1940] 
Caste Determination in Ants 
107 
perhaps somewhat reduced in size, or else typical working 
individuals.” In none of Ezhikov's publications which I have 
been able to examine have I found any further description of 
his experiments than is suggested in the above quotation. 
It is the purpose of the present paper to describe an 
experiment designed to test whether the castes of the female 
sex of Leptothorax curvispinosus are determined blastogene- 
tically or trophogenetically. 
Experimental. 
The procedure consisted in subjecting two groups of larvae, 
as nearly identical as possible, to controlled conditions 
differing between the two groups only in the amount of food 
supplied. During the summer, a quantity of larvae (about 
250) was collected from several nests of Leptothorax cur- 
vispinosus. These larvae were thoroughly mixed, then intro- 
duced into a colony of Leptothorax longispinosus from which 
queen and brood had been removed. This was done to insure 
that no further curvispinosus larvae would be produced. The 
resulting mixed colony remained about two weeks at summer 
temperature, during which time about 80 of the larvae dis- 
appeared, presumably as a result of a certain amount of 
resistance to adopting them on the part of the longispinosus. 
The remainder grew a little. The nest was then placed 
in a cold room (2° C.) to hibernate. Five months later 
(March), the colony was removed from hibernation and 
immediately divided into two practically equal portions. 
In order to secure an impartial division of the larvae, the 
smaller and shriveled specimens were discarded, the remain- 
der gathered into a pile, thoroughly mixed together, then 
the pile was divided into halves through the center. At this 
time, the larvae were 1/10-1/6 of pupation size. These two 
divisions may be designated colonies A and B, composed 
as follows: 
Colony A — 27 longispinosus workers; 44 larvae. 
Colony B — 80 longispinosus workers; 44 larvae. 
Both colonies were maintained simultaneously under condi- 
tions as nearly identical as possible as to nest size and 
construction, feeding space, moisture, temperature and il- 
lumination, but differed in the amount of food administered. 
