402 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



There is no marked constriction between crop and gizzard. The 

 armature of the gizzard consists of four heavy triangular proces- 

 ses or tubercles, each with small teeth. , 



The Ventriculus or Midgut occupies most of the third, all of 

 the fourth, and the anterior two thirds of the fifth segment. It is 

 usually three-lobed, above the portion into which the gizzard 

 projects being of the greatest diameter, the middle one about 

 twice as wide as lon^, and the posterior part oval and tapering- 

 down to meet the Small Intestine. It is supported behind by a 

 muscular diaphragm. 



The Small Intestine thus begins near the union of the fifth and 

 sixth segments, where it lies just dorsal to the nerve cord, runs 

 a short distance caudad, turns directly dorsad, expands dorsally 

 to form the Pre-rectal Ampulla ("Ampoule Prerectale" of Sa- 

 dones), narrows abruptly again and enters the rectum above the 

 median axis of the abdomen. The anterior half of the small in- 

 testine is comparatively small in diameter; the posterior part or 

 ampulla is a large, thin sac forced well to the dorsal region by the 

 pressure of the adjacent parts. It is trilobed when viewed from 

 above. 



The Rectum fills segments six to ten and consists of two por- 

 tions: the Branchial Basket and the Vestibule. The former is 

 so large as not only to crowd out the other organs from the sixth 

 to the ninth segments but also to make this the thickest part of 

 the abdomen. It tapers gradually from the beginning of the 

 eighth to the middle of the tenth segment. The structure and 

 functions of this organ are fully discussed by Tillyard (1917). 

 The Vestibule is a short, cylindrical rectal chamber leading to the 

 anus. Its walls are supplied with tracheae, and to them the 

 dorsal and ventral dilator muscles of the rectum attach. 



Numerous Malpighian Tubules open into the alimentary canal 

 as usual at the hind end of the ventriculus. 



The Reproductive System 

 (Plate II, figure 6) 



Male: — The Testes are well developed, irregularly cylindrical 

 in shape, and lie lateral to and below the Dorsal Tracheal Trunks. 

 Their position -vfill be made clear by reference to plate XXII, 



