ASCARIS LUMBRICOIDES. 301 



CHAPTER X. 



NEMATODA. 



The Nematoda, or round worms infesting man — General and specific characters of 

 Ascaris lumhricoides — Structure and development — ^Views of Czermak, Eberth, and 

 Schneider — Experiments of Richter, Verloren, Davaine, and the author — Practical 

 considerations — Remarkable cases — Treatment. 



I COME now to the consideration of the third large group of human 

 helminths, commonly called the round worms, or Nematoda ; and, 

 as the ordinal characters are already given in the first part of 

 this volume, I need here only remark upon one or two peculiari- 

 ties of the group, which I have, hitherto, designedly omitted. Thus, 

 it may be noted, that our knowledge of the life-phases and migra- 

 tions of the larvae of these parasites is much more limited than 

 obtains in the case of the Cestoda, although the metamorphoses 

 displayed by the latter are much more complicated. With the 

 exception of Trichina spiralis, I am not aware that we have a 

 thorough knowledge of the entire life-history of any of the nema- 

 tode species which infest the human body ; nor, indeed, can I call 

 to mind any round- worm infesting the lower animals, whose life- 

 phases, migrations, and peculiarities of structure, during develop- 

 ment, are satisfactorily known. Notwithstanding all this, we are, at 

 length, acquainted with a multitude of highly-important and 

 extremely interesting facts, part of which I hope to enunciate 

 briefly in the following pages, and, in doing so, I shall be neces- 

 sitated to pass over many of those extremely minute structural 

 details, which are of httle practical utility, at the same time that I 



