﻿234 
  Mr. 
  R. 
  C. 
  L. 
  Perkins 
  on 
  

  

  between 
  host 
  and 
  parasite 
  are 
  not 
  infrequent, 
  but 
  that 
  

   they 
  occur 
  in 
  the 
  burrow 
  itself 
  and 
  are 
  rarely 
  observed 
  in 
  

   consequence. 
  The 
  fight 
  between 
  Halictus 
  and 
  Sphecodes 
  

   observed 
  by 
  me 
  was 
  begun 
  there, 
  and 
  Shuckard 
  says 
  of 
  

   Anthophora 
  : 
  "if 
  they 
  catch 
  the 
  intruder 
  " 
  (Melecta) 
  

   "in 
  her 
  invasion, 
  they 
  will 
  draw 
  her 
  forth 
  and 
  deUver 
  

   battle 
  with 
  great 
  fury." 
  The 
  Hedychnmi 
  alluded 
  to 
  

   above 
  was 
  caught 
  in 
  the 
  burrow 
  by 
  its 
  host. 
  It 
  must 
  

   often 
  happen 
  that 
  the 
  rightful 
  owner 
  of 
  the 
  burrow 
  comes 
  

   home 
  and 
  surprises 
  the 
  parasite 
  within, 
  but 
  what 
  takes 
  

   place 
  beneath 
  the 
  surface, 
  in 
  which 
  the 
  burrow 
  is 
  formed, 
  

   is, 
  except 
  in 
  special 
  instances, 
  as 
  cited 
  above, 
  quite 
  un- 
  

   certain. 
  The 
  niain 
  object 
  of 
  the 
  parasite 
  must 
  be 
  a 
  safe 
  

   escape, 
  and 
  one 
  may 
  suppose 
  that 
  the 
  hardness 
  of 
  the 
  

   cuticle 
  helps 
  to 
  ensure 
  this. 
  It 
  is 
  said 
  that 
  in 
  the 
  case 
  of 
  

   Nomada 
  sexfasciata 
  and 
  its 
  host 
  Eucera 
  the 
  latter 
  gives 
  

   way 
  to 
  the 
  parasite, 
  but 
  accurate 
  and 
  detailed 
  information 
  

   on 
  such 
  points 
  is 
  much 
  wanted. 
  It 
  seems 
  improbable 
  

   that 
  any 
  host 
  would 
  tolerate 
  an 
  interference 
  with 
  the 
  

   performance 
  of 
  its 
  labour. 
  It 
  is 
  certain 
  that 
  the 
  parasites 
  

   exhibit 
  care 
  or 
  caution 
  in 
  entering 
  the 
  burrows, 
  for 
  one 
  

   often 
  notices 
  many 
  of 
  our 
  Nomadas 
  hovering 
  over 
  the 
  

   openings 
  for 
  some 
  time 
  before 
  they 
  determine 
  to 
  enter, 
  

   or 
  pass 
  on 
  to 
  investigate 
  another 
  burrow. 
  It 
  would 
  appear 
  

   that 
  either 
  they 
  wish 
  to 
  ascertain 
  the 
  presence 
  or 
  absence 
  

   of 
  the 
  maker, 
  or 
  else 
  perhaps, 
  by 
  some 
  unknown 
  means, 
  

   to 
  learn 
  the 
  condition 
  of 
  the 
  contents 
  of 
  the 
  burrow, 
  as 
  to 
  

   its 
  fitness 
  or 
  readiness 
  for 
  the 
  reception 
  of 
  an 
  egg. 
  Whether 
  

   the 
  odours 
  of 
  the 
  Nomadae 
  and 
  other 
  parasites 
  play 
  any 
  

   part 
  in 
  the 
  event 
  of 
  collision 
  between 
  them 
  and 
  their 
  

   hosts, 
  or 
  whether 
  they 
  are 
  otherwise 
  protective, 
  e.g., 
  

   against 
  predaceous 
  creatures, 
  or, 
  again, 
  are 
  only 
  of 
  sexual 
  

   significance 
  we 
  have 
  no 
  evidence. 
  

  

  In 
  the 
  case 
  of 
  the 
  conflict 
  between 
  Halictus 
  and 
  Sphecodes 
  

   observed 
  by 
  me, 
  it 
  would 
  appear 
  that 
  the 
  latter 
  was 
  the 
  

   aggressor, 
  but 
  this 
  may 
  only 
  have 
  been 
  apparent 
  and 
  not 
  

   really 
  the 
  case. 
  When 
  the 
  female 
  Psithyrus 
  insinuates 
  

   itself 
  into 
  the 
  nest 
  of 
  Bombus, 
  it 
  is 
  probable 
  that 
  the 
  

   beginning 
  of 
  the 
  actual 
  combat 
  may 
  be 
  due 
  to 
  either 
  one 
  

   of 
  them 
  according 
  to 
  circumstances, 
  but 
  the 
  harder 
  

   Psithyrus 
  is 
  assumed 
  to 
  be 
  generally 
  victorious. 
  

  

  It 
  is 
  a 
  notorious 
  fact 
  that 
  in 
  many 
  cases 
  the 
  number 
  

   of 
  individuals 
  of 
  a 
  parasite 
  compared 
  with 
  that 
  of 
  the 
  

   host 
  varies 
  extremely 
  in 
  different 
  seasons. 
  Thus 
  one 
  year 
  

  

  