DR. THEODOR NEUMANN. 209 



means complicated body, and their simple construction, 

 penetrate deeply into the living body of their host, and 

 often leave no track at all on the road by which they 

 come. Indeed, we find parasites not only in the organs 

 of the body which are open to the outside, such as 

 intestines, lungs, etc., but also in the eyes, iu the lieart, 

 the brains, and other parts of the body which have no 

 connection at all with the outer world. Thus the study 

 of parasites, the discovery of their mysterious methods 

 of development, the explanation of their remarkable 

 ways and means of living and of creating new genera- 

 tions is to-day one of the most interesting and brilliant 

 chapters of biology, allowing us, as scarcely any other 

 does, to look into the innermost connections of the dif- 

 ferent shapes and phases of animal life. 



When we consider the circumstance that an animal 

 which draws its food from another one does not kill the 

 latter entirely, but only taps it, we have at once the ex- 

 planation of the fact that parasites are always small and 

 weak, the host big and strong, superior in force ; for if 

 it were otherwise, the parasite would not be satisfied 

 with a mere extraction of vital juice, but would eat up 

 its host. There is no more question that the parasites 

 are throughout small, and belong to the lower classes of 

 the animal kingdom, while their hosts are large and more 

 highly developed. 



Since from the very nature of getting food from some 

 other animal a parasite is always obliged to go to its 

 host, it is a very natural consequence that a large num- 

 ber of parasites simplify this by taking permanent quar- 

 ters on or in the host ; in other words, the latter provides 

 not only food for its guest but also shelter. On the other 

 hand we must not. draw the conclusion that an animal 

 which is found on or in another one is at once character- 

 ized as a parasite ; it is necessary to prove also that the 

 food is drawn from the animal inhabited. 



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