15 
and of which other species of stronger structure were deprived ; and having that 
protection, whatever it might be, they were on that account fit and likely subjects for 
imitation. So far from conflicting with the theory, he felt no surprise whatever at 
finding a structurally-stronger insect mimicking a Malacoderm. 
The President also exhibited diagrams of the under surface of the abdomen of the 
:females of Obrium cantharinum and other Longicornia, showing the presence of large 
lumps or tufts of hair on particular segments; he was anxious to ascertain whether 
-such a structure was invariably present in the female; he had reason to believe that in 
.Some Australian genera (Penthea and Sympbyletes) it was not invariably present, but 
further observation was required. If it should prove that it was not invariably present 
in the female, this would furnish another instance of “ dimorphism,’ by which he 
(Mr. Pascoe) meant a case where there was an addition to or alteration of a part or 
organ; the term, in his opinion, ought to be confined to such a phenomenon, and was 
not applicable to simple variation, such, e.g., as variation in colour. 
Mr. A. R. Wallace exhibited specimens of Papilio Memnon, P. Pammon, P. The- 
seus, P. Ormenus, P. Erectheus and P. Tydeus, for the purpose of illustrating his views 
on “ polymorphism.” Mr. Wallace remarked that he did not apply the term “ dimor- 
phism” to simple variation; on the contrary, he regarded “ polymorphism,” of which 
“dimorphism” was but the first and least complicated stage, as a totally different 
phenomenon from “ variation,” and one which required a separate name. Under the 
common term “ variety” many distinct phenomena were confounded; he proposed to 
confine that term to those cases in which there was indefiniteness and irregularity in 
the variation. “ Variation,” then, was an indefinite and inconstant phenomenon, the 
instances of which passed from one to the other by irregular, often by insensible, grada- 
tions; “polymorphism,” on the other hand, consisted in the existence of several 
distinct forms of the same insect which do not graduate into each other. Thus, in 
Papilio Memnon, the male was in each locality constant; it had rounded hind wings, 
and was always nearly black, with a few ashy rays; the female, however, existed under 
two distinct forms; the first had the wings shaped like those of the male, but had a 
very different colouration, being more or less olive-coloured, and often banded on the 
hind wings with whitish yellow, and with marginal black spots; the second form of 
female differed remarkably from the first, the hind wings being produced into a large 
spatulate tail, and marked with white patches radiating from the base. Both these 
forms exhibited varieties in the same locality, but there were no connecting links 
between them. The males paired with both forms of female, and in each case the 
resulting brood assumed the distinct forms above described. This was a case of 
dimorphism. Papilio Pammon was a parallel case; there was a form of female 
resembling the male, and there was a second aberrant form of female, viz. the form 
which had been called P. Polytes: he believed that P. Romulus would prove to be a 
third form of the female of P. Pammon, though of this he had not evidence at present; 
but the male of P. Romulus had never been found, whilst the females occurred along 
with P. Pammon in every collection from India: if that were so, then P. Pammon 
would exhibit an instance of trimorphism. P. Ormenus was certainly trimorphic, for 
three distinct forms of female were found, all differing greatly from the male; and 
Mr. Wallace had reason to believe that to some males of Papilio as many as four 
distinct wives must be assigned. These forms had hitherto been glassed as varieties, 
but the physiological differences presented by them were striking. 
Mr. Wallace further distinguished between a “variety” and a “local form” or 
