218 THE REPRODUCTIVE SYSTEM [CH. 



suggest that the whole of the accessory apparatus originally arose 

 from a slight depression in the second sternite, close under the 

 anterior edge of the third. In this, perhaps, the male originally 

 deposited sticky sperm-capsules, which the female sought for, 

 during pairing, by bending her abdomen forward under that of 

 the male. 



The accessory portions of the apparatus consist of the support- 

 ing framework of the genital fossa, together with one or two pairs 

 of hamules for the guidance of the ovipositor into position. The 

 framework consists of the following parts : 



(i) laterally, the two latero-ventral margins of the second 

 tergite (tg 2 ), 



(ii) anteriorly, a specialized bifid plate, the anterior lamina (al), 

 developed from the anterior part of the second sternite, and 



(iii) posteriorly, a less specialized and narrower plate of the 

 same sternite, bordering segment 3 anteriorly, and called the 

 posterior lamina. 



The hamules consist of anterior and posterior pairs. The 

 anterior hamules only occur in the Aeschnidae; they are absent 

 alike in the Zygoptera and the rest of the Anisoptera. They are 

 of complicated form, and function as claspers. In Aeschna (A) we 

 distinguish two principal parts : the hamular fold (hf), and the 

 hamular process (hp) carrying a distinct tuft of bristles (tb). 

 Posterior hamules (ph) occur in all Dragonflies. They are of simple 

 form in the Zygoptera and Aeschnidae. In the Libellulidae, 

 however, they become highly differentiated, with outer and inner 

 branches, the latter usually in the form of a sharp hook (hk). 

 (See also fig. 176.) 



In the Libellulidae (E) an additional complication is introduced 

 by the projections of the postero-lateral angles of the second 

 tergite, which form well-developed genital lobes (gl). 



The anterior lamina (al) varies much in shape. In Zygoptera 

 and Aeschnidae it has a deep median cleft (cl). In the former it 

 is produced backwards to form two strong posterior lobes (pi), which 

 probably play the same part as the anterior hamules of Aeschnidae. 

 In the latter, a sharp spine (sp) often occurs on the lamina, on 

 either side of the cleft. In the Libellulidae, the anterior lamina 

 is hood-shaped, hairy, and either entire or slightly notched (P). 



