l6o NEMATHELMINTHES CHAP. 



which they live, their bodily structure shows a very striking 

 uniformity, the same is by no means the case with their litt 1 - 

 history, which exhibits an astounding variety. Yon Linstow l 

 has arranged the various modifications, which occur under four- 

 teen heads. He includes in his list the Gordian worms, which 

 we have placed under a different heading. The following account 

 has been taken from his paper, with a few alterations : 



1. The embryos develop, with a larval stage and without any 

 change of medium, directly into the mature sexual forms. They 

 live in fresh, brackish, or salt water, in plants, in the earth or 

 in decaying organic matter : examples, Dorylaimus, Unojilus, 

 Plcctus, Monliystera. 



2. The larvae live in the earth, the sexual forms in plants : 

 examples, Tylenclms tritici and T. devastatrix, Hetcrodera schachtii 

 (Figs. 77 and 78). 



3. The larvae live in animals, after whose death and decay 

 they are set free and develop into the sexual animals in the earth : 

 example, Rhabditis pellio. 



4. The bisexual forms live in the earth, and the fertilised 

 females bore into animals (insects), and here produce embryos : 

 example, Sphaerularia bombi (Fig. 76). 



5. The bisexual forms live in the earth ; the females do not 

 develop, but the males make their way into Insects (Beetles), 

 and becoming hermaphrodite, develop ova which give rise to the 

 bisexual form: example, Bradynema rigidum. 



6. The larvae live in the earth, the sexual form in Vertebrates : 

 examples, Dochmius, Strongylus. 



7. The Nernatode lives as a hermaphrodite in animals, the 

 offspring of this, by an alternation of generations, become sexual 

 in the earth : example, Khabdonema in Frog. 



8. A bisexual free form gives origin to a bisexual parasitic form 

 living in an animal : example, Leptodera appendiculata in Snails. 



9. The eggs develop in the earth, and give rise to embryos 

 which are transferred whilst still in the egg-cell to the body of 

 an animal. The embryos hatch out and form bisexual parasites : 

 examples, Oxyuris, Trichocepkalus. 



10. The larvae live in insects, the sexual worms in water or 

 in the earth : example, Mermis. 



11. The larva lives encapsuled and is passively transferred to 



1 Zeitschr. wins. ZooL Bd. xlii. 1885, j>. 70S. 



