﻿451 
  Prof. 
  M'Intosh 
  on 
  the 
  

  

  the 
  proboscis. 
  By 
  rigid 
  contraction, 
  as 
  formerly 
  mentioned, 
  

   the 
  blood 
  can 
  be 
  almost 
  entirely 
  driven 
  from 
  the 
  tentacles. 
  

   The 
  organs 
  thus 
  capture 
  prey 
  and 
  aid 
  in 
  aerating 
  the 
  blood. 
  

  

  VIII. 
  The 
  Reproductive 
  System. 
  

  

  The 
  sexual 
  elements 
  are 
  developed 
  in 
  great 
  profusion 
  

   from 
  the 
  epithelium 
  of 
  the 
  body-wall 
  of 
  the 
  posterior 
  region. 
  

   In 
  males 
  the 
  whole 
  space 
  between 
  the 
  dorsal 
  and 
  ventral 
  

   longitudinal 
  muscles 
  is 
  occupied 
  by 
  a 
  mass 
  of 
  sperm-cells 
  

   and 
  spermatozoa, 
  especially 
  in 
  summer 
  — 
  the 
  animals, 
  indeed, 
  

   assuming 
  an 
  opaque 
  greyish 
  hue 
  from 
  this 
  cause. 
  The 
  head 
  

   of 
  the 
  spermatozoon 
  is 
  shaped 
  like 
  a 
  conical 
  bullet 
  with 
  a 
  

   pointed 
  tip, 
  and 
  two 
  rounded 
  bodies 
  at 
  the 
  base, 
  from 
  the 
  

   centre 
  of 
  which 
  the 
  elongated 
  tail 
  projects. 
  The 
  movements 
  

   of 
  the 
  sperms 
  are 
  most 
  active. 
  Many 
  circular 
  cells 
  are 
  also 
  

   observed 
  amongst 
  them. 
  

  

  The 
  ova 
  are 
  similarly 
  developed 
  in 
  the 
  females, 
  in 
  the 
  

   posterior 
  region, 
  within 
  a 
  very 
  fine 
  limiting 
  membraue 
  or 
  

   ovary, 
  and 
  quite 
  fill 
  up 
  the 
  perivisceral 
  chamber 
  with 
  the 
  

   exception 
  of 
  the 
  alimentary 
  canal 
  and 
  the 
  region 
  for 
  the 
  

   dorsal 
  and 
  ventral 
  blood-vessels. 
  They 
  abounded 
  in 
  examples 
  

   at 
  the 
  end 
  of 
  June 
  and 
  had 
  attained 
  considerable 
  size. 
  

  

  In 
  both 
  males 
  and 
  females 
  with 
  developed 
  sexual 
  products 
  

   peculiar 
  structures 
  occur 
  on 
  each 
  side 
  of 
  the 
  body 
  (invariably 
  

   on 
  the 
  segment 
  immediately 
  behind 
  the 
  mouth— 
  and 
  in 
  this 
  

   it 
  first 
  attains 
  perfection), 
  as 
  well 
  as 
  on 
  many 
  of 
  the 
  poste- 
  

   rior 
  segments, 
  even 
  in 
  those 
  of 
  reproduced 
  tails. 
  In 
  trans- 
  

   verse 
  section 
  at 
  the 
  tenth 
  segment 
  the 
  central 
  structure 
  is 
  

   observed 
  to 
  lie 
  within 
  special 
  projections 
  of 
  the 
  body-wall 
  

   outside 
  the 
  vertical 
  muscle, 
  which 
  is 
  coated 
  by 
  a 
  granular 
  

   layer. 
  It 
  resembles 
  a 
  folded 
  mass, 
  the 
  folds 
  at 
  first 
  sight 
  

   simulating 
  a 
  convoluted 
  duct. 
  In 
  the 
  living 
  animal 
  the 
  

   organ 
  is 
  first 
  noticed 
  in 
  the 
  middle 
  of 
  each 
  segment 
  as 
  a 
  

   somewhat 
  ovoid 
  projection 
  of 
  the 
  lateral 
  wall, 
  and 
  invested 
  

   by 
  cuticle, 
  hypoderm, 
  and 
  basement-tissue. 
  It 
  gradually 
  

   increases 
  in 
  size, 
  and, 
  when 
  fully 
  developed, 
  presents 
  from 
  

   the 
  ventral 
  surface 
  the 
  form 
  of 
  a 
  semicircular 
  pad 
  on 
  each 
  

   side. 
  Closer 
  inspection, 
  however, 
  shows 
  that 
  the 
  latter 
  is 
  a 
  

   tongue-shaped 
  lamella, 
  which 
  curves 
  upward 
  to 
  cover 
  the 
  

   folded 
  membrane, 
  while 
  superiorly 
  there 
  is 
  a 
  slipper-shaped 
  

   fold 
  of 
  similar 
  structure 
  which 
  arches 
  over 
  the 
  upper 
  part 
  

   of 
  the 
  membrane, 
  its 
  edge 
  being 
  incurved 
  laterally 
  and 
  

   inferiorly. 
  Such 
  hypodermic 
  folds 
  seem 
  to 
  be 
  formed 
  by 
  

   an 
  outgrowth 
  and 
  splitting 
  of 
  the 
  body-wall. 
  The 
  peculiar 
  

   membranous 
  structure 
  is 
  thus 
  to 
  some 
  extent 
  exposed 
  to 
  the 
  

  

  