304 L. R. CLEVELAND. 



SUMMARY. 



All results were obtained from laboratory colonies which have 

 been carefully studied during the past three years. Many of 

 these results have been verified by field observations. 



At every stage in the life-cycle of any caste where wood is 

 eaten, protozoa are present. When wood is not eaten or ob- 

 tained in some way, protozoa are never present. 



Second and third form young adults have lost the ability to 

 eat wood. The protozoa in these castes disappear concomitantly 

 with the loss of the ability of their host to feed on wood, and 

 by the time the wood-eating ability is lost, they have all dis- 

 appeared. This occurs about the time of the final molt and is 

 perhaps brought about by the feeding of salivary secretions 

 which take the place of the wood diet. In all castes, the protozoa 

 are lost during molting, but they are soon regained, except in the 

 final molt of the second and third forms, in which forms they 

 are never regained because, owing perhaps to the degeneration 

 of their jaw muscles, these forms have lost the ability to eat 

 wood. What causes the jaw muscles to degenerate is not defi- 

 nitely known. It may be inherent in these castes, as much a 

 part of them as anything else. If it is, then the salivary-f eeding 

 is hereby made necessary and takes the place of the wood diet 

 when the jaw muscles degenerate. But a more plausible possi- 

 bility is that these forms are fed so much salivary secretion that 

 they cease to feed on wood and because of this their jaw muscles 

 degenerate through disuse, and thus the ability to feed on wood 

 is lost forever. 



The first form and the worker always eat wood, except in the 

 post-adult stage of the life-cycle of the first form, where it, too, 

 after having attained an old age loses the ability to eat wood 

 and becomes dependent on the workers and young undifter- 

 entiated nymphs (when present) which it has reared. It is 

 noteworthy that mostly workers are raised in the first brood. 



Adult soldiers, owing to their large mandibles, cannot eat 

 wood (cannot chew it), though they obtain it, together with 

 protozoa from the ani of the xylophagous members of the colony. 

 Soldiers, like workers, harbor protozoa throughout their life- 

 cycle. Young soldiers (soldier nymphs), before they obtain the 



