Dr. L. Orlej on Nematodes. 305 



The difference, on the other hand, between the free-living 

 and truly parasitic forms is much greater ; for we find distinc- 

 tive characters both in the structure of the cuticle, and in that 

 of the reproductive organs and nervous system. The cuticle 

 of the free-living forms is tolerably thin in comparison with 

 that of the parasites ; the genital tube is simple and devoid 

 of convolutions in the former, while in the latter the structure 

 is complicated and there are many convolutions. In the para- 

 sitic forms the nervous system is represented exclusively by 

 an oesophageal ring made up of nerve-fibres and nerve- cells, 

 while in the free-living forms it is either entirely absent or 

 consists only of a few fibres. A study of the cellular mass 

 belonging to the nervous system (?) which surrounds tlie 

 oesophagus in the free-living group discloses another impor- 

 tant difference. On the other hand, the lihabditiforniffi stand 

 near the free-living forms in these latter points, and are sepa- 

 rated from the parasitic forms by the same characters ; though, 

 at the same time, the parasitic stage of Rliahditis rngrovenosa 

 approaches flic parasites in many points. Oxyuris is not to 

 be joined to the Rhabditiformai ; for it has higher structural 

 relations. 



Differences are to be detected Avhicli perhaps may connect 

 the simplest with the most complicated metamorphosis. In 

 the first place, every IS' ematode has a larval stage ; in this 

 stage all are alike, and all, with few exceptions, lead a free 

 existence, a proof that the parasitic are derived from the free- 

 living forms. But while the parasitic larva; must of necessity 

 perish if they are unable by any means to reach the interior of 

 other animals, the free-living forms develop into sexually 

 mature worms witliout changing their abode. But how is it 

 with the llhabditiformse ? Schneider's investigations have 

 already shown us that most Rhabditida?, require for their de- 

 velopment soil or liquid which has become foul ; and later 

 experiments appear to establisli the conclusion that the deve- 

 lopment of the llhabditidai is carried out in tlie midst of de- 

 composing matter. Rhabditis ntgrovenosa and aj^pendiculata 

 also require a nidus of filth for their later developmental stages, 

 but have the power of developing into the sexually mature con- 

 dition in this position, while their nearest allies, the Oxyurids, 

 can only develop within the bodies of other animals. And 

 this development into the sexual state apart from a host cha- 

 racterizes both free-livers and the llhabditiforma!, while the 

 contrary is the distinguishing mark of the parasites. If we 

 study those Rhabditiformai which are found in the interior of 

 man and the higher animals, we find, from the researches of 

 various investigators, that these species reach the mature cou- 



