﻿358 
  ANNUAL. 
  REPOKT 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  rays 
  which 
  are 
  the 
  inducing 
  agent. 
  Similar 
  but 
  less 
  extensive 
  findings 
  

   have 
  been 
  made 
  in 
  the 
  case 
  of 
  the 
  mutant 
  character 
  called 
  "scute" 
  

   and 
  its 
  normal 
  alternative, 
  "nonscute."^ 
  The 
  mutations 
  arising 
  as 
  

   a 
  result 
  of 
  X-raying 
  are, 
  therefore, 
  not 
  merely 
  destructive 
  changes, 
  not 
  

   merely 
  losses. 
  If 
  some 
  are 
  losses, 
  others, 
  then, 
  are 
  gains. 
  Doubtless, 
  

   as 
  in 
  the 
  case 
  of 
  most 
  chemical 
  reactions, 
  most 
  mutations 
  too 
  are 
  

   changes 
  involving 
  substitutions 
  and 
  rearrangements, 
  rather 
  than 
  mere 
  

   losses 
  or 
  gains. 
  

  

  It 
  should 
  be 
  mentioned 
  that, 
  in 
  addition 
  to 
  the 
  changes 
  in 
  indivi- 
  

   dual 
  genes 
  which 
  X 
  rays 
  bring 
  about, 
  they 
  also 
  cause 
  — 
  with 
  consider- 
  

   able 
  frequency, 
  as 
  Altenburg 
  and 
  I 
  have 
  shown 
  — 
  breakages 
  of 
  entire 
  

   chromosomes 
  or 
  strings 
  of 
  genes, 
  accompanied 
  by 
  reattachments 
  of 
  

   the 
  broken-off 
  fragments 
  to 
  different 
  chromosomes 
  or 
  to 
  the 
  chromo- 
  

   some-remainder 
  from 
  which 
  they 
  were 
  broken, 
  at 
  a 
  point 
  different 
  

   from 
  that 
  of 
  before. 
  The 
  rearrangements 
  of 
  genes 
  thus 
  resulting 
  

   can 
  be 
  analyzed 
  by 
  breeding 
  tests, 
  and 
  at 
  the 
  same 
  time 
  checked 
  up 
  

   by 
  studies 
  of 
  the 
  chromosomes 
  as 
  seen 
  through 
  the 
  microscope, 
  an 
  

   undertaldng 
  which 
  Dr. 
  Painter 
  and 
  I 
  have 
  been 
  cooperatively 
  

   engaged 
  upon 
  during 
  the 
  past 
  two 
  years. 
  In 
  this 
  way 
  we 
  have 
  

   obtained 
  light 
  on 
  the 
  structure 
  and 
  behavior 
  of 
  the 
  genes 
  and 
  chromo- 
  

   somes 
  from 
  a 
  new 
  angle, 
  though 
  space 
  does 
  not 
  permit 
  me 
  to 
  touch 
  

   upon 
  these 
  results 
  now.^ 
  There 
  is 
  evidence 
  that 
  such 
  rearrangements 
  

   of 
  chromosome 
  parts, 
  as 
  well 
  as 
  mutations 
  in 
  individual 
  genes, 
  have 
  

   occurred 
  during 
  the 
  course 
  of 
  natural 
  evolution. 
  

  

  The 
  question 
  may 
  now 
  be 
  raised. 
  To 
  what 
  extent 
  can 
  all 
  these 
  

   results 
  be 
  regarded 
  as 
  mere 
  curiosities, 
  effects 
  confined 
  to 
  the 
  mature 
  

   sperm-cells 
  of 
  the 
  fruit 
  fly, 
  and 
  of 
  little 
  significance 
  elsewhere? 
  In 
  

   this 
  connection, 
  it 
  may 
  first 
  be 
  pointed 
  out 
  that 
  my 
  results 
  on 
  the 
  

   fruit 
  fly 
  were 
  promptly 
  confirmed 
  by 
  Weinstein, 
  working 
  at 
  Columbia 
  

   University, 
  and 
  later 
  by 
  others 
  (Hanson, 
  Patterson, 
  Harris, 
  Oliver) 
  

   at 
  this 
  laboratory, 
  and 
  more 
  recently 
  by 
  Serebrovsky 
  and 
  his 
  col- 
  

   leagues 
  in 
  Russia 
  and 
  by 
  Doctor 
  and 
  Mrs. 
  Timofeeff-Ressovsky 
  in 
  

   Berlin. 
  In 
  my 
  own 
  work, 
  the 
  treatments 
  were 
  not 
  confined 
  to 
  sperm 
  

   cells, 
  but 
  were 
  also 
  applied 
  to 
  the 
  females, 
  and 
  it 
  was 
  found 
  that 
  

   both 
  the 
  mature 
  eggs 
  and 
  the 
  immature 
  female 
  germ 
  cells 
  (oogonia) 
  

   were 
  susceptible 
  to 
  the 
  mutation 
  effect. 
  Harris 
  has 
  recently 
  extended 
  

   the 
  finding 
  to 
  the 
  immature 
  germ 
  cells 
  of 
  the 
  adult 
  male. 
  Patterson 
  

   has 
  found 
  that 
  the 
  early 
  germ 
  cells 
  of 
  both 
  male 
  and 
  female 
  larvse 
  

  

  2 
  Since 
  the 
  above 
  was 
  written, 
  two 
  papers 
  have 
  appeared 
  by 
  Timofeeff-Ressovsky, 
  describing 
  various 
  

   cases 
  of 
  the 
  induction, 
  by 
  X 
  rays, 
  of 
  mutations 
  in 
  each 
  of 
  two 
  opposite 
  directions. 
  

  

  ' 
  The 
  production 
  of 
  such 
  changes 
  in 
  chromosome 
  structure 
  by 
  means 
  of 
  X 
  rays 
  has 
  been 
  confirmed 
  by 
  

   Weinstein 
  and 
  later 
  by 
  Serebrovsliy 
  by 
  means 
  of 
  breeding 
  tests 
  on 
  Drosophila. 
  By 
  means 
  of 
  cytologica! 
  

   analysis, 
  Goodspeed 
  and 
  Olson 
  have 
  found 
  similar 
  effects 
  in 
  tobacco, 
  and 
  so 
  have 
  Blakeslee 
  and 
  his 
  asso- 
  

   ciates 
  in 
  the 
  Jimson 
  weed. 
  The 
  work 
  of 
  the 
  present 
  author 
  and 
  his 
  colleagues, 
  in 
  studying 
  such 
  changes 
  

   in 
  Drosophila 
  by 
  means 
  of 
  breeding 
  tests 
  and 
  cytological 
  analysis 
  combined, 
  has 
  recently 
  been 
  repeated 
  

   in 
  an 
  elaborate 
  manner 
  by 
  Dobzhansky, 
  with 
  results 
  that 
  are 
  for 
  the 
  most 
  part 
  in 
  striking 
  agreement 
  with 
  

   those 
  that 
  had 
  been 
  announced 
  by 
  us. 
  

  

  