202 
Psyche 
[September 
THORACIC MODIFICATIONS ACCOMPANYING THE 
DEVELOPMENT OF SUBAPTERY AND APTERY 
IN THE GENUS MONOMORIUM 1 
By George S. Tulloch. 
The occasional appearance of forms intermediate be- 
tween the alate and the apterous castes of the Formicidse 
offers some ontological evidence of early stages in the 
origin of castes and has an important bearing on the ques- 
tion of development of organic forms through continuous 
or saltatory variation. The differentiation into castes is a 
condition which has existed for a long period of time since 
it is clearly shown in the many beautifully preserved ants 
of the Baltic amber from the Lower Oligocene Tertiary. 
In several genera of ants it is possible to trace all the 
transitional stages in the thoracic structure from that of 
the winged female to the wingless worker, except that the 
wings show no transitions, being perfectly developed in the 
typical female and entirely lacking in all the other forms 
of the series. In two genera gradational changes in the 
wing structure have been figured, one in the genus Mono- 
morium (Wheeler, 17) and the other in the genus Pogono- 
myrmex (Tulloch, 30). The series of P. calif ornicus which 
was given to the writer by Professor Harlow Shapley of 
the Harvard College Observatory exhibited various transi- 
tional stages of the wing from the completely venated type 
to a veinless wing sac. However, the appearance of these 
forms was considered to be pathological (since they only 
occurred in one colony) and, therefore, are perhaps not 
as instructive as the case noted by Dr. Wheeler in the 
genus Monomorium. Here it was discovered that at least 
two species exhibited a normal and unsuspected condition 
of subaptery in the female. 
1 Contribution from the Entomological Laboratory of Harvard 
University, No. 336. 
