﻿174 
  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  They 
  are 
  usually 
  pyriform, 
  having 
  a 
  process 
  emerging 
  from 
  

   the 
  pointed 
  end, 
  which 
  process 
  is 
  directed 
  radially, 
  i. 
  e. 
  towards 
  

   the 
  inner 
  surface, 
  thus 
  differing 
  from 
  the 
  corresponding 
  cells 
  

   in 
  the 
  Plagiostomata, 
  where 
  the 
  corresponding 
  cells 
  send 
  pro- 
  

   cesses 
  in 
  a 
  transverse 
  direction 
  towards 
  the 
  outer 
  side. 
  There 
  

   also 
  occur 
  others 
  which 
  have 
  a 
  fusiform 
  shape 
  ; 
  these 
  send 
  a 
  

   process 
  from 
  each 
  end, 
  one 
  being 
  larger 
  than 
  the 
  other. 
  The 
  

   fusiform 
  specimens 
  are 
  found 
  in 
  the 
  part 
  of 
  the 
  ganglion 
  which 
  

   is 
  situated 
  close 
  to 
  the 
  inner 
  edge, 
  while 
  the 
  pyriform 
  ones 
  

   are 
  found 
  near 
  the 
  outer 
  edge. 
  Their 
  size 
  varies 
  between 
  

   82 
  /i 
  long 
  by 
  4 
  jj, 
  broad 
  and 
  60 
  fi 
  long 
  by 
  5 
  jjl 
  broad. 
  

  

  These 
  cells 
  resemble 
  the 
  cells 
  of 
  the 
  ventral 
  ganglion 
  of 
  the 
  

   spinal 
  cord 
  as 
  to 
  the 
  nuclei 
  and 
  nucleoli, 
  though 
  differing 
  

   much 
  in 
  shape. 
  The 
  nuclei 
  are 
  more 
  deeply 
  stained 
  than 
  the 
  

   cell-contents, 
  and 
  the 
  nucleoli 
  have 
  a 
  clear 
  space 
  round 
  them. 
  

   Occasionally 
  these 
  cells 
  exhibit 
  two 
  nucleoli, 
  which 
  are 
  situa- 
  

   ted 
  a 
  short 
  distance 
  apart 
  ; 
  in 
  this 
  case 
  the 
  clear 
  space 
  is 
  

   single 
  but 
  elongated 
  in 
  shape, 
  and 
  meanwhile 
  the 
  nucleus 
  

   remains 
  unaffected 
  ; 
  whether 
  these 
  were 
  cases 
  of 
  cell-division 
  

   I 
  could 
  not 
  determine, 
  the 
  staining-fluid 
  employed 
  not 
  showing 
  

   any 
  pattern 
  of 
  karyokinesis. 
  

  

  A 
  ganglion 
  containing 
  cells 
  which 
  resemble 
  these 
  in 
  form 
  

   and 
  position 
  are 
  found 
  in 
  the 
  corpora 
  quadrigemina 
  of 
  Echidna. 
  

   This 
  fact 
  gives 
  an 
  additional 
  argument 
  in 
  favour 
  of 
  the 
  theory 
  

   that 
  the 
  optic 
  lobes 
  of 
  fishes 
  homologize 
  with 
  the 
  corpora 
  

   quadrigemina 
  of 
  Mammals 
  ; 
  as 
  these 
  bodies 
  in 
  Echidna 
  are 
  

   undoubtedly 
  the 
  same 
  as 
  in 
  the 
  Mammalia, 
  so 
  if 
  the 
  former 
  

   correspond 
  to 
  the 
  optic 
  lobes 
  in 
  fishes, 
  the 
  latter 
  must 
  do 
  so 
  

   also, 
  since 
  things 
  that 
  are 
  equal 
  to 
  the 
  same 
  are 
  equal 
  to 
  each 
  

   other. 
  

  

  At 
  the 
  posterior 
  part 
  of 
  the 
  optic 
  lobe 
  there 
  is 
  a 
  proble- 
  

   matical 
  body 
  (PI. 
  XII. 
  fig. 
  8, 
  d) 
  which 
  I 
  have 
  not 
  met 
  with 
  

   elsewhere 
  ; 
  it 
  is 
  situated 
  at 
  the 
  outer 
  and 
  lower 
  edge 
  of 
  the 
  

   lobe, 
  where 
  it 
  forms 
  a 
  swelling 
  apparently 
  attached 
  to 
  the 
  

   outer 
  side 
  of 
  the 
  lobe, 
  from 
  which 
  it 
  is 
  distinct. 
  It 
  consists 
  

   of 
  small 
  spherical 
  cells 
  imbedded 
  in 
  a 
  network 
  with 
  large 
  

   meshes 
  composed 
  of 
  fibrils 
  ; 
  its 
  signification 
  is 
  not 
  apparent, 
  

   but 
  it 
  appears 
  to 
  be 
  connected 
  with 
  the 
  transverse 
  commissure 
  

   of 
  the 
  medulla 
  oblongata. 
  

  

  Cerebellum. 
  

  

  The 
  cerebellum 
  (PI. 
  XIII. 
  fig. 
  10) 
  has 
  a 
  structure 
  corre- 
  

   sponding 
  to 
  that 
  found 
  in 
  Plagiostomata 
  and 
  Teleostei, 
  and, 
  

   indeed, 
  of 
  the 
  whole 
  vertebrate 
  kingdom. 
  

  

  