﻿Structure 
  of 
  Magelona. 
  453 
  

  

  and 
  it 
  is 
  waved 
  about 
  in 
  a 
  vermiform 
  manner 
  in 
  all 
  directions. 
  

   The 
  facility 
  with 
  which 
  the 
  blood-vessels 
  form, 
  and 
  the 
  

   accuracy 
  with 
  which 
  the 
  various 
  currents 
  keep 
  the 
  required 
  

   direction 
  in 
  the 
  developing 
  tentacles 
  and 
  other 
  parts, 
  is 
  inter- 
  

   esting. 
  The 
  developing 
  papillae 
  in 
  the 
  growing 
  organ 
  first 
  

   appear 
  as 
  short 
  pale 
  elevations 
  of 
  the 
  hypoderm, 
  and 
  at 
  a 
  

   later 
  stage 
  are 
  more 
  acutely 
  pointed 
  than 
  in 
  the 
  complete 
  

   structures. 
  At 
  first 
  they 
  are 
  also 
  few 
  in 
  number, 
  but 
  

   gradually 
  increase 
  with 
  the 
  growth 
  of 
  the 
  tentacle. 
  

  

  While 
  the 
  hypodermic 
  and 
  cuticular 
  tissues 
  of 
  the 
  tentacle 
  

   are 
  continuous 
  with 
  those 
  enveloping 
  the 
  body 
  generally, 
  

   the 
  chitinous 
  basement-tissue 
  and 
  the 
  muscles 
  of 
  these 
  

   organs 
  have 
  a 
  special 
  arrangement. 
  "Where 
  the 
  tentacle 
  

   joins 
  the 
  body-wall 
  the 
  basement-tissue 
  bounding 
  the 
  ventral 
  

   longitudinal 
  muscle 
  is 
  specially 
  thickened, 
  and 
  to 
  this 
  is 
  

   attached 
  the 
  basal 
  chitinous 
  layer 
  of 
  the 
  tentacle, 
  by 
  a 
  short 
  

   anterior 
  and 
  a 
  long 
  posterior 
  curve 
  (as 
  seen 
  from 
  above). 
  

   The 
  special 
  muscles 
  of 
  the 
  tentacle 
  take 
  origin 
  from 
  this 
  

   point. 
  Moreover, 
  at 
  the 
  termination 
  of 
  the 
  median 
  cephalic 
  

   muscle, 
  certain 
  fibres 
  of 
  the 
  transverse 
  muscle, 
  boldly 
  marked 
  

   at 
  first 
  (and 
  in 
  keeping 
  with 
  those 
  of 
  the 
  ceutral 
  muscle), 
  

   pass 
  outward 
  and 
  backward 
  to 
  the 
  base 
  of 
  each 
  tentacle, 
  

   where 
  they 
  are 
  lost. 
  Such 
  are 
  probably 
  attached 
  to 
  the 
  

   chitinous 
  basement-tissue, 
  and, 
  as 
  formerly 
  noticed, 
  aid 
  in 
  

   the 
  movements 
  of 
  the 
  region. 
  

  

  In 
  a 
  large 
  male 
  loaded 
  with 
  spermatozoa 
  the 
  tentacles 
  

   were 
  comparatively 
  short 
  and 
  inert, 
  and 
  from 
  the 
  appear- 
  

   ance 
  of 
  other 
  specimens 
  it 
  is 
  possible 
  that 
  at 
  the 
  reproduc- 
  

   tive 
  season 
  degeneration 
  of 
  the 
  organs 
  may 
  occur 
  in 
  some 
  

   instances, 
  or 
  the 
  animals 
  themselves 
  may 
  perish. 
  Degenera- 
  

   tion 
  of 
  the 
  tips 
  of 
  the 
  tentacles 
  is 
  common 
  in 
  confinement. 
  

  

  On 
  the 
  whole 
  the 
  tentacles 
  show 
  a 
  further 
  differentiation 
  

   of 
  the 
  ciliated 
  hypodermic 
  groove 
  observed 
  in 
  Polydora 
  

   ciliata 
  and 
  other 
  Spionidse, 
  in 
  Phyllochcetopterus 
  and 
  Spio- 
  

   chcetopterus. 
  The 
  entire 
  absence 
  of 
  cilia, 
  however, 
  demon- 
  

   strates 
  that 
  these 
  organs 
  are 
  not 
  always 
  distinctive 
  of 
  a 
  

   respiratory 
  function, 
  as 
  M. 
  Claparede 
  seems 
  to 
  think. 
  The 
  

   structure 
  of 
  the 
  papillae, 
  again, 
  would 
  indicate 
  that 
  particles 
  

   may 
  be 
  passed 
  from 
  the 
  one 
  to 
  the 
  other, 
  and 
  they 
  often 
  

   jerk 
  independently. 
  Further, 
  in 
  regard 
  to 
  the 
  circulation 
  of 
  

   the 
  organs, 
  the 
  great 
  contractility 
  of 
  the 
  muscular 
  afferent 
  

   vessel 
  has 
  an 
  important 
  physiological 
  bearing, 
  since 
  it 
  not 
  

   only 
  sends 
  a 
  swift 
  current 
  to 
  the 
  tip, 
  but 
  through 
  the 
  

   numerous 
  capillaries 
  which 
  join 
  it 
  to 
  the 
  efferent. 
  The 
  latter 
  

   also 
  possesses 
  a 
  rapid 
  current, 
  but 
  dilates 
  very 
  readily, 
  espe- 
  

   cially 
  when 
  an 
  obstruction 
  occurs, 
  as 
  in 
  the 
  movements 
  of 
  

  

  