262 B. GRASSI AND A. SANDIAS. 
are undifferentiated; but when they have attained an 
average length of 2 mm. they are divisible into two groups, 
one with a large head, little narrowed anteriorly (Pl. 16, 
fig. 2), the other with a small head, more evidently narrowed 
towards the apex (PI. 16, fig. 1). 
The former have become soldier larve, and will ulti- 
mately become soldiers. The latter are still undifferentiated ; 
they reach alength of 4mm. and acquire twelve pilose antennal 
joints (vide supra); the character of the head either remains 
unchanged, and continues to be undifferentiated, or be- 
comes modified by an increase in size and in the width of the 
anterior portion, so that they become soldier larve. 
Small soldiers (Pl. 16, fig. 16) are to be found which are 
derived from these very larvee ; they are less than 5 mm. long, 
and possess twelve pilose antennal joints, with an ill-marked 
suture between the 4th and 5th. 
It may be well to observe at once that soldiers of me- 
dium size with thirteen or fourteen pilose antennal joints, 
and large soldiers (Pl. 16, fig. 5) with fifteen to seventeen 
pilose antennal joints also exist. Further, the antenne of 
many soldiers are evidently mutilated. 
Moreover I have often found soldiers with antenne of twelve, 
thirteen (Pl. 16, fig. 19), or fourteen all pilose joints, of which 
the third is in process of division into two, both pilose ; some- 
times the division is completed in one antenna and hardly 
indicated in the other. In short, all intermediate stages exist 
between small, medium-sized, and large soldiers, and the fore- 
going distinctions have therefore a relative value alone. 
For a considerable time I supposed that the soldier of 
medium size originated from the small soldier, and grew itself 
into a large soldier; but as I have not succeeded in proving 
my hypothesis, in spite of long-continued research, I can no 
longer consider it to be well founded. 
Turning to the undifferentiated or small-headed larve, we 
have already seen that they can acquire antenne of twelve 
entirely pilose joints, and a length of 4mm. Subsequently a 
thirteenth joint is added, and their length increases to 6 mm., 
