PARASITES OF ANIMALS. 



71 



,' measles " in pork (Figure 49). These are cavities or cysts 

 produced by inflammation, containing whitish fluid and enclos- 

 ing small, bladder-like, translucent, vesicles, filled with a watery 

 fluid, and which contain the proper head and neck of the young 

 worm coiled up spirally in the interior in an inverted position. 

 By gentle pressure the head and neck may be made to protrude 

 by inversion, like the finger of a glove, and will then present 

 the appearance shown in figure 50, the vesicle of fluid now 

 forming the flask-like caudal portion of the worm. The head 

 may now be seen to have four suckers and a central promi- 

 nence surrounded by two circles of hooks, as in the adult. In 

 this condition, enclosed in the cysts, they will remain living 



Figure 53. ' Figure 54. 



for a long time in the hog, even surviving the death of their 

 host for a considerable period. If one or more of these young 

 worms or measles be swallowed by a human being, the mus- 

 cular fibres and the cysts will be digested, and each young 

 worm thus liberated will evert its head, and losing its bladder- 

 like portion, will pass into the intestine. There it will fasten 

 itself to the inner membrane by its suckers and hooks, and 

 grow rapidly by absorbing the digested food by which it is 

 surrounded. New joints will be rapidly formed as the older 

 ones grow larger, until it becomes a mature tape-worm, with 

 joints ready to be cast off. There may be but one tape-worm in 



Figure 53. Head of Tcenia solium, magnified. From Cobbold. 

 Figure 54. — A joint ov proglottis of Tcenia solium, magnified ; a, branches of the 

 uterus ; h, external oi'ifice ; c, male organ. From Cobbold. 



