﻿510 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [22] 
  

  

  A 
  more 
  advanced 
  stage 
  is 
  shown 
  in 
  fig. 
  21, 
  plate 
  iv, 
  measuring 
  about 
  

   3.5 
  mm 
  in 
  length. 
  The 
  pectoral 
  fin 
  at 
  this 
  stage 
  has 
  already 
  partially 
  

   rotated 
  on 
  its 
  base. 
  The 
  dorsal 
  fin 
  is 
  more 
  developed, 
  while 
  the 
  tail 
  

   begins 
  to 
  show 
  signs 
  of 
  the 
  development 
  of 
  the 
  permanent 
  rays 
  from 
  

   the 
  coalescence 
  of 
  the 
  embryonic 
  rays 
  or 
  actinotrichia. 
  The 
  circulation 
  

   is 
  more 
  developed 
  and 
  the 
  blood 
  may 
  be 
  seen 
  circulating 
  through 
  the 
  

   gill 
  arches, 
  but 
  there 
  are 
  still 
  no 
  filaments 
  formed. 
  A 
  more 
  enlarged 
  

   view 
  of 
  the 
  head 
  of 
  this 
  stage 
  is 
  shown 
  in 
  fig. 
  12, 
  plate 
  iii, 
  where 
  the 
  four 
  

   gill 
  arches 
  are 
  more 
  clearly 
  indicated. 
  

  

  I 
  must 
  here 
  take 
  exception 
  to 
  certain 
  of 
  McMurrich's 
  statements 
  in 
  

   his 
  paper 
  already 
  cited 
  in 
  reference 
  to 
  the 
  development 
  of 
  the 
  fins. 
  He 
  

   says 
  (p. 
  648) 
  : 
  " 
  In 
  the 
  young 
  stages 
  an 
  anal 
  is 
  present, 
  which, 
  how- 
  

   ever, 
  does 
  not 
  pass 
  beyond 
  the 
  stage 
  in 
  which 
  fibrillation 
  [development 
  

   of 
  actrinotrichia] 
  begins, 
  but 
  aborts 
  and 
  is 
  entirely 
  wanting 
  in 
  the 
  

   adult." 
  This 
  is 
  an 
  error, 
  because 
  a 
  careful 
  inspection 
  of 
  the 
  adults 
  of 
  

   both 
  sexes 
  of 
  Siphostoma 
  fuscum, 
  apparently 
  the 
  same 
  species 
  as 
  was 
  

   used 
  in 
  his 
  studies, 
  reveals 
  a 
  small 
  but 
  undoubted 
  anal 
  fin 
  just 
  behind 
  

   the 
  vent. 
  The 
  erector 
  and 
  depressor 
  muscles 
  are 
  also 
  not 
  attached 
  to 
  

   the 
  oval 
  cartilaginous 
  nodules 
  at 
  the 
  bases 
  of 
  the 
  fin-rays, 
  as 
  stated 
  by 
  

   McMurrich, 
  but 
  to 
  the 
  bases 
  of 
  the 
  fin-rays 
  themselves. 
  This 
  author's 
  

   statement 
  that 
  the 
  tail 
  of 
  Siphostoma 
  is 
  heterocercal 
  at 
  first 
  is 
  not 
  borne 
  

   out 
  either 
  by 
  the 
  method 
  of 
  development 
  of 
  the 
  tails 
  of 
  fishes 
  generally, 
  

   or 
  by 
  the 
  evidence 
  supplied 
  by 
  figs. 
  19 
  and 
  20 
  of 
  this 
  species 
  here 
  given 
  ; 
  

   these 
  two 
  stages 
  just 
  referred 
  to 
  being 
  really 
  much 
  younger 
  than 
  any 
  

   figured 
  by 
  McMurrich, 
  and 
  they 
  serve 
  to 
  show 
  that 
  the 
  young 
  of 
  Siphos- 
  

   toma 
  pass 
  through 
  what 
  I 
  have 
  called 
  an 
  archicercal 
  stage. 
  

  

  A 
  very 
  curious 
  and 
  interesting 
  morphological 
  fact 
  is 
  revealed 
  by 
  a 
  

   study 
  of 
  the 
  development 
  of 
  the 
  Lophobranchii, 
  namely, 
  the 
  manner 
  in 
  

   which 
  the 
  neural 
  arches 
  are 
  duplicated 
  several 
  times 
  on 
  each 
  vertebral 
  

   centrum. 
  The 
  proximal 
  parts 
  of 
  the 
  parallel 
  cartilaginous 
  bars 
  sup- 
  

   porting 
  the 
  rays 
  of 
  the 
  dorsal 
  fin 
  in 
  Hippocampus 
  and 
  Siphostoma 
  afford 
  

   the 
  basis 
  for 
  the 
  ossification 
  of 
  about 
  five 
  neural 
  arches 
  to 
  a 
  single 
  cen- 
  

   trum 
  in 
  the 
  region 
  of 
  the 
  dorsal 
  fin. 
  And, 
  since 
  the 
  more 
  anterior 
  and 
  

   posterior 
  vertebrae 
  also 
  have 
  a 
  number 
  of 
  dorsal 
  arches, 
  it 
  is 
  probable 
  

   that 
  the 
  cartilaginous 
  rudiments 
  of 
  such 
  arches 
  are 
  also 
  duplicated 
  in 
  

   those 
  regions 
  in 
  an 
  analogous 
  manner, 
  but 
  at 
  a 
  somewhat 
  later 
  stage 
  of 
  

   development. 
  This 
  peculiar 
  method 
  of 
  development 
  and 
  duplication 
  of 
  

   the 
  neural 
  arches 
  will 
  very 
  probably 
  serve 
  to 
  distinguish 
  the 
  Lopho- 
  

   branchiates 
  from 
  other 
  families 
  of 
  fishes. 
  

  

  In 
  plate 
  xvii 
  of 
  my 
  first 
  paper 
  on 
  the 
  Lophobranchiates, 
  cited 
  above, 
  

   I 
  fell 
  into 
  an 
  error 
  in 
  the 
  identification 
  of 
  the 
  cranial 
  cartilages 
  of 
  Hip- 
  

   pocampus, 
  as 
  pointed 
  out 
  by 
  McMurrich. 
  In 
  the 
  skull, 
  figured 
  on 
  the 
  

   plate 
  indicated, 
  the 
  names 
  of 
  several 
  cartilaginous 
  elements 
  must 
  be 
  

   changed. 
  The 
  unpaired 
  element 
  sy, 
  given 
  as 
  " 
  symplectic," 
  must 
  be 
  re- 
  

   garded 
  as 
  geniohyoid, 
  the 
  "element 
  x" 
  is 
  the 
  quadrate 
  and 
  pterygoid, 
  

   while 
  a 
  is 
  not 
  "labial," 
  but 
  pterygopalatine 
  and 
  not 
  "ethino 
  palatine," 
  

  

  