﻿208 
  E. 
  KAY 
  LANKESTKR. 
  

  

  the 
  symmetry, 
  likeness 
  of 
  constituent 
  parts 
  inter 
  se, 
  and 
  

   absence 
  of 
  specialised 
  pigment, 
  as 
  well 
  as 
  the 
  fact 
  that 
  they 
  

   differ 
  little 
  from 
  any 
  average 
  feather 
  of 
  birds 
  in 
  general, 
  

   mark 
  the 
  contour 
  feather 
  as 
  primitively 
  simple, 
  and 
  as 
  the 
  

   starting-point 
  from 
  which 
  the 
  highly 
  elaborated 
  eye-painted 
  

   tail 
  feather 
  has 
  gradually 
  evolved. 
  

  

  Applying 
  these 
  principles 
  to 
  the 
  consideration 
  of 
  the 
  

   Arachnida, 
  we 
  arrive 
  at 
  the 
  conclusion 
  that 
  the 
  smaller 
  and 
  

   simpler 
  Arachnids 
  are 
  not 
  the 
  more 
  primitive, 
  but 
  that 
  the 
  

   Acari 
  or 
  mites 
  are, 
  in 
  fact, 
  a 
  degenerate 
  group. 
  This 
  was 
  

   maintained 
  by 
  Lankester 
  in 
  1878 
  (19), 
  again 
  in 
  1881 
  (20) 
  ; 
  it 
  

   was 
  subsequently 
  announced 
  as 
  a 
  novelty 
  by 
  Claus 
  in 
  1885 
  

   (21). 
  Though 
  the 
  aquatic 
  members 
  of 
  a 
  class 
  of 
  animals 
  are 
  

   in 
  some 
  instances 
  derived 
  from 
  terrestrial 
  forms, 
  the 
  usual 
  

   transition 
  is 
  from 
  an 
  aquatic 
  ancestry 
  to 
  more 
  recent 
  land- 
  

   living 
  forms. 
  There 
  is 
  no 
  doubt, 
  from 
  a 
  consideration 
  of 
  

   the 
  facts 
  of 
  structure, 
  that 
  the 
  aquatic 
  water-breathing 
  

   Arachnids, 
  represented 
  in 
  the 
  past 
  by 
  the 
  Eurypterines 
  and 
  

   to-day 
  by 
  the 
  sole 
  survivor 
  Liimilus, 
  have 
  preceded 
  the 
  

   terrestrial 
  air-breathing 
  forms 
  of 
  that 
  group. 
  Hence 
  we 
  see 
  

   at 
  once 
  that 
  the 
  better-known 
  Arachnida 
  form 
  a 
  series 
  

   leading 
  from 
  Limulus-like 
  aquatic 
  creatures 
  through 
  scorpions, 
  

   spiders, 
  and 
  harvestmen 
  to 
  the 
  degenerate 
  Acari 
  or 
  mites. 
  

   The 
  spiders 
  are 
  specialised 
  and 
  reduced 
  in 
  apparent 
  com- 
  

   plexity, 
  as 
  compared 
  with 
  the 
  scorpions, 
  but 
  they 
  cannot 
  be 
  

   regarded 
  as 
  degenerate, 
  since 
  the 
  concentration 
  of 
  structure 
  

   which 
  occurs 
  in 
  them 
  results 
  in 
  greater 
  efficiency 
  and 
  power 
  

   than 
  are 
  exhibited 
  by 
  the 
  scorpion. 
  The 
  determination 
  of 
  

   the 
  relative 
  degree 
  of 
  perfection 
  of 
  organisation 
  attained 
  by 
  

   two 
  animals 
  compared 
  is 
  difficult 
  when 
  we 
  introduce, 
  as 
  seems 
  

   inevitable, 
  the 
  question 
  of 
  efficiency 
  and 
  power, 
  and 
  do 
  not 
  

   conGne 
  the 
  question 
  to 
  the 
  perfection 
  of 
  morphological 
  de- 
  

   velopment. 
  We 
  have 
  no 
  measure 
  of 
  the 
  degree 
  of 
  power 
  

   manifested 
  by 
  various 
  animals, 
  though 
  it 
  would 
  be 
  possible 
  

   to 
  arrive 
  at 
  some 
  conclusions 
  as 
  to 
  how 
  that 
  " 
  power" 
  should 
  

   be 
  estimated. 
  It 
  is 
  not 
  possible 
  here 
  to 
  discuss 
  that 
  matter 
  

   further. 
  We 
  must 
  be 
  content 
  to 
  point 
  out 
  that 
  it 
  seems 
  that 
  

  

  