﻿SPEEMATOZOA. 
  1*1 
  

  

  In 
  Hyla 
  arhorea 
  the 
  head 
  is 
  spindle-shaped, 
  acutely 
  

   pointed 
  in 
  front, 
  obtusely 
  behind 
  ; 
  the 
  tail 
  filiform, 
  

   and 
  about 
  twice 
  as 
  long. 
  

  

  In 
  Uana 
  esculenta 
  and 
  arvalis 
  the 
  head 
  is 
  staff- 
  

   shaped 
  and 
  obtuse 
  in 
  front, 
  and 
  about 
  half 
  as 
  long 
  as 
  

   the 
  filiform 
  tail; 
  and 
  in 
  Rana 
  temporaria 
  and 
  agilis 
  

   the 
  head 
  is 
  very 
  long 
  and 
  thin, 
  not 
  or 
  but 
  scarcely 
  

   longer 
  than 
  the 
  tail, 
  and 
  attenuate 
  into 
  a 
  fine 
  point 
  at 
  

   both 
  ends. 
  

  

  The 
  spermatozoa 
  of 
  R. 
  grseca 
  and 
  latastii 
  bear 
  a 
  

   greater 
  resemblance 
  to 
  those 
  of 
  R, 
  arvalis, 
  but 
  have 
  a 
  

   more 
  elongate 
  head, 
  the 
  diameter 
  ten 
  to 
  twelve 
  times 
  

   in 
  the 
  length 
  ; 
  the 
  head 
  is 
  cylindrical, 
  feebly 
  attenuate, 
  

   and 
  quite 
  obtuse 
  at 
  both 
  ends. 
  

  

  The 
  spermatozoa 
  of 
  R. 
  earner 
  ani 
  and 
  R. 
  iherica 
  are 
  

   still 
  unknown. 
  

  

  Attention 
  has 
  been 
  drawn 
  above 
  to 
  the 
  importance 
  

   of 
  securing 
  for 
  comparison 
  the 
  seminal 
  elements 
  in 
  

   their 
  fully 
  ripe 
  condition. 
  La 
  Valette 
  St. 
  George 
  has 
  

   shown 
  that 
  at 
  certain 
  stages 
  of 
  development 
  these 
  are 
  

   almost 
  identical 
  in 
  R. 
  esculenta 
  and 
  R. 
  temp 
  or 
  aria 
  ; 
  

   and 
  that 
  accumulations 
  of 
  protoplasm 
  at 
  certain 
  

   points 
  of 
  the 
  unripe 
  element 
  or 
  spermatocyte, 
  as 
  he 
  

   calls 
  it, 
  produce 
  a 
  shape 
  which 
  may 
  be 
  very 
  unlike 
  

   that 
  of 
  the 
  true 
  spermatozoon. 
  So 
  careful 
  an 
  observer 
  

   as 
  Leydig 
  has 
  unfortunately 
  fallen 
  into 
  the 
  error 
  of 
  

   figuring 
  spermatocytes 
  as 
  spermatozoa 
  iu 
  Bomhinator, 
  

   Bufo, 
  and 
  Hyla. 
  

  

  Pfliiger 
  has 
  observed 
  that 
  spermatozoa 
  with 
  pointed 
  

   heads 
  possess 
  a 
  greater 
  facility 
  for 
  penetrating 
  the 
  

   envelops 
  of 
  the 
  ova 
  of 
  other 
  species 
  to 
  reach 
  the 
  

   nucleus, 
  a 
  fact 
  which 
  explains 
  the 
  difi'erent 
  results 
  

   obtained 
  in 
  attempts 
  at 
  crossing 
  in 
  both 
  directions, 
  

   to 
  which 
  highly 
  interesting 
  experiments 
  allusion 
  will 
  

   again 
  be 
  made 
  in 
  the 
  chapter 
  on 
  hybrids. 
  

  

  