TURBELLARIA. 671 



copulatory organ 1 . They are often dilated into seminal reservoirs, or in 

 some instances a vesicula seminalis is formed from or attached to the 

 penis. One or more accessory glands are usually present, and their 

 secretion is mixed with the sperm. The penis is either a protrusible or 

 an evaginable organ, and is often contained within a sheath and armed 

 with chitinous spines, especially in Rhabdocoela. In the Polyclad Anony- 

 mus there are 2-15 copulatory organs on each side the body, and 2-4 occur 

 in three other instances in the same group. The ovaries are two and 

 simple (Acoela, Rhabdocoele Macrostomidae} ; they are numerous and 

 simple in Polycladida. In some Rhabdocoela^ e. g. Prorhynchus^ the two 

 glands, though simple externally, are functionally divisible each into a 

 germarium and vitellarium, and this division becomes marked externally, 

 and the two parts have their separate ducts in other Rhabdocoela ; whilst 

 in Tricladida there is on each side of the body a single anterior ovary 

 connected to a long oviduct, which is beset on its outer side by follicular 

 or branching vitellaria 2 . Many Acoela and Alloiocoela have no specialised 

 ducts, but the ova like the sperm pass into spaces in the parenchyma. 

 A network of ciliated tubules connects the ovaries of Polycladida. They 

 unite into a canal on each side of the body. Each canal is dilated into 

 a uterus, to which accessory glands are attached. The two uteri unite into 

 a common canal, which is dilated and receives a number of shell-glands. 

 Its termination is often muscular, forming a female copulatory organ. 

 The male and female ducts open into a genital atrium in all Tricladida 

 and most Rhabdocoelida. To this atrium is commonly appended a uterus, 

 and in some Rhabdocoela a bursa copulatrix and receptaculum seminis 3 . 

 Or in other Rhabdocoelida^ and in Polycladida with the exception of two 

 genera, the two ducts open separately, the male usually in front of the 

 female, and both behind the pharynx. In Prorhynchus (Rhabdocoele) and 

 Stylostomum (Polyclad) the penis opens into the mouth ; and in many 

 Rhabdocoela the penis with its chitinous hooks is employed to catch and 



1 lijima denies this connection between the testes and the vasa deferentia in the fresh-water 

 Tricladida which he examined. He thinks that the sperm is set free into the spaces of the paren- 

 chyma, and is taken up thence by lateral openings in the walls of the vasa deferentia. But as the 

 latter do not extend far forwards, the sperm of the anteriorly placed testes never reaches them at all. 

 See Z. W. Z. xl. pp. 405-408. When ducts are absent, as in Acoela, the sperm traverses the 

 parenchyma. 



2 lijima states that the vitellaria do not communicate directly with the oviducts in the fresh- water 

 Tricladida which he examined. The ducts have openings into the spaces of the parenchyma, and 

 in these spaces the vitelline cells accumulate just as do the spermatozoa. The openings in question 

 are closed each by a peculiar large cell before the vitellaria ripen (Z. W. Z. xl. pp. 415-16). 



3 The uterus of the fresh-water Tricladida does not serve as a store-house of ova as do the uteri 

 of the Polycladida. It is single, and is probably a gland secreting the material for the cocoon. 

 Albumen glands usually open into its duct ( = so-called vagina) or into the oviducts. A structure 

 called ' muscular glandular organ ' opens into the atrium genitale, but it appears to be variably 

 present. Its walls are stout and muscular, and lijima believes that it receives the ducts of various 

 glands. See Z. W. Z xl. pp. 419-26. 



