PHYLOGENETIC ORIGIN OF TERMITE CASTES. 1 27 



to the fact that they are not so enlarged as the females. In the 

 related genus Arrhinotermes males of the third form are of com- 

 mon occurrence. 



The colonies of Reticulitermes flavipes and virginicus found in 

 the southeastern United States in the spring, often contain 

 nymphs of the second form, sometimes in large numbers, asso- 

 ciated with either nymphs of the first form or winged sexual 

 adults. These young reproductive types of the second form 

 (Fig. 2) have attained their mature pigmentation at about the 

 same time that the colonizing winged adults or reproductive 

 types of the first form swarm, but after the swarm they are not 

 found in the parent colonies. We may ask why they are pro- 

 duced and what becomes of them? They are not needed in the 

 parent colony any more than the winged colonizing forms and 

 it may be that they are impelled to leave the old colony by the 

 same irresistible force that induces the swarm or flight. It may 

 be, that, accompanied by workers and soldiers, they leave the 

 parent colony by means of subterranean passages and establish 

 a new colony. Since the origin of the castes is due to intrinsic 

 causes, Thompson (1917), a certain proportionate number of 

 these nymphs of the second form may be produced each year in 

 long established colonies with parent first form adults. They 

 would evidently be superfluous if the original reproductive forms 

 of the parent colony were present, and might therefore be forced 

 to migrate. 



In certain colonies of termites, reproductive individuals of 

 the second form occur with a small proportion of males to a large 

 proportion of females. In the genus Reticulitermes as many as 

 eight males together with thirty-two females, and fifteen males 

 with twenty-eight females, both sexes of the second form, have 

 been found (T. E. S.). In other colonies of Reticulitermes there 

 are only reproductive individuals of the third form. Sometimes, 

 again, a male of the first form is found with numerous (sixteen) 

 mature females of the second form. Grassi would have described 

 these second form females as "substitute" queens, produced by 

 the workers to fill the place of a missing "true" queen. 



It is an open question how they are to be accounted for with 

 our present knowledge, and we have no exact data as to the 



