TYPE PLATTHBLMINTHES. 155 



tioned the suckers which frequently occur upon the scolex, 

 and serve with the hooks, when these are present, to attach 

 the parasite to its host. In Taenia these suckers are four in 

 number, and have the form of circular depressions whose 

 walls are richly supplied with muscle-fibres, while in Bothrio- 

 cephalus they have the form of elongated grooves, situated on 

 the edges of the somewhat flattened scolex. 



As might be expected from the great development of the 

 muscles, a well-defined nervous system is present. It consists 

 of a brain lying imbedded in the tissues of the anterior por- 

 tion of the scolex, evidently composed by the union of two 

 ganglionic masses and giving rise to two main nerve-cords, 

 which pass backwards through the entire length of the 

 strobila without interruption (Fig. 82, n). So, too, the excre- 

 tory system (Fig. 82, ne) extends through the entire* strobila 

 uninterruptedly. It consists of two nephridial tubes, which 

 in the anterior part of the scolex may be united by a cross 

 branch, as they are at the posterior edge of each proglottid, 

 and open to the exterior by a pore situated at the centre of 

 the posterior edge of the last proglottid. As each proglottid 

 separates from the chain, a new pore forms in the one pre- 

 ceding it, which becomes the terminal one, so that an opening 

 for the system is always present. 



The reproductive system (Fig. 82) possesses a complexity 

 similar to what has been described for the Trematoda, and 

 hermaphroditism prevails throughout the class. In the stro- 

 bilar Cestodes each proglottid contains a complete set of 

 organs, both male and female ; the testes (Fig. 82, te) are 

 usually very numerous, consisting of small spherical masses 

 scattered through the parenchyma, each being provided with 

 a small duct, which after a short course unites with similar 

 ducts coming from other testes, all finally uniting to a 

 single vas deferens {vd), which opens to the exterior after 

 passing through a muscular organ, the cirrus-sac, by the con- 

 traction of which its terminal portion, often provided on its 

 inner surface with barbed hooks, is protruded to the exterior 

 as an intromittent organ or cirrus (c). The female apparatus 

 varies somewhat in its arrangement. In the majority of forms 

 the ovary is a bilobed organ (ov), lying near the posterior 



