ME.  C.  SPEJS^CE  BATE  ON  THE  DEVELOPMENT  OE  DECAPOD  OEUSTACEA.  595 
no  change  beyond  an  increase  in  their  general  size,  and  a little  in  the  relative  propor- 
tion of  the  appendages  to  the  base  on  which  they  are  supported,  and  the  addition  of  a 
few  hairs  to  the  extremity  of  each. 
We  come  now  to  that  portion  of  the  animal  in  which  the  greatest  amount  of  progress 
is  apparent.  In  the  first  stage  we  perceived  a series  of  sac-like  vesicles,  the  germs  of  the 
perdopoda,  which  have  since  been  gradually  produced  (Plate  XLI.  figs.  C,  10  to  14), 
probably  at  the  rate  of  a single  articulation  at  every  moult,  since  one  or  two  are  at  first 
perceived,  then  more,  and  lastly  the  entire  seven  (figs.  10,  11'  and  11").  At  the  base  of 
the  legs  the  future  branchiae  may  be  detected  in  the  form  of  simple  sacs.  The  anterior 
pair  exhibit  at  this  early  date  the  chelae  of  the  adult  organ. 
The  pleon  (Plate  XLI.  fig.  C")  exhibits  the  seven  segments  proper  to  the  adult. 
This  increase  appears  to  have  taken  place  by  the  bisection  of  the  posterior  segment, 
with  which  it  continues  in  close  connexion.  The  three  central  segments  have  at  the 
posterior  lateral  extremities  of  each  a strong  tooth-like  process,  and  upon  the  inferior 
sm’face  certain  oar-like  appendages — the  undeveloped  pleopoda.  These  rapidly  increase 
and  have  their  margins — those  which  are  anterior  being  the  earlier — furnished  with 
small  dots,  the  germs  of  the  future  cilia.  Upon  the  second  segment  (figs.  C'"  and  D",  16), 
the  two  strong  tooth-like  organs  projecting  anteriorly  and  externally  are  still  present. 
The  telson  (C"  and  D",  21),  or  last  segment,  has  lost  some  of  the  teeth  with  which 
the  external  margm  was  armed.  Internally  a few  small  hairs  are  added.  The  cleft 
between  these  appears  less  deep,  and  the  styliform  processes  not  quite  so  long. 
Plate  XLII.  fig.  E. — If  we  examine  the  growing  animal  after  a few  more  moults, 
when  it  has  increased  to  about  three  lines  in  length,  we  shall  find  its  outline  still  hold- 
ing a resemblance,  though  a less  close  one,  to  the  previous  appearance. 
The  form  of  the  carapax  scarcely  differs  except  in  the  shorter  relative  length  of  the 
anterior  and  dorsal  spines,  and  the  whole  animal  appears  stouter  and  more  robust.  The 
gnathopoda  cease  to  be  used  as  natatory  organs ; the  pereiopoda  are  more  fully  developed, 
and  assist  in  their  proper  capacity,  and  the  pleon  has  lost  its  forked  extremity. 
Upon  examimng  the  several  parts  in  detail,  the  organs  are  found  generally  to  have 
progressed.  The  anterior  antenna  (fig.  2)  differs  scarcely  from  that  in  the  adult.  The 
posterior  (fig.  3)  has  increased  in  length ; the  olfactory  organ  [a]  is  present  in  an 
immature  form,  and  the  appendages  proper  to  the  larval  state  are  lost.  The  7nandihle 
(fig.  4)  has  assumed  the  form  of  the  adult  organ,  and  the  appendage  is  present.  The 
mcujcilloe  (figs.  5 and  6)  have  progressed  a little,  but  still  retain  some  of  their  early  con- 
ditions. The  maxilliped  (fig.  7),  which  is  found  wanting  in  the  two  preceding  forms 
that  have  been  examined,  is  now  present,  and  differs  in  no  very  important  feature  from 
that  of  the  adult.  The  gnathopoda  (figs.  8 and  9)  have  considerably  progressed,  though 
they  have  not  yet  assumed  (particularly  the  posterior)  the  form  of  the  parent  organ. 
The  appendages  on  each  have  outgrown  the  basal  articulation,  which  latter  has  sunk 
into  an  unimportant  part.  The  first  two  joints  have  considerably  increased,  whereas  the 
others,  and  theii'  complementaiy  appendage,  appear  not  much  changed. 
