DR. THEODOK NEUMAT^N. 283 



gruesome foe from our doors and from our bodies 

 through a strict, general and systematic examination of 

 every piece of pork which is to be eaten. 



In the life history of trichina we have the simplest pos- 

 sible way before us in which the development of a para- 

 site may proceed. The young forms are introduced into 

 a host, mature there and produce progeny which grow 

 up in the same spot and then wait for another transfer. 

 The whole development happens inside of the host. In 

 most other parasites, however, the eggs get outside and 

 are scattered around, where they often encounter dif- 

 ferent fates before finding such conditions as enable them 

 to finish their development. The embyro may leave the 

 egf^ already in the interior of the old host and thus go 

 outside as larvae. In other cases the embryo does not 

 leave the egg before the latter has reached the outside 

 world, and then it may be able to do so spontaneously, 

 leaving the egg of its own free will and moving a'ound 

 independently, or it may be obliged to wait for delivery 

 inside the egg for weeks, months, or years, this delivery 

 occurring only after the egg has been swallowed by a 

 certain new host whose alimentary canal grants condi- 

 tions which are necessary for development of the embryo. 

 Both kinds of embryos are built accordingly, the former 

 having organs of locomotion, either muscles (young ne- 

 matods), or cilia (Bothriocephalus, trematods), in some 

 cases even eyes, while the latter, who need not perform 

 any extensive migrations, have scarcely any such or- 

 gans or decidedly none. In both instances, however, 

 the eggs must succeed in reaching a locality where they 

 can remain alive for a long time, i. <?., water or moist 

 places, for it would be a rare case if a new host were at once 

 on hand to take up the germs. Consequently, probably 

 all parasites possess in this state of development the 

 ability to wait a very long while, not only months, but 

 even years; nay, some of them seem actually to need 



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