318 Dr. Frederick A. Dixey on 
A full illustration of this position would require a 
larger series of diagrams than could well be given in this 
place; it is hoped, however, that the series of figures on 
Plate VII. may suffice to show the more important 
links in each chain, or at any rate to make the drift of 
my statements intelligible. It should be borne in mind 
that all the forms here spoken of are neotropical. 
1. The “agna” line. The first of these lines of 
development may be called the agna line, inasmuch as it 
leads towards a well-marked group of distasteful forms 
of which Aerie agna, Godm. and Salv., (Pl. VIT., fig. 6) is 
a good example. Starting from a white Pieris of ordinary 
aspect like P. phalve, we find that the first step in the 
growth of this mimetic pattern is furnished by the pro- 
longation of the diagonal dark bar, which in P. phaloe 2 * 
extends from the costa to the distal end of the cell in 
the forewing, to meet the dark hind margin as in P. caly- 
donia § (fig. 1, %). All stages in the development of 
this first feature can indeed be traced by comparing 
specimens of both sexes of P. calydonia itself. The next 
step is the extension of the dark hind border of the 
forewing, already more pronounced in P. calydonia & 
than in P. phaloe 9, along the inner margin, as in P. 
demophile 2 (fig. 3, 1). Simultaneously with this change 
the dark border of the hindwing is much broadened 
(ib., 4), and in some specimens of P. demophile 2, as in 
the one figured, the white ground colour is replaced by 
vellow. These changes are sufficient strongly to suggest 
the general aspect of the protected group referred to, 
and it seems difficult to believe that the appearance of 
the yellow female of P. demophile has not a significance 
derived from this fact. 
2. The “atthis”? line. But the last-named form, viz., 
the yellow P. demophile § , though the final Pierine term 
in one transitional series, is but an intermediate term in 
another. ‘This second line of development, starting 
afresh from P. demophile @ , passes into an unmistakable 
mimetic relation with the protected group that centres 
round such forms as Heliconius atthis (fig. 8) and 
Tithorea pavonit. 
Comparing P. viardi 2 with P. demophile &, we find 
that in the former insect a further stage of divergence 
* See Trans. Ent. Soc. Lond. 1896, pl. III., fig. 2, . 
