﻿372 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  16 
  

  

  we 
  worked 
  with 
  too 
  small 
  a 
  supply 
  of 
  animals, 
  and 
  could 
  not 
  get 
  

   noticeable 
  results 
  within 
  the 
  short 
  time 
  available. 
  The 
  roots 
  were 
  

   attacked 
  by 
  Heterodera 
  but 
  the 
  effect 
  of 
  the 
  Mononchus 
  was 
  not 
  deter- 
  

   mined. 
  With 
  further 
  experiments 
  along 
  this 
  line, 
  it 
  should 
  be 
  quite 
  

   possible 
  to 
  observe 
  results 
  from 
  the 
  external 
  appearance 
  of 
  the 
  host 
  

   plants. 
  

  

  IV. 
  THE 
  LIFE-HISTORY 
  OF 
  MONONCHUS 
  PAPILLATUS 
  BASTIAN 
  

  

  Comparatively 
  little 
  is 
  accurately 
  known 
  about 
  the 
  life-history 
  of 
  

   free-living 
  nematodes. 
  About 
  the 
  only 
  forms 
  that 
  have 
  been 
  studied 
  

   are 
  those 
  living 
  on 
  decaying 
  matter, 
  such 
  as 
  species 
  of 
  Rhabditis, 
  

   Cephalobus, 
  Plectus 
  and 
  Diplogaster. 
  Most 
  of 
  these 
  genera 
  have 
  a 
  very 
  

   rapid 
  development 
  and 
  are 
  in 
  this 
  way 
  somewhat 
  adapted 
  to 
  the 
  

   ephemeras 
  of 
  dead 
  and 
  decaying 
  bodies 
  that 
  serve 
  as 
  food. 
  From 
  a 
  

   study 
  of 
  these 
  forms 
  it 
  would 
  be 
  impossible 
  to 
  generalize 
  and 
  state 
  that 
  

   all 
  soil 
  or 
  free-living 
  nematodes 
  have 
  a 
  rapid 
  development 
  and 
  short 
  

   life. 
  The 
  results 
  we 
  obtained 
  in 
  rearing 
  Mononchus 
  papillatus 
  showed 
  

   that 
  the 
  life 
  of 
  this 
  form 
  may 
  be 
  of 
  considerable 
  length, 
  and 
  the 
  same 
  

   thing 
  may 
  be 
  true 
  of 
  many 
  of 
  the 
  other 
  soil 
  nematodes. 
  

  

  In 
  order 
  to 
  judge 
  the 
  value 
  of 
  M. 
  papillaius 
  for 
  fighting 
  other 
  

   nematodes 
  it 
  is 
  necessary 
  to 
  have 
  a 
  complete 
  knowledge 
  of 
  its 
  life 
  

   history, 
  the 
  time 
  required 
  to 
  reach 
  the 
  adult 
  stage, 
  the 
  number 
  of 
  eggs 
  

   produced 
  and 
  the 
  length 
  of 
  life 
  after 
  the 
  cessation 
  of 
  egg 
  production. 
  

  

  Nematodes 
  live 
  in 
  the 
  soil 
  as 
  members 
  of 
  an 
  association 
  of 
  living 
  

   forms, 
  among 
  which 
  there 
  exist 
  interrelationships. 
  It 
  is 
  important 
  

   to 
  know 
  what 
  effect 
  Mononchus 
  as 
  a 
  predatory 
  form 
  may 
  have 
  on 
  the 
  

   associated 
  nematode 
  population 
  of 
  the 
  soil, 
  and 
  especially 
  its 
  influence 
  

   on 
  the 
  diminution 
  of 
  forms 
  causing 
  root-knot 
  and 
  similar 
  diseases; 
  

   if 
  the 
  monoch 
  has 
  a 
  high 
  rate 
  of 
  propagation, 
  and 
  lives 
  for 
  a 
  long 
  time, 
  

   it 
  has 
  naturally 
  a 
  more 
  rapid 
  and 
  beneficial 
  effect. 
  

  

  A. 
  The 
  hermaphroditism 
  of 
  Mononchus 
  papillatus. 
  — 
  Hermaphrodit- 
  

   ism 
  in 
  numerous 
  species 
  of 
  the 
  genus 
  Mononchus 
  was 
  first 
  observed 
  

   by 
  Cobb. 
  Males 
  have 
  been 
  described 
  in 
  very 
  few 
  species, 
  and 
  seem 
  

   to 
  be 
  extremely 
  rare 
  in 
  most 
  of 
  them. 
  A 
  gradation 
  exists 
  in 
  this 
  

   genus 
  similar 
  to 
  that 
  found 
  in 
  the 
  genera 
  Rhabditis 
  and 
  Diplogaster, 
  

   where 
  we 
  find 
  some 
  species 
  in 
  which 
  there 
  is 
  an 
  equal 
  number 
  of 
  males 
  

   and 
  females, 
  some 
  in 
  which 
  from 
  ten 
  per 
  cent 
  to 
  forty 
  per 
  cent 
  or 
  more 
  

   are 
  males, 
  some 
  species 
  in 
  which 
  not 
  even 
  one 
  per 
  cent 
  are 
  to 
  be 
  found 
  

   and 
  still 
  others 
  in 
  which 
  males 
  seem 
  never 
  to 
  occur. 
  

  

  Conditions 
  similar 
  to 
  these 
  are 
  found 
  in 
  the 
  genus 
  Mononchus: 
  

   the 
  Antarctic 
  M. 
  gerlachei 
  seems 
  to 
  produce 
  an 
  equal 
  number 
  of 
  males 
  

  

  