586 SIDNEY I. KORNHAUSER 
chitinous pockets arising from the caudal border of the eighth 
sternum. The presence of these tell us immediately that the 
nymph is a female, as does also the pigmented area on the eighth 
sternum anterior to these pockets. On the ninth segment is a 
pair of narrow pockets more deeply pigmented at their posterior 
border. In the fourth instar the three pairs of nymphal append- 
ages which form the three pairs of adult gonapophyses can be 
most plainly seen (fig. 45). 
The pair arising from the eighth somite, which in the adult 
form the sheath covering the ovipositor, have grown consider- 
ably caudad, partly overlapping the median and anterior pair of 
the ninth segment which eventually produce the ovipositor 
itself. Lateral to the anterior pair of the ninth segment are 
two lightly pigmented, slender, curved pockets, and in these 
the posterior gonapophyses of the ninth segment are produced. 
The pigmented area of the eighth sternum is similar to that 
of the third instar. ‘The fifth instar (fig. 46) shows a con- 
siderable growth and closer approximation of all three pairs of 
appendages. Those of the eighth segment extend caudad be- 
yond the narrower pair of pockets which form the ovipositor. 
The posterior appendages of the ninth segment now form broad 
lateral pockets, partly overlapping the two median pairs. As 
the adult appendages develop they are seen through the 
nymphal cuticula, the most anterior gonapophyses extending 
from the pigmented cephalic border of the eighth segment be- 
yond the tip of the ovipositor. 
Thus we see that the genitalia develop quite differently in the 
two sexes and are determined quite early in ontogeny. The 
above description goes back merely to the third instar, at which 
stage one can distinguish the sexes with ease from surface views; 
but long before this the anlage for the gonapophyses are formed. 
Careful examination of whole mounts of second instars also 
reveals the differences: the form of the genital area on the ninth 
segment is broad and in the form of a semicircle in the male, 
whereas in the female it is much narrower and resembles that of 
the third instar. In the female one can also see the beginnings 
of the gonapophyses of the eighth segment as two minute chit- 
