﻿1875.] 
  

  

  and 
  Development 
  of 
  MyriotheTa. 
  

  

  251 
  

  

  and 
  which 
  here 
  develops 
  minute 
  mutable 
  pseudopodia, 
  which 
  are 
  being 
  con- 
  

   stantly 
  projected 
  and 
  withdrawn. 
  Indeed 
  the 
  yibratile 
  cilia 
  appear 
  to 
  be 
  

   but 
  a 
  modification 
  of 
  these 
  pseudopodial 
  processes 
  of 
  protoplasm. 
  

  

  Interposed 
  between 
  the 
  endoderm 
  and 
  the 
  ectoderm 
  is 
  the 
  fibrillated 
  

   layer. 
  It 
  is 
  extremely 
  well 
  developed, 
  and 
  consists 
  of 
  longitudinal 
  mus- 
  

   cular 
  fibrillse, 
  closely 
  adherent 
  to 
  the 
  outer 
  surface 
  of 
  a 
  structureless 
  

   hyaline 
  membrane 
  — 
  the 
  " 
  Stiitzlamelle 
  " 
  of 
  Eeichert. 
  The 
  fibrillated 
  

   layer, 
  with 
  its 
  supporting 
  membrane, 
  is 
  so 
  strong 
  as 
  to 
  remain 
  entire 
  in 
  

   a 
  section 
  of 
  the 
  animal 
  after 
  the 
  tissues 
  on 
  both 
  sides 
  of 
  it 
  have 
  been 
  

   broken 
  down. 
  

  

  The 
  ectoderm 
  is 
  composed 
  of 
  two 
  zones, 
  a 
  superficial 
  and 
  a 
  deep. 
  The 
  

   superficial 
  zone 
  consists 
  mainly 
  of 
  two 
  or 
  three 
  layers 
  of 
  small 
  round 
  

   cells 
  containing 
  yellowish 
  granules. 
  Among 
  these 
  cells 
  the 
  thread-cells 
  

   may 
  be 
  seen, 
  lying 
  chiefly 
  near 
  the 
  outer 
  surface 
  of 
  the 
  body. 
  Two 
  

   forms 
  of 
  thread-cells 
  may 
  be 
  here 
  distinguished 
  — 
  one 
  ovate, 
  with 
  the 
  in- 
  

   vaginated 
  tube 
  occupying 
  the 
  axis 
  ; 
  the 
  other 
  fusiform, 
  with 
  the 
  invagi- 
  

   nated 
  tube 
  oblique. 
  

  

  The 
  deeper 
  zone 
  of 
  the 
  ectoderm 
  consists 
  of 
  a 
  very 
  remarkable 
  tissue, 
  

   composed 
  of 
  peculiar 
  membraneless 
  cells, 
  each 
  of 
  which 
  is 
  prolonged 
  into 
  

   a 
  tail-like 
  process, 
  so 
  that 
  the 
  cells 
  assume 
  a 
  claviform 
  shape. 
  In 
  most 
  

   situations, 
  where 
  this 
  tissue 
  is 
  developed, 
  the 
  processes 
  from 
  several 
  such 
  

   cells 
  unite 
  with 
  one 
  another, 
  so 
  as 
  to 
  form 
  branching, 
  somewhat 
  botrylli- 
  

   form 
  groups, 
  whose 
  common 
  stalk 
  can 
  be 
  followed 
  into 
  the 
  fibrillated 
  

   layer. 
  The 
  author 
  is 
  thus 
  enabled 
  so 
  far 
  to 
  confirm 
  the 
  observations 
  of 
  

   Kleinenberg 
  on 
  cells 
  of 
  apparently 
  the 
  same 
  significance 
  in 
  Hydra. 
  In 
  

   Myriothela, 
  however, 
  these 
  cells 
  do 
  not, 
  as 
  in 
  Hydra, 
  reach 
  the 
  surface. 
  

   With 
  the 
  exception, 
  apparently, 
  of 
  their 
  condition 
  in 
  the 
  transitory 
  arms 
  

   of 
  the 
  Actinula 
  or 
  locomotive 
  embryo, 
  they 
  form 
  everywhere 
  a 
  deep 
  zone 
  

   interposed 
  between 
  the 
  muscular 
  layer 
  and 
  the 
  superficial 
  layer 
  of 
  the 
  

   ectoderm. 
  This 
  zone 
  is 
  designated 
  by 
  the 
  author 
  as 
  the 
  zone 
  of 
  

   claviform 
  tissue. 
  Though 
  it 
  is 
  in 
  intimate 
  association 
  with 
  the 
  fibril- 
  

   lated 
  layer, 
  the 
  author 
  did 
  not 
  succeed 
  in 
  tracing 
  a 
  direct 
  continuity 
  of 
  

   the 
  individual 
  fibrillsD 
  with 
  the 
  processes 
  of 
  the 
  cells, 
  as 
  described 
  by 
  

   Kleinenberg 
  in 
  Hydra. 
  

  

  The 
  author 
  adopts, 
  as 
  a 
  probable 
  hypothesis, 
  the 
  views 
  of 
  Kleinenberg 
  

   respecting 
  the 
  caudate 
  cells 
  of 
  Hydra, 
  which 
  he 
  regards 
  as 
  representing 
  

   a 
  nervous 
  system. 
  "While 
  the 
  deep 
  layer 
  of 
  ectodermal 
  cells 
  in 
  Myriothela 
  

   would 
  thus 
  constitute 
  a 
  nervous 
  layer, 
  the 
  superficial 
  layer 
  would 
  repre- 
  

   sent 
  an 
  epidermis 
  ; 
  and 
  since 
  recent 
  researches 
  justify 
  us 
  in 
  regarding 
  

   the 
  ectoderm 
  and 
  endoderm 
  of 
  the 
  Coelenterata 
  as 
  respectively 
  repre- 
  

   . 
  senting 
  in 
  a 
  permanent 
  condition 
  the 
  upper 
  and 
  lower 
  leaf 
  of 
  the 
  blas- 
  

   toderm 
  in 
  the 
  development 
  of 
  the 
  higher 
  animals, 
  we 
  should 
  thus 
  find 
  

   Myriothela 
  offering 
  no 
  exception 
  to 
  the 
  general 
  law, 
  which 
  derives 
  both 
  

   epidermic 
  and 
  nervous 
  tissues 
  from 
  the 
  upper 
  leaf 
  of 
  the 
  blastoderm. 
  

  

  The 
  structure 
  of 
  the 
  tentacles 
  is 
  in 
  the 
  highest 
  degree 
  interesting. 
  In 
  

  

  x2 
  

  

  