274 THE ANIMAL PARASITES OF MAN 



larval stage (in insects), and when adult live free in moist soil, or 

 in water. 



(c) CLASSIFICATION OF THE NEMATODES. 



The Nematodes are usually divided into a number of families, amongst 



which a few aberrant groups are included. Although there are objections 



to such a classification it is here maintained for practical reasons : 



Fam. i. EnoplidcB consists only of free species usually inhabiting the sea. 



Fam. 2. AnguillulidcB, Nematodes, most of which live free in fresh water, 



in soil, or in macerating substances ; amongst them there are some which 



live parasitically on plants, more rarely on animals. They are, as a 



rule, very small, and are particularly distinguished by the fact that 



their oesophagus possesses a double dilatation ; many are provided with 



a chitinous spine or with teeth in the oral cavity. The males possess 



two spicules, sometimes also a bursa copulatrix ; the females have 



pointed tails, the vulva is situated in the middle of the body (Anguil- 



lula, Rhabditis, Heterodera, &>c.~). 



Fam. 3. A ngioslomidce , characterised by heterogony (Rhabdonema, Angios- 



toma, Allantonema, <S>c.). 



Fam. 4. Gnathostomida, a small family only comprising the genus Gnatho- 

 stoma s. Cheir acanthus, the members of which live in the stomach of 

 vertebrates, especially mammals ; recognisable by numerous ramified 

 spines -which cover either the whole body or only the anterior part. 

 Fam. 5. Filariidce, very long filiform Nematodes, the oral aperture of 

 which is often surrounded by papillae or by two lips ; the oesophagus 

 is slender and without bulb ; the male has one or two uneven spicules ; 

 the vulva is usually situated in the anterior half of the body ; generally 

 ovoviviparous (Filaria, Spiroptera, Dispharagus, <S-c.). 



Fam. 6. Trichotrachelidce , recognisable by the oesophagus, which resembles 

 a necklet of pearls ; the anterior paf t of the body is usually of thread- 

 like slenderness, the posterior part of the body, which contains the 

 genitalia, is more or less thickened ; there may be no spicules or only one. 

 There is a single ovary ; vulva situated at the border line between 

 the anterior and posterior parts of the body (Trichinella, Tricho- 

 cephalus, Trichosoma, cS-c.). 



Fam. 7. StvongylidcB , a very large group divided into several sub-families ; 

 it is characterised by the possession of six oral papillae ; the male 

 possesses a bursa copulatrix and one or two spicules at the posterior 

 extremity ; species usually small (Eustrongylus , Strongylus, Syngamus, 

 Sclerostoma, Ankylostoma, Dochmius, &c.}. 



Fam. 8. Ascaridce. Mouth with three papillae, one dorsal and two 

 ventral ; oesophagus with bulb ; one or two spicules ; ovary double 

 (Ascaris, Oxyuris, Heterakis.} , 



Addendum. Gordiacea, greatly elongated Nematodes, which, in the larval 

 stage, live parasitically in insects, but in their adult condition are free 

 living ; they have no lateral ridges and no spicules ; the posterior extremity 

 of the male is bifurcated ; two testes ; the male and female generative 

 organs open through the anus. The intestine is partly obliterated. (Gor- 

 dius, Mermis, <>.) 



