﻿92 
  Prof. 
  M'lntosh's 
  Notes 
  from 
  the 
  

  

  continued 
  laterally 
  to 
  the 
  first 
  branchia. 
  This 
  is 
  followed 
  

   by 
  another 
  median 
  elevation 
  or 
  boss 
  -with 
  a 
  ridge 
  on 
  each 
  

   side 
  to 
  the 
  second 
  branchia. 
  The 
  parts, 
  however, 
  vary 
  much 
  

   according 
  to 
  the 
  degree 
  of 
  contraction 
  or 
  extension, 
  the 
  first- 
  

   mentioned 
  median 
  fold 
  in 
  extension 
  becomes 
  a 
  boss, 
  in 
  front 
  

   of 
  which 
  a 
  groove 
  "with 
  a 
  fillet 
  at 
  each 
  side 
  passes 
  to 
  the 
  

   mouth. 
  Behind 
  the 
  second 
  branchial 
  ridge 
  is 
  a 
  distinct 
  and 
  

   longer 
  one 
  on 
  each 
  side 
  of 
  a 
  median 
  elevation, 
  and 
  ter- 
  

   minating 
  laterally 
  in 
  the 
  first 
  bristle-papilla. 
  The 
  bristle- 
  

   tufts 
  are 
  directed 
  upward 
  and 
  backward, 
  commencing 
  with 
  

   three 
  smaller 
  tufts, 
  the 
  first 
  two 
  of 
  which 
  spring 
  from 
  the 
  

   outer 
  ends 
  of 
  ventral 
  ridges 
  connected 
  with 
  median 
  eleva- 
  

   tions, 
  whilst 
  the 
  third 
  has 
  only 
  a 
  lateral 
  lamella. 
  No 
  hooks 
  

   occur 
  on 
  these 
  anterior 
  feet. 
  The 
  fourth 
  foot 
  presents 
  a 
  

   large 
  lamella 
  and 
  stronger 
  bristles, 
  and 
  the 
  five 
  or 
  six 
  

   following 
  have 
  also 
  strong 
  bristles, 
  after 
  which 
  they 
  

   diminish 
  to 
  the 
  last, 
  which 
  are 
  minute 
  — 
  that 
  is, 
  not 
  half 
  

   the 
  size 
  of 
  the 
  first 
  tuft. 
  The 
  structure 
  of 
  all 
  these 
  tufts 
  

   of 
  somewhat 
  brittle 
  bristles 
  is 
  the 
  same, 
  though 
  the 
  

   anterior 
  and 
  especially 
  the 
  posterior 
  show 
  certain 
  modifi- 
  

   cations. 
  Each 
  has 
  two 
  kinds 
  of 
  stout 
  bristles, 
  viz. 
  (1) 
  that 
  

   in 
  which 
  the 
  strong 
  shaft, 
  after 
  widening 
  a 
  little 
  above 
  the 
  

   base, 
  tapers 
  gradually 
  to 
  a 
  somewhat 
  rigid 
  sharp 
  tip, 
  and 
  

   (2) 
  a 
  shorter 
  series 
  in 
  which 
  the 
  stout 
  shaft 
  tapers 
  to 
  the 
  

   commencement 
  of 
  the 
  translucent 
  terminal 
  portion, 
  where 
  

   a 
  rudimentary 
  double 
  wing 
  appears, 
  and 
  then 
  it 
  dilates 
  into 
  

   a 
  flattened 
  spear-head 
  tapered 
  to 
  a 
  fine 
  point. 
  The 
  broad 
  

   flattened 
  tij) 
  is 
  marked 
  by 
  fine 
  stria3 
  directed 
  distally. 
  The 
  

   serrations 
  are 
  large 
  at 
  the 
  base 
  of 
  the 
  terminal 
  region, 
  

   rapidly 
  becom.e 
  finer, 
  then 
  indistinct, 
  and, 
  finally, 
  leave 
  the 
  

   delicate 
  hair-like 
  tip 
  smooth. 
  The 
  shafts 
  of 
  all 
  are 
  striated 
  

   longitudinally, 
  and 
  are 
  also 
  crossed 
  at 
  intervals 
  by 
  trans- 
  

   verse 
  bars, 
  which, 
  however, 
  do 
  not 
  aff"ect 
  the 
  outline. 
  In 
  

   the 
  first 
  tuft 
  of 
  bristles 
  the 
  two 
  kinds 
  are 
  more 
  nearly 
  of 
  

   equal 
  length, 
  and 
  in 
  the 
  last 
  tuft 
  the 
  tips 
  of 
  the 
  simple 
  

   forms 
  are 
  more 
  gently 
  tapered 
  as 
  well 
  as 
  often 
  fractured 
  ; 
  

   whilst 
  the 
  great 
  length 
  and 
  tenuity 
  of 
  the 
  tips 
  of 
  the 
  

   second 
  type 
  cause 
  them 
  almost 
  to 
  equal 
  the 
  length 
  of 
  

   the 
  stronger. 
  In 
  transverse 
  section 
  these 
  bristles 
  are 
  

   rounded 
  (not 
  circular). 
  

  

  The 
  hooks 
  have 
  a 
  short 
  horizontal 
  shaft, 
  a 
  gentle 
  curve, 
  

   six 
  teeth 
  along 
  the 
  front 
  edge 
  in 
  lateral 
  view, 
  then 
  a 
  broader 
  

   part 
  which, 
  at 
  first 
  sight, 
  looks 
  like 
  a 
  seventh 
  tooth, 
  but 
  

   which 
  really 
  is 
  a 
  series 
  of 
  more 
  minute 
  teeth, 
  as 
  in 
  the 
  

   typical 
  Pcctinaria 
  beh/ica, 
  tlien 
  the 
  keel 
  below 
  shows 
  a 
  

   convexity, 
  a 
  hollow, 
  and 
  a 
  small 
  knob 
  at 
  the 
  edge. 
  

  

  