ME.  C.  SPENCE  BATE  ON  THE  DEVELOPMENT  OF  DECAPOD  CEUSTACEA.  603 
Perceiving  that  in  its  passage  to  maturity  the  larva  of  Carcinus  passes  through  forms 
that  are  known  to  be  adult,  it  is  legitimate  to  infer  that  those  forms  hold  a lower  grade 
in  the  rank  of  perfect  animals  than  the  adult  Carcinus.  When  it  first  exhibits  con- 
ditions that  approximate  to  the  decapod  character,  it  bears  a very  close  resemblance  to  the 
triangular  BracJiyura.  This  gradually  disappears  with  the  development  of  the  hepatic 
regions,  and  the  constantly  increasing  resemblance  to  the  form  of  the  adult. 
The  Leptopodiadce  have  generally  been  ranked  by  carcinologists  as  the  highest  of  the 
crustacean  type ; but  the  similarity  of  their  appearance  to  an  immature  form  of  the 
young  Carcinus.,  is  a circumstance  that  must  induce  the  philosophical  naturalist  to  recon- 
sider the  subject.  It  is  not  without  a knowledge  of  the  facts  upon  which  zoologists 
have  adopted  the  arrangement,  that  the  above  remark  is  made. 
Carcinologists  generally  admit  that  consolidation  of  the  nervous  system  is  a marked 
elevation  in  the  character  of  the  animal,  and  Professor  Dana  has  enunciated  the  doctrine, 
that  “ a centralization  of  the  nervous  ganglia  is  true  cephalization.” 
It  is  true  that  in  the  Spider-crabs  there  exists  no  hollow  space  in  the  centre  of  the 
consolidated  gangha ; but  those  which  are  thus  consolidated  homologize  with  the  sepa- 
rate ganglia  that  supply  the  limbs  of  the  animal  with  nerves,  not  with  those  ganglia  that 
supply  the  organs  that  are  endowed  with  the  power  of  sensation. 
This  idea  receives  support  from  the  known  characters  of  the  respective  animals.  The 
Portunidce,  of  which  the  Carcinus  is  placed  as  the  highest  form,  are  active  and  vivacious 
creatures,  whereas  the  Leptopodiadce  are  inanimate  and  sluggish,  fulfilling  in  their  habits 
the  existence  of  the  faku’s  of  eastern  tradition ; they  continue  so  long  without  move- 
ment, that  weeds  take  root  upon  their  surface,  the  growth  of  which  prevents  them  from 
being  distinguished  from  the  surrounding  objects. 
Again,  the  general  littoral  character  of  the  Portunidce,  and  of  Carcinus  in  particular — 
which  differs  not  widely  in  form  from  the  terrestrial  Gegarcinus — together  with  the  fact 
that  all  the  Leptopodiadm  are  deep-sea  genera,  is  in  accordance  with  the  doctrine  laid 
down  by  Professor  Agassiz,  that  all  land  and  freshwater  animals  assume  a higher  and 
more  perfect  form  than  their  allied  types  of  the  ocean. 
Description  op  the  Plates. 
Fig.  1.  The  eye. 
Fig.  2.  Anterior  antenna.  2'.  Internal  structure,  d.  Secondary  appendage. 
Fig.  3.  Posterior  antenna : — a.  Permanent  antenna,  g.  Squamiform  process,  h.  Styli- 
form  process. 
Fig.  4.  Mandibles ; Q.  of  Amphipoda.  [Talitrus.) 
Fig.  5.  Anterior  maxilla ; . Q.  of  Amphipoda. 
Fig.  6.  Posterior  maxilla. 
