48 



VARIOUS FORMS OF TAPEWORMS. 



to the intestine. There is no proof yet, however, that the fox 

 does harhour this worm. It can be distinguished by having a 

 circle of hooks around its head, which is shghtly drawn out into 

 a rostellum, and by its four suckers. In length it varies from 

 twelve to sixteen inches when adult, and is constituted of about 

 two hundred distinct segments. The pale proglottides full of 

 eggs are passed out on to the ground in the sheep-dog's excre- 

 ment, and there remaining for a short period, they burst, re- 

 leasing thousands of ova (a). These are taken off the gi'ass by 



Fig. 12. — Sthbdy in Sheep 

 (Cmnurus cereltralis and Tcsnia ccenurus). 



A, Ovum. E, Embryo, o, Sexual worm (Tcenia ccEmirus) : p, proglottides ; n, neck ; 

 s, suckers, d, Canurus cerebralis : c, cerebral hemispheres ; c6, cerebellum ; m, 

 medulla, e, Hook &om c. 



the lambs, or even two-year-old sheep ; sometimes even whole 

 segments may be devoured. In either case the embryos become 

 released in the stomach of the sheep. The six-hooked larvae 

 then commence to bore their way through the walls of the ovine 

 intestine, and finally enter the blood, by which they are carried 

 to various parts of the body. Should any of these embryos 

 reach the brain or spinal cord, as very often happens, further 

 development takes place ; otherwise they apparently die a pre- 

 mature death. After the larva has reached the cranium, it com- 



