10 
or supplement information obtained from rocks. I slionld 
add that the theory of continental drift, though pnt for- 
ward by geologists, appears to be much more acceptable to 
biologists who find it a satisfactory explanation for many 
anomalies in distribution, than it is to geophysicists who 
have to provide an explanation of how it came about. 
Another student of butterfly sj^stematics, E. B. Ford, 
became interested in the different types of pigments in 
the scales of butterflies' wings and decided to see what in- 
formation they would give on relationships. One of the 
difficulties here was that if the investigation was to 
cover a wide range of species, museum specimens must be 
used. Curators of museums will very naturally only allow 
their specimens to be tested if they will not be damaged in 
any way and this is not so easy for a chemical test. 
The colours from ivory to deep yellow in butterflies 
may be due to various pigments, one group of which are 
the flavones, which are obtained directly from the food 
plants of the caterpillars. Ford devised a simple test for 
flavones which could be apphed to white and pale yellow 
colours. These pigments combine with ammonia to produce 
compounds of a deeper shade of yellow which in butterflies 
are unstable so that the specimen soon retui ns to its oi'ig- 
iual colour. By exposing a specimen to ammonia fumes he 
could say, if its colour changed to a deep yellow, that 
flavones were present. 
T'^p to that time flavones had only been reported in 
one or two instances in butterflies. Ford studied their 
distribution in the famdy Pieridae which inclndes the 
butterflies known as ‘‘whites” and “yellows.” There are 
five subfamilies of Pieridae, one of which, the Di^mor- 
phiinae, is rather primitive and almost confined to Central 
and South America where there are 98 species. However, 
the genus Leptidea, the “wood whites,” which has thi-ee 
species in Europe and Asia, had also been included in 
Dismorphiinae by an earlier worker, Talbot, although this 
seems a peculiar distribution. Ford found that all 
Lepiidea had flavones and so did all species of one genus 
and some of the second genus of South American T)is- 
morphiinae. In the other subfamilies of Pieridae. oidy two 
out of 233 species he examined had flavones. Thus bio- 
chemistry supported the relationships postulated on struc- 
tural grounds. He was able to go further and in th.e genus 
that contained some species with flavones and some with- 
out, showed that there were correlated morphological dif- 
ferences and it should be split into two genera. Ford 
considers that chemical differences are not of any greater 
significance than structural differences, but provide a 
