﻿16 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  6T 
  

  

  describe 
  them. 
  Couch 
  simply 
  states 
  that 
  P. 
  hirtellus 
  hatches 
  as 
  

   a 
  zoea. 
  The 
  following 
  descriptions 
  are 
  based 
  on 
  Cano. 
  

  

  FIRST 
  ZOEA 
  (fig. 
  177) 
  

  

  The 
  zoea 
  of 
  Pilumnus 
  is 
  distinguished 
  by 
  its 
  slender 
  rostral 
  spine 
  

   and 
  relatively 
  large 
  antenna. 
  The 
  buds 
  of 
  all 
  the 
  thoracic 
  append- 
  

   ages 
  are 
  present 
  and 
  that 
  of 
  the 
  third 
  maxilliped 
  is 
  obviously 
  bira- 
  

   mous. 
  

  

  Cephalic 
  appendages. 
  — 
  The 
  antennule 
  (fig. 
  183) 
  has 
  the 
  usual 
  

   conical 
  form. 
  The 
  antenna 
  (fig. 
  183) 
  is 
  nearly 
  twice 
  as 
  long 
  as 
  the 
  

   small 
  rostral 
  spine. 
  The 
  exopodite 
  is 
  as 
  long 
  as 
  the 
  antennal 
  spine 
  

   and 
  bears 
  a 
  lateral 
  hair 
  near 
  its 
  tip. 
  The 
  remaining 
  cephalic 
  ap- 
  

   pendages 
  are 
  typical. 
  

  

  Thoracic 
  appendages 
  and 
  abdomen. 
  — 
  The 
  first 
  and 
  second 
  maxilli- 
  

   peds 
  are 
  typical. 
  The 
  third 
  maxilliped 
  and 
  the 
  pereiopods 
  are 
  pre- 
  

   cociously 
  developed. 
  The 
  buds 
  are 
  all 
  large 
  and 
  that 
  of 
  the 
  third 
  

   maxilliped 
  is 
  biramous. 
  The 
  telson 
  (fig. 
  192) 
  has 
  three 
  median 
  

   spines, 
  two 
  lateral 
  spines 
  — 
  one 
  very 
  minute 
  — 
  and 
  one 
  dorsal 
  spine 
  

   on 
  each 
  cornu. 
  

  

  SECOND 
  ZOEA 
  (fig. 
  178) 
  

  

  The 
  second 
  zoea 
  shows 
  the 
  usual 
  changes. 
  There 
  are 
  six 
  swim- 
  

   ming 
  hairs 
  on 
  each 
  maxilliped. 
  The 
  gill 
  buds 
  have 
  appeared 
  on 
  the 
  

   thoracic 
  appendages. 
  Cano 
  does 
  not 
  give 
  a 
  detailed 
  description 
  of 
  

   the 
  stage. 
  

  

  THIRD 
  ZOEA 
  

  

  Cano 
  seems 
  to 
  have 
  overlooked 
  the 
  third 
  zoeal 
  stage. 
  His 
  third 
  

   stage 
  apparently 
  is 
  the 
  fourth 
  zoea. 
  

  

  FOURTH 
  ZOEA 
  (fig. 
  179) 
  

  

  The 
  fourth 
  zoea 
  has 
  ten 
  to 
  twelve 
  swimming 
  hairs, 
  six 
  abdominal 
  

   segments, 
  and 
  biramous 
  pleopods. 
  

  

  Cephalic 
  appendages. 
  — 
  The 
  antennule 
  (fig. 
  184) 
  now 
  has 
  a 
  swollen 
  

   basal 
  segment 
  for 
  the 
  statocyst. 
  The 
  inner 
  of 
  the 
  two 
  distal 
  rami 
  

   shows 
  several 
  constrictions 
  and 
  bears 
  several 
  sensory 
  hairs; 
  the 
  outer 
  

   is 
  a 
  simple 
  bud. 
  The 
  antenna 
  (fig. 
  184) 
  shows 
  an 
  endopodite 
  that 
  

   nearly 
  equals 
  its 
  spine 
  in 
  length. 
  

  

  Thoracic 
  appendages 
  and 
  abdomen. 
  — 
  The 
  third 
  maxilliped 
  and 
  

   pereiopods 
  are 
  greatly 
  enlarged 
  and 
  all 
  their 
  segments 
  are 
  differen- 
  

   tiated. 
  The 
  pleopods, 
  except 
  that 
  of 
  the 
  sixth 
  segment, 
  are 
  bifur- 
  

   cated. 
  The 
  telson 
  (fig. 
  193) 
  is 
  somewhat 
  larger 
  than 
  in 
  earlier 
  

   stages 
  but 
  otherwise 
  is 
  not 
  changed. 
  

  

  FIRST 
  MEGALOPS 
  (fig. 
  180) 
  

  

  The 
  rostral 
  spine 
  leaves 
  a 
  slight 
  remnant. 
  The 
  thoracic 
  appen- 
  

   dages 
  reach 
  what 
  is 
  practically 
  the 
  adult 
  condition. 
  The 
  abdominal 
  

  

  