428 Mr. G. A. K. Marslmll on 



character which is non-acrreiform and purely aposematic 

 is far more emphasized than in tlie latter species. It is 

 probable tliat scsamics ]-eprescnts a later development, and 

 that in it the synaposeniatic elements have been gradually 

 strengtliencd and the peculiar aposematic character cor- 

 respondingly reduced. 



We now pass to the consideration of a species in which 

 the conspicuous characters of the under-side of the wet 

 phase are probably entirely peculiar and aposematic. 



Mr. Marshall's suggestion in 1896 that Preris pclasgis is 

 the wet phase of P. archesia has never been confirmed by 

 breeding the one form from the other. It is, however, 

 certain that his conclusion was sound. The two forms 

 have often been captured in coitu. The female jielasf/is 

 represented in Plate XII, fig. 4, was captured by Mr. 

 Marshall in eoitn with the male archesia shown in Fig. 5 of 

 the .same plate. Intermediate forms are mucli commoner 

 than in the case of sesamus and antilnpc; and above all the 

 relationship of wet phase to dry is far closer in archesia, so 

 that it is possible to see how tlie one was derived from 

 the otlier more fully than in any of the species with mark- 

 edly-different seasonal forms. The under-side of one of the 

 commonest forms of the dry phase is represented in Fig. 6, 

 Plate XIII, and opposite to it that of the typical wet phase 

 in Fig. '). At first siglit they ajapear totally different, and 

 certainly the latter is as conspicuous as the former is well 

 concealed. An uncoloured illustration cannot do justice 

 to the varied shades of brown and grey on the under-.side 

 ol arclicsia {Y'lg. G), and a long series of specimens would be 

 required to show the immense range of individual variation 

 by wdiich all kinds of common appearances presented by dead 

 leaves are reproduced. Among such variations is one in 

 which the dark-brown ground-colour is almost uniform 

 and unmottled inside the mid-iib-like stripe (Fig. 7). From 

 this we pass to forms in which tlie stripe widens into a 

 light band (Fig. 8), clearly showing its homology with the 

 still more cou.spicuous band of pclasgis (compare Figs. 5 and 

 8). Such a variety as that shown in Fig. 8 is still a long wa}'' 

 on the archesia side of a form intermediate between the 

 wet and dry phase, and would certainly be cryptic ratlier 

 than conspicuous in nature, although not so well concealed 

 as the form shown in Fig. 7, and still less so than that 

 shown in Fig. G. Truly intermediate varieties between 

 the Avet and dry phases are not uncommon, in which 



