594  MU.  C.  SPENCE  BATE  ON  THE  DETELOP3IENT  OF  DECAPOD  C'EUSTACEA. 
long  slightly-curved  styliform  processes,  armed  upon  the  external  margin  with  two  or  thi-ee 
teeth.  Upon  the  inside,  near  the  base  of  each,  is  a small  lobe  that  supports  three  strong 
spinous  denticulated  hairs,  and  between  the  two  lobes  debouches  the  intestinal  canal. 
Having  traced  the  structure  of  the  individual  parts  of  the  laiwa  as  it  exists  immedi- 
ately upon  quitting  the  ovum,  our  next  object  will  be  to  compare  the  same  with  others 
of  later  growth.  Eepeated  moults,  probably  at  intervals  of  seven  or  eight  days,  succeed 
each  other,  producing  at  each  stage  but  little  change  to  the  eye  but  that  of  size.  K we 
examine  one  probably  a month  old  (Plate  XLI.  fig.  C),  it  "will  be  found  to  have  acquired 
no  distinct  feature  to  mark  it  generally  from  the  preceding.  It  has  attained  the  length 
of  two  lines,  that  is,  about  as  long  again  as  the  laiwa  when  it  quits  the  ovum.  Tire 
examination  of  individual  parts  will,  however,  exhibit  some  progress  in  the  development 
of  each  member  in  relation  to  the  whole. 
The  carapax  differs  not  from  that  of  the  younger  form,  except  that  certain  bead-like 
spots  noticeable  in  the  former  have  become  developed  into  hams  in  this.  These  exist 
mostly  upon  the  long  dorsal  process  and  the  posterior  margin  of  the  carapax.  The  eye 
has  become  more  distinctly  pedunculated,  and  appears  capable  of  independent  move- 
ment. The  anterior  antenna  (Plate  XLI.  fig.  C,  2)  has  the  number  of  auditory  cilia 
increased  from  two  to  eight  or  nine,  and  a small  process  [d)  is  discernible  near  the  base 
of  these  cilia,  which  is  evidently  the  secondary  filament  of  the  perfect  organ.  This  goes 
on  increasing  with  the  succeeding  moults.  The  stem  of  the  organ  exhibits  a joint  in  the 
middle  (Plate  XLI.  fig.  D,  2),  and  the  basal  articulation  considerably  increases  in  dia- 
meter, so  that  before  the  animal  throws  off  the  larval  condition,  the  anterior  antenna  has 
arrived  at  a point  of  development  approximating  to  the  character  of  the  adult  organ. 
The  second  or  posterior  antenna  (Plate  XLI.  fig.  3)  likewise  exliibits  signs  of  pro- 
gress. The  squamiform  [cj)  and  spinous  processes  (/?)  are  unchanged,  but  the  small  papilla 
at  their  base  has  increased,  first  to  a length  which  scarcely  equals  that  of  the  adjoming 
spine.  In  another  moult  it  becomes  longer  ( jf,  3").  So  it  continues  to  increase,  and  with 
it  distinct  articulations,  one  probably  being  added  at  every  moult. 
The  progress  in  the  next  succeeding  pair  (the  mandibles,  Plate  XLI.  D,  fig.  4)  is  ex- 
ternally so  little  as  to  be  scarcely  appreciable.  They  appear  more  powerful  in  general 
structure,  and  the  calcareous  tendon  and  internal  lever  process  can  be  detected  by  dis- 
section. 
The  first  pair  of  maxillae  (Plate  XLI.  D,  fig.  5)  have  more  cilia  developed  upon  the 
margins  of  each  plate ; and  a small  lash  (z)  (the  fiabella  of  the  adult  organ)  is  likeAUse 
present ; and  it  may  be  assumed,  from  the  much  greater  relative  size,  that  it  fulfils  a 
more  efficient  office  in  the  larva  than  in  the  adult. 
The  second  pair  of  maxillae  (Plate  XLI.  D,  fig.  6)  have  likewise  an  increased  number 
of  ciliated  hairs  developed  upon  the  margin  of  each  plate ; those  upon  the  fiabella  have 
increased  from  four  to  a considerable  number. 
The  next  succeeding  pair  are  still  undiscoverable  to  the  closest  observation. 
The  two  pairs  of  gnatliopoda  (Plate  XLI.  1),  figs.  8 and  9)  appear  to  have  undergone 
