 

 pupae are of a generally dark brown colour on which a strong metallic lustre 

 has a tendency of spreading more and more. Of the different species, some 

 are in a more advanced stage than others as regards this process. Now in 

 the case of pupae normally produced in daylight, when this process takes place 

 in the dark a disturbance is caused resulting in a decreased distribution of the 

 metallic lustre. 



The Memnon pupae, like those of P. Machaon L., P. Philodamas L., 

 and P. Demoleus L., are dimorphic, i. c. light green and dark greyish or 

 brownish, which is termed bark-coloured. A dark environment may cause the 

 former to turn to dark green, as has been observed in the case of the two 

 pupae of P. Polites L. ; moreover, with ordinary treatment or even when reared 

 in dark boxes, green as well as greyish or brownish coloured pupae may be 

 produced; very susceptible individuals only in that case acquire a dark colour. 

 A particularly great susceptibility to this evolutionary change seems to occur 

 in P. Memnon L. the same as in P. Machaon L., hence the slightest darkening 

 of its environment, when pupation takes place against a branch or bark, is 

 sufficient to cause them to become brown -grey, except as to the persistent green 



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