﻿aet. 
  3 
  STUDIES 
  ON 
  LARVAE 
  OF 
  CRABS 
  HYMAN 
  7 
  

  

  final 
  molt 
  approaches 
  it 
  seeks 
  a 
  crevice 
  in 
  some 
  shell 
  or 
  stone 
  near 
  

   the 
  tide 
  line. 
  

  

  C 
  ephalotherax. 
  — 
  An 
  astonishing 
  change 
  in 
  the 
  form 
  of 
  the 
  cara- 
  

   pace 
  occurs 
  when 
  the 
  zoea 
  changes 
  to 
  the 
  megalops. 
  The 
  dorsal 
  and 
  

   lateral 
  spines 
  disappear 
  completely. 
  The 
  frontal 
  spine 
  remains 
  as 
  

   a 
  short, 
  notched 
  projection 
  anteriorly. 
  It 
  is 
  quite 
  inconspicuous. 
  

   The 
  whole 
  cephalothorax 
  is 
  now 
  depressed 
  rather 
  than 
  compressed. 
  

  

  Cephalic 
  appendages. 
  — 
  The 
  antennule 
  (fig. 
  81) 
  now 
  acquires 
  very 
  

   nearly 
  its 
  permanent 
  form. 
  The 
  basal 
  part 
  is 
  composed 
  of 
  four 
  

   large 
  segments. 
  The 
  most 
  proximal 
  of 
  these 
  is 
  swollen 
  and 
  con- 
  

   tains 
  the 
  statocyst. 
  The 
  bud 
  of 
  the 
  outer 
  flagellum 
  is 
  elongated 
  and 
  

   separated 
  from 
  the 
  basal 
  segments 
  by 
  a 
  joint. 
  It 
  carries 
  a 
  few 
  hairs 
  

   at 
  its 
  tip. 
  The 
  inner 
  flagellum 
  arises 
  from 
  the 
  tip 
  of 
  the 
  distal 
  

   segment 
  of 
  the 
  basal 
  portion. 
  It 
  is 
  composed 
  of 
  two 
  or 
  three 
  seg- 
  

   ments, 
  each 
  bearing 
  several 
  hairs. 
  

  

  The 
  antenna 
  (fig. 
  83) 
  now 
  assumes 
  practically 
  the 
  adult 
  condi- 
  

   tion. 
  It 
  is 
  composed 
  of 
  a 
  basal 
  portion 
  of 
  three 
  large 
  segments 
  and 
  

   a 
  distal 
  flagellum 
  of 
  about 
  nine 
  segments. 
  

  

  The 
  mandible 
  (fig. 
  85) 
  is 
  completely 
  formed. 
  Its 
  palp 
  shows 
  

   three 
  segments. 
  

  

  The 
  maxillule 
  (fig. 
  88) 
  changes 
  considerably. 
  The 
  two 
  lobes 
  of 
  

   the 
  basal 
  portion 
  become 
  greatly 
  elongated. 
  The 
  distal 
  part 
  loses 
  

   its 
  joint, 
  becomes 
  flattened, 
  and 
  is 
  bent 
  sharply 
  outward. 
  

  

  The 
  changes 
  in 
  the 
  maxilla 
  (fig. 
  91) 
  are 
  similar 
  to 
  those 
  of 
  the 
  

   maxillule, 
  although 
  not 
  so 
  pronounced. 
  The 
  basal 
  lobes 
  are 
  elon- 
  

   gated 
  and 
  the 
  distal 
  part 
  becomes 
  a 
  flattened 
  plate 
  bent 
  slightly 
  

   outward. 
  

  

  Thoracic 
  appendages. 
  — 
  The 
  maxillipeds 
  all 
  undergo 
  profound 
  

   changes. 
  On 
  the 
  first 
  maxilliped 
  (fig. 
  94) 
  there 
  appears 
  a 
  large 
  

   epipodite 
  for 
  the 
  first 
  time. 
  The 
  basipodite 
  is 
  produced 
  into 
  three 
  

   or 
  four 
  lobes 
  along 
  its 
  median 
  margin 
  and 
  is 
  much 
  enlarged. 
  The 
  

   exopodite 
  loses 
  its 
  joint, 
  but 
  is 
  permanently 
  flexed 
  medially 
  at 
  that 
  

   point. 
  Its 
  hairs 
  are 
  reduced 
  to 
  four 
  or 
  five 
  and 
  these 
  are 
  small. 
  The 
  

   endopodite 
  loses 
  its 
  joints 
  and 
  becomes 
  a 
  flattened 
  plate 
  with 
  few 
  

   hairs. 
  The 
  appendage 
  has 
  lost 
  its 
  locomotor 
  function 
  and 
  becomes 
  

   an 
  organ 
  of 
  mastication 
  with, 
  possibly, 
  some 
  sensory 
  function. 
  

  

  The 
  second 
  maxilliped 
  (fig. 
  97) 
  is 
  changed 
  much 
  like 
  the 
  first. 
  Its 
  

   epipodite 
  appears. 
  Its 
  basipodite 
  forms 
  obscure 
  median 
  lobes, 
  but 
  

   is 
  only 
  slightly 
  enlarged. 
  The 
  changes 
  in 
  the 
  exopodite 
  are 
  like 
  

   those 
  in 
  the 
  first 
  maxilliped 
  but 
  the 
  retrogression 
  is 
  not 
  so 
  great. 
  

   The 
  endopodite 
  becomes 
  four-segmented 
  and 
  flattened. 
  

  

  The 
  third 
  maxilliped 
  (fig. 
  100) 
  is 
  greatly 
  enlarged, 
  becoming 
  the 
  

   most 
  robust 
  of 
  the 
  three. 
  It 
  has 
  a 
  large 
  epipodite. 
  Its 
  basipodite 
  

   is 
  scarcely 
  larger. 
  The 
  exopodite 
  is 
  similar 
  to 
  that 
  of 
  the 
  other 
  

  

  