170 PHILIP P. CALVERT. 



margin of the terga. In the Aeschninse and in the Libelhilidse a 

 longitudinal lateral carina is developed on either side of the terga, 

 and distinctly separates the dorsal from the ventral surface of the 

 abdomen. A longitudinal mid-dorsal carina frequently occurs. A 

 transverse carina is present near the base and near the apex of each 

 abdominal segment of most Odonata and, as well as the other carinse, 

 is frequently denticulated. Additional transverse carina occur in 

 some Libellulinse {Pantala, Tramea, etc.) and additional longitudinal 

 carinse in some Aeschninse (Anax). The sternum of the first seg- 

 ment is a simple, usually flat piece, whose lateral margins are more 

 closely united to the tergum than in the succeeding segments. On 

 either side is a stigma (spiracle). The sterna of 2-9 are elongated 

 pieces narrowing posteriorly, having on each side, near the anterior 

 end one or two processes directed outwards and upwards, whereof 

 the anterior is the slenderer. Lying in the pleural membrane, a 

 short distance behind the second lateral sternal process, is a spiracle 

 in 2-8. The sternum of 2 is modified in the males in consequence 

 of the existence of ventral accessory genital organs at that place. 

 The external orifice (vulva) of the oviduct in the females is situated 

 at the apex of the sternum of 8, and the posterior margin of that 

 sternum is known as the vulvar lamina. The ninth segment has no 

 spiracles ; its sternum, in the males, is pierced by a median opening 

 for the vas deferens, which opening is guarded by two small chitinous 

 flaps, one on either side ; in the females it is entire, and may be va- 

 riously bent or grooved in different forms. The sternum of 10 is 

 very small or wanting. 



The apex of the abdomen of the males is provided with two supe- 

 rior, and one (Anisoptera) or two (Zygoptera) inferior, unjointed, 

 chitinous appendages, whose function is to clasp the prothorax of the 

 female in copulation and often during oviposition. Their shape is 

 usually characteristic for the species. The cavity of the superior 

 appendages is continuous with that of the tenth segment, to which 

 they belong. The pair of inferior appendages of the Zygoptera 

 belong to the anal segment or telson, the anus opening between 

 them ; the single median inferior appendage of the Anisoptera be- 

 longs to the same segment the anus lying in a tubercle (anal seg- 

 ment) beneath the appendage. 



A secondary sexual modification presented by the males of most 

 Aeschnidpe and of the Cordulinie, is a pair of protuberances (auri- 

 cles), one on either side of 2, and which are usually denticulated. 



