500 CAROLINE BURLING THOMPSON 



in the third instar. The transformation of a soldier takes place during 

 the third period of quiescency, so that after ecdysis the differentiation 

 is most decided. A difference between majors and minors of the same 

 caste is observable at the beginning of the fourth instar. The smaller 

 grow but little and become adult minors. The larger increase to twice 

 their length and several times their bulk and become adult majors. 



THE FIRST FORM OF T. ANGUSTICOLLIS 



The first form has three well-defined phases of development: 

 a) nymphs of the first form, with long wing pads and creamy 

 white bodies; 6) winged adults of the first form, with long wings 

 and dark brown bodies, length variable, 11 to 13 mm; c) the 

 older males and females the post adults of the first form, with 

 enlarged abdomen and the 'scales' or bases of the shed wings, 

 average length 15 mm., greatest length observed 17 mm. 



The nymph of the first form 



According to their age, these nymphs present two different 

 appearances, which are so diverse that they at first seem to belong 

 to two different castes. The younger, immature, nymphs of the 

 first form — (fig. 2) 10 to 12 mm. and under, with probably two 

 molts to undergo^ — may be distinguished from the mature nymphs 

 — (fig. 1) 11 to 13 mm., and with only one more molt — by the 

 appearance of the wing pads and the size and color of the com- 

 pound eyes. The immature nymphs have small colorless or pale 

 brown eyes and thin transparent wing pads, extending back to 

 the third abdominal segment; the mature nymphs have larger 

 dark brown eyes and thick wing pads with greatly convoluted 

 tissue and indistinct venation, extending back likewise to the third 

 abdominal segment. The mesonotum and metanotum are narrow 

 from side to side in the mature nymphs, a character found in the 

 first form adult, but are broad in the younger immature nymphs. 

 Both immature and mature nymphs of the first form may be 

 distinguished from mature second-form nymphs by the slightly 

 smaller compound eyes of the latter and its very short wing pads, 

 which extend only to the first abdominal segment. 



The mature nymphs of the first form are found shortly before 

 the period of swarming, which occurs in California from May to 



