﻿30 
  Descent 
  

  

  Summing 
  up 
  the 
  main 
  points 
  of 
  these 
  intro- 
  

   ductory 
  remarks, 
  I 
  propose 
  to 
  deal 
  with 
  the 
  sub- 
  

   jects 
  mentioned 
  above 
  at 
  some 
  length, 
  devoting 
  

   to 
  each 
  of 
  them, 
  if 
  possible 
  at 
  least 
  an 
  entire 
  

   lecture. 
  The 
  decisive 
  facts 
  and 
  discussions 
  

   upon 
  which 
  the 
  conclusions 
  are 
  based 
  will 
  be 
  

   given 
  in 
  every 
  case. 
  Likewise 
  I 
  hope 
  to 
  point 
  

   out 
  the 
  weak 
  places 
  and 
  the 
  lacunae 
  in 
  our 
  pres- 
  

   ent 
  knowledge, 
  and 
  to 
  show 
  the 
  way 
  in 
  which 
  

   each 
  of 
  you 
  may 
  try 
  to 
  contribute 
  his 
  part 
  to- 
  

   wards 
  the 
  advancement 
  of 
  science 
  in 
  this 
  sub- 
  

   ject. 
  Lastly 
  I 
  shall 
  try 
  to 
  prove 
  that 
  sudden 
  

   mutation 
  is 
  the 
  normal 
  way 
  in 
  which 
  nature 
  

   produces 
  new 
  species 
  and 
  new 
  varieties. 
  These 
  

   mutations 
  are 
  more 
  readily 
  accessible 
  to 
  ob- 
  

   servation 
  and 
  experiment 
  than 
  the 
  slow 
  and 
  

   gradual 
  changes 
  surmised 
  by 
  Wallace 
  and 
  his 
  

   followers, 
  which 
  are 
  entirely 
  beyond 
  our 
  pres- 
  

   ent 
  and 
  future 
  experience. 
  

  

  The 
  theory 
  of 
  mutations 
  is 
  a 
  starting-point 
  

   for 
  direct 
  investigation, 
  while 
  the 
  general 
  belief 
  

   in 
  slow 
  changes 
  has 
  held 
  back 
  science 
  from 
  such 
  

   investigations 
  during 
  half 
  a 
  century. 
  

  

  Coming 
  now 
  to 
  the 
  subdivisions 
  and 
  headings 
  

   under 
  which 
  my 
  material 
  is 
  to 
  be 
  presented, 
  I 
  

   propose 
  describing 
  first 
  the 
  real 
  nature 
  of 
  the 
  

   elementary 
  species 
  and 
  retrograde 
  varieties, 
  

   both 
  in 
  normal 
  form 
  and 
  in 
  hybridizations. 
  A 
  

   discussion 
  of 
  other 
  types 
  of 
  varieties, 
  includ- 
  

  

  