XXXVII 



pupating a definite amount of illumination, in this case a darkened environment, 

 may bring about this effect, but that, on the other hand, an unusually strong 

 illumination or one caused by specific light rays corresponding to certain colours 

 of the environment, may retard or interrupt this process. 



How and why? To a large extent the answer is still "we know not". 

 PouLTON, in order to prove that the influence of colour, alluded to, on the 

 pupa could not be the result of some response through the sense of sight on 

 the part ot the larva, covered the eyes of the latter with a certain varnish 

 during the said period before pupation so as to blind the larva. It may be 

 presumed that this was, indeed, superfluous; at that period when the skin — 

 and with it that of the head — is nearly severed from the body and has 

 probably but little connection with it, as is evidenced by the change of colour, 

 it may be assumed that the optical function no longer operates by means of 

 the eyes and that the pupal stage in this respect has already been assumed. 

 Nevertheless, even if we do not know in what manner, it may be taken as 

 very probable that the animal remains susceptible to influences of light, for we 

 are here concerned with a class of animals endowed with extreme sensitiveness 

 in this respect. Most of the Heterocera are unable to endure daylight and 

 hide away from it, some even passing the day in an extremely somnolent 

 state; on the other hand many swiftly fly towards any light in the darkness 

 such as the strongly lighted white tropical dwellings. Some Rhopalocera also 

 seek semi-dark spots in the dense forest while others again continually prefer 

 the full glare of the sun, many species being evidently unable to dispense with 

 it, sothat they cease to fly directly the sun disappears, even if only for a few 

 moments, behind the clouds, although the temperature may remain unchanged. 

 It cannot, therefore, appear strange that light, or the absence of it, should 

 exercise a strong influence on such animals and especially at a particularly 

 critical period of their life which would bring a particularly great susceptibility 

 in its train. In many animals devoid of eyes this is, indeed, also the case. 



Now if an environment conducing to a decrease of light promotes the 

 natural development of the colour process in pupae, it stands to reason that 

 the reverse condition should likewise exercise certain effects. Hereto, more- 

 over, certain phenomena sometimes seem to appear which accord to such an 

 extent with other facts, whose occurrence has been observed through the action 

 of other abnormal influences on the pupae in the resuhing imagines, that they 

 also are by no means surprising. 



Blue surroundings had no effect whatever on pupae of Pieris Brassicae L., 

 and P. Rapae L., so that no susceptibility for this colour was present, black 

 or white surroundings, or even those of any other colour except blue and the 



