VI " WING-PATTERN SENSITIVENESS 335 



probable. The scales when first formed are pallid, and the physi- 

 ology of their pigmentation is not fully ascertained ; it is, how- 

 ever, known that when the scales are pallid the hypodermis is 

 either pigmented or in close contact with pigmentary matter, 

 and that as tlie scales become coloured this pigmentation of the 

 hypodermis diminishes ; so that it is clear that the colour of 

 the scales is obtained from matter in the interior of the develop- 

 ing wing, and probably l)y the agency of the liypodermis. 



The pattern on the wings of Lepidoptera is formed before 

 the emergence from the pupa. In the Tortoiseshell butterfiy, 

 according to Schiiffer, it commences to appear about the ninth 

 day of the pupal life, and tlie pattern is completed about the 

 eleventh or twelfth day. He also states that the process varies 

 in its rapidity, and this, lie thinks, may depend on the previous 

 condition of the larva. According to Bnckell the pupa of 

 Nemcoljius lucina is sufficiently transparent to allow the develop- 

 ment of the colour of the imago to be watched. He says that 

 the coloration occurred first in front ; that its entire production 

 occupied less than twenty-four hours, and only commenced about 

 forty-eight hours before the imago emerged.^ When the butter- 

 fly leaves the pupal skin the wings are soft, crumpled sacs, of 

 comparatively small size, but, as everyone knows, they rapidly 

 expand and become rigid ; the physiology of this process is 

 apparently still unknown. 



A great deal of evidence, both direct and indirect, has 

 accumulated showing that the organisation of many Lepidoptera 

 is excessively sensitive, so that slight changes of condition pro- 

 duce remarkable results ; and it has also been shown that in the 

 early part of the life this sensitiveness is especially great at the 

 period of ecdysis. Numerous butterflies produce more than one 

 generation a year, and sometimes the generations are so different 

 that they have passed current with entomologists as distinct 

 species. The phenomena of this character are styled " seasonal 

 variations " or " seasonal dimorphism." It has, however, been 

 shown that, by careful management, the eggs of a generation (say 

 form a) may be made to produce form a, whereas in the usual 

 course of nature they would produce form h. A very remarkable 

 condition is exhibited by the North American Fapilio ajax. There 

 are three forms of the species, known as P. ajax, P. telamonides, 

 1 Bnt. Record, vi. 1895, p. 258. 



