ANS 
in especial of Mr.G. A. K. MARSHALL, who has proved by breed- 
ing that some of the forms of the genus Precis, most distinct from 
one another in aspect, are nevertheless related to one another as 
offspring to parent. One of the most remarkable of these instances, 
Precis octavia-natalensis and P. sesamus, is here shown on the 
screen. It has also been proved by the same indisputable evidence 
that, in many cases, forms of African Pierine, notably in the 
genus Zeracolus, which had previously been described and named 
as distinct, were merely seasonal phases of the same species. In 
very many, probably most, of these examples of seasonal dimor- 
phism as exhibited by tropical Butterflies, the dry season phase is 
far more closely assimilated in aspect to its inanimate surroundings 
than is the wet; in a few instances, while the dry season form is 
well concealed when reposing among dead leaves or on the 
ground, the wet season form of the same species is comparatively 
conspicuous, and bears more or less resemblance to another But- 
terfly of remote affinity. On the other hand there is a case where 
the model (Mylothris agathina) is sexually, not seasonally dimor- 
phic. One of its mimics (Belenoís thysa) is both seasonally and 
sexually dimorphic. The male of Belenois thysa copies the same 
sex of the Mylothris in both seasons, but much better in the dry 
season than in the wet; while the female Belenois is a close mimic 
of the female Mylothris in the dry season, but frequently departs 
altogether from its model in the wet. 
We have learned then that in seasonal, as in sexual dimorphism, 
it may happen that one phase of the species may be mimetic and 
the other not. 
Let us now turn to the consideration of the actual nature of the 
resemblances themselves. The outstanding feature which must 
strike everyone who gives them his attention is, that they are purely 
superficial. Take the case of Limnas chrysippus, the female of 
Hypolimnas misippus, and the trophonius-form of the female of 
Papilio dardanus, three Butterflies which we have already noted 
as presenting a remarkable and even deceptive likeness in general 
aspect. One of these Butterflies is a Danaine, another is a Nym- 
phaline, and the third a Papilio. I need hardly remind any of my 
present audience that each of these groups is characterised by 
certain features, which are called «structural», belonging especially 
to the segments and appendages of the legs, and to the number 
and arrangement of the veins in the wings. But do we find any 
mutual approach in these structural particulars corresponding to 
the very striking assimilation in obvious aspect? We do not; and 
