OH. XI] THE REPRODUCTIVE SYSTEM 217 



The apparatus is developed from the whole of the second 

 sternite, together with the anterior part of the third. It consists 

 of a penis, a vesicle for the storage of the sperm-capsules, and 

 a number of complicated accessory structures arranged so as to 

 . protect the penis and also to guide and hold the ovipositor of the 

 female during copulation. These are all lodged in a conspicuous 

 depression of the second sternite, known as the genital fossa. 

 This fossa opens posteriorly into a small sac, the vesicle of the 

 penis (vp), developed from, and attached posteriorly to, the anterior 

 border of the third sternite. From the distal end of this vesicle, 

 which projects forwards, arises the strongly-chitinized median 

 organ called the penis (p). Its lumen is continuous with that of 

 the vesicle, arid opens to the exterior near its distal end. 



In the Anisoptera (A-C), the penis is complicated, three- 

 jointed, and bent somewhat in the form of the conventional 

 figure of the fish known as the "sea-horse." The basal joint (p^ 

 is large and strongly chitinized, and bent near its middle. It 

 sometimes carries a fringe of hairs, or a long fleshy process. The 

 second joint (p 2 ) is smaller, and generally more or less curved. 

 The orifice of the penis (or) opens on its convex surface. The 

 third joint (p 3 ) is small, wider than the second, and very variable 

 in shape. It consists of a hard middle piece (mp 3 ) with two larger 

 soft lateral flaps (Ip 3 ), which are folded up when at rest, but ex- 

 panded when the penis is erected. Long fleshy processes and 

 other outgrowths may occur on this joint. When withdrawn, 

 the penis is protected by a chitinous arch arising from the floor 

 of the fossa, and called the sheath of the penis (A, sh). 



In the Zygoptera (D), the form and disposition of the above parts 

 is simpler. The penis (p) is not distinctly jointed, and occupies the 

 same position as the sheath in Anisoptera (with which it is probably 

 homologous). Its lumen opens basally into the body-cavity, not 

 into the vesicle, and it does not open distally to the exterior. Also, 

 whereas the penis of Anisoptera is supplied with muscles, nerves 

 and tracheae, these all seem to be absent in connection with the 

 penis of Zygoptera. It is difficult to say what part a poorly developed 

 organ of this kind can play in copulation, unless it serves as a kind 

 of hinge or link, by means of which the female pore is held in 

 contact with the vesicle. The structure is primitive enough to 



