﻿Dr. 
  II. 
  Ludwig 
  on 
  Ophiopteron 
  elegans. 
  47 
  

  

  In 
  the 
  basal 
  part 
  of 
  the 
  arm 
  the 
  fins 
  show 
  some 
  variations. 
  

   In 
  the 
  first 
  place, 
  on 
  the 
  first 
  three 
  free 
  arm-joints 
  {i. 
  e. 
  those 
  

   not 
  entering 
  into 
  the 
  disk) 
  the 
  two 
  fins 
  which 
  belong 
  to 
  each 
  

   arm-joint 
  are 
  not 
  separated 
  from 
  each 
  other, 
  but 
  are 
  united 
  

   into 
  one 
  on 
  the 
  dorsal 
  surface 
  by 
  fusion 
  of 
  their 
  hinder 
  mar- 
  

   gins. 
  In 
  the 
  second 
  place, 
  on 
  the 
  (four) 
  arm-joints 
  situated 
  

   within 
  the 
  disk 
  the 
  fins 
  behave 
  otherwise 
  than 
  on 
  the 
  free 
  

   arm. 
  The 
  first 
  of 
  these 
  joints, 
  that 
  lying 
  nearest 
  to 
  the 
  

   mouth, 
  bears 
  on 
  each 
  side 
  only 
  two 
  small 
  spinules, 
  which 
  in 
  

   their 
  position 
  correspond 
  with 
  the 
  hooks 
  and 
  spinulose 
  spines 
  ; 
  

   the 
  first 
  arm-joint 
  also 
  is 
  destitute 
  of 
  the 
  tentacular 
  scale. 
  

   From 
  the 
  second 
  arm-joint 
  onwards 
  the 
  tentacular 
  scale 
  is 
  

   present 
  ; 
  the 
  second 
  joint 
  further 
  possesses 
  on 
  each 
  side 
  a 
  

   distinct 
  hook, 
  a 
  spinulose 
  spine, 
  and, 
  instead 
  of 
  the 
  fin, 
  a 
  

   smooth 
  spine. 
  On 
  the 
  third 
  arm-joint 
  there 
  is 
  on 
  each 
  side 
  

   the 
  hook, 
  the 
  spinulose 
  spine, 
  and 
  two 
  or 
  three 
  smooth 
  spines 
  

   united 
  by 
  swimming-membranes. 
  On 
  the 
  fourth 
  joint 
  the 
  

   fin- 
  structure 
  is 
  already 
  complete. 
  

  

  The 
  feet, 
  as 
  in 
  many 
  other 
  Ophiurans, 
  are 
  beset 
  with 
  small 
  

   warts 
  on 
  their 
  surface 
  ; 
  the 
  buccal 
  feet 
  also 
  show 
  the 
  same 
  

   character. 
  

  

  No 
  less 
  worthy 
  of 
  notice 
  than 
  the 
  fins 
  of 
  the 
  arms 
  are 
  the 
  

   peculiar 
  structures 
  into 
  which 
  the 
  dorsal 
  spines 
  of 
  the 
  disk 
  

   have 
  been 
  developed. 
  If 
  the 
  disk 
  be 
  examined 
  from 
  above 
  

   under 
  a 
  low 
  power, 
  it 
  is 
  seen 
  to 
  be 
  covered 
  with 
  a 
  delicate, 
  

   close, 
  satiny 
  down, 
  which, 
  on 
  closer 
  examination, 
  proves 
  to 
  

   consist 
  of 
  a 
  number 
  of 
  fine, 
  generally 
  hexagonal, 
  funnels. 
  

   Each 
  funnel 
  consists 
  of 
  a 
  short 
  thick 
  spine, 
  which 
  at 
  its 
  outer 
  

   end 
  is 
  continued 
  into 
  six 
  comparatively 
  long 
  fine 
  spines 
  of 
  

   unequal 
  length, 
  so 
  united 
  to 
  each 
  other 
  by 
  a 
  thin 
  membrane 
  

   that 
  a 
  funnel 
  is 
  produced, 
  the 
  delicate 
  membranous 
  wall 
  of 
  

   which 
  is 
  supported 
  by 
  the 
  six 
  fine 
  spines. 
  Sometimes, 
  how- 
  

   ever, 
  only 
  five 
  such 
  supporting 
  spines 
  are 
  present. 
  The 
  

   thick 
  stalk 
  of 
  the 
  funnel 
  is 
  articulated 
  upon 
  a 
  dense 
  but 
  very 
  

   fine 
  calcareous 
  reticular 
  tissue, 
  lying 
  in 
  the 
  dorsal 
  skin 
  of 
  

   the 
  disk. 
  The 
  dorsal 
  skin 
  of 
  the 
  disk 
  further 
  contains 
  very 
  

   thin 
  radial 
  scutes, 
  of 
  which, 
  in 
  the 
  uninjured 
  disk, 
  only 
  the 
  

   distal 
  points 
  are 
  uncovered 
  by 
  the 
  funnels 
  ; 
  so 
  that 
  it 
  is 
  only 
  

   when 
  the 
  latter 
  are 
  removed 
  that 
  it 
  is 
  seen 
  that 
  the 
  thin 
  radial 
  

   scutes 
  are 
  of 
  a 
  rounded 
  triangular 
  form 
  and 
  joined 
  together 
  in 
  

   pairs 
  by 
  their 
  longest 
  sides. 
  

  

  On 
  the 
  thin, 
  soft, 
  translucent 
  skin 
  of 
  the 
  ventral 
  surface 
  of 
  

   the 
  disk 
  the 
  funnels 
  are 
  wanting, 
  and, 
  indeed, 
  at 
  the 
  periphery 
  

   of 
  the 
  dorsal 
  skin 
  they 
  separate 
  from 
  each 
  other 
  and 
  become 
  

   less 
  numerous 
  in 
  the 
  direction 
  of 
  the 
  interradii. 
  In 
  place 
  of 
  

   them 
  we 
  find 
  in 
  the 
  ventral 
  skin 
  scattered, 
  rather 
  distant, 
  

  

  