286 Professor E. B. Poulton on Mimetic Forms of 



of trimcni fiourod on Plate XVIII, Fio-. 1, and XIX, Fiff. 1, 

 and by compaiison with the hipjyocoon forms on tlie same 

 plates (XVIII 2, XIX 2-8), why it is that the subnjarginal 

 yellow ground colour should be represented in the mimetic 

 females by a^mtV o/joalc 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-G), but Avas 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 i?incr gcqis in hiack 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 trimeni. 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 trimeni re- 

 presented on Plate XIX, Fig. 1, is a $ form of the east 

 coast sub-species tihvUus 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. C83). 

 Nevertheless the " costal gap " can be clearly recognized. 

 It is seen in Fig. 1 that the inner 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 liipjjocoon (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 

 tropho7iius represented on Fig. 7 of Plate XVII, and the 



