ANATOMY OF CESTODA 



87 



segment of the tape-worm. From this fact and the anatomical 

 relations of the vagina, it is becoming increasingly probable that 

 the so-called uterus of Trematodes is an organ corresponding to 

 the vagina of Cestodes, and not to the uterus of Cestodes. The 

 latter opens to the exterior in Schistocephalus, Bothriocephalus, 

 and some other Cestodes of fishes by a special pore (Fig. 41, 

 uto). Through this, some of the eggs (which in these genera 

 give rise to ciliated larvae) are enabled to escape, and need not 

 wait for the detachment of the proglottis, as must happen in the 

 Taeniidae, where the uterus is closed. This uterus, a true physio- 

 logical one, is probably the homologue of the " canal of Laurer " 

 (" Laurer-Stieda canal," or " vagina ") of Trematoda. The fertilised 



Fig. 42. A, Free-swimming, six-hooked larva of Bothriocephalus latus Brems. (the 

 broad tape -worm of Man), still enclosed in a ciliated (possibly cellular) double 

 membrane or mantle. In this condition it may continue to live in water for a week 

 or more, but eventually throws off its ciliated coat (as in B) and commences to 

 creep about vigorously by the aid of its hooks, in search of its first host, which is at 

 present unknown. (After Schauinsland.) x 600. 



ovum and yolk are brought together into the " ootype," where 

 the shell-gland forms the egg-shell around them (Fig. 41, sh.gl), 

 and the egg is then passed into the uterus. The ovum segments 

 to form a minute six- hooked larva, which may (Bothriidae, Fig. 42) 

 or may not (Taeniidae) be ciliated. Thus in Taenia serrata the 

 proglottides are shed with the faeces of the host (dog), and they 

 protect the young from the desiccating influence of the surround- 

 ings. If inadvertently eaten by a rabbit along with herbs, the 

 proglottis and larval envelope are digested, and by its six hooks 

 the tiny larva bores through the gastric wall into the portal vein, 

 and so into the liver. Here the hooks are thrown off, and the 

 solid mass of cells becomes vacuolated. At one pole an invagi- 



