252 
DARWINISM 
CHAP. 
difference, in the important character of the neuration of the 
wings, between these butterflies, which really belong to very 
distinct and not at all closely allied genera. Other important 
characters are—(1) The existence of a small basal cell in the 
hind wings of I tuna which is wanting in Thyridia ; (2) the 
division of the cell between the veins lb and 2 of the 
hind wings in the former genus, while it is undivided in the 
latter ; and (3) the existence in Thyridia of scent-producing 
tufts of hair on the upper edge of the hind wing, while in 
Ituna these are wanting ; but in place of them are extensible 
processes at the end of the abdomen, also emitting a powerful 
scent. These differences characterise two marked subdivisions 
of the Danaoid Heliconinse, each containing several distinct 
genera; and these subdivisions are further distinguished by very 
different forms of larvae, that to which Ituna belongs having 
from two to four long threadlike tentacles on the back, while 
in that containing Thyridia these are always absent. The 
former usually feed on Asclepiadeae, the latter on Solanacese 
or Scrophulariacese. 
The two species figured, though belonging to such distinct 
and even remote genera, have acquired almost identical tints 
and markings so as to be deceptively alike. The surface of 
the wings is, in both, transparent yellowish, with black trans¬ 
verse bands and white marginal spots, while both have similar 
black- and white-marked bodies and long yellow antennae. 
Dr. Muller states that they both show a preference for the 
same flowers growing on the edges of the forest paths. 1 
We will now proceed to give the explanation of these 
curious similarities, which have remained a complete puzzle 
for twenty years. Mr. Bates, when first describing them, 
suggested that they might be due to some form of parallel 
variation dependent on climatic influences; and I myself 
adduced other cases of coincident local modifications of 
colour, which did not appear to be explicable by any form 
of mimicry. 2 But we neither of us hit upon the simple 
explanation given by Dr. Fritz Muller in 1879. 
His theory is founded on the assumed, but probable, 
1 From Professor Meldola’s translation of Dr. F. Muller’s paper, in Proc. 
Ent. Soc. Load., 1879, p. xx. 
~ Island Life, p. 255. 
