﻿THE 
  " 
  WEISSER 
  JURA 
  " 
  OF 
  BAVARIA. 
  163 
  

  

  (ii) 
  The 
  method 
  of 
  " 
  Atrophy 
  " 
  differs 
  from 
  the 
  method 
  of 
  Sport 
  

   in 
  its 
  gradual 
  character, 
  and 
  in 
  the 
  number 
  of 
  stages 
  passed 
  through 
  

   before 
  the 
  same 
  result 
  is 
  reached 
  as 
  is 
  attained 
  at 
  one 
  stroke 
  by 
  the 
  

   sport. 
  And 
  even 
  then 
  the 
  resultant 
  figure 
  is 
  not 
  the 
  same 
  : 
  atrophy 
  

   of 
  one 
  part 
  nearly 
  always 
  depends 
  on 
  the 
  hypertrophy 
  of 
  another 
  

   part; 
  hence 
  symmetry 
  is 
  destroyed. 
  Thus 
  in 
  Eudesicrinus 
  and 
  

   Holopus 
  one 
  radial 
  grows 
  large 
  and 
  the 
  others 
  small, 
  the 
  calyx 
  is 
  

   crookedly 
  set 
  on 
  the 
  stem 
  and 
  is 
  lop-sided* 
  ; 
  Eug. 
  nutans 
  is 
  similarly 
  

   affected 
  ; 
  in 
  Torynocriuus 
  canon, 
  Seeley, 
  the 
  asymmetry 
  amounts 
  to 
  

   distortion! 
  ; 
  and 
  in 
  Gymnocrinus 
  one 
  ray 
  seems 
  to 
  have 
  usurped 
  the 
  

   place 
  of 
  all 
  the 
  others. 
  Or 
  atrophy 
  may 
  take 
  place 
  in 
  two 
  rays, 
  

   thus 
  changing 
  the 
  symmetry 
  from 
  pentagonal 
  to 
  trigonal, 
  as 
  in 
  

   Baerocrinus. 
  Dr. 
  P. 
  H. 
  Carpenter, 
  however, 
  seems 
  to 
  consider 
  this 
  

   as 
  a 
  persistent 
  sport, 
  for 
  he 
  writes 
  : 
  — 
  ' 
  - 
  It 
  is, 
  perhaps, 
  best 
  regarded 
  

   as 
  a 
  permanent 
  larval 
  form, 
  which 
  has 
  only 
  developed 
  three 
  of 
  its 
  

   five 
  arms." 
  In 
  the 
  allied 
  genus 
  Hybocrinus, 
  however, 
  we 
  seem 
  to 
  

   see 
  gradual 
  atrophy 
  of 
  one 
  arm; 
  but 
  of 
  this, 
  too, 
  Dr. 
  Carpenter 
  

   writes 
  : 
  — 
  " 
  This 
  may 
  be, 
  and 
  probably 
  is, 
  one 
  of 
  the 
  variations 
  of 
  

   growth 
  to 
  which 
  this 
  early 
  and 
  simple 
  type 
  is 
  subject 
  " 
  £. 
  Anyhow 
  

  

  Fig. 
  1. 
  — 
  Diagrams 
  of 
  Hybocrinus 
  and 
  Baerocrinus. 
  

  

  A 
  B 
  

  

  A. 
  Calyx 
  of 
  a 
  typical 
  Hybocrinus 
  dipentas, 
  as 
  seen 
  in 
  outline 
  from 
  above. 
  

  

  B. 
  A 
  similar 
  view 
  of 
  Baerocrinus 
  Ungerni. 
  The 
  two 
  edges 
  of 
  every 
  arm- 
  

  

  bearing 
  radial 
  are 
  joined 
  by 
  dotted 
  lines. 
  After 
  Grewingk. 
  

  

  there 
  is 
  plenty 
  of 
  room 
  for 
  a 
  different 
  opinion. 
  Similar 
  irregularity 
  

   is 
  seen 
  in 
  Pourtalesia 
  among 
  Echinoidea, 
  and 
  in 
  Pentephyllum 
  

   among 
  Blastoidea. 
  It 
  is 
  further 
  to 
  be 
  observed 
  that, 
  whereas 
  a 
  

   sport 
  is 
  usually 
  confined 
  to 
  individuals, 
  producing 
  an 
  unstable 
  

  

  * 
  For 
  remarks 
  on 
  the 
  bilateral 
  symmetry 
  thus 
  induced, 
  see 
  C. 
  Wyville 
  Thom- 
  

   son, 
  " 
  On 
  the 
  Structure 
  and 
  Eelations 
  of 
  the 
  genus 
  Holopus" 
  Proc. 
  Roy. 
  Soc. 
  

   Edinburgh, 
  vol. 
  ix. 
  pp. 
  405-410 
  (1877) 
  ; 
  on 
  p. 
  408 
  : 
  and 
  P. 
  H. 
  Carpenter, 
  " 
  The 
  

   Stalked 
  Crinoids 
  of 
  the 
  Caribbean 
  Sea," 
  Bull. 
  Mus. 
  Comp. 
  Zool. 
  Harvard, 
  

   x. 
  no. 
  4, 
  pp. 
  165-179 
  (Cambridge, 
  U. 
  S., 
  1882) 
  ; 
  on 
  p. 
  178. 
  

  

  t 
  H. 
  G. 
  Seeley, 
  "Notice 
  of 
  Torynocrinus 
  " 
  &c, 
  Ann. 
  & 
  Mag. 
  Nat. 
  Hist. 
  ser. 
  3, 
  

   xvii. 
  pp. 
  173-4. 
  Figured 
  in 
  Seeley's 
  ' 
  Phillips, 
  Manual 
  of 
  Geology, 
  Part 
  I. 
  

   Phys. 
  Geol. 
  & 
  Palajont. 
  (London, 
  1885), 
  p. 
  487, 
  f. 
  100. 
  

  

  % 
  P. 
  H. 
  Carpenter, 
  " 
  On 
  the 
  Relations 
  of 
  Hybocrinus. 
  Baerocrinus, 
  and 
  Hybo- 
  

   cystites," 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxviii. 
  pp. 
  298-312, 
  pi. 
  xi. 
  (1882); 
  see 
  

   p. 
  304 
  and 
  fig. 
  2, 
  A, 
  B. 
  I 
  here 
  take 
  the 
  opportunity 
  of 
  expressing 
  my 
  thanks 
  

   f 
  ~ 
  Dr. 
  P. 
  H. 
  Carpenter 
  for 
  permission 
  to 
  use 
  his 
  figures, 
  and 
  for 
  many 
  other 
  

   a 
  ' 
  ? 
  ^ 
  kindness 
  in 
  connexion 
  with 
  the 
  present 
  paper. 
  

  

  