98 ZOOLOGY 
ously regarded as excretory in nature, and as material for 
counteracting the acidity of the digestive fluids of their host. 
The excretory system consists of an annular ring in the 
head, from which four ducts corresponding in position with 
the suckers pass backward. Two of these soon disappear, and 
the other two pass down one on each side of the proglottides, 
just inside the longitudinal muscle layer (Fie. 67). These 
10 get) (22 abies 
ii "W) ~ ui alhl \) my r" { y 
\ AVG TeR PANY 
i Lor) ito VAY! \ 
itl) NN |. Riis \ 
HV Ah inlA AG (liyave j(o 
aan ht 
oN 
YA fy soft. | 
Iyi! f at) 
Gi) i 
-O 
Fic. 67.—Transverse section through a mature proglottis of Taenia. 
1. Cuticle. 6. Ovary. 
2. Tailed cells of ectoderm. 7. Follicle of testes with sperm morulae. 
3. Longitudinal muscle fibres cut across. 8. Longitudinal excretory canal. 
4. Layer of circular muscles. 9. Longitudinal nerve cord. 
5. Split in the parenchyma which lodges 10. Uterus. 
a calcareous corpuscle. 11. Oviduct. 
two lateral ducts coalesce at the posterior end of the last 
proglottis, and open there by a common vesicle. A transverse 
vessel at the posterior end of each proglottis serves to place the 
two longitudinal ducts in communication. The main ducts are 
provided with valves, which only permit the flow of fluid 
towards the external opening. <A series of secondary ducts 
arise from these main ones and ramify all over the body. The 
secondary ducts give off still finer tubules, each of which ends 
in a flame cell. The cilium of this cell hangs down into the 
lumen of the tubule, which is here slightly enlarged and 
funnel-shaped. Some observers maintain that this funnel- 
shaped end of the tubule opens by a pore into the splits in the 
parenchyma which represent the coelom, but this is a disputed 
point. 
There is a central nervous system in the head. This gives 
