ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 247 



young lung larva, the half grown lung larva, the fully grown lung 

 larva with boring teeth, the same with three lips, and the sexual fonn. 

 The Nematohelminths exhibit no less than fourteen diflferent 

 modifications of developmental history : — 



I. The embryos develope, without any larval stage, in one medium ; 

 they may live in fresh, salt, or brackish water, in plants, on the 

 earth, or in decaying substances (Dorylamius, Enoplus, Plectus, 

 Bhahditis, &c.). 



'2. The larva lives in earth, the sexual form in plants (Tylenchus 

 tritici, &c.). 



3. The larva lives in animals (worms) after the death and decay 

 of which they become free and in earth develope into sexual forms 

 (^Bhahditis pellio). 



4. The worm lives bisexually in earth, the fertilized female 

 passes into animals (bees) and there produces descendants {Spliasru- 

 laria bomhi). 



5. The larvfB live in earth, the sexual forms are developed in a 

 vertebrate (Bochmius, Strongylus). 



6. The worm lives as a hermophrodite in an animal, while the 

 progeny are developed by alternation of generation sexually in earth 

 (Bhabdonema, Angiostomum). 



7. A sexually differentiated fertilizing form developes by alterna- 

 tion of generation another bisexual form which lives parasitically 

 in a snail (Leptodera appendiculata). 



8. The egg developes in earth into the embryo, and this passes 

 into an animal where it becomes sexually diflferentiated (^Trichocephalus, 

 Oxyuris). 



9. The larva lives in insects, the adult in earth or water (Mermis). 



10. The larva is encapsuled in an animal and passes passively 

 into another species where it becomes matured (Ascaris, Filaria, 

 Cucullanus). 



II. One form lives for a short time bisexually in the intestine, 

 whence it produces larvae which bore through the enteric wall, and 

 become encapsuled in the muscles (Trichina spiralis). 



12. The sexually mature form lives in the trachea of birds, the 

 females produce eggs, which contain the developed embryo ; these are 

 ejected by the host in coughing ; in the earth the embryo becomes 

 mobile, and is now taken up by the bird with food ; in the stomach 

 and oesophagus the embryo loses its investing membrane, to wander 

 into the air-sacs and bronchi, whence the grown larva passes into the 

 trachea (Syngamus trachealis). 



13. There are two larval forms, the first of which is foimd in 

 mollusca, the second in aquatic beetles and Orthoptera, while the 

 sexual form is found in water (Gordius aqiiaticus). 



14. There are two larval forms, one of which lives in water, and 

 the other in the lung of an Amphibian, whence it wanders into the 

 intestine to differentiate and develope its sexual organs [Nematoxys 

 longicauda). This last, which is new to science, corresponds to the 

 mode of development of Polystomum integerrimum among Trematodes. 

 The only rule which we can deduce is that Nematoids found in living 



