﻿GIG 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [12] 
  

  

  or 
  even 
  nearly 
  colorless, 
  while 
  the 
  number 
  of 
  visual 
  elements 
  may 
  be 
  

   either 
  very 
  milch 
  less 
  or 
  very 
  much 
  greater 
  than 
  usual. 
  The 
  eyes 
  of 
  

   the 
  species 
  of 
  Glyphocranr/on 
  and 
  of 
  Benthonectcs 
  are 
  good 
  examples 
  of 
  

   well-developed 
  eyes 
  of 
  this 
  class. 
  In 
  many 
  cases 
  the 
  presence 
  of 
  light- 
  

   colored 
  pigment 
  is 
  accompanied 
  with 
  reduction 
  in 
  the 
  number 
  of 
  visual 
  

   elements 
  precisely 
  as 
  in 
  black 
  eyes, 
  Parapasiphae 
  sulcatifrons, 
  P. 
  cris- 
  

   tata, 
  Acanthephyra 
  microphthalma, 
  and 
  the 
  species 
  of 
  Hymenodora 
  being- 
  

   good 
  examples. 
  

  

  In 
  other 
  cases 
  there 
  are 
  apparently 
  radical 
  modifications 
  in 
  the 
  struct- 
  

   ural 
  elements 
  of 
  the 
  eye 
  without 
  manifest 
  obsolescence. 
  The 
  large 
  and 
  

   highly 
  developed 
  but 
  very 
  short-stalked 
  eyes 
  of 
  the 
  species 
  of 
  Glypho- 
  

   crangon, 
  apparently 
  specialized 
  for 
  use 
  in 
  deep 
  water, 
  probably 
  repre- 
  

   sent 
  one 
  of 
  the 
  earlier 
  stages 
  of 
  a 
  transformation 
  which 
  results 
  finally 
  

   in 
  the 
  obliteration 
  of 
  the 
  visual 
  elements 
  of 
  the 
  normal 
  eye 
  and 
  the 
  

   substitution 
  of 
  an 
  essenti 
  ally 
  different 
  sensory 
  structure. 
  In 
  Pontophilus 
  

   abyssi 
  the 
  transformation 
  has 
  gone 
  further; 
  the 
  eyes, 
  though 
  fully 
  as 
  

   large 
  as 
  in 
  the 
  allied 
  shallow-water 
  species, 
  are 
  nearly 
  colorless, 
  not 
  

   very 
  distinctly 
  faceted, 
  and 
  have 
  probably 
  begun 
  to 
  lose 
  the 
  normal 
  

   visual 
  elements 
  over 
  a 
  portion 
  of 
  the 
  surface. 
  In 
  the 
  eyes 
  of 
  several 
  of 
  

   the 
  species 
  of 
  Munidopsis 
  the 
  normal 
  visual 
  elements 
  have 
  entirely 
  dis- 
  

   appeared 
  and 
  there 
  is 
  an 
  expanded 
  transparent 
  cornea 
  backed 
  by 
  whit- 
  

   ish 
  pigment 
  and 
  some 
  kind 
  of 
  nervous 
  elements. 
  I 
  am 
  very 
  well 
  aware 
  

   that 
  there 
  is 
  as 
  yet 
  no 
  conclusive 
  evidence 
  that 
  these 
  colorless 
  eyes 
  in 
  

   the 
  species 
  of 
  Munidopsis 
  are 
  anything 
  more 
  than 
  the 
  functionless 
  rem- 
  

   nants 
  of 
  embryonic 
  or 
  inherited 
  organs, 
  but 
  the 
  fact 
  that 
  in 
  some 
  spe- 
  

   cies 
  they 
  are 
  as 
  large 
  as 
  the 
  normal 
  eyes 
  of 
  allied 
  shallow-water 
  species 
  

   is 
  certainly 
  a 
  strong 
  argument 
  against 
  this 
  view. 
  

  

  In 
  the 
  species 
  of 
  Pentacheles 
  there 
  is 
  better 
  evidence 
  that 
  the 
  eyes 
  are 
  

   not 
  functionless, 
  for, 
  although 
  they 
  have 
  retreated 
  beneath 
  the 
  front 
  of 
  

   the 
  carapax, 
  they 
  are 
  still 
  exposed 
  above 
  by 
  the 
  formation 
  of 
  a 
  deep 
  

   sinus 
  in 
  the 
  margin, 
  and 
  the 
  ocular 
  lobe 
  itself 
  has 
  thrown 
  off 
  a 
  process 
  

   which 
  is 
  exposed 
  in 
  a 
  special 
  sinus 
  in 
  the 
  ventral 
  margin. 
  It 
  is 
  very 
  

   easy 
  to 
  conceive 
  how 
  the 
  eyes 
  of 
  Pentacheles, 
  probably 
  as 
  highly 
  modi- 
  

   fied 
  as 
  those 
  of 
  any 
  deep 
  water 
  species, 
  may 
  have 
  been 
  derived 
  from 
  

   eyes 
  like 
  those 
  of 
  the 
  species 
  of 
  Glyphocrangon 
  and 
  Pontophilus 
  abyssi 
  

   through 
  a 
  stage 
  like 
  the 
  eyes 
  of 
  Calocaris, 
  which 
  are 
  practically 
  sessile, 
  

   have 
  lostall 
  the 
  normal 
  visual 
  elements, 
  and 
  haveonly 
  colorless 
  pigment, 
  

   but 
  still 
  present 
  large 
  flattened 
  transparent 
  non-faceted 
  corneas 
  at 
  the 
  

   anterior 
  margin 
  of 
  the 
  carapax. 
  It 
  is 
  interesting 
  to 
  note 
  that 
  the 
  highly 
  

   modified 
  eyes 
  of 
  Pentacheles 
  are 
  found 
  in 
  a 
  well-defined 
  group 
  confined 
  

   to 
  deep 
  water 
  and 
  of 
  which 
  all 
  the 
  species 
  have 
  probably 
  been 
  inhabi- 
  

   tants 
  of 
  deep 
  water 
  for 
  considerable 
  geological 
  periods, 
  while 
  the 
  equally 
  

   deep-water 
  species 
  with 
  less 
  modified 
  or 
  obsolescent 
  eyes 
  are 
  much 
  

   more 
  closely 
  allied 
  to 
  shallow- 
  water 
  species, 
  from 
  whose 
  ancestors 
  they 
  

   may 
  have 
  been 
  derived 
  in 
  comparatively 
  recent 
  times. 
  

  

  Many 
  of 
  the 
  deep-water 
  Caridea 
  have 
  a 
  peculiar 
  papilla 
  like 
  process 
  

  

  