PLA TYHELMINTHES 



intestine of an ox. Here the egg shell is dissolved by the 

 action of the digestive juices, and a small embryo, the proscolex, 

 emerges (Fig. 66, G). The proscolex is a minute spherical 

 embryo provided with three pairs of hooks, by the aid of which 

 it burrows its way through the wall of the alimentary canal, 

 and eventually passes into some blood-vessel, or into the body- 

 cavity. If the former is the case, it is carried either to the 

 liver, brain, lungs, muscles, connective tissue, or eye (Fig. 68). 

 Its presence causes a cyst to be formed round it, pathological 

 changes being induced in the surrounding tissues of the host. 



The embryo soon loses its hooks and begins to grow. 

 Some of the cells in its interior liquefy, and a vesicle full of 

 fluid results. These vesicles attain a length of 4 to 8 mm., and 

 when found between the muscle fibres of beef or pork, the meat 

 is technically termed measly. At one side of the vesicle the 

 head commences to be formed ; it arises inside out as a projec- 

 tion into the lumen of the vesicle (Fig. 68). This projection 

 is hollow, and on its walls, facing its own lumen, the suckers 

 and rudimentary ring of hooks arise, whilst in the substance 

 of its walls the excretory system is being formed. The head 

 then turns inside out, and the result is a Cysticercus or bladder 

 worm. The Cysticercus consists then of the head and short 

 neck, termed the scolex, and of the bladder or vesicle. That 

 formed by the embryos of Taenia saginata is known as 

 Cysticercus bovis, from the host it inhabits (Fig. 68). As 

 long as it remains in the body of the ox, the Cysticercus is 

 incapable of further developement ; if, however, it is swallowed 

 by a man, the vesicle is digested, whilst the head fixes itself to 

 the walls of the intestine, and commences to divide into pro- 

 glottides. 



Life-History of Taenia Saginata. 



Scolex iu man gives rise by strobilisation to the 



Proglottides these leave their host carrying with them the 



Ova which, when found on gi'ass or in water, contain the 



! 



Six-hooked embryo or proscolex. This passes into alimentary canal of an 



j ox, aud working its way into the tissues of this intermediate 



I host, becomes the 



Cysticercus or bladder-worm. When this is eaten by man it develops 



I into the 



Scolex. 



