244 ENTO-PAEASITES AND HYGIENE. 



no one had any idea of their being real worms. Kuchen- 

 meisier succeeded in proving that when brought into the 

 alimentary canal of another animal they lose the bladder 

 and grow up to be tape-worms. These are a necessary stage 

 in the development of the tape-worms, so that the latter 

 may be said to have a regular metamorphosis. Quite 

 frequently there is not one head being developed in the 

 bladder of the cysticercus but several, even a great num- 

 ber, so that we are justij&ed in calling this form the nurse 

 or grand-nurse, producing a new generation by means of 

 budding. This new progeny does not leave its place of' 

 birth but remains in contact with the nurse exactly as 

 the redia did, until the nurse gets into the body of the 

 final host and produces there in a sexual manner the gen- 

 eration of sexual individuals, the tape-worm chain. 



Still more interesting and more noteworthy, because 

 sometimes infecting human beings, is another tape- 

 worm, taenia echinococcus, whose cysticercus produces 

 a much greater number of growths developing into a 

 scolex. Its embryonal state is known as echinococcus 

 or " sheath- worm." It is a very small tape-worm whose 

 chain is composed of not more than four or five joints. 

 The last one only is mature, but as soon as it is thrown 

 off the following one ripens. The worm lives in the in- 

 testines of the dog, the cysticercus is developed in cat- 

 tle and often also in man, where it many times is the 

 cause of death. The structure of this cysticercus is 

 rather remarkable: the skin hard and firm, while the 

 young tape-worm heads do not grow directly on the 

 inner side of the wall of the bladder, but on the outside 

 of little bladders which have grown from the walls of 

 the primary bladder. Later they are turned inside out 

 as described before, and closely packed in the interior 

 of the cysticercus, waiting for a chance to be transported 

 into a final host. 



The size of this parasite varies; ordinarily it is about 



1S2 



