﻿74 
  INTRODUCTION. 
  

  

  Our 
  larger 
  species 
  of 
  toads 
  and 
  frogs 
  do 
  not 
  

   appear 
  to 
  be 
  able 
  to 
  propagate 
  until 
  four 
  or 
  five 
  

   years 
  old. 
  But 
  it 
  lias 
  been 
  ascertained 
  on 
  specimens 
  

   kept 
  in 
  confinement 
  that 
  Alytes, 
  Bomhinator, 
  Felohates, 
  

   and 
  Ri/la 
  — 
  which 
  are 
  of 
  proportionally 
  larger 
  size 
  

   immediately 
  after 
  transformation 
  — 
  attain 
  much 
  sooner 
  

   their 
  full 
  development, 
  and 
  may 
  breed 
  in 
  the 
  third 
  

   year 
  of 
  their 
  existence. 
  

  

  A 
  curious 
  fact, 
  for 
  which 
  we 
  can 
  at 
  present 
  find 
  no 
  

   explanation, 
  is 
  the 
  very 
  considerable 
  excess 
  of 
  males 
  

   over 
  females 
  in 
  the 
  genera 
  Pelodytes, 
  Pelobates, 
  and 
  

   Bufo, 
  when 
  adult 
  at 
  least, 
  as 
  has 
  been 
  observed 
  not 
  

   only 
  during 
  the 
  breeding 
  season, 
  but 
  also 
  at 
  other 
  

   times, 
  and 
  especially 
  during 
  the 
  winter, 
  when 
  numbers 
  

   congregate 
  in 
  holes. 
  In 
  other 
  genera 
  the 
  proportion 
  of 
  

   both 
  sexes 
  appears 
  about 
  equal 
  ; 
  Born 
  and 
  Yung 
  have 
  

   even 
  ascertained 
  that 
  in 
  the 
  young 
  of 
  the 
  genus 
  Bana 
  

   the 
  females 
  are 
  in 
  the 
  proportion 
  of 
  54 
  to 
  61 
  per 
  cent. 
  

   It 
  is 
  believed 
  that 
  in 
  some 
  lower 
  animals 
  abundance 
  

   of 
  food 
  is 
  an 
  important 
  factor 
  determining 
  sex. 
  The 
  

   two 
  above-mentioned 
  physiologists 
  have 
  conducted 
  a 
  

   series 
  of 
  experiments 
  on 
  tadpoles 
  of 
  frogs 
  {Bana 
  

   temporai'ia), 
  and 
  by 
  giving 
  them 
  a 
  more 
  abundant 
  

   or 
  more 
  artificial 
  food 
  have 
  obtained 
  a 
  much 
  higher 
  

   ratio 
  of 
  females, 
  viz. 
  70 
  to 
  95 
  per 
  cent. 
  -A. 
  von 
  

   Griesheim, 
  after 
  examining 
  the 
  sexes 
  of 
  440 
  specimens 
  

   of 
  the 
  common 
  frog 
  captured 
  immediately 
  after 
  the 
  

   metamorphosis, 
  found 
  only 
  36 
  per 
  cent, 
  of 
  males. 
  It 
  

   would 
  be 
  highly 
  interesting 
  to 
  make 
  a 
  similar 
  investi- 
  

   gation 
  on 
  the 
  young 
  of 
  some 
  species, 
  such 
  as 
  Bufo 
  

   vulgaris 
  or 
  Pelobates 
  fuscus, 
  in 
  which 
  the 
  number 
  of 
  

   adult 
  males 
  far 
  exceeds 
  that 
  of 
  females. 
  

  

  