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  XIII. 
  On 
  the 
  Mechanism, 
  of 
  the 
  Male 
  Genital 
  Tube 
  in 
  

   Coleoptera. 
  By 
  Frederick 
  Muir. 
  

  

  [Read 
  October 
  15th, 
  1919.] 
  

  

  Plate 
  XXI. 
  

  

  Although 
  we 
  have 
  considerable 
  knowledge 
  of 
  the 
  skeleton 
  

   of 
  the 
  male 
  genital 
  tube 
  of 
  a 
  number 
  of 
  species 
  of 
  Coleoptera, 
  

   but 
  little 
  is 
  known 
  as 
  to 
  the 
  mechanism 
  and 
  muscles 
  of 
  this 
  

   organ. 
  Some 
  of 
  the 
  most 
  detailed 
  work 
  on 
  this 
  subject, 
  

   such 
  as 
  Straus-Durckheim 
  on 
  Melolontha 
  vulgaris, 
  was 
  

   done 
  by 
  workers 
  who 
  did 
  not 
  recognise 
  the 
  importance 
  of 
  

   the 
  internal 
  sac 
  and 
  the 
  predominant 
  role 
  it 
  plays 
  in 
  copula- 
  

   tion. 
  For 
  these 
  reasons 
  the 
  following 
  remarks 
  on 
  some 
  of 
  

   the 
  types 
  and 
  their 
  manner 
  of 
  functioning, 
  with 
  a 
  few 
  details 
  

   relating 
  to 
  muscles 
  in 
  a 
  couple 
  of 
  " 
  ring 
  " 
  types, 
  may 
  be 
  

   of 
  interest, 
  notwithstanding 
  their 
  desultory 
  character. 
  

  

  Orientation. 
  

  

  For 
  the 
  sake 
  of 
  clearness 
  it 
  is 
  necessary 
  to 
  define 
  the 
  

   terms 
  of 
  orientation 
  employed. 
  For 
  this 
  purpose 
  I 
  accept 
  

   for 
  orientation 
  the 
  point 
  between 
  the 
  abdomen 
  and 
  thorax, 
  

   as 
  defined 
  by 
  Dr. 
  Sharp,* 
  as 
  basal. 
  The 
  portion 
  of 
  any 
  

   segment 
  or 
  appendage 
  nearest 
  to 
  that 
  point 
  being 
  the 
  base, 
  

   and 
  the 
  portion 
  most 
  distant 
  being 
  the 
  apex. 
  In 
  measuring 
  

   the 
  respective 
  distances 
  a 
  continuous 
  line 
  on 
  the 
  body 
  wall 
  

   must 
  be 
  followed, 
  a 
  dorsal, 
  pleural 
  or 
  ventral 
  line 
  for 
  their 
  

   respective 
  areas. 
  Thus 
  the 
  tarsus 
  of 
  a 
  front 
  leg 
  lying 
  

   against 
  the 
  basal 
  point 
  would 
  still 
  be 
  the 
  apex 
  of 
  the 
  leg, 
  

   and 
  the 
  coxa 
  the 
  base. 
  This 
  orientation 
  applies 
  equally 
  to 
  

   invaginations, 
  struts 
  or 
  glands, 
  and 
  evaginations, 
  tegminal 
  

   lobes, 
  etc. 
  Thus 
  the 
  base 
  of 
  a 
  tegminal 
  lobe 
  is 
  that 
  part 
  

   nearest 
  the 
  body 
  of 
  the 
  tegmen, 
  and 
  the 
  apex 
  is 
  the 
  free 
  

   end 
  ; 
  and 
  the 
  base 
  of 
  the 
  tegminal 
  strut 
  is 
  where 
  it 
  joins 
  

   the 
  tegmen, 
  and 
  the 
  apex 
  is 
  the 
  free 
  end; 
  the 
  apex 
  of 
  the 
  

   median 
  lobe 
  is 
  the 
  free 
  end, 
  and 
  the 
  base 
  of 
  the 
  internal 
  

   sac 
  is 
  where 
  it 
  joins 
  the 
  median 
  lobe. 
  The 
  terms 
  anterior 
  

   or 
  cephahc 
  and 
  posterior 
  or 
  caudal 
  are 
  relative 
  to 
  the 
  head 
  

   and 
  tail, 
  hence 
  the 
  anterior 
  margin 
  of 
  a 
  thoracic 
  segment 
  

  

  * 
  " 
  Cambridge 
  Natural 
  History," 
  V, 
  " 
  Insects," 
  I, 
  p. 
  112, 
  fig. 
  62. 
  

   TRANS. 
  ENT. 
  SOC. 
  LOND. 
  1919. 
  — 
  PARTS 
  III, 
  IV. 
  (dEC.) 
  

  

  