TYPE PLATYHELMINTHE8. 159 



larval stage. Among these may be mentioned Bothriocephaliis latus, which 

 occurs in the human intestine, where it may reach a length of as much as 

 13 metres, in such cases consisting of many thousand proglottids. These 

 may readily be recognized by the convoluted uterus, and by the open- 

 ings of the reproductive organs on the median line of one of the flat sur- 

 faces, wliile the head is characterized by being flattened, and provided 

 on the margin with two elongated suckers. The ova give rise to a ciliated 

 larva which becomes transformed into the six-hooked embryo, this latter 

 making its way into the tissues of certain fish, which serve as the first host. 

 Man becomes infected with the worm by eating improperly cooked or salted 

 fish, the Pike being the more usual primary host, though this part may also 

 be played by other forms. 



The genus Tcenia furnishes two human parasites. The genus is char- 

 acterized by the head being provided with four circular suckers, as well as 

 in some cases with one or more crowns of hooks ; the genital pore is situ- 

 ated upon the margin of the proglottids, and the uterus is a straight tube 

 with a varying number of lateral transverse pouches. 



Tceitia solium is by far the most frequent tapeworm of man, and may 

 reach a length of 3-3 metres, and consist of 800-900 proglottides. The 

 head, in addition to the four suckers, is provided with a rostellum bearing 

 a double crown of from 26-28 hooks. The proglottids are about 5 mm. 

 broad and 10-12 mm. long, and the uterus has 7-9 stout lateral pouches. 

 The Cysticercus state of this worm occurs in the muscles of pigs, whence 

 man becomes infected by eating improperly cooked or salted pork. It 

 measures 8-10 mm., and possesses when imbedded in the muscles an ellip- 

 tical shape, its long axis being parallel with the long axis of the muscle 

 fibres. In addition to its occurrence in swine muscle, however, it has also 

 been found occasionally in man, encysted in the muscles, brain, or eye. 

 The source of the infection of man is, in many cases at least, cress, lettuce, 

 and such articles of food which have been watered with liquid manure 

 containing the fertilized ova of the worm. The six-hooked embryo encysts 

 itself in the tissues named, and man becomes the intermediate host of the 

 worm. 



TcEnia sayinata, also known as T. mediocanellata, is of less frequent 

 occurrence than T. solium, from which it is easily distinguished by its 

 greater length, 7-8 metres, and by the greater number of proglottids, 

 1200-1300. The head has no rostellum or crown of hooks, and the pro- 

 glottids are recognizable by their size, measuring 5-7 mm. in breadth and 

 18-20 mm. in length, and also by the lateral branches of the uterus being 

 slender and 20 or 30 in number. The Cysticercus occurs in the muscles or 

 occasionally in other organs of cattle, improperly cooked beef being the 

 source of infection for man. 



In addition to being occasionally the intermediate host of T. solium, 

 man may also be the host of the Echinococcus of T. echinococcus, a small 

 worm about 4 mm. in length and with only three proglottids, which occurs 

 in its adult state in the intestine of the dog. The ova may be received into 



