318 Experimental Zoology 
at first to be all alike, and potentially have the power to become 
workers, soldiers, or substitute royal forms. The workers and 
the soldiers have rudimentary reproductive organs and are of 
both sexes. Their development is, in a sense, arrested, although 
they are something more than simply undeveloped individuals, 
since they have peculiarities that belong to their caste. The 
substitute royal forms are, however, according to Grassi, neotenic. 
individuals in which the sexual organs develop, but the wings do 
not. In this and in some other respects they represent sexually 
mature larval forms. Although attempts have been made to 
discover the nature of the food that determines the fate of 
individuals of the colony, nothing definite has as yet been 
ascertained. 
Grassi succeeded in establishing colonies in small glass tubes 
that could be carried about in his waistcoat pocket and studied 
through the walls of the tube. Colonies of from 15 to 40 indi- 
viduals of different ages were thus established, made up of 
workers, soldiers, and young, but without sexual forms. After 
a few days, from two to six incipient substitute pairs appeared, 
characterized by pigmented eyes. In fact, Grassi says, even 
after 30 or 40 hours in summer he could tell which individu- 
als would acquire the ocular pigment. The formation of these 
incipient royal substitutes does not take place if a royal pair is 
present; but if the king or the queen is removed for 24 or 48 
hours, a few substitute forms begin to appear. In one case a 
nest was made up of only three large larve, and in two weeks one 
of these exhibited pigmented eyes, and was in process of be- 
coming a substitute form. If a nest contains adults ready to 
fly, z.e. royal forms that have not yet paired, the formation of 
royal substitutes takes place nevertheless, as described above. 
In other words, the winged sexual forms if present do not be- 
come kings and queens, when these are needed in the nest, but 
substitute forms are made. Only after the nuptial flight do the 
royal forms become the heads of new colonies. 
The food of Calotermes consists of wood, matter excreted 
or disgorged by other individuals, the exuvie, the corpses of 
