ORIGIN OF CASTES OF TERMITES 105 



In the present study of L. flavipes I have divided the period 

 between hatching and the first molt, which is, of course, a con- 

 tinuous series of phases, into the early, middle, and late phases 

 of growth. 



In selecting specimens for preliminary study, body length 

 was at first used as a criterion of age, but, except with living 

 material, body length is such a variable quantity, depending 

 largely upon the presence or absence of food in the alimentary 

 tract, that it was soon abandoned, and the exact age of a speci- 

 men was determined by the number of antennary segments and 

 the condition of the third segment, whether entire or grooved, 

 bare or hairy. 



In the phases selected for description, see table 1, the number 

 of antennary segments is as follows: early phases, (1) nine, 

 third segment grooved; (2) ten, third segment entire and bare; 

 middle phases, (3) ten, third segment grooved; (4) eleven; end 

 phases, (5) twelve, third segment entire and bare ; (6) twelve, third 

 segment hairy. The approximate body lengths for these phases 

 are: early phases, 1.1 to 1.2 mm.; middle phases, 1.3 to 1.6 mm.; 

 end phases, 1.7 to 2 mm. 



It will be noted that the number of antennary segments in 

 the newly hatched nymphs of both L. flavipes and L. virginicus 

 is nine, which differs from the number, eleven, stated by Grassi 

 for L. lucifugus. It will further be noted, table 1 and figures 

 1, 3, 6, 7, 39, that two distinct types, which I have termed the 

 reproductive type and the worker-soldier type, are distinguish- 

 able at the time of hatching, and thereafter may be traced through- 

 out the series of phases froin hatching to the first molt, figures 6 to 

 17. In other words, the 'small-headed' and 'large-headed' forms 

 of Grassi do not appear for the first time after the first molt, 

 but may be traced back to their prototypes in the newly hatched 

 nymphs, namely, to the reproductive type and to the worker- 

 soldier type respectively. 



The general characters by which the reproductive type and 

 the worker-soldier type may be distinguished are: (1) the size 

 and character of the brain and its relation to the size of the head; 



