V CESTODA ' 177 



striking feature is its very small, almost microscopic, size — the whole 

 worm, which consists of a scolex and 3 or 4 proglottides, measuring only 

 about 2-5 to 6 mm. in length. In correlation with this minute size the tape- 

 worm usually occurs in the dog's intestine not singly or. only as a few 

 individuals but in enormous numbers together. The bladder-worm phase 

 of the life-history occurs in various animals, especially ox, sheep, and pig 

 and occasionally in man. Whereas the tape-worm stage is extraordinarily 

 small, the bladder-worm on the other hand is relatively enormous, reach- 

 ing sometimes a diameter of 7 inches. As in the case of T. coenurus, the 

 wall of the bladder-worm produces not one merely but a large number of 

 scolices, and in this case pocket-Uke ingrowths of the wall are formed 

 which become separated off, drop into the cavity as secondary bladders, 

 and go on actively producing crops of scolices. Ordinarily the sur- 

 rounding tissues of the host endeavour to protect themselves by enclosing 

 the bladder-worm in tough connective tissue, the whole forming one 

 variety of what the surgeon terms hydatid cysts — easily identified as a 

 rule when large by drawing off the contained fluid and searching it for 

 hooks or complete scolices. 



The bladder-worm of Taenia echinococcus is a very dangerous parasite, 

 both from the large size to which it may grow within some important 

 organ such as the liver, and also owing to the small size of the proglottis 

 which renders it liable to be swallowed complete with its numerous con- 

 tained eggs, each of which may develop into a bladder-worm. 



Fortunately it is not common in most localities. Where a dog is 

 infected the shed proglottides or their disintegrated remains are liable 

 to get mixed up with the fur ; thence they get on to the animal's tongue 

 and are then ready to be deposited, when the animal licks a plate or a 

 hand, in a position from which they may readily be transferred to the 

 mouth of a human being. 



BOTHRIOCEPHALUS 



B. laius (Fig. 80, C) is again one of the large tape-worms — reaching 

 a length of thirty feet. The genus Bothriocephalus is readily dis- 

 tinguished from Taenia by the fact that the "head" is somewhat 

 lance-shaped, is without hooks, and possesses only two suckers, each 

 in the form of a longitudinal slit along the side of the head. The 

 mature proglottides are much broader in proportion to their length 

 than in Taenia, and the reprodufctive openings are situated not on one 

 side of the proglottis but in the mid line of its flat surface. The small 

 bladder-worm occurs amongst the muscles of various fresh-water fish, 



N 



