﻿406 
  E" 
  T. 
  Young, 
  

  

  Taenia 
  pisifonnis 
  ^) 
  and 
  the 
  fragmentation 
  of 
  spermatocytes 
  in 
  Jfome^icr 
  

   — 
  fide 
  Child 
  (1907, 
  II); 
  the 
  absence 
  or 
  great 
  rarity 
  of 
  definite 
  pro-, 
  

   ana-, 
  and 
  telophases 
  in 
  the 
  second 
  oocyte 
  mitosis; 
  the 
  irregular 
  

   occurrence 
  of 
  mitosis 
  in 
  cleavage 
  ^) 
  ; 
  the 
  usual 
  rarity 
  of 
  somatic 
  

   mitoses 
  in 
  Moniezia 
  — 
  fide 
  Child 
  (1907, 
  IV) 
  ^) 
  and 
  its 
  occasional 
  

   abundance 
  in 
  the 
  same 
  tissues 
  (Child, 
  1910); 
  their 
  great 
  rarity 
  

   in 
  several 
  different 
  species 
  of 
  cestodes, 
  and 
  their 
  occasionally 
  

   common 
  occurence 
  in 
  one 
  species 
  (Anoplocephala 
  sp.)^), 
  (Young, 
  1910); 
  

   all 
  indicates 
  that 
  mitosis 
  in 
  cestodes 
  is 
  a 
  degenerating 
  process, 
  prob- 
  

   ably 
  in 
  correlation 
  with 
  their 
  otherwise 
  degenerate 
  character. 
  

  

  The 
  other 
  alternative 
  to 
  this 
  hypothesis, 
  which 
  is 
  maintained 
  

   by 
  RiCHAEDs 
  (1911), 
  is 
  that 
  of 
  periodicity 
  of 
  mitosis. 
  Were 
  this 
  

   view 
  opposed 
  by 
  nothing 
  but 
  negative 
  evidence, 
  namely 
  absence 
  or 
  

   rarity 
  of 
  mitoses 
  in 
  most 
  cestode 
  tissues 
  and 
  species, 
  so 
  far 
  as 
  

   observed 
  ^), 
  I 
  should 
  hesitate 
  to 
  agree 
  with 
  this 
  author 
  that 
  "The 
  

   failure 
  to 
  find 
  evidence 
  of 
  a 
  certain 
  process 
  ... 
  is 
  ... 
  positive 
  evi- 
  

   dence 
  of 
  the 
  lack 
  of 
  that 
  process" 
  (1. 
  c, 
  p. 
  127). 
  But 
  when, 
  in 
  con- 
  

   junction 
  with 
  this 
  negative 
  evidence, 
  there 
  is 
  such 
  positive 
  evidence 
  

   of 
  amitosis 
  as 
  I 
  have 
  found 
  in 
  the 
  spermatogonial 
  divisions, 
  for 
  

   example, 
  and 
  of 
  degeneration 
  of 
  mitosis 
  as 
  in 
  the 
  spermatocytic 
  and 
  

   oocytic 
  divisions, 
  I 
  believe 
  that 
  the 
  balance 
  of 
  evidence 
  is 
  in 
  favor 
  

   of 
  my 
  hypothesis 
  as 
  opposed 
  to 
  that 
  of 
  Richards, 
  which, 
  as 
  he 
  

   himself 
  admits, 
  "is 
  based 
  first 
  upon 
  certain 
  a 
  priori 
  considerations" 
  

   (1. 
  c, 
  p. 
  159). 
  

  

  BovERi 
  (1907) 
  has 
  established 
  three 
  criteria 
  which 
  must 
  be 
  met 
  

   in 
  order 
  to 
  prove 
  that 
  cells 
  which 
  have 
  once 
  divided 
  amitotically 
  

   can 
  later 
  divide 
  by 
  mitosis, 
  namely: 
  1. 
  that 
  the 
  supposedly 
  amitotic 
  

   figures 
  actually 
  represent 
  this 
  process 
  and 
  are 
  not 
  due 
  simply 
  to 
  a 
  

   lobulate 
  or 
  binucleate 
  condition; 
  2. 
  that 
  a 
  division 
  of 
  cytoplasm 
  

  

  T. 
  serrata 
  and 
  myself 
  (see 
  above 
  pages 
  377 
  and 
  386) 
  in 
  both 
  testis 
  and 
  

   ovary 
  of 
  the 
  latter. 
  

  

  1) 
  "With 
  four 
  doubtful 
  exceptions, 
  see 
  page 
  377, 
  

  

  2) 
  Common 
  in 
  later 
  but 
  not 
  earlier 
  .cleavages 
  in 
  Taenia 
  pisiformis,. 
  

   common 
  in 
  all 
  stages 
  in 
  Moniezia 
  — 
  fide 
  Richards 
  (1911). 
  

  

  3) 
  Richards 
  (1911, 
  p. 
  140) 
  says 
  that 
  in 
  the 
  anläge 
  of 
  the 
  female 
  

   reproductive 
  organs 
  of 
  Moniezia 
  "mitoses 
  occur 
  . 
  . 
  . 
  not 
  as 
  frequently 
  as 
  

   one 
  would 
  expect 
  from 
  conditions 
  in 
  other 
  tissues". 
  

  

  4) 
  According 
  to 
  a 
  recent 
  examination 
  of 
  this 
  form 
  by 
  DOUTHITT 
  in 
  

   Ward's 
  laboratory, 
  it 
  probably 
  belongs 
  to 
  Beriiella 
  not 
  Anoplocephala. 
  

  

  5) 
  Fide 
  BuGGE 
  (1902), 
  Child 
  (1904, 
  1907, 
  I— 
  V), 
  Spätlich 
  (1909), 
  

   Richards 
  (1909, 
  1911), 
  Young 
  (1908, 
  1910). 
  

  

  