Phylogeny of the Pierine. 291 
instance, C. bithys (Fig. 2), C. toca, and C. colla. In other 
species of the same genus, the next steps are shown by 
the enlargement of the pale spots (as in C. anaitis ¢), 
their assumption of a purer white colour (as in U. 
anattis ©), and the confluence of those of the inner row, 
as in CU. trezene and C. ctemene ¢. In the latter insect 
the enlargement and confluence of the white patches has 
proceeded so far that the white must now be considered 
the ground colour, the original dark neutral tint being 
confined to the base and apices of the forewings, a 
narrow and interrupted marginal band on the hind- 
wings, and the course of the nervures with their branches 
(Fig. 3). In C. corcyra, the same process is continued 
almost to its furthest limit, the new ground colour has 
supplanted the old in every place except the apex and a 
narrow slip along the costa of the forewing. C. corcyra 
is thus practically a ‘‘ white” butterfly; and so within the 
single genus Catasticta a complete transition is to be 
found, from a dark almost black ground colour, with 
small and indistinct pale greyish patches, to a ground 
colour of dead white, with hardly more than a trace 
remaining of the original dark surface tint. This 
passage from C. bithys to C. corcyra is really an epitome 
of the whole range of variation in pattern throughout 
the entire group of Pierinzx. 
In such species of Catasticta as C. semiramis, where 
the pale patches are tolerably distinct, and have not yet 
coalesced, the dark marginal and submarginal series of 
spots, so characteristic of the Pierines as a whole, are 
visible at an early stage of their emergence. As has 
been shown above, on p. 267, the marginal series (called 
M) is formed by the remains of the dark ground colour 
between the outer series of primitive pale patches 
and the outer border of the wing; while the sub- 
marginal series S comes into view between the outer and 
inner series of pale patches. Besides these, a relic of 
the dark ground colour is seen to remain about the 
disco-cellular nervules in the forewing, which forms the 
first beginning of a definite discoidal spot ; and another 
row of minute pale patches, each occupying the centre 
of an interspace on the extreme outer margin of the 
wing, begins to split up the marginal series in the 
manner already spoken of. The definite character of 
series M is assumed sooner on the forewing than on the 
