﻿Beecher 
  — 
  Natural 
  Classification 
  of 
  the 
  Trilobites. 
  97 
  

  

  and 
  the 
  first 
  inaxillge 
  ; 
  and 
  the 
  seventh, 
  by 
  the 
  neck 
  lobe, 
  or 
  

   occipital 
  ring, 
  and 
  the 
  second 
  pair 
  of 
  maxillae. 
  The 
  five 
  annu- 
  

   lations, 
  or 
  lobes, 
  of 
  the 
  axis 
  of 
  the 
  cranidium, 
  since 
  they 
  pri- 
  

   marily 
  carry 
  fulcra 
  for 
  the 
  attachment 
  of 
  muscles 
  supporting 
  or 
  

   moving 
  the 
  appendages, 
  could 
  thus 
  be 
  interpreted 
  in 
  terms 
  of 
  

   the 
  ventral 
  structure, 
  making 
  the 
  first 
  lobe 
  the 
  antennulary, 
  

   the 
  second 
  the 
  antennary, 
  the 
  third 
  the 
  mandibular, 
  the 
  fourth 
  

   the 
  first 
  maxillary, 
  and 
  the 
  fifth 
  the 
  second 
  maxillary. 
  

  

  No 
  other 
  group 
  of 
  Crustacea 
  furnishes 
  such 
  constant 
  and 
  well- 
  

   developed 
  structures' 
  representing 
  the 
  second 
  theoretical 
  head 
  

   segment, 
  which 
  is 
  obscure 
  or 
  obsolete 
  in 
  all 
  the 
  living 
  groups, 
  

   excepting 
  probably 
  the 
  stalked 
  eyes 
  of 
  some 
  Crustacea 
  and 
  the 
  

   movable 
  occular 
  segment 
  of 
  the 
  Stomatopods. 
  For 
  this 
  reason, 
  

   in 
  addition 
  to 
  the 
  many 
  other 
  important 
  differences 
  previously 
  

   noted 
  in 
  the 
  table 
  of 
  comparative 
  morphology, 
  the 
  trilobites 
  

   are 
  regarded 
  as 
  a 
  subclass, 
  and 
  the 
  relative 
  denomination 
  and 
  

   structural 
  relations 
  of 
  this 
  second 
  segment, 
  along 
  with 
  other 
  

   characters, 
  are 
  considered 
  as 
  of 
  sufficient 
  physiological 
  and 
  

   morphological 
  importance 
  to 
  determine 
  the 
  ordinal 
  divisions. 
  

  

  Principles 
  of 
  a 
  Natural 
  Classification. 
  

  

  Most 
  satisfactory 
  and 
  conclusive 
  results 
  have 
  already 
  come 
  

   from 
  the 
  application 
  of 
  the 
  law 
  of 
  morphogenesis, 
  or 
  the 
  

   recapitulation 
  theory, 
  to 
  various 
  groups 
  of 
  animals, 
  by 
  means 
  

   of 
  which 
  their 
  natural 
  classification 
  and 
  phylogenetic 
  relations 
  

   have 
  been 
  determined. 
  Hyatt 
  21 
  says 
  on 
  this 
  point 
  (1889) 
  : 
  " 
  We 
  

   have 
  endeavored 
  to 
  demonstrate 
  that 
  a 
  natural 
  classification 
  

   may 
  be 
  made 
  by 
  means 
  of 
  a 
  system 
  of 
  analysis 
  in 
  which 
  the 
  

   individual 
  is 
  the 
  unit 
  of 
  comparison, 
  because 
  its 
  life 
  in 
  all 
  its 
  

   phases, 
  morphological 
  and 
  physiological, 
  healthy 
  or 
  pathologi- 
  

   cal, 
  embryo, 
  larva, 
  adolescent, 
  and 
  old 
  (ontogeny), 
  correlates 
  

   with 
  the 
  morphological 
  and 
  physiological 
  history 
  of 
  the 
  group 
  

   to 
  which 
  it 
  belongs 
  (phylogeny)." 
  It 
  is 
  also 
  interesting 
  to 
  

   note 
  that 
  Agassiz 
  1 
  recognized 
  in 
  ontogeny 
  a 
  standard 
  of 
  classi- 
  

   fication. 
  One 
  of 
  his 
  strongest 
  statements 
  is 
  as 
  follows: 
  " 
  Em- 
  

   bryology 
  [=ontogeny] 
  will 
  in 
  the 
  end 
  furnish 
  us 
  with 
  the 
  

   means 
  of 
  recognizing 
  the 
  true 
  affinities 
  among 
  all 
  animals, 
  and 
  

   of 
  ascertaining 
  their 
  relative 
  standing 
  and 
  normal 
  position 
  in 
  

   their 
  respective 
  classes 
  with 
  the 
  utmost 
  degree 
  of 
  accuracy 
  and 
  

   precision." 
  

  

  These 
  principles 
  can 
  be 
  best 
  applied 
  in 
  a 
  group 
  of 
  animals 
  

   which 
  has 
  a 
  geological 
  history 
  more 
  or 
  less 
  complete, 
  and 
  

   which 
  is 
  not 
  wholly 
  parasitic 
  or 
  greatly 
  degenerated. 
  It 
  is 
  of 
  

   the 
  greatest 
  importance, 
  also, 
  to 
  study 
  the 
  ontogeny 
  of 
  primi- 
  

   tive 
  and 
  non-specialized 
  species, 
  because 
  without 
  very 
  complete 
  

   paleontological 
  evidence, 
  the 
  development 
  of 
  a 
  much 
  later 
  

  

  