﻿408 
  Mr. 
  Frederick 
  Muir 
  on 
  the 
  

  

  The 
  second 
  line 
  of 
  development, 
  the 
  elongation 
  of 
  the 
  

   tubular 
  median 
  lobe 
  (the 
  Phytophagoidea 
  type), 
  necessitates 
  

   a 
  greater 
  or 
  lesser 
  amount 
  of 
  play 
  between 
  the 
  median 
  lobe 
  

   and 
  the 
  tegmen. 
  The 
  limit 
  to 
  the 
  length 
  of 
  a 
  stiff, 
  chitinous 
  

   median 
  lobe 
  is 
  soon 
  reached 
  on 
  account 
  of 
  its 
  want 
  of 
  

   fiexibihty, 
  but 
  this 
  is 
  overcome 
  by 
  a 
  portion 
  becoming 
  

   membranous 
  and 
  thus 
  capable 
  of 
  folding 
  up. 
  When 
  the 
  

   sac 
  is 
  shorter, 
  or 
  but 
  httle 
  longer, 
  than 
  the 
  median 
  lobe 
  

   the 
  retractor 
  muscles 
  can 
  ply 
  between 
  the 
  sac 
  and 
  the 
  median 
  

   lobe, 
  but 
  when 
  the 
  sac 
  becomes 
  much 
  longer 
  than 
  the 
  

   median 
  lobe 
  this 
  method 
  of 
  invagination 
  would 
  lead 
  to 
  a 
  

   great 
  crumpling 
  up 
  of 
  the 
  sac. 
  This 
  problem 
  is 
  met 
  by 
  

   one 
  or 
  two 
  areas 
  on 
  the 
  median 
  lobe, 
  to 
  which 
  the 
  retractor 
  

   muscles 
  actuating 
  the 
  sac 
  are 
  attached, 
  becoming 
  invagin- 
  

   ated, 
  lengthened 
  and 
  chitinised. 
  In 
  this 
  method 
  the 
  median 
  

   struts 
  arise 
  which 
  reach 
  a 
  wonderful 
  state 
  of 
  perfection 
  and 
  

   slenderness 
  in 
  some 
  of 
  the 
  Rhynchophora 
  ; 
  in 
  the 
  Longicorns 
  

   the 
  struts 
  are 
  long, 
  wide 
  and 
  flat 
  (a 
  state 
  also 
  found 
  in 
  the 
  

   Brenthidae). 
  In 
  this 
  type 
  the 
  tegmen 
  is 
  reduced 
  to 
  a 
  

   more 
  or 
  less 
  slender 
  ring 
  and 
  a 
  strut, 
  or 
  even 
  to 
  a 
  Y 
  ; 
  the 
  

   tegminal 
  lobes 
  are 
  found 
  in 
  every 
  condition 
  from 
  large 
  

   (Longicorns, 
  Brenthids) 
  to 
  total 
  absence. 
  

  

  The 
  third 
  type 
  (the 
  Melolonthid) 
  is 
  not 
  so 
  uniform 
  as 
  the 
  

   other 
  two, 
  but 
  equally 
  worthy 
  of 
  notice. 
  In 
  this 
  type 
  the 
  

   median 
  lobe 
  is 
  greatly 
  reduced 
  and 
  the 
  tegmen 
  is 
  formed 
  into 
  

   a 
  more 
  or 
  less 
  complete 
  tube. 
  It 
  is 
  found 
  in 
  the 
  Scara- 
  

   baeidae 
  and 
  in 
  certain 
  Tenebrionidae. 
  Every 
  degree 
  in 
  size 
  

   of 
  the 
  sac 
  is 
  found 
  among 
  these 
  forms. 
  

  

  In 
  the 
  Staphylinid 
  type, 
  as 
  we 
  have 
  already 
  stated, 
  there 
  

   is 
  an 
  automatons 
  bulb 
  with 
  a 
  small 
  foramen, 
  which 
  by 
  

   contraction 
  can 
  exert 
  blood 
  pressure 
  upon 
  the 
  sac. 
  In 
  the 
  

   Phytophagoidea 
  and 
  Melolonthid 
  types 
  there 
  is 
  no 
  such 
  

   development 
  of 
  the 
  median 
  lobe, 
  and 
  the 
  median 
  orifice 
  is 
  

   large. 
  The 
  blood 
  pressure 
  must 
  therefore 
  be 
  brought 
  about 
  

   by 
  some 
  other 
  mechanism. 
  In 
  the 
  Phytophagoidea 
  type, 
  and 
  

   in 
  many 
  of 
  the 
  Melolonthids, 
  this 
  is 
  most 
  likely 
  effected 
  by 
  

   the 
  reduction 
  of 
  the 
  abdominal 
  cavity, 
  either 
  by 
  the 
  con- 
  

   traction 
  of 
  the 
  abdominal 
  walls 
  or 
  by 
  the 
  distention 
  of 
  the 
  

   air 
  sacs 
  in 
  the 
  abdomen, 
  or 
  by 
  a 
  combination 
  of 
  the 
  two. 
  

  

  In 
  Melolontha 
  vulgaris 
  Straus-Durckheim 
  describes 
  and 
  

   figures 
  some 
  large 
  muscles, 
  which 
  he 
  styles 
  " 
  les 
  deux 
  chefs 
  

   du 
  constricteur 
  du 
  canal 
  ejaculatoire." 
  In 
  an 
  Anomala 
  

   which 
  I 
  have 
  examined 
  these 
  form 
  a 
  large 
  bulb 
  of 
  circular 
  

   muscles 
  at 
  the 
  base 
  of 
  the 
  median 
  lobe, 
  the 
  basal 
  edge 
  

  

  