68 
Psyche 
[March 
that which was evolved to accommodate the legs. With a 
return to a terrestrial environment it is natural to expect 
that the character most recently acquired should be the first 
to disappear. In the series of intermediate forms of 
Pogonomyrmex from queen to worker this is precisely 
what has happened. The appearance of functionless wings, 
the reduction in the size of the thorax due to the reduction 
in size of the wing muscles, and the simplification of the 
mesonotal region presents a stage in the evolution of the 
apterous forms from the winged forms. This progressive 
reduction in size of the thorax and wings, and the simpli- 
fication of the pleural as well as the notal regions represents 
a recessive stage in the evolutionary series. The loss of 
vestigial wings and a progressive reduction in size repre- 
sents a further step, and the true worker type marks the 
culmination of a long series of evolutionary stages from 
the winged to the apterous condition. Usually the inter- 
mediate forms have disappeared, and only the first and final 
stages are present, but occasionally abnormal forms such 
as these persist and give us a convenient series of connect- 
ing forms. Moreover, one is not compelled to formulate 
any hypotheses or construct any hypothetical figures as 
has been done in the case of the evolutionary stages from 
the wingless ancestors to the winged insects; here we have 
living examples of the connecting stages, a condition which 
is not usually met with in evolutionary study. The writer 
is very fortunate in having at his disposal these connect- 
ing links in most of the subfamilies of the ants. These 
series will be considered in a later and more comprehensive 
paper. 
The wings of the queen and winged pseudogynes are 
illustrated in the textfigure. The wing of the queen is 
about 6 mm. in length and is much reduced in the distal 
region (Fig. a). The venation of the wing of the first 
pseudogyne is much reduced, especially in the anal and 
cubital region. The vestiges in forms similar to Fig. C 
consist of a small veinless wing sac. The grouping of the 
winged intermediate forms roughly in order of the develop- 
ment of vestiges by Shapley follows : 
With minute veinless wing-sacs, or with stubs of broken 
wings — 385. 
