1915} Cocoons Among Ants 339 
have become pale yellow or pale red or brown. Their eyes 
have diminished greatly in size or have disappeared. The 
males and females of these hypogeic forms, however, retain 
their deep pigmentation and large eyes because they retain the 
instinct to mate in the sunlight. The principal groups of 
hypogeic ants which exhibit this retrogressive color-develop- 
ment, at least in the workers, are: Solenopsis, (most species), 
Machomyrma, Oligomyrmex, Carebara, Tranopelta, Aéromyrma, 
some species of Pheidole and Crematogaster, the whole tribe 
Dacetoniu, Brachymyrmex and the yellow species of Lasius, 7. e., 
those of the circumpolar subgenus Chthonolasius and of the 
North American subgenus Acanthomyops, many small Ponerine, 
Ainictus, Dorylus, some species of Eciton, Leptanilla, etc. 
2. A number of species exhibit a progressive development 
from red, brown or black to the interference colors. This 
tendency to what may be called ‘‘metallescence”’ is observable 
in ants living in very hot, dry, sunny places, and is most pro- 
nounced in Australia, where it occurs in the following genera: 
Chalcoponera (nearly all species), Rhytidoponera (convexa var. 
violacea Forel), Myrmecia (tarsata F. Sm.), Diacamma, Lobo- 
pelta. (some varieties of conigera Mayr), Iridomyrmex (many 
species, notably detectus F. Sm., discors Forel, bicknelli Forel, 
cyanea Wheeler, etc.), Leptomyrmex, Camponotus (some species 
of the subgenus Myrmocamelus), Calomyrmex (splendidus Mayr, 
purpureus Mayr and an undescribed species from the Cape York 
Peninsula), Melophorus (eneovirens Lowne and others), and 
Polyrhachis (hookert Lowne, schencki Forel and turneri Forel). 
Some of the most conspicuous and widely distributed Australian 
ants, such as Iridomyrmex detectus, which is beautifully metallic 
purple, and other smaller species of the same genus, may be 
seen running about in the sunlight at a temperature of 115° to 
120° F, when other ants are hiding in the soil, and in the deserts 
of Central Australia, where the temperature may rise even 
higher and the aridity is excessive, the tendency to metal- 
lescence is still greater. It is in this region that Calomyrmex 
splendidus and purpureus and their varieties occur and that 
I. detectus takes on the pronounced metallic green color of the 
var. viridieneus Viehmeyer. The prevalence of interference 
colors in Australian ants is in marked contrast with their 
rare and sporadic occurrence in other regions. They occur in 
