380 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



The anus is located in the tip of the al^domen in l>oth sexes. 

 The genital pore of the male, with its pair of longitudinally placed 

 valvules perforates the ninth sternite. As mentioned, the organs 

 of intromission in the male are developed in the sterna of the 

 second and third segments. In the female the genital pore lies 

 between the eighth and ninth segments ventrally and is covered by 

 the accompanjdng gonapophyses which originate from these 

 sterna. The gonapophyses vary from three well-developed 

 pairs — the anterior and median processes for piercing and sawing, 

 and the valves — in the Zygoptera, to a reduced bifid or entire 

 vulvar lamina or scale in some Anisoptera. 



Springing from the dorso-laterai regions of the tenth segment 

 in both sexes is a pair of anal (superior) appendages. An "infe- 

 rior" median appendage lies just above the anus in the males 

 only of the Anisoptera. A pair of true inferior appendages (hom- 

 ologs of the cerci, according to Heymons) lie right and left of the 

 anus in the male Zygoptera. In both groups these anal append- 

 ages in the male are highly adapted for grasping the head or the 

 prothorax of the female while pairing. 



Larvae < 



In the larvae the form is very much shorter and thicker, espe- 

 cially in the Anisoptera. It may be quite cylindrical (Zygop- 

 tera), subcylindrical (Aeshninae), or greatly flattened (Gom- 

 phinae and some Libellulinae). It possesses the same segments 

 as that of the imago but their sclerites are far simpler in structure 

 and function. The tergum is a great arch but it has, in Ani- 

 soptera at least, no ventral portion. The sternum is a flat, rec- 

 tangular plate, and the pleura are chitinized and approach a 

 horizontal position (Plate XXIII, figure 9). Spiracles may be 

 present but are nonfunctional. Lateral spines occur frequently 

 towards the hind end of the boch^, and dorsal spines are possessed 

 by many running water forms. The anal appendages need not 

 be described here. 



GROUPS COMPARED 



The results recorded in this paper were obtained from the 

 dissection and study of the following material. Many species 

 not listed here were used for comparison, especially of external 

 anatomj^ 



