368 ZOOLOGY. 



3. The Nephridia or Excretory Tubes. Kunning 

 through all the segments are on each side two excretory 

 tubules : these are united with one another in the head by 

 a transverse annular vessel, and also in the posterior border 

 of each segment by a straight transverse anastomosis. As 

 in the liver-fluke, the longitudinal vessels open, in the 

 entire tape- worm before the ripe proglottides have begun to 

 detach themselves at the posterior end, into a caudal 

 vesicle which opens to the exterior. In some tape-worms 

 there are other lateral openings as well. Communicating 

 with the longitudinal vessels are numerous ramified tubules, 

 the extremities of which are formed by flame-cells similar 

 in structure to those of the liver-fluke. 



4. The Nervous System consists firstly of a broad 

 transverse band in the head behind the rostellum: this 

 contains nerve cells chiefly aggregated in two swellings 

 forming indistinct ganglia ; and secondly of two longitu- 

 dinal nerve cords which pass backwards, one on each side, 

 through all the proglottides. Nerves pass from the anterior 

 band or brain to the suckers. Sensory terminations of the 

 nerves given off from the longitudinal cords have been 

 described in the cuticle, but no organs of the higher senses 

 such as eyes, auditory or olfactory organs, are present : in 

 an internal parasite living in the dark immersed in semi- 

 liquid nutriment such sense-organs are not required. 



5. Reproductive Organs. As in the liver-fluke, these 

 are complicated, hermaphrodite, and highly developed. 

 The testes are a number of minute spherical sacs, some- 

 what resembling in shape and arrangement the vitelline 

 glands of the liver-fluke, scattered through the dorsal 

 region of the proglottis, each of which has its own com- 

 plete system of reproductive organs independent of those 

 in every other proglottis. Each testis has its own fine 

 duct, and these ducts unite together into larger and fewer 

 branches or " factors " until all are united into a single 

 convoluted vas deferens, which runs from the central 

 region transversely to the right or left margin of the pro- 

 glottis. The end of the vas deferens forms a long narrow 



