﻿1875.] 
  

  

  and 
  Development 
  of 
  Myriothela. 
  

  

  253 
  

  

  In 
  the 
  female, 
  the 
  primitive 
  plasma 
  becomes 
  gradually 
  differentiated 
  

   into 
  a 
  multitude 
  of 
  cell-like 
  bodies 
  having 
  all 
  the 
  characters 
  of 
  true 
  ova 
  

   with 
  their 
  germinal 
  vesicle 
  and 
  spot. 
  They 
  are 
  entirely 
  destitute 
  of 
  

   enveloping 
  membrane. 
  

  

  These 
  bodies 
  next 
  begin 
  to 
  coalesce 
  with 
  one 
  another 
  into 
  numerous 
  

   roundish 
  masses 
  of 
  protoplasm, 
  which 
  develop 
  over 
  their 
  surface 
  minute 
  

   pseudopodial 
  retractile 
  processes. 
  

  

  The 
  masses 
  thus 
  formed 
  still 
  further 
  coalesce 
  with 
  one 
  another 
  ; 
  and 
  

   there 
  results 
  a 
  single 
  spheroidal 
  plasma 
  mass, 
  through 
  which 
  are 
  dis- 
  

   persed 
  numerous 
  small 
  spherical 
  vesicles, 
  mostly 
  provided 
  with 
  a 
  nucleus. 
  

   These 
  vesicles 
  appear 
  to 
  be 
  nothing 
  more 
  than 
  the 
  nucleolated 
  nuclei 
  of 
  

   the 
  coalesced 
  ovum-like 
  cells. 
  

  

  About 
  the 
  time 
  of 
  the 
  completion 
  of 
  this 
  last 
  coalescence, 
  the 
  resulting 
  

   plasma 
  mass, 
  enveloped 
  in 
  an 
  external, 
  very 
  delicate, 
  structureless 
  mem- 
  

   brane, 
  is 
  expelled, 
  by 
  the 
  contraction 
  of 
  the 
  sporosac, 
  through 
  an 
  aper- 
  

   ture 
  formed 
  by 
  rupture 
  in 
  its 
  summit. 
  

  

  Immediately 
  after 
  its 
  expulsion, 
  it 
  is 
  seized, 
  in 
  a 
  manner 
  which 
  for- 
  

   cibly 
  suggests 
  the 
  supposed 
  action 
  of 
  the 
  Fallopian 
  tube 
  on 
  the 
  mammalian 
  

   ovum 
  at 
  the 
  moment 
  of 
  its 
  escape 
  from 
  the 
  Graafian 
  follicle, 
  by 
  the 
  

   sucker-like 
  extremities 
  of 
  certain 
  remarkable 
  bodies, 
  to 
  which 
  the 
  author 
  

   gave 
  the 
  name 
  of 
  claspers, 
  which 
  are 
  developed 
  among 
  the 
  blastostyles, 
  

   and 
  resemble 
  long 
  filiform 
  and 
  very 
  contractile 
  tentacles. 
  

  

  It 
  is 
  apparently 
  now 
  that 
  fecundation 
  is 
  effected 
  ; 
  for 
  the 
  plasma 
  be- 
  

   comes 
  again 
  resolved 
  into 
  a 
  multitude 
  of 
  roundish 
  masses. 
  This 
  phe- 
  

   nomenon 
  may 
  be 
  regarded 
  as 
  representing 
  the 
  yelk-cleavage 
  of 
  an 
  

   ordinary 
  ovum. 
  Reasons 
  are 
  assigned 
  for 
  believing 
  that 
  it 
  is 
  through 
  the 
  

   agency 
  of 
  the 
  claspers 
  that 
  fecundation 
  takes 
  place 
  ; 
  and 
  the 
  claspers 
  are 
  

   compared 
  to 
  the 
  hectocotylus 
  of 
  Cephalopods, 
  and 
  to 
  certain 
  organs 
  by 
  

   which 
  fecundation 
  is 
  effected 
  among 
  the 
  Algae. 
  

  

  The 
  mulberry-like 
  mass 
  thus 
  formed, 
  surrounded 
  by 
  its 
  structureless 
  

   membrane, 
  which 
  has 
  now 
  acquired 
  considerable 
  thickness 
  and 
  forms 
  a 
  

   firm 
  capsule, 
  continues 
  to 
  be 
  held 
  in 
  the 
  grasp 
  of 
  the 
  claspers 
  during 
  cer- 
  

   tain 
  subsequent 
  stages 
  of 
  its 
  development. 
  An 
  endoderm 
  and 
  ectoderm 
  

   with 
  a 
  true 
  multicellular 
  structure 
  become 
  differentiated, 
  a 
  central 
  cavity 
  

   is 
  formed 
  by 
  excavation, 
  aud 
  the 
  germ 
  becomes 
  thus 
  converted 
  into 
  a 
  

   spheroidal 
  non-ciliated 
  Planula. 
  This, 
  after 
  acquiring 
  certain 
  external 
  

   appendages, 
  ultimately 
  escapes, 
  by 
  the 
  rupture 
  of 
  the 
  capsule, 
  as 
  a 
  free 
  

   actinuloid 
  embryo. 
  

  

  The 
  actinuloid, 
  on 
  its 
  escape 
  from 
  its 
  capsule, 
  is 
  provided 
  not 
  only 
  

   with 
  the 
  long 
  arms 
  already 
  noticed 
  by 
  Cocks 
  and 
  Alder, 
  but 
  with 
  short 
  

   scattered 
  clavate 
  tentacles. 
  The 
  short 
  clavate 
  tentacles 
  become 
  the 
  per- 
  

   manent 
  tentacles 
  of 
  the 
  fully 
  developed 
  hydroid 
  ; 
  the 
  long 
  arms, 
  on 
  the 
  

   other 
  hand, 
  are 
  purely 
  embryonic 
  and 
  transitory. 
  

  

  The 
  long 
  embryonic 
  arms 
  originate 
  in 
  the 
  spheroidal 
  Planula. 
  They 
  

   are 
  formed 
  by 
  a 
  true 
  invagination, 
  and 
  at 
  first 
  grow 
  inwards 
  into 
  the 
  

  

  