﻿3 
  86 
  E. 
  RAY 
  LANKESTEB. 
  

  

  comprising 
  in 
  addition 
  the 
  ocular 
  prosthomere.'^ 
  When 
  the 
  

   pra3genital 
  somite 
  or 
  traces 
  of 
  it 
  are 
  present 
  it 
  should 
  not 
  be 
  

   called 
  " 
  the 
  sevenlh 
  prosomatic 
  " 
  or 
  the 
  " 
  first 
  mesosomatic," 
  

   but 
  simply 
  the 
  "preegenital 
  somite." 
  The 
  first 
  segment 
  of 
  

   the 
  mesosoma 
  of 
  Scorpio 
  and 
  Limulus 
  thus 
  remains 
  the 
  first 
  

   segment^ 
  and 
  can 
  be 
  identified 
  as 
  such 
  throughout 
  the 
  Eu- 
  

   arachnida, 
  carrying 
  as 
  it 
  always 
  does 
  the 
  genital 
  apertures. 
  

   But 
  it 
  is 
  necessary 
  to 
  remember, 
  in 
  the 
  light 
  of 
  recent 
  dis- 
  

   coveries, 
  that 
  the 
  sixth 
  prosomatic 
  pair 
  of 
  appendages 
  is 
  car- 
  

   ried 
  on 
  the 
  seventh 
  somite 
  of 
  the 
  whole 
  series, 
  there 
  being 
  

   two 
  prosthomeres 
  or 
  somites 
  in 
  front 
  of 
  the 
  mouth, 
  the 
  first 
  

   carrying 
  the 
  eyes^ 
  the 
  second 
  the 
  chelicerse 
  ; 
  also 
  that 
  the 
  

   first 
  mesosomatic 
  or 
  genital 
  somite 
  is 
  not 
  the 
  seventh 
  or 
  eveu 
  

   the 
  eighth 
  of 
  the 
  whole 
  series 
  of 
  somites 
  which 
  have 
  been 
  

   historically 
  present, 
  but 
  is 
  the 
  ninth, 
  owing 
  to 
  the 
  presence 
  or 
  

   to 
  the 
  excalation 
  of 
  a 
  prasgenital 
  somite. 
  It 
  seems 
  that 
  con- 
  

   fusion 
  and 
  trouble 
  will 
  be 
  best 
  avoided 
  by 
  abstaining 
  from 
  

   the 
  introduction 
  of 
  the 
  non-evident 
  somites, 
  the 
  ocular 
  and 
  

   the 
  prajgenital, 
  into 
  the 
  numerical 
  nomenclature 
  of 
  the 
  com- 
  

   ponent 
  somites 
  of 
  the 
  three 
  great 
  body 
  regions. 
  We 
  shall 
  

   therefore, 
  ignoring 
  the 
  ocular 
  somite, 
  speak 
  of 
  the 
  first, 
  second, 
  

   third, 
  fourth, 
  fifth, 
  and 
  sixth 
  leg-bearing 
  somites 
  of 
  the 
  pro- 
  

   soma, 
  and 
  indicate 
  the 
  appendages 
  by 
  the 
  Roman 
  numerals, 
  

   I, 
  II, 
  III, 
  IV, 
  V, 
  VI, 
  and 
  whilst 
  ignoring 
  the 
  prtegenital 
  

   somite 
  we 
  shall 
  speak 
  of 
  the 
  first, 
  second, 
  tliird, 
  etc., 
  somite 
  

   of 
  the 
  mesosoma 
  or 
  opisthosoma 
  (united 
  mesosoma 
  and 
  meta- 
  

   soma), 
  and 
  indicate 
  them 
  by 
  the 
  Arabic 
  numerals. 
  

  

  There 
  are 
  a 
  number 
  of 
  other 
  important 
  points 
  of 
  structure 
  

   besides 
  those 
  referring 
  to 
  the 
  somites 
  and 
  appendages 
  in 
  

   which 
  Limulns 
  agrees 
  with 
  Scorpio 
  or 
  other 
  Arachnida, 
  and 
  

   differs 
  from 
  other 
  Arthropoda. 
  The 
  chief 
  of 
  these 
  are 
  as 
  

   follows 
  : 
  

  

  1. 
  The 
  Composition 
  of 
  the 
  Head 
  (that 
  is 
  to 
  say, 
  of 
  the 
  

   anterior 
  part 
  of 
  the 
  prosoma), 
  with 
  especial 
  reference 
  to 
  

   the 
  Region 
  in 
  Front 
  of 
  the 
  Mouth. 
  — 
  It 
  appears 
  (see 
  

  

  • 
  See 
  the 
  article 
  Arthropoda 
  for 
  the 
  use 
  of 
  tiie 
  term 
  "prosthomere." 
  

  

  