222 ENTO-PARA SITES AND HYGIENE. 



after continued treatment some may remain in the 

 intestines and produce a repetition of the former symp- 

 toms. 



Apart from this and similar cases, however, the en- 

 to-parasites possess no apparatus which may be used to 

 wound and injure the inner organs of the host, although 

 quite a number of the former do not live on the lym- 

 phatic liquids of their bearer, but on their blood as such. 

 Then the upper part of the alimentary canal is trans- 

 formed into a sucking apparatus, which produces a so- 

 called diapedesis, or an emigration of the corpuscles of 

 the blood through the walls of the capillaries. Mostly 

 trematods do this, whose very name comes from this 

 action of sucking (rp^/ior, a pore or a sucker). We shall 

 have occasion to speak about them and their dangerous 

 influence later. 



N"ot only the presence but also the condition of the 

 food in which these animals live, and their surroundings, 

 exercise a certain influence upon their organization. 

 When we think that all the food which is being taken 

 up has already been prepared by the host, transformed 

 into liquid state, and represents then material which may 

 be absorbed without delay ; that in consequence of this, 

 a great part of sometimes rather tedious and hard work 

 is spared the intestines of the worm ; then we shall 

 scarcely be surprised to find that this intestinal apjDara- 

 tus has been simplified to a very great extent. Never 

 does its length surpass that of the body; never is its 

 inner surface enlarged through folds or bags; in many 

 cases it lacks entirely those glands which are such impor- 

 tant additions in the alimentary apparatus of nourpara- 

 sitic animals — in short, the canal is built in the simplest 

 way possible. But this degeneration does not stop even 

 here; it may go on so that the rear end, ordinarily used 

 for the throwing off of unused material, disappears, the 

 alimentary canal is a blind alley, and everything which 



leo 



