PHYLI'M PLATYHELMINTHES 



243 



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

 situated behind the other. From each testis there runs forwards 

 a duct, the vas deferens, the two \'asa deferentia {v.d.) opening 

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

 which a narrow tube — the cjaculatory d%ict (Fig. 189, ej.d?) — leads 

 to the male aperture at the ex- 

 tremity of the cirrus. The female 

 part of the reproductive apparatus 

 consists of a single ovary (ger- 

 marium), an oviduct, a uterus, an 

 ootype, vitelline glands, vitelline ducts, 

 and shell-glands. The germarium 

 (Fig. 188, 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 vitelline 

 glands (yit.) consist of very nu- 

 merous, minute, rounded follicles, 

 which occupy a considerable zone in 

 the lateral regions of the body. On 

 each side are two large ducts, 

 anterior and posterior, uniting to 

 form a single main lateral duct, 

 right or left ; and these run nearly 

 transversely inwards to open into a 

 small sac, the yolk reservoir. From this a single median vitelline 

 duct runs backwards for a short distance to join the oviduct. 

 Around the junction are grouped a mass of unicellular shell-glands 

 {sh. gl.), each of which is produced into a narrow process or duct 

 opening into the end of th,e oviduct in the region of the latter to 

 which the term ootype is applied. The uterus (ut.) is a wide con- 

 voluted tube, formed by the union of the oviduct and median 

 vitelline duct ; in front it opens close to the base of the cirrus. 

 When the cirrus is withdrawn, a small cavity, the genital atrium or 

 cloaca, is formed common to the external apertures of both male 

 and female ducts. A canal, termed' the canal of Laurer, leads 

 from the junction of the oviduct and median vitelline duct to 

 open externally on the dorsal surface. 



Development. — Each ovum on impregnation becomes sur- 

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

 yolk-glands. It then becomes enclosed, while passing through the 

 ootype, in a chitinous shell, the substance of which is usually said 

 to be derived fi'om the shell-glands.^ The completed egg remains 



' The agency of the shell-glands in producing the material of the egg-shell is 

 not universally acknowledged. This point will be referred to in the section 

 dealing with the general organisation. 



R 2 



Fig. 189.— Pasciola bepatica. Ter- 

 minal part of the reproductive 

 apparatus, ej. cjaculatory duct ; /. 

 female aperture ; g. unicellular 

 glands ; od. terminal part of oviduct ; 

 p. cirrus ; ps. cirrus-sbeath ; s. 

 sucker ; v. d. vasa deferentia ; v. s. 

 vesicula seminalis. (After Sommer.) 



