﻿78 
  INTEODUCTION. 
  

  

  XI. 
  Eggs. 
  

  

  The 
  eggs 
  are 
  spherical 
  vitelline 
  bodies, 
  surrounded 
  

   by 
  a 
  thin, 
  elastic, 
  cortical 
  membrane 
  or 
  chorion 
  and 
  

   one 
  or 
  two 
  gelatinous 
  envelops, 
  formed 
  during 
  their 
  

   passage 
  down 
  the 
  oviducts 
  : 
  the 
  outer 
  capsule 
  swells 
  

   out 
  in 
  the 
  water 
  after 
  oviposition, 
  and 
  varies 
  accord- 
  

   ing 
  to 
  the 
  families 
  or 
  genera; 
  the 
  inner 
  is 
  absent 
  in 
  

   the 
  Pelohatidce. 
  With 
  the 
  exception 
  of 
  Alytes, 
  the 
  

   upper 
  pole 
  of 
  the 
  vitelline 
  sphere 
  is 
  always 
  pigmented, 
  

   varying 
  from 
  pale 
  brown 
  to 
  black, 
  and 
  this 
  coloration 
  

   may 
  extend 
  on 
  the 
  whole 
  sphere, 
  — 
  as, 
  ior 
  instance, 
  in 
  

   Bufo 
  vulgaris, 
  or 
  on 
  the 
  whole 
  save 
  a 
  small 
  whitish 
  

   spot 
  at 
  the 
  lower 
  pole, 
  as 
  in 
  Eana 
  temporaria. 
  The 
  

   inner 
  mucilaginous 
  envelop 
  is 
  formed 
  in 
  the 
  upper 
  

   portion 
  of 
  the 
  oviduct, 
  and 
  surrounds 
  each, 
  ovum 
  ; 
  the 
  

   outer, 
  which 
  has 
  been 
  termed 
  " 
  adhesive 
  envelop," 
  is 
  

   formed 
  lower 
  down 
  the 
  oviduct, 
  and 
  either 
  surrounds 
  

   each 
  single 
  ovum, 
  whether 
  free 
  or 
  agglutinated 
  in 
  

   masses, 
  or 
  forms 
  a 
  common 
  investment 
  in 
  which 
  the 
  

   ova 
  are 
  disposed 
  irregularly 
  or 
  in 
  files. 
  

  

  All 
  eggs, 
  except 
  those 
  of 
  Alytes, 
  are 
  deposited 
  in 
  

   the 
  water. 
  If 
  laid 
  singly, 
  each 
  is 
  fixed 
  by 
  its 
  adhesive 
  

   envelop 
  to 
  submerged 
  bodies 
  ; 
  if 
  in 
  strings 
  or 
  bands, 
  

   these 
  are 
  twined 
  round 
  plants. 
  Egg-masses 
  are 
  usually 
  

   also 
  fixed 
  to 
  plants, 
  except 
  those 
  of 
  Rana 
  temiDoraria, 
  

   which 
  are 
  endowed 
  with 
  a 
  peculiar 
  buoyancy, 
  and 
  

   simply 
  float 
  on 
  the 
  surface. 
  

  

  The 
  eggs 
  of 
  some 
  Batrachians 
  have 
  a 
  strong 
  odour 
  

   of 
  fish, 
  this 
  being 
  most 
  noticeable, 
  among 
  European 
  

   forms, 
  in 
  Pelohates 
  fuscus. 
  

  

  The 
  amount 
  of 
  protection 
  which 
  the 
  mucilaginous 
  

   envelops 
  afford 
  the 
  embryo 
  varies 
  considerably. 
  In 
  

   Discoglossus, 
  Pelodytes, 
  Pelohates, 
  and 
  Bufo 
  they 
  soon 
  

   partly 
  dissolve, 
  so 
  as 
  to 
  release 
  the 
  embryos 
  almost 
  

   before 
  these 
  are 
  able 
  to 
  execute 
  any 
  spontaneous 
  move- 
  

   ments 
  ; 
  the 
  embryos^ 
  so 
  to 
  say, 
  drop 
  out 
  and 
  become 
  

   fixed 
  by 
  their 
  adhesive 
  subbuccal 
  apparatus 
  to 
  the 
  

  

  