254 NEW YORK STATE MUSEUM 
the sheath of the penis with indications of the posterior por- 
tion of its framework at g; h, the single pair of hamules de- 
veloping upon the anterior portion of the framework g, and 
on segment 3, the penis and vesicle are clearly indicated. The 
posterior lobe is the vesicle while the anterior lobe is the penis 
which extends well upon segment 2 in the imago. 
The cross-section (7) made through these 
parts at the level of the hamules, shows 
the extent of the ventral: pocket that is 
formed by the overgrowth of the hamules 
h. It shows also at the thickened angles 
either side of 7, the points where the thick- 
ened margins of the sheath are forming. 
The external indications of the struct- 
ures developing in nymphs on segment 2 
Se are shown in figure 20; (+) represents 
6 those of Zygoptera, (4) those of. Libel- 
MS BO lulidae and (zg) those of Gomphidae. 1 
in each case represents the anterior lamina, p the penis in Lestes 
while o indicates the penis and vesicle in the case of Libellula and 
Ophiogomphus and wu the vesicle alone in Zygoptera. 
In Lestes, the representative of the suborder Zygoptera, one 
may note that the anterior lamina has already approximated 
the form found in the imago. The two rounded structures, one 
on either side of the penis, are the two lobes of the well 
a 
Fig. 20 
divided lamina found in this suborder. u is the vesicle on 
segment 3, not so large as the vesicle appears in the Anisop- 
tera because of the fact that on segment 3 in the Anisoptera we 
not only find the vesicle but the penis closely joined to it. 
The space posterior to m in lLibellulidae (jy) figure 20 is 
no doubt the place occupied by the fully developed penis and 
sheath, now unable to be seen through the chitin, In the more 
