SOLDIER CASTE IN GENUS TERMOPSIS. 149 



oral arrangement as in younger colonies, but tbey are relatively 

 longer, more slender and more flexible. Tbis feature tends grad- 

 ually to disappear as development progresses, yet spines of this 

 character can be found to persist even into the penultimate instar. 



Measurements of 192 individuals in the second instar, in the 

 case of T. ncvadensis, possessed a head width of 0.77 mm. in 13 

 specimens 0.86 mm. in 71 examples, 0.92 mm. in 78 individuals. 

 0.96 mm. in 28 others while 2 measured i.o mm. From among 

 these 50 individuals were selected, treated with caustic potash, 

 stained with magenta and compared. In every instance there were 

 fifteen antennal segments; and the distribution of the spines over 

 the body closely conformed to plan represented in PI. I, Fig. 2. 

 In the case of T. angusticollis the average head width amounted 

 to 1.026 mm. with the usual range of variation. The number 

 of antennal joints was sixteen ; otherwise in its general proportions 

 and distribution of spines the individuals of this instar closely re- 

 semble those of the same stage in T. iici'ttdcnsis (PI. II, Fig. 8). 



Out of 117 individuals of T. nci'adcnsis in the third instar the 

 average head width amounted to 1.22 mm. The number of 

 antennal segments was seventeen in 48 out of 50 specimens, the 

 exceptions being due to the lack of the normal division between 

 the third and fourth joints. The general appearance of the in- 

 sect at this stage is represented in PI. I, Fig. 3. In regard to 

 T. angusticollis the average head width of individual in the third 

 instar amounts to 1.3 mm. The number of antennal segments is 

 almost invariably eighteen. Further details are shown in PI. II, 

 Fig. 9. 



The fourth instar in T. nevadensis is characterized by an average 

 head width of 1.65 mm. on the basis of 161 individuals. In the 

 majority of instances the number of antennal joints was nineteen 

 although ii out of 50 had developed eighteen on one or both sides. 

 For the distribution of the spines see PI. I. Fig. 4. Comparing 

 the same stage in T. angnsticoUis, the average head width 

 amounted to 1.8 mm., and with few exceptions the number of 

 antennal joints was twenty. Other external features are repre- 

 sented in PI. II, Fig. 10. 



The average head width of 136 specimens in the fifth instar 

 was 2.35 mm. in the case of T. nci'adcnsis. The number of anten- 



