52 ENTOZOA. 



CHAPTER IV. 



NEMATODA. 



The order of round worms, or Nematoda — Aspect, habits, and distribution — Probable 

 number of known species — Classification — Anguillulidge — The common vinegar eel 

 as a tjTpe — Genera — Gordiidffi, or family of hair-worms — Dujardin's account of the 

 structure of Ifermis nigrescens — The views of Meissner, Yon Siebold, and Yan 

 Beneden respecting the development of Mermis— Genera — Structure of Sphaaru- 

 laria — Osyru'idas, or thread-worms— Organization of Oxyuris curvula — Genera. 



In tlie foregoing chapters I have devoted as much space as could 

 be spared for a general description of the sterelminthic group of 

 worms ; and, therefore, I now pass to the consideration of the third 

 order of helminths, or, in other words, to the Nematoda. This 

 order is, as we have seen, equivalent to the second sub-class or coelel- 

 minths, in which the internal organs are loosely suspended within 

 a well defined perivisceral cavity. The term JSTematoda {vr]^ia-elho<i) 

 imphes the possession of a more or less thread-like form of body, 

 but, in conformity with the most obvious and general character 

 presented by nearly every member of the group, these helminths 

 are with greater frequency denominated round ivorms. So far as 

 I am aware, all the forms (except that of a new genus — Simondsia, 

 T. S. C.) are very much longer than they are broad, and it is 

 only in a few exceptional cases that we find a tendency towards 

 the flattened character seen in other helminthic types. 



Aspect. — The Nematodes as a whole, and especially the more 

 typical and better known forms, bear a marked external resem- 

 blance to the common earthworm ; but their internal organization, 

 when compared with that of the latter, will be found to difier most 

 materially. The majority of the species are of small size, varying 



