Phylogeny of the Pierines. 267 
reduced. P. soracta, however, shows M with sufficient 
distinctness; and even in P. crategi M itself is in some 
instances visible, while the dark prolongations along the 
course of the nervules is a well-known and conspicuous 
feature. 
Delias and Prioneris help to show us what is in all 
probability the earliest condition of the present as well 
as of the former series. ‘The upper surface of both fore 
and hindwing in the female of D. eucharis presents once 
more the familiar pattern of Metaporia agathon and 
Nepheronia gea ?. ILthas already been pointed out that 
there is an easy passage from this system of marking 
to that which we find in D. belladonna, D. pasithoe, and 
several other species; while the same features are un- 
doubtedly visible with but slight modification in the 
American genera Huterpe, Catasticta, Leodonta, and 
Eucheira (see p. 258). A comparison of the insects just 
named, to which may be added Prioneris thestylis and 
other species of the same genus, can hardly fail to suggest 
the probability of the origin of both M and S as portions 
of the original dark ground-colour marked off from one 
another with gradually increasing distinctness by the ap- 
pearance, enlargement, and confluence of whitish patches 
in the interspaces between nervules. ‘The alternate 
character of the two series S and M, when broken 
up into spots, is seen to be a consequence of the shape 
and position of the original dusky white touches that 
first bring them into view. These touches may be seen 
for example in D. belladonna (Fig. 4) to be divisible into 
two sets, which we may call marginal and basal, both 
occupying the central areas of the interspaces. Between 
the two sets is included the portion of ground colour cor- 
responding to 8, the constituent spots of which, when iso- 
lated, will necessarily have their centres in the interspaces. 
But the marginal set of light marks tends to reach by 
tapering extremities to the edge of the wing (see Fig. 5) ; 
so that the interposed marginal patches of unaltered 
ground colour, forming the first beginnings of M, are of 
necessity focussed round points in the nervules and not 
in the interspaces, And when in consequence of the 
further development and fusion of the white or pale 
markings, the marginal relics of dark ground colour 
become reduced to a row of isolated dark spots, these 
spots are, as we have already seen in S. daplidice (p. 263) 
