286 Professor E. B. Poulton on Mimetic Forms of 
of trimeni figured on Plate XVIII, Fig. 1, and XIX, Fig. 1, 
and by comparison with the hippocoon forms on the same 
plates (XVIII 2, XTX 2-3), why it is that the submarginal 
yellow ground colour should be represented in the mimetic 
females by a pair of pale spots between each pair of nervules. 
It is evidently because the marginal development of black 
was brought about not only by a growth in width of the 
two marginal black bands of the male (Plate XVII, 
Figs. 1-6), but was also aided to an important extent 
by the appearance of black inter-nervular streaks. These 
naturally cut the ground colour still persisting between 
each pair of nervules into two halves. 
(y) Traces of costal and inner gaps in black margin of 
hind-wing of trimeni, etc. 
Apart from the indication of the “inner gap” afforded 
by the special development of the corresponding pair of 
pale submarginal spots, other distinct traces of both gaps 
are among the primitive features of tviment. They are 
especially strongly developed in the specimen shown in 
Plate XVIII, Fig. 1. The “costal gap” is remarkably 
clear in the figure, while the site of the “inner gap” is 
rendered visible by two faint yellow streaks passing 
outwards into the broad black margin. They are better 
seen in the right hind-wing of Fig. 1. The trvmeni re- 
presented on Plate XIX, Fig. 1, is a 2 form of the east 
coast sub-species ¢abul/us in which the black band of the 
male is more developed than elsewhere, while the gaps are 
reduced to a minimum (Trans. Ent. Soc. Lond. 1904, p. 683). 
Nevertheless the “costal gap” can be clearly recognized. 
It is seen in Fig. 1 that the mner border of the black 
margin is not curved parallel with its outer border forming 
the edge of the wing but is made up of two straight lines 
meeting in an obtuse angle. This angle is the point where 
the central yellow invades the black margin most deeply 
and represents the costal gap of the male. This identi- 
fication will be at once admitted when Fig. 1 on Plate 
XVIII is compared with Fig. 1 on XIX. The squarish 
shape thus originating persists in many examples of the 
more specialized female forms. It may be distinctly seen 
on the two hippocoon (Figs. 7,8) and three of the cenea 
(Figs. 5, 6, 10) forms represented on Plate XXXI of 
Trans. Ent. Soc. 1904; and in the present memoir in 
trophonvus represented on Fig. 7 of Plate XVII, and the 
