﻿6 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  67 
  

  

  show 
  a 
  sharp 
  constriction 
  indicating 
  a 
  division 
  into 
  two 
  segments. 
  

   The 
  endopodite 
  of 
  the 
  second 
  maxilliped 
  is 
  significantly 
  enlarged. 
  

   The 
  third 
  maxillipeds 
  and 
  the 
  remaining 
  thoracic 
  appendages 
  are 
  

   more 
  prominent. 
  

  

  Abdomen. 
  — 
  The 
  telson 
  is 
  now 
  divided 
  from 
  the 
  sixth 
  abdominal 
  

   segment. 
  Each 
  segment 
  except 
  the 
  first 
  shows 
  a 
  pair 
  of 
  buds 
  — 
  the 
  

   abdominal 
  appendages. 
  The 
  lateral 
  spines 
  on 
  the 
  third, 
  fourth, 
  and 
  

   fifth 
  segments 
  are 
  further 
  prolonged. 
  A 
  fourth 
  median 
  spine 
  ap- 
  

   pears 
  on 
  each 
  cornu 
  of 
  the 
  telson 
  (fig. 
  74). 
  

  

  fourth 
  zoea 
  (figs. 
  49 
  and 
  SO) 
  

  

  The 
  fourth 
  and 
  last 
  zoea 
  is 
  larger 
  and 
  heavier 
  and 
  correspondingly 
  

   clumsier. 
  It 
  is 
  found 
  most 
  commonly 
  on 
  the 
  bottom, 
  where 
  it 
  swims 
  

   spasmodically 
  upward 
  toward 
  the 
  light 
  at 
  intervals, 
  but 
  in 
  the 
  main 
  

   is 
  rolled 
  along 
  by 
  the 
  sweep 
  of 
  the 
  tides. 
  

  

  Cephalothorax. 
  — 
  The 
  body 
  is 
  now 
  appreciably 
  increased 
  in 
  weight 
  

   while 
  the 
  spines 
  are 
  scarcely 
  longer 
  than 
  in 
  the 
  previous 
  stage. 
  

  

  Cephalic 
  appendages. 
  — 
  The 
  basal 
  portion 
  of 
  the 
  antennule 
  (fig. 
  40) 
  

   is 
  now 
  swollen 
  and 
  partially 
  separated 
  from 
  the 
  distal 
  region 
  by 
  a 
  

   deep 
  constriction. 
  The 
  beginning 
  of 
  the 
  statocyst 
  appears 
  in 
  the 
  

   swollen 
  part. 
  The 
  tip 
  of 
  the 
  antennule 
  is 
  divided 
  into 
  two 
  rami. 
  

   The 
  inner 
  ramus 
  bears 
  five 
  or 
  six 
  sensory 
  hairs; 
  the 
  outer 
  is 
  a 
  short 
  

   blunt 
  bud. 
  The 
  flagellar 
  bud 
  of 
  the 
  antenna 
  (fig. 
  63) 
  is 
  elongated. 
  

   Its 
  cuticle 
  is 
  not 
  segmented 
  but 
  the 
  internal 
  fleshy 
  part 
  shows 
  four 
  or 
  

   five 
  segments 
  distally. 
  The 
  mandible 
  (fig. 
  44) 
  now 
  shows 
  the 
  anlage 
  

   of 
  its 
  palp 
  as 
  a 
  simple 
  bud. 
  

  

  Thoracic 
  appendages. 
  — 
  There 
  are 
  now 
  twelve 
  swimming 
  hairs. 
  

   The 
  third 
  maxilliped 
  is 
  well-developed 
  although 
  slender 
  and 
  weak 
  

   in 
  comparison 
  with 
  the 
  first 
  and 
  second. 
  Its 
  exopodite 
  carries 
  a 
  

   few 
  hairs 
  distally. 
  Its 
  endopodite 
  shows 
  indications 
  of 
  five 
  seg- 
  

   ments. 
  The 
  pereiopods 
  are 
  large 
  and, 
  although 
  they 
  are 
  short, 
  all 
  of 
  

   their 
  segments 
  are 
  clearly 
  marked. 
  A 
  number 
  of 
  gill 
  buds 
  are 
  dis- 
  

   tinguishable 
  at 
  this 
  stage 
  as 
  follows: 
  One 
  on 
  the 
  third 
  maxilliped, 
  

   two 
  on 
  the 
  cheliped, 
  and 
  one 
  on 
  each 
  of 
  the 
  second 
  and 
  third 
  pereio- 
  

   pods. 
  

  

  Abdomen. 
  — 
  The 
  lateral 
  spines 
  and 
  the 
  cornua 
  of 
  the 
  telson 
  (fig. 
  

   75) 
  now 
  reach 
  their 
  maximum 
  development. 
  The 
  buds 
  of 
  the 
  ab- 
  

   dominal 
  appendages 
  are 
  elongated 
  and 
  cleft 
  into 
  exopodite 
  and 
  mi- 
  

   nute 
  endopodite. 
  

  

  megalops 
  (figs. 
  76 
  and 
  77) 
  

  

  According 
  to 
  Birge, 
  there 
  are 
  at 
  least 
  four 
  molts 
  during 
  the 
  

   megalops 
  stage. 
  The 
  changes 
  at 
  each 
  molt 
  are 
  slight, 
  however. 
  The 
  

   megalops 
  is 
  an 
  active 
  and 
  powerful 
  swimmer. 
  It 
  occurs 
  most 
  com- 
  

   monty 
  at 
  the 
  surface, 
  but 
  may 
  be 
  taken 
  near 
  the 
  bottom. 
  As 
  its 
  

  

  