﻿482 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [56] 
  

  

  mate 
  the 
  suilline 
  Ungulates 
  in 
  the 
  distribution 
  of 
  the 
  vibrissa} 
  in 
  the 
  

   fcetai 
  condition. 
  The 
  Delphinoid 
  forms, 
  on 
  the 
  other 
  hand, 
  show 
  three 
  

   types 
  of 
  distribution 
  of 
  the 
  same 
  organs, 
  namely, 
  that 
  seen 
  in 
  Inia, 
  

   which 
  approaches 
  that 
  of 
  the 
  pigs, 
  that 
  of 
  Phoccena, 
  which 
  approxi- 
  

   mates 
  slightly 
  that 
  of 
  the 
  Carnivora, 
  and 
  a 
  third 
  which 
  approaches 
  

   neither, 
  all 
  indications 
  of 
  vibrissa} 
  beiug 
  absent 
  even 
  in 
  the 
  foetal 
  con- 
  

   dition. 
  That 
  the 
  distribution 
  of 
  tactile 
  hairs 
  cannot 
  be 
  of 
  much 
  im- 
  

   portance 
  in 
  taxonomy 
  is 
  shown 
  by 
  the 
  fact 
  that 
  a 
  cluster 
  of 
  tactile 
  hairs 
  

   is 
  found 
  above 
  the 
  eyes 
  in 
  the 
  pig, 
  dog, 
  and 
  seal, 
  and 
  another 
  at 
  the 
  

   lower 
  border 
  of 
  the 
  cheek 
  near 
  the 
  angle 
  of 
  the 
  lower 
  jaw 
  in 
  Dicotyles 
  

   and 
  Canis. 
  

  

  It 
  may 
  occur 
  to 
  the 
  reader 
  to 
  ask 
  why 
  the 
  dermal 
  follicles 
  fouud 
  about 
  

   the 
  muzzle 
  of 
  cetacean 
  embryos 
  should 
  be 
  considered 
  to 
  give 
  rise 
  to 
  

   vibrissas 
  and 
  not 
  simply 
  to 
  hairs. 
  The 
  reasons 
  why 
  I 
  chose 
  to 
  consider 
  

   them 
  in 
  the 
  former 
  light 
  is 
  this 
  : 
  They 
  resemble 
  singly 
  very 
  strikingly 
  

   in 
  the 
  cetacean 
  foetus 
  the 
  appearance 
  of 
  the 
  single 
  follicles 
  forming 
  the 
  

   cluster 
  found 
  in 
  the 
  same 
  vicinity, 
  but 
  above 
  the 
  mouth 
  only, 
  in 
  the 
  

   foetus 
  of 
  the 
  cat 
  and 
  seal. 
  A 
  tactile 
  hair 
  or 
  vibrissa 
  is 
  only 
  a 
  hair 
  de- 
  

   veloped 
  to 
  an 
  unusual 
  size, 
  and 
  in 
  Cetacea 
  as 
  well 
  as 
  in 
  Carnivora 
  these 
  

   organs 
  seem 
  to 
  have 
  their 
  follicular 
  rudiments 
  formed 
  in 
  the 
  latter 
  at 
  

   least 
  before 
  the 
  follicles 
  which 
  give 
  rise 
  to 
  the 
  general 
  hairy 
  covering 
  

   of 
  the 
  body 
  are 
  apparent. 
  Their 
  situation 
  .. 
  lose 
  to 
  the 
  mouth 
  is 
  another 
  

   reason. 
  The 
  remarkably 
  regular 
  arrangement 
  of 
  the 
  vibrissa} 
  of 
  the 
  

   muzzle 
  of 
  Carnivora 
  in 
  rows, 
  which 
  may 
  be 
  traced 
  in 
  two 
  directions 
  at 
  

   an 
  acute 
  angle 
  with 
  each 
  other, 
  is 
  not 
  apparent 
  in 
  any 
  cetacean. 
  

  

  In 
  none 
  of 
  the 
  early 
  foetuses 
  have 
  I 
  found 
  vibrissa} 
  actually 
  developed 
  

   so 
  as 
  to 
  be 
  outwardly 
  visible 
  ; 
  the 
  follicles 
  which 
  give 
  rise 
  to 
  the 
  latter 
  

   alone 
  seem 
  so 
  far 
  to 
  have 
  been 
  formed 
  in 
  the 
  foetuses. 
  This 
  is 
  the 
  case 
  

   so 
  far 
  as 
  I 
  have 
  been 
  able 
  to 
  make 
  out 
  in 
  both 
  the 
  early 
  foetuses 
  of 
  Car- 
  

   nivora 
  and 
  Cetacea. 
  

  

  IX. 
  — 
  Summary. 
  

  

  The 
  results 
  of 
  the 
  preceding 
  studies 
  may 
  be 
  briefly 
  embodied 
  in 
  the 
  

   following 
  paragraphs 
  : 
  

  

  1. 
  The 
  structure 
  of 
  the 
  pinnipeds 
  indicates 
  that 
  the 
  process 
  by 
  which 
  

   their 
  hind 
  limbs 
  were 
  directed 
  backward 
  and 
  partially 
  included 
  together 
  

   with 
  the 
  tail 
  in 
  a 
  common 
  integumentary 
  investment, 
  would, 
  if 
  exag- 
  

   gerated, 
  lead 
  to 
  the 
  translocation 
  and 
  fusion 
  of 
  the 
  feet 
  with 
  the 
  end 
  of 
  

   the 
  sides 
  of 
  the 
  tail 
  as 
  in 
  the 
  cetaceans, 
  in 
  which 
  the 
  now 
  degenerate, 
  

   backwardly-displaced 
  feet 
  are 
  represented 
  by 
  the 
  flukes. 
  

  

  This 
  general 
  thesis 
  is 
  supported 
  by 
  the 
  following 
  minor 
  considera- 
  

   tions 
  which 
  have 
  been 
  developed 
  in 
  the 
  successive 
  subdivisions 
  of 
  the 
  

   preceding 
  memoir 
  as 
  follows 
  : 
  

  

  1. 
  The 
  inconstancy 
  of 
  the 
  dorsal 
  fin 
  ; 
  its 
  variability 
  in 
  size, 
  from 
  none 
  

   at 
  all 
  to 
  a 
  well-developed 
  one, 
  and 
  its 
  variable 
  position. 
  

  

  2. 
  The 
  non-connection 
  of 
  the 
  dorsal 
  fin 
  with 
  any 
  muscles 
  and 
  its 
  

  

  