32 ILLINOIS BIOLOGICAL MONOGRAPHS [312 



almost to the posterior end of the body. They have no branches and 

 terminate blindly. In caliber they vary from 0.04 to 0.116 mm. 



The testis is spherical or oval, usually slightly longer than broad, 

 and measures 0.29 to 0.39 mm. in width and 0.36 to 0.5 mm. in length. 

 It is near or slightly anterior to the middle of the body. The sperm 

 duct arises at its anterior margin and, lying dorsal to the ootype, passes 

 anteriad. In front of the ovary it turns ventrad and expands into the 

 seminal vesicle. At the outer end of the seminal vesicle the duct is 

 encircled by a sphincter muscle, and then known as the ejaculatory 

 duct passes thru the cirrus sac to open into the genital atrium (Figs. 

 3, 13). The cirrus sac is almost spherical, and consists of an external 

 muscular capsule filled with parenchymatous tissue enclosing a central 

 canal. In the dorsal part of the sac there are radial muscles passing 

 from the wall to the central duct, and among these fibers a few large 

 nuclei. More ventrally there are sets of muscles developed around the 

 central duct and these are connected to the wall of the sac. Externally 

 the central canal terminates at the apex of a papilla which is separated 

 by a deep depression from the muscular ring that bears the hooks of 

 the genital coronet. This conical muscular ring is protrusible and is 

 separated from the wall of the cirrus sac by a second depression. The 

 invaginations on either side of the genital coronet allow for the extru- 

 sion of the coronet of hooks with the genital papilla on the contraction 

 of the wall of the cirrus sac, while the muscles attached to the central 

 canal and the muscular ring bearing the genital hooks serve as retract- 

 ors. The genital coronet consists of sixteen hooks, similar in size and 

 shape ; they have an external sickle-shaped part or shank which turns 

 outward and a root or basal part of about the same length embedded 

 in the musculature (Figs. 2, 13). The basal part is straight and hollow 

 and the internal end is bifurcate. It bears many fine cuticular processes 

 which are particularly prominent near its union with the shank. In the 

 body parenchyma around the terminal part of the cirrus sac there are 

 large unicellular glands (Figs. 12, 13). 



The ovary is lateral and may be situated on either side of the body. 

 It is 0.1 to 0.25 mm. anterior to the testis. It is ovoid in shape, with 

 the larger part in which the ova are being formed anterior and ventral, 

 and the oviduct arising from the dorsal posterior region. In sections it 

 appears to be marked into zones, with larger and fewer cells present in 

 each succeeding zone. It is 0.1 to 0.148 mm. in width, 0.14 to 0.185 mm. 

 in length and in one specimen cut in cross sections 0.175 mm. in depth. 

 The oviduct arises as a very small tube and immediately expands (Fig. 

 3). This expanded portion extends posteriad and ventrad and by means 

 of a short constricted tube opens into the ootype, a specialized region 



