﻿184 
  

  

  E. 
  RAY 
  LANKESTER. 
  

  

  chilaria 
  of 
  Limulus 
  (see 
  Figs. 
  13 
  and 
  20), 
  may 
  in 
  part 
  repre- 
  

   sent 
  in 
  the 
  adult 
  the 
  sternum 
  of 
  the 
  excalated 
  prfegenital 
  

   somite. 
  This 
  has 
  not 
  been 
  demonstrated 
  by 
  an 
  actual 
  following 
  

   out 
  of 
  the 
  development, 
  but 
  the 
  position 
  of 
  these 
  pieces, 
  and 
  

   the 
  fact 
  that 
  they 
  are 
  (in 
  Limulus) 
  supplied 
  by 
  an 
  independent 
  

  

  Fig. 
  24. 
  — 
  Diagrams 
  of 
  the 
  development 
  and 
  adult 
  structure 
  of 
  

   one 
  of 
  the 
  paired 
  central 
  eyes 
  of 
  a 
  Scorpion. 
  A, 
  early 
  condition 
  

   before 
  tlie 
  lens 
  is 
  deposited, 
  sliowing 
  the 
  folding 
  of 
  the 
  epidermic 
  

   cell-layer 
  into 
  three; 
  B, 
  diagram 
  sliowing 
  the 
  nature 
  of 
  this 
  infold- 
  

   ing; 
  C, 
  section 
  through 
  the 
  fully 
  formed 
  eye; 
  h, 
  epidermic 
  cell- 
  

   layer; 
  r, 
  the 
  retinal 
  portion 
  of 
  the 
  same 
  which, 
  owing 
  to 
  the 
  infold- 
  

   inof, 
  lies 
  between 
  _^/, 
  the 
  corneagen 
  or 
  lens-forming 
  portion, 
  and 
  pr, 
  

   the 
  post-retinal 
  or 
  capsular 
  portion 
  or 
  fold 
  ; 
  I, 
  cuticular 
  lens 
  ; 
  

   g, 
  line 
  separating 
  lens 
  from 
  the 
  lens-forming 
  or 
  corneagen 
  cells 
  of 
  

   the 
  epidermis; 
  n, 
  nerve-fibres; 
  rh, 
  rhabdomeres. 
  (From 
  Korschelt 
  

   and 
  Heider.) 
  How 
  the 
  inversion 
  of 
  the 
  nerve-end 
  cells 
  and 
  their 
  

   connection 
  with 
  the 
  nerve-fibres 
  is 
  to 
  be 
  reconciled 
  with 
  the 
  con- 
  

   dition 
  found 
  in 
  the 
  adult, 
  or 
  with 
  that 
  of 
  the 
  monostichous 
  eye, 
  has 
  

   not 
  hitherto 
  been 
  explained. 
  

  

  segmental 
  nerve, 
  favours 
  the 
  view 
  that 
  they 
  may 
  comprise 
  

   the 
  sternal 
  area 
  of 
  the 
  vanished 
  prasgenital 
  somite. 
  This 
  

   interpretation, 
  however, 
  of 
  the 
  " 
  metasternites 
  '^ 
  of 
  Limulus 
  

   and 
  Scorpio 
  is 
  opposed 
  by 
  the 
  co-existence 
  in 
  Thelyphonus 
  

   (Figs. 
  55, 
  57, 
  and 
  58) 
  of 
  a 
  similar 
  metasternite 
  with 
  a 
  complete 
  

   preegenital 
  somite. 
  Hansen 
  (10) 
  has 
  recognised 
  that 
  the 
  

  

  