PHYLUM PLATYHELMINTHES 



229 



v.s 



Fit 



testcs, casa deferentia, and cirrus. The tcsfc* (fi>.) are two greatly 

 ramified tubes, which occupy the middle part of the body, one 

 situated behind the other. From each testis there runs forwards 

 a duct, the i~as dc/crens, the two vasa deferentia (v.d.) opening 

 anteriorly into an elongated sac, the vesicula seminalis (v. s.), from 

 which a narrow tube the cjacnlatory duct (Fig. 178 cj.d.) leads 

 to the male aperture at the ex- 

 tremity of the penis. The female 

 part of the reproductive apparatus 

 consists of a single ovary, an ovi- 

 duct, a uterus, vitelline glands, vitel- 

 line ducts, and shell-glands. The 

 ovary (Fig. 177, ov.) is a branched 

 tube situated on the right-hand 

 side in front of the testes ; the 

 branches open into a common 

 narrow tube, the oviduct (od.). The 

 vitellinc glands (vit.') consist of very 

 numerous, minute, rounded folli- 

 cles, which occupy a considerable 

 zone in the lateral regions of the 

 body. On each side are two large 

 ducts, anterior and posterior, unit- 

 ing to form a single main lateral 

 duct, right or left ; and these run 

 nearly transversely inwards to open 

 into a small sac, the yolk reser- 

 voir. From this a single median 



vitclline duct runs backwards for a short distance to join the 

 oviduct. Around the junction are grouped amass of unicellular 

 shell-glands (sh. gl.), each of which is produced into a narrow 

 process or duct opening into the end of the oviduct or the be- 

 ginning of the uterus. The -uterus (ut.} is a wide convoluted tube, 

 formed by the union of the oviduct and median vitelline duct ; 

 in front it opens close to the base of the penis. When the penis 

 is withdrawn, a small cavity, the genital sinus or cloaca, is formed, 

 common to the external apertures of both male and female ducts. 

 A canal, termed the canal of Laurer, leads frrtm the junction of 

 the oviduct and median vitelline duct to open externally on the 

 dorsal surface. 



Development. Each ovum on impregnation bceomes sur- 

 rounded by a mass of vitelline matter or yolk derived from the 

 yolk-glands. It then becomes enclosed in a chitinous shell, the 

 substance of which is derived from the shell-glands. The com- 

 pleted egg remains for a little time in the uterus while the con- 

 tained ovum is undergoing the process of segmentation : eventually 

 it is discharged, and passing down the bile-ducts of the Sheep 



. ITS. Distcmum hepaticum. 



Terminal part of the reproductive 

 apparatus. <;/'. ejaculatory duct ; /. 

 female aperture ; ;/. unicellular 

 glands ; oil. terminal part of oviduct ; 

 p. penis ; //x. penis sheath ; .?. sucker ; 

 i'. ('. vasa deferentia ; >. .. vesicula 

 suminalis. (After Summer.) 



