254 



NEW YORK STATE MUSEUM 





m 



-mm 



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 (n) 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 i, 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 

 are shown in figure 20; (.r) represents 

 those of Zygoptera, (y) those of Libel- 

 lulidae and {z) those of Gomphidae. n 

 in each case represents the anterior lamina, p the penis in Lestes 

 while indicates the penis and vesicle in the case of Libellula and 

 Ophiogomphus and u 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 



Fig. 19 



J{ 



n 



P 



X 



IM 



z 



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 n in Libellulidae (y) 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 



