﻿STRUCTURb; 
  AND 
  CLASSIFICATION 
  OP 
  THE 
  AKACHNIDA. 
  225 
  

  

  the 
  more 
  primitive 
  types 
  of 
  Nymplionomorplia 
  ; 
  but 
  those 
  of 
  

   the 
  first 
  pair 
  are 
  either 
  rudimentary, 
  as 
  in 
  the 
  AscorhynchidEe, 
  

   or 
  atrophied^ 
  as 
  in 
  the 
  Colossendeidaj. 
  In 
  tlie 
  latter 
  a 
  further 
  

   specialisation 
  is 
  shown 
  in 
  the 
  fusion 
  of 
  the 
  body 
  segments. 
  

  

  Two 
  families 
  : 
  1. 
  AscorhyuchidEe 
  (genera 
  Ascorhynch 
  us 
  

   and 
  Ammothea) 
  ; 
  2. 
  ColossendeidEe 
  (genera 
  Colosseudeis 
  

   and 
  Discoarachne). 
  

  

  Order 
  3. 
  Pycnogonomorpha^ 
  Pocock 
  (nov.)- 
  — 
  Derivative 
  

   forms 
  in 
  which 
  the 
  reduction 
  in 
  number 
  of 
  the 
  anterior 
  

   appendages 
  is 
  carried 
  farther 
  than 
  in 
  the 
  other 
  orders, 
  

   reaching 
  its 
  extreme 
  in 
  the 
  Pycnogouida3, 
  where 
  the 
  first 
  and 
  

   second 
  pairs 
  are 
  absent 
  in 
  both 
  sexes, 
  and 
  the 
  third 
  pair 
  also 
  

   are 
  absent 
  in 
  the 
  female. 
  In 
  the 
  Hannoniidee, 
  however, 
  which 
  

   resemble 
  the 
  Pycnogonidas 
  in 
  the 
  absence 
  of 
  the 
  third 
  pair 
  in 
  

   the 
  female, 
  and 
  of 
  the 
  second 
  pair 
  in 
  both 
  sexes, 
  the 
  first 
  

   pair 
  are 
  retained 
  in 
  both 
  sexes. 
  

  

  Two 
  families: 
  1. 
  Hannoniidte 
  (genus 
  Hannonia) 
  ; 
  2. 
  

   Pycnogonida3 
  Cgenera 
  Pycuogonum 
  and 
  Phoxichilus). 
  

  

  Remarks. 
  — 
  The 
  Pantopoda 
  are 
  not 
  known 
  in 
  the 
  fossil 
  

   condition. 
  They 
  are 
  entirely 
  marine, 
  and 
  are 
  not 
  uncommon 
  

   in 
  the 
  coralline 
  zone 
  of 
  the 
  sea-coast. 
  The 
  species 
  are 
  few, 
  

   not 
  more 
  than 
  fifty 
  (23). 
  Some 
  large 
  species 
  of 
  peculiar 
  

   genera 
  are 
  taken 
  at 
  great 
  depths. 
  Their 
  movements 
  are 
  

   extremely 
  sluggish. 
  They 
  are 
  especially 
  remarkable 
  for 
  the 
  

   small 
  size 
  of 
  the 
  body 
  and 
  the 
  extension 
  of 
  viscera 
  into 
  the 
  

   legs. 
  Their 
  structure 
  is 
  eminently 
  that 
  of 
  degenerate 
  foi-ms. 
  

   Many 
  frequent 
  growths 
  of 
  coralline 
  Alga3 
  and 
  Hydroid 
  polyps, 
  

   upon 
  the 
  juices 
  of 
  which 
  they 
  feed, 
  and 
  in 
  some 
  cases 
  a 
  species 
  

   of 
  gall 
  is 
  produced 
  in 
  Hydroids 
  by 
  the 
  penetration 
  of 
  the 
  

   larval 
  Pantopoda 
  into 
  the 
  tissues 
  of 
  the 
  polyp. 
  

  

  Sub-class 
  II 
  (of 
  the 
  Nomomeristic 
  Arachnida). 
  EUARACH- 
  

   NIDA. 
  — 
  These 
  start 
  from 
  highly 
  developed 
  and 
  specialised 
  

   aquatic 
  branchiferous 
  forms, 
  exhibiting 
  prosoma 
  with 
  six 
  

   pediform 
  pairs 
  of 
  appendages, 
  an 
  intermediate 
  prasgenital 
  

   somite, 
  a 
  mesosoma 
  of 
  six 
  somites 
  bearing 
  lamelliform 
  pairs 
  

   of 
  appendages, 
  and 
  a 
  metasoma 
  of 
  six 
  somites 
  devoid 
  of 
  

   appendages, 
  and 
  the 
  last 
  provided 
  with 
  a 
  post-anal 
  spine. 
  

  

  