DR. THEODOR NEUMANN. 225 



which at first servfe as legs are changed to organs of fast- 

 ening; in other parasites strong, muscular sucking-cups 

 perform that service. Our leeches, which are temporary- 

 parasites, show us their development in a very significant 

 way. Such sucking cups may be strengthened by hooks 

 or frames of chitin, and their size is sometimes so enor- 

 mous that the parasites cannot be removed by a mere 

 pull, but are torn if the attempt is made. Parasites in 

 the inner parts of the body do not need such highly de- 

 veloj)ed clinging apparatus, and if they have it, we 

 usually find as the reason that they have located in ex- 

 posed and dangerous places, for instance near the rear 

 end of the alimentary canal. They would be hopelessly 

 lost if they were swept away, and as that danger is rather 

 imminent if they are not firmly fixed, the worms must 

 look out for a secure and entirely safe settlement. In 

 all inner organs, on the other hand, which are entirely 

 away from the outside world, the danger of being dis- 

 connected is small for any parasite. Thus we see that 

 their organs of fixation are essentially smaller and lighter. 

 Trematods living in the interior of bodies have only one 

 or two sucking cups; nematods have none at all; cestods, 

 however, show a larger development of the same. They 

 have largely two (bothriocephalus) or four (taenia) cups, 

 consisting of hemispherical, hollow muscles; in some 

 cases the later may be transformed into large, separate ap- 

 pliances which contain chitin frames for support. Some- 

 times these cups bear in addition a regular crown of 

 hooks placed on a special elevation of the head. These 

 hooks point backward; thrust into the mucous membrane 

 of the intestine, they effect a firm hold of the worm. 



These influences of parasitism, degenerative as well as 

 progressive, on the condition of life of the individual, 

 are however not the only ones of which we have knowl- 

 edge. They all had a bearing on the organization of these 

 animals. Let us direct our attention once to the embryol- 



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