﻿127 
  

  

  ON 
  SEXUAL 
  CHARACTERS 
  IN 
  THE 
  SHELL 
  AND 
  RADULA 
  OF 
  

   POM 
  ATI 
  AS 
  ELEGANS 
  (MULLER). 
  

  

  V>j 
  Dr. 
  A. 
  E. 
  Boycott, 
  F.R.S., 
  etc. 
  

  

  Bead 
  10th 
  November, 
  1916. 
  

  

  Some 
  years 
  since 
  ^ 
  I 
  examined 
  the 
  shells 
  of 
  a 
  series 
  of 
  Pomatias 
  elegans 
  

   from 
  Ashtead 
  in 
  Surrey 
  for 
  sexual 
  characters 
  and 
  found 
  that 
  tlie 
  

   females 
  were 
  longer 
  and 
  wider 
  than 
  tlie 
  males, 
  but 
  not 
  more 
  tumid, 
  

   i.e. 
  the 
  ratio 
  of 
  length 
  to 
  breadth 
  was 
  the 
  same 
  in 
  the 
  two 
  sexes. 
  

   In 
  the 
  present 
  communication 
  1 
  give 
  the 
  results 
  of 
  the 
  examination 
  

   of 
  soTiie 
  400 
  specimens, 
  collected 
  on 
  about 
  a 
  hundred 
  yards 
  length 
  of 
  

   chalky 
  hedge 
  bank 
  in 
  the 
  ])arish 
  of 
  St. 
  Stephen, 
  near 
  Aldenham, 
  

   in 
  Hertfordshire, 
  on 
  28th 
  June 
  and 
  1st 
  July, 
  1916, 
  when 
  they 
  were 
  

   crawling 
  freely 
  on 
  tlie 
  surface 
  after 
  rain. 
  All 
  specimens 
  found 
  

   were 
  taken 
  without 
  selection. 
  The 
  two 
  lots 
  were 
  analysed 
  separately, 
  

   but 
  no 
  significant 
  difference 
  was 
  found 
  in 
  any 
  respect 
  and 
  they 
  are 
  

   treated 
  below 
  as 
  forming 
  one 
  series.'' 
  

  

  The 
  shells 
  were 
  measured 
  with 
  sliding 
  callipers 
  to 
  O'l 
  mm., 
  the 
  

   length 
  (altitude) 
  being 
  taken 
  parallel 
  to 
  the 
  axis 
  of 
  the 
  shell 
  and 
  

   the 
  breadth 
  (diameter) 
  at 
  right 
  angles 
  to 
  the 
  length. 
  The 
  fraction 
  

  

  4^-^ 
  X 
  100 
  gives 
  a 
  measure 
  of 
  tumidity. 
  These 
  figures 
  do 
  not 
  of 
  

  

  diameter 
  

  

  course 
  afford 
  a 
  complete 
  description 
  of 
  the 
  shells; 
  with 
  regard 
  to 
  

  

  the 
  shape 
  of 
  whorls, 
  depth 
  of 
  suture, 
  size 
  and 
  shape 
  of 
  mouth, 
  and 
  

  

  the 
  like, 
  1 
  can 
  only 
  say 
  that 
  by 
  visual 
  inspection 
  I 
  can 
  detect 
  no 
  

  

  difference 
  between 
  males 
  and 
  females. 
  

  

  In 
  comparing 
  males 
  and 
  females 
  it 
  is 
  necessary 
  in 
  the 
  first 
  instance 
  

  

  to 
  take 
  only 
  mature 
  specimens, 
  and 
  as 
  the 
  criterion 
  of 
  maturity 
  

  

  the 
  completion 
  of 
  the 
  peristome 
  has 
  been 
  used.^ 
  There 
  will 
  obviously 
  

  

  be 
  a 
  certain 
  number 
  of 
  specimens 
  in 
  which 
  it 
  is 
  a 
  matter 
  of 
  opinion 
  

  

  rather 
  than 
  of 
  fact 
  whetlier 
  the 
  peristome 
  is 
  complete 
  or 
  not; 
  but 
  

  

  such 
  specimens 
  are 
  few 
  in 
  number, 
  and, 
  noting 
  also 
  the 
  texture 
  

  

  of 
  the 
  edge 
  of 
  the 
  shell 
  and 
  the 
  depth 
  within 
  the 
  mouth 
  where 
  

  

  the 
  operculum 
  makes 
  a 
  good 
  fit, 
  there 
  does 
  not 
  seem 
  to 
  be 
  much 
  

  

  danger 
  of 
  any 
  substantial 
  inconsistency 
  in 
  the 
  determination 
  of 
  

  

  maturity, 
  at 
  any 
  rate 
  within 
  the 
  same 
  series 
  of 
  shells 
  examined 
  at 
  

  

  ^ 
  Journal 
  of 
  Conchology, 
  vol. 
  xii, 
  1909, 
  p. 
  323. 
  

  

  - 
  e.g. 
  in 
  the 
  first 
  lot 
  males 
  formed 
  54 
  per 
  cent 
  of 
  130 
  mature 
  specimens, 
  in 
  the 
  

   second 
  61 
  per 
  cent 
  of 
  187, 
  a 
  difference 
  easily 
  compatible 
  with 
  the 
  two 
  lots 
  

   being 
  random 
  samples 
  of 
  the 
  same 
  series. 
  

  

  " 
  I 
  do 
  not 
  know 
  whether 
  sexual 
  activity 
  is 
  restricted 
  to 
  individuals 
  which 
  are 
  

   mature 
  bv 
  this 
  standard 
  ; 
  anatomically 
  the 
  sexual 
  apparatus 
  seems 
  to 
  be 
  

   pretty 
  fully 
  developed 
  in 
  the 
  larger 
  immature 
  specimens 
  (e.g. 
  in 
  many 
  of 
  

   the 
  males 
  of 
  11-5 
  mm. 
  altitude). 
  In 
  species 
  where 
  the 
  growth 
  of 
  the 
  shell 
  

   reaches 
  a 
  definitive 
  termination 
  (e.g. 
  Tachea), 
  completion 
  of 
  the 
  shell 
  

   seems 
  to 
  precede 
  sexual 
  action. 
  The 
  six 
  pairs 
  taken 
  in 
  cop. 
  in 
  the 
  present 
  

   series 
  were 
  all 
  mature. 
  

  

  