﻿26 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  2 
  

  

  The 
  jointed 
  cestodes 
  represent 
  the 
  strobila 
  stage 
  of 
  Aurelia, 
  but 
  

   are 
  somewhat 
  more 
  completely 
  unified, 
  the 
  proglottides 
  sharing 
  a 
  

   common 
  nervous 
  and 
  excretory 
  system 
  and 
  their 
  detachment 
  being 
  

   greatly 
  retarded. 
  The 
  pronounced 
  bilateral 
  symmetry 
  of 
  most 
  ces- 
  

   todes 
  and 
  the 
  marked 
  difference 
  in 
  the 
  two 
  sides 
  of 
  the 
  proglottides 
  

   seen 
  in 
  others 
  together 
  with 
  certain 
  features 
  connected 
  with 
  the 
  

   budding 
  of 
  the 
  scolex 
  suggest 
  their 
  relationship 
  with 
  the 
  graptolites 
  

   of 
  which 
  they 
  are 
  possibly 
  the 
  recent 
  representatives. 
  

  

  By 
  a 
  further 
  consolidation 
  and 
  unification 
  of 
  the 
  jointed 
  cestode 
  

   body 
  correlated 
  with 
  a 
  loss 
  of 
  the 
  individuality 
  of 
  the 
  component 
  

   segments 
  the 
  annelid 
  body 
  type 
  was 
  evolved, 
  and 
  a 
  further 
  consolida- 
  

   tion 
  gave 
  rise 
  to 
  the 
  crustaceans, 
  within 
  which 
  group 
  the 
  tendency 
  is 
  

   to 
  compress 
  all 
  of 
  the 
  functions 
  of 
  the 
  body 
  within 
  the 
  compass 
  of 
  a 
  

   few 
  anterior 
  segments, 
  and 
  the 
  insects, 
  in 
  which 
  there 
  are 
  three 
  small 
  

   groups 
  of 
  segments 
  each 
  with 
  a 
  definite 
  function, 
  (a) 
  the 
  head, 
  most 
  

   unified, 
  controlling 
  and 
  directing, 
  (b) 
  the 
  thorax, 
  less 
  unified, 
  loco- 
  

   motor, 
  and 
  (c) 
  the 
  abdomen, 
  largest 
  and 
  least 
  unified, 
  enclosing 
  the 
  

   digestive, 
  reproductive 
  and 
  other 
  organs. 
  

  

  Most 
  crustaceans 
  are 
  more 
  or 
  less, 
  and 
  many 
  are 
  conspicuously, 
  

   asymmetrical, 
  while 
  in 
  all 
  there 
  is 
  noticeable 
  a 
  great 
  development 
  of 
  

   the 
  dorsal 
  surface 
  as 
  compared 
  with 
  the 
  ventral. 
  Both 
  of 
  these 
  fea- 
  

   tures 
  are 
  especially 
  characteristic 
  of 
  certain 
  barnacles, 
  become 
  greatly 
  

   accentuated 
  in 
  the 
  Pelmatozoa, 
  and 
  reach 
  an 
  extreme 
  development 
  

   in 
  the 
  unattached 
  echinoderms 
  in 
  which 
  the 
  body 
  consists 
  of 
  five 
  

   half 
  segments 
  only 
  arranged 
  in 
  a 
  circle 
  and 
  enclosed 
  entirely 
  by 
  the 
  

   dorsal 
  surface, 
  the 
  ventral 
  having 
  almost 
  completely 
  disappeared.^ 
  

  

  The 
  evolution 
  of 
  solitary 
  animals 
  through 
  the 
  progressive 
  consolida- 
  

   tion 
  of 
  a 
  colony 
  correlated 
  with 
  increasing 
  loss 
  of 
  individuality 
  by 
  

   the 
  component 
  units 
  can 
  thus 
  be 
  traced 
  from 
  the 
  coelenterates 
  through 
  

   the 
  cestodes 
  to 
  the 
  arthropods 
  and 
  echinoderms. 
  

  

  Closely 
  allied 
  to 
  the 
  cestodes 
  are 
  the 
  trematodes, 
  and 
  from 
  them 
  

   or 
  from 
  very 
  similar 
  organisms 
  another 
  very 
  different 
  line 
  of 
  develop- 
  

   ment 
  has 
  arisen. 
  

  

  The 
  development 
  of 
  the 
  liver 
  fluke, 
  like 
  that 
  of 
  the 
  tapeworm, 
  

   in 
  the 
  division 
  of 
  the 
  sporocysts 
  and 
  the 
  subsequent 
  development 
  of 
  

   cercariae 
  from 
  sporocysts 
  and 
  rediae 
  is 
  comparable 
  in 
  its 
  essential 
  

   features 
  to 
  strobilization, 
  but 
  the 
  budding 
  takes 
  place, 
  so 
  to 
  speak, 
  

   within 
  a 
  closed 
  scyphistoma; 
  that 
  is, 
  the 
  sporocysts 
  and 
  rediae 
  undergo 
  

  

  * 
  Smith. 
  Misc. 
  Coll. 
  27: 
  No. 
  11, 
  1-20. 
  July 
  20, 
  1921. 
  

  

  