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GIFT  OF 


BiOLOGY 

LIBRARY 

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' 


COMPARATIVE    ZOOLOGY 


STRUCTURAL  AND  SYSTEMATIC 


FOR  USE  IN  SCHOOLS  AND  COLLEGES 


BY  JAMES   ORTON,  A.M.,  Pu.D. 

LATE   PROFESSOR  OF  NATURAL  HISTORY   IN  VA3SAR  COLLEGE;    CORRESPONDING  MEMBER 

OF  THE   ACADEMY  OF  NATURAL   SCIENCES,  PHILADELPHIA,  AND  OF  THE 

LYCEUM  OF  NATURAL  HISTORY,  NEW  YORK;    AUTHOR 

OF  "THE  ANDES  AND  THE  AMAZON,"  ETC. 


REVISED   EDITION 


"  The  education  of  a  naturalist  now  consists  chiefly  in  learning  how  to 
compare. ' ' — AG  ASSIZ  . 


NEW    YORK 
HARPER   &  BROTHERS,  FRANKLIN  SQUARE 

1889 


z 


Entered  according  to  Act  of  Congress,  in  the  year  1876,  by 

HARPER  &  BROTHERS, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


Copyright,  1883,  by  HARPER  &  BROTHERS. 


3--  1  4. 


PREFACE. 


THE  distinctive  character  of  this  work  consists  in  the 
treatment  of  the  whole  Animal  Kingdom  as  a  unit;  in 
the  comparative  study  of  the  development  and  variations 
of  organs  and  their  functions,  from  the  simplest  to  the 
most  complex  state ;  in  withholding  Systematic  Zoology 
until  the  student  has  mastered  those  structural  affinities 
upon  which  true  classification  is  founded ;  and  in  being 
fitted  for  High  Schools  and  Mixed  Schools  by  its  lan- 
guage and  illustrations,  yet  going  far  enough  to  constitute 
a  complete  grammar  of  the  science  for  the  undergraduate 
course  of  any  College. 

It  is  designed  solely  as  a  manual  for  instruction.  It  is 
not  a  work  of  reference,  nor  a  treatise.  So  far  as  a  book 
is  encyclopedic,  it  is  unfit  for  a  text-book.  This  is  pre- 
pared on  the  principle  of  "  just  enough,  and  no  more." 
It  aims  to  present  clearly,  and  in  a  somewhat  new  form, 
the  established  facts  and  principles  of  Zoology.  All  the- 
oretical and  debatable  points,  and  every  fact  or  statement, 
however  valuable,  which  is  not  absolutely  necessary  to  a 
clear  and  adequate  conception  of  the  leading  principles, 
are  omitted.  It  is  written  in  the  light  of  the  most  recent 
phase  of  the  science,  but  not  in  the  interest  of  any  par- 
ticular theory.  To  have  given  an  exhaustive  survey  of 
animal  life  would  have  been  not  only  undesirable,  but 
impossible.  Even  Cuvier's  great  work  must  be  supple- 

258235 


IV  PREFACE. 

inented  by  museums,  monographs,  and  microscopes.  Nat- 
ural History  has  outgrown  the  limits  of  a  single  book. 
Trial  has  proved  the  folly  of  giving  the  student  so  many 
things  to  learn  that  he  has  no  time  to  understand,  and  the 
error  of  condemning  the  student  to  expend  his  strength 
upon  the  details  of  classification,  which  may  change  in 
the  coming  decade,  instead  of  upon  structure,  which  is 
permanent.  Of  course,  specialists  will  miss  many  things, 
and  find  abundant  room  for  criticism  in  what  they  regard 
as  deficiencies;  but  the  work  should  be  judged  by  what 
it  does  contain,  rather  than  by  what  it  does  not. 

What  is  claimed,  in  the  language  of  inventors,  is  the 
selection  and  arrangement  of  essential  principles  and 
typical  illustrations  from  the  standpoint  of  the  teacher. 
The  synthetic  method  is  employed,  as  being  the  most 
natural:  to  begin  with  complex  Man,  instead  of  the  sim- 
plest forms,  would  give  a  false  idea.  Man  is  not  a  model, 
but  a  monstrosity,  the  most  modified  of  Vertebrates. 
But  these  outlines  must  be  filled  up,  on  the  part  of  the 
teacher,  by  lectures,  and  by  the  exhibition  of  specimens ; 
and,  on  the  part  of  the  student,  by  observation  (noting, 
above  all,  the'  characteristic  habits  of  animals),  and  by  per- 
sonal work  with  the  knife  and  microscope.  No  text-book 
can  take  the  place  of  nature,  or  supersede  oral  instruction 
from  a  competent  teacher. 

Suggestions  and  corrections  from  naturalists  and  teach- 
ers will  be  thankfully  received. 

In  a  work  of  this  character,  which  is  but  a  compound 
of  the  labors  of  all  naturalists,  it  would  be  superfluous  to 
make  acknowledgments.  The  works  referred  to  on  page 
397  have  been  specially  consulted. 


REVISER'S   NOTE. 


IN  revising  the  work  of  Professor  Orton,  the  writer  lias 
not  attempted  to  rewrite  the  book  nor  to  introduce  new 
ideas.  His  plan  has  been  to  insert  such  changes  as  the 
author  would  have  been  likely  to  make  if  he  had  lived  to 
revise  his  book.  On  only  two  points  has  the  reviser  de- 
parted from  this  plan  of  altering  only  minor  details.  The 
chapter  on  Development  has  been  largely  rewritten,  and 
the  classification  of  the  Invertebrates  has  been  changed 
so  as  to  separate  the  worms  from  the  Arthropoda  and 
the  sponges  from  the  Protozoa.  In  both  these  cases  the 
change  seemed  imperatively  demanded  by  the  progress  of 
Zoology  in  those  directions.  It  is  hoped  that  the  altera- 
tions in  the  book  will  increase  its  accuracy  and  useful- 
ness. 

EDW.  A.  BIEGE. 

UNIVERSITY  OF  WISCONSIN. 


CONTENTS. 


INTRODUCTION. 

PAGE 

Definition  of  Zoology,  and  its  Place  among  the  Sciences 11 

Historical  Sketch 14 


PART  I.— STRUCTURAL  ZOOLOGY. 

CHAPTER  I. 
MINERALS  AND  ORGANIZED  BODIES  DISTINGUISHED 19 

CHAPTER  II. 
PLANTS  AND  ANIMALS  DISTINGUISHED 21 

CHAPTER  III. 
RELATION  BETWEEN  MINERALS,  PLANTS,  AND  ANIMALS 27 

CHAPTER  IV. 
LIFE 28 

CHAPTER  V. 

ORGANIZATION 30 

1.  Cells 31 

2.  Tissues 32 

3.  Organs,  and  their  Functions. 41 

CHAPTER  VI. 
NUTRITION 45 

CHAPTER  VII. 
THE  FOOD  OF  ANIMALS...  .  47 


Viii  CONTENTS. 


CHAPTER  VIII.  PAGK 

How  ANIMALS  EAT 49 

1.  The  Prehension  of  Food 49 

2.  The  Mouths  of  Animals 55 

JJ.  The  Teeth  of  Animals 63 

4.  Deglutition,  or  How  Animals  Swallow 72 

CHAPTER  IX. 
THE  ALIMENTARY  CANAL 74 

CHAPTER  X. 
How  ANIMALS  DIGEST 91 

CHAPTER  XI. 
THE  ABSORBENT  SYSTEM 94 

CHAPTER  XII. 
THE  BLOOD  OF  ANIMALS 97 

CHAPTER  XIII. 
THE  CIRCULATION  or  THE  BLOOD 103 

CHAPTER  XIV. 
How  ANIMALS  BREATHE ill 

CHAPTER  XV. 
SECRETION  AND  EXCRETION 121 

CHAPTER  XVI. 
THE  SKIN  AND  SKELETON 127 

CHAPTER  XVII. 

How  ANIMALS  MOVE 154 

1.  Muscle.... 154 

2.  Locomotion 157 

CHAPTER  XVIII. 
1  HE  NERVOUS  SYSTEM 166 

1.  The  Senses 1 76 

2.  Instinct  and  Intelligence 184 

3.  The  Voices  of  Animals...  .   188 


CONTENTS. 


CHAPTER  XIX.  PAOK 

REPRODUCTION 191 

CHAPTER  XX. 

DEVELOPMENT 197 

1 .  Metamorphosis 207 

2.  Alternate  Generation  211 

3.  Growth  and  Repair 214 

4.  Likeness  and  Variation 215 

5.  Homology,  Analogy,  and  Correlation  217 

6.  Individuality  220 

7.  Relations  of  Number,  Size,  Form,  and  Rank 221 

8.  The  Struggle  for  Life 226 


PART  II.— SYSTEMATIC  ZOOLOGY. 

CHAPTER  XXI. 

THE  CLASSIFICATION  OF  ANIMALS 231 

Protozoa 238 

Spongida 244 

Coelenterata 246 

Echinodermntn 257 

Vermes 263 

Mollusca 269 

Arthropoda 281 

Tunicata 305 

Vertebrata 306 

CHAPTER  XXII. 
SYSTEMATIC  ARRANGEMENT  OF  REPRESENTATIVE  FORMS 362 

CHAPTER  XXIII. 
THE  DISTRIBUTION  OF  ANIMALS .  371 


NOTES 381 

THE  NATURALIST'S  LIBRARY 397 

INDEX..  ..  399 


The  first  thing  to  be  determined  about  a  new  specimen  is  not  its  name, 
but  its  most  prominent  character.  Until  you  know  an  animal,  care  not  for 
its  name. — AGASSIZ. 

The  great  benefit  which  a  scientific  education  bestows,  whether  as  train- 
ing or  as  knowledge,  is  dependent  upon  the  extent  to  which  the  mind  of  the 
student  is  brought  into  immediate  contact  with  facts — upon  the  degree  to 
which  he  learns  the  habit  of  appealing  directly  to  Nature. — HUXLEY. 


INTRODUCTION. 


1.  Definition  of  Zoology,  and  its  Place  among  the 
Sciences. — The  province  of  Natural  History  is  to  describe, 
compare,  and  classify  natural  objects.  These  objects  have 
been  divided  into  the  "organic"  and  the  "inorganic,"  or 
those  which  are,  and  those  which  are  not,  the  products  of  life. 
Biology  is  the  science  of  the  former,  and  Mineralogy  the  sci- 
ence of  the  latter.  Biology  again  separates  into  Botany,  or  the 
Natural  History  of  Plants,  and  Zoology ',  or  the  Natural  His- 
tory of  Animals  ;  while  Mineralogy  divides  into  Mineralogy 
proper,  the  science  of  mineral  species,  and  Lithology,  the 
science  of  mineral  aggregates  or  rocks.  Geology  is  that  com- 
prehensive knowledge  of  the  earth's  structure  and  develop- 
ment which  rests  on  the  whole  doctrine  of  Natural  History. 

If  we  examine  a  piece  of  chalk,  and  determine  its  physical 
and  chemical  characters,  its  mode  of  occurrence  and  its  uses, 
so  as  to  distinguish  it  from  all  other  forms  of  matter,  we 
have  its  Mineralogy.  But  chalk  occurs  in  vast  natural  beds  : 
the  examination  of  these  masses — their  origin,  structure,  po- 
sition, and  relation  to  other  rocks — is  the  work  of  the  Li- 
thologist.  Further,  we  observe  that  while  chalk  and  marble 
are  chemically  alike,  they  widely  differ  in  another  respect. 
Grinding  a  piece  of  chalk  so  thin  that  we  can  see  through 
it,  and  putting  it  under  a  microscope,  we  find  imbedded  in  it 
innumerable  bodies,  about  the  hundredth  of  an  inch  in  diame- 
ter, having  a  well-defined,  symmetrical  shape,  and  chambered 
like  a  Nautilus.  We  cannot  say  these  are  accidental  aggre- 
gations, nor  are  they  crystals  :  if  the  oyster- shell  is  formed 
by  an  oyster,  these  also  must  be  the  products  of  life.  In- 
deed, the  dredge  brings  up  similar  microscopic  skeletons 
from  the  bottom  of  the  Atlantic.  So  we  conclude  that  chalk 
is  but  the  dried  mud  of  an  ancient  sea,  the  cemetery  of  count- 


12  INTRODUCTION. 

less  animals  that  lived  and  died  long  ago.  The  considera- 
tion of  their  fossil  remains  belongs  to  Paleontology,  or  that 
part  of  Biology  which  describes  the  relics  of  extinct  forms 
of  life.  To  study  the  stratigraphical  position  of  the  chalk- 
bed,  and  by  the  aid  of  its  Paleontology  to  determine  its  age 
and  part  in  the  world's  history,  is  the  business  of  Geology. 

Of  all  the  sciences,  Zoology  is  the  most  extensive.  Its 
field  is  a  world  of  varied  forms — hundreds  of  thousands  in 
number.  To  determine  their  origin  and  development,  their 
structure,  habits,  distribution,  and  mutual  relations,  is  the 
work  of  the  Zoologist.  But  so  many  and  far-reaching  are 
the  aspects  under  which  the  animal  creation  may  be  contem- 
plated, that  the  general  science  is  beyond  the  grasp  of  any 
single  person.  Special  departments  have,  therefore,  arisen  ; 
and  Zoology,  in  its  comprehensive  sense,  is  the  combined  re- 
sult of  the  labors  of  many  workers,  each  in  his  own  line  of 
research. 

Structural  Zoology  treats  of  the  organization  of  animals. 
There  are  two  main  branches  :  Anatomy,  which  considers 
the  constitution  and  construction  of  the  animal  frame  ;  and 
Physiology,  which  is  the  study  of  the  apparatus  in  action. 
The  former  is  separated  into  Embryology,  or  an  account  of 
the  successive  modifications  through  which  an  animal  passes 
in  its  development  from  the  egg  to  the  adult  state  ;  and 
Morphology,  which  includes  all  inquiries  concerning  the  form 
of  mature  animals,  or  the  form  and  arrangement  of  their  or- 
gans. The  microscopical  examination  of  any  part,  especial- 
ly the  tissues,  belongs  to  Histology.  Comparative  Zoology 
is  the  comparison  of  the  anatomy  and  physiology  of  all  ani- 
mals, existing  and  extinct,  to  discover  the  fundamental  like- 
ness underneath  the  superficial  differences,  and  to  trace  the 
adaptation  of  organs  to  the  habits  and  spheres  of  life.  It  is 
this  comparative  science  which  has  led  to  such  grand  gen- 
eralizations as  the  unity  of  structure  amidst  the  diversity  of 
form  in  the  animal  creation,  and  by  revealing  the  degrees  of 
affinity  between  species  has  enabled  us  to  classify  them  in 
natural  groups,  and  thus  laid  the  foundation  of  Systematic 
Zoology.  When  the  study  of  structure  is  limited  to  a  par- 
ticular class  or  species  of  animals,  or  to  a  particular  organ 
or  part,  monographic  sciences  are  created,  as  Ornitliotomy , 


INTRODUCTION.  13 

or  anatomy  of  birds ;  Osteology,  or  the  science  of  bones  ; 
and  Odontography,  or  the  natural  history  of  teeth. 

Systematic  Zoology  is  the  classification  or  grouping  of  ani- 
mals according  to  their  structural  and  developmental  rela- 
tions. The  systematic  knowledge  of  the  several  classes, 
as  Insects,  Reptiles,  and  Birds,  has  given  rise  to  subordinate 
sciences,  like  Entomology,  Herpetology,  or  Ornithology.1* 

Distributive  Zoology  is  the  knowledge  of  the  successive  ap- 
pearance of  animals  in  the  order  of  time  (Paleontology  in 
part),  and  of  the  geographical  and  physical  distribution  of 
animals,  living  or  extinct,  over  the  surface  of  the  earth. 

Theoretical  Zoology  includes  those  provisional  modes  of 
grouping  facts,  and  interpreting  them,  which  still  stand 
waiting  at  the  gate  of  science.  They  may  be  true,  but  we 
cannot  say  that  they  are  true.  The  evidence  is  incomplete. 
Such  are  the  theories  which  attempt  to  explain  the  origin  of 
life  and  the  origin  of  species. 

Suppose  we  wish  to  understand  all  about  the  Horse.  Our 
first  object  is  to  study  its  structure.  The  whole  body  is  en- 
closed within  a  hide,  a  skin  covered  with  hair  ;  and  if  this 
hide  be  taken  off,  we  find  a  great  mass  of  flesh  or  muscle, 
the  substance  which,  by  its  power  of  contraction,  enables 
the  animal  to  move.  On  removing  this,  we  have  a  series  of 
bones,  bound  together  with  ligaments,  and  forming  the  skel- 
eton. Pursuing  our  researches,  we  find  within  this  frame- 
work two  main  cavities  :  one,  beginning  in  the  skull  and 
running  through  the  spine,  containing  the  brain  and  spinal 
marrow  ;  the  other,  commencing  with  the  mouth,  contains 
the  gullet,  stomach,  intestines,  and  the  rest  of  the  apparatus 
for  digestion,  and  also  the  heart  and  lungs.  Examinations 
of  this  character  would  give  us  the  Anatomy  of  the  Horse, 
or,  more  precisely,  Hippotomy.  The  study  of  the  bones 
alone  would  be  its  Osteology  /  the  knowledge  of  the  nerves 
would  belong  to  Neurotomy.  If  we  examined,  under  the 
microscope,  the  minute  structure  of  the  hair,  skin,  flesh, 
blood,  and  bone,  we  would  learn  its  Histology.  The  consid- 
eration of  the  manifold  changes  undergone  in  developing 
from  the  egg  to  the  full-grown  animal,  would  be  the  Embry- 

*  Numbers  like  this  refer  to  the  Notes  at  the  end  of  the  volume. 


14  INTRODUCTION. 

ology  of  the  Horse ;  and  its  Morphology,  the  special  study 
of  the  form  of  the  adult  animal  and  of  its  internal  organs. 

Thus  far  we  have  been  looking,  as  it  were,  at  a  steam- 
engine,  with  the  fires  out,  and  nothing  in  the  boiler  ;  but  the 
body  of  the  living  Horse  is  a  beautifully  formed,  active  ma- 
chine, and  every  part  has  its  different  work  to  do  in  the 
working  of  that  machine,  which  is  what  we  call  its  life. 
The  science  of  such  operations  as  the  grinding  of  the  food 
in  the  complex  mill  of  the  mouth  ;  its  digestion  in  the  labo- 
ratory of  the  stomach  ;  the  pumping  of  the  blood  through  a 
vast  system  of  pipes  over  the  whole  ]?ody ;  its  purification 
in  the  lungs  ;  the  process  of  growth,  waste,  and  repair  ;  and 
that  wondrous  telegraph,  the  brain,  receiving  impressions, 
sending  messages  to  the  muscles,  by  which  the  animal  is  en- 
dowed with  voluntary  locomotion — this  is  Physiology.  '  But 
Horses  are  not  the  only  living  creatures  in  the  world  ;  and 
if  we  compare  the  structures  of  various  animals,  as  the  Horse, 
Zebra,  Dog,  Monkey,  Eagle,  and  Codfish,  we  shall  find  more 
or  less  resemblances  and  differences,  enough  to  enable  us  to 
classify  them,  and  give  to  each  a  description  which  will  dis- 
tinguish it  from  all  others.  This  is  the  work  of  Systematic 
Zoology.  Moreover,  the  Horses  now  living  are  not  the  only 
kinds  that  have  ever  lived  ;  for  the  examination  of  the 
earth's  crust — the  great  burial-ground  of  past  ages — reveals 
the  bones  of  numerous  horse-like  animals  :  the  study  of  this 
pre-adamite  race  belongs  to  Paleontology.  The  chronologi- 
cal and  geographical  distribution  of  species  is  the  depart- 
ment of  Distributive  Zoology.  Speculations  about  the  ori- 
gin of  the  modern  Horse,  whether  by  special  creation,  or  by 
development  from  some  allied  form  now  extinct,  are  kept 
aloof  from  demonstrative  science,  under  the  head  of  Theo- 
retical Zoology. 

2.  History. — The  Greek  philosopher  Aristotle  (B.C.  384- 
322)  is  called  the  "  Father  of  Zoology."  Certainly,  he  is  the 
only  great  representative  in  ancient  times,  though  his  fre- 
quent allusions  to  familiar  works  on  anatomy  show  that 
something  had  been  done  before  him.  His  "  History  of 
Animals,"  in  nine  books,  displays  a  wonderful  knowledge  of 
external  and  internal  structure,  habits,  instincts,  and  uses. 
His  descriptions  are  incomplete,  but  generally  exact,  so  far 


INTRODUCTION.  15 

as  they  go.  Alexander,  it  is  said,  gave  him  nine  hundred 
talents  to  collect  materials,  and  put  at  his  disposal  several 
thousand  men,  for  hunting  specimens  and  procuring  infor- 
mation. 

The  Romans  accomplished  little  in  natural  science,  though 
their  military  expeditions  furnished  unrivalled  opportuni- 
ties. Nearly  three  centuries  and  a  half  after  Aristotle,  Pliny 
(A.D.  23-79)  wrote  his  "Natural  History."  He  was  a  volu- 
minous compiler,  not  an  observer  :  he  added  hardly  one  new 
fact.  He  states  that  his  work  was  extracted  from  over  two 
thousand  volumes,  most  of  which  are  now  lost. 

During  the  Middle  Ages,  Natural  History  was  studied  in 
the  books  of  the  ancients ;  and  at  the  close  of  the  fifteenth 
century  it  was  found  where  Pliny  had  left  it,  with  the  addi- 
tion of  many  vague  hypotheses  and  silly  fancies.  Albertus 
Magnus,  of  the  thirteenth  century,  and  Conrad  Gesner  and 
Aldrovandus,  of  the  sixteenth,  were  voluminous  writers,  not 
naturalists.  In  the  latter  half  of  the  sixteenth  century,  men 
began  to  observe  nature  for  themselves.  The  earliest  note- 
worthy researches  were  made  on  Fishes,  by  Rondelet  (1507- 
1556)  andBelon  (1517-1564),  of  France,  and  Salviani  (1514- 
1572),  of  Italy.  They  were  followed  by  valuable  observa- 
tions upon  Insects,  by  Redi  (1626-1698),  of  Italy,  and  Swam- 
merdam  (1637-1680),  of  Holland  ;  and  towards  the  end  of 
the  same  century,  the  Dutch  naturalist,  Leeuwenhoeck 
(1632-1723),  opened  a  new  world  of  life  by  the  use  of  the 
microscope. 

But  there  was  no  real  advance  of  Systematic  Zoology  till 
the  advent  of  the  illustrious  John  Ray  (1628-1705),  of  Eng- 
land. His  "  Synopsis,"  published  in  1693,  contained  the  first 
attempt  to  classify  animals  according  to  structure.  Ray  was 
the  forerunner  of  "the  immortal  Swede,"  Linnaeus  (1707- 
1778),  "the  great  framer  of  precise  and  definite  ideas  of 
natural  objects,  and  terse  teacher  of  the  briefest  and  clearest 
expressions  of  their  differences."  His  chief  merit  was  in  de- 
fining generic  groups,  and  inventing  specific  names.8  Scarce- 
ly less  important,  however,  was  the  impulse  which  he  gave 
to  the  pursuit  of  Natural  History.  The  spirit  of  inquiry, 
which  his  genius  infused  among  the  great,  produced  voyages 
of  research,  which  led  to  the  formation  of  national  museums. 


16  INTKODUCTION. 

The  first  expedition  was  sent  forth  by  George  III.  of  Eng- 
land, in  1765.  Reaumur  (1683-1757)  made  the  earliest 
zoological  collection  in  France  ;  and  the  West  Indian  col- 
lections of  Sir  Hans  Sloane  (1660-1752)  were  the  nucleus  of 
the  British  Museum.  The  accumulation  of  specimens  sug- 
gested comparisons,  which  eventually  resulted  in  the  high- 
est advance  of  the  science. 

The  brilliant  style  of  Buff  on  (1707-1788)  made  Zoology 
popular  not  only  in  France,  but  throughout  Europe.  While 
the  genius  of  LinnaBus  led  to  classification,  that  of  Buffon 
lay  in  description.  He  was  the  first  to  call  attention  to  the 
subject  of  Distribution.  Lamarck  ( 1745-1829),  of  Paris, 
was  the  next  great  light.  The  publication  of  his  "  Animaux 
sans  Vertebres,"  in  1801,  was  an  epoch  in  the  history  of  the 
lower  animals.  He  was  also  the  first  prominent  advocate  of 
the  transmutation  of  species. 

But  the  brightest  luminary  in  Zoology  was  George  Cuvier 
(1769-1832),  a  German,  born  on  French  soil.  Before  his 
time,  "  there  was  no  great  principle  of  classification.  Facts 
were  accumulated,  and  more  or  less  systematized,  but  they 
were  not  yet  arranged  according  to  law  ;  the  principle  was 
still  wanting  by  which  to  generalize  them  and  give  meaning 
and  vitality  to  the  whole."  It  was  Cuvier  who  found  the 
key.  He  was  the  first  so  to  interpret  structure  as  to  be  able 
from  the  inspection  of  one  bone  to  reconstruct  the  entire 
animal,  and  assign  its  position.  His  anatomical  investiga- 
tions revealed  the  natural  affinities  of  animals,  and  led  to  the 
grand  generalization,  that  the  most  comprehensive  groups 
in  the  kingdom  were  based,  not  on  special  characters,  but  on 
different  plans  of  structure.  Palissy  had  long  ago  (1580) 
asserted  that  petrified  shells  were  of  animal  origin  ;  but  the 
publication  of  Cuvier's  "  Memoir  on  Fossil  Elephants,"  in 
1800,  was  the  beginning  of  those  profound  researches  on  the 
remains  of  ancient  life  which  created  Paleontology.  The 
discovery  of  the  true  relation  between  all  animals,  living 
and  extinct,  opened  a  boundless  field  of  inquiry  ;  and  from 
that  day  the  advance  of  Zoology  has  been  unparalleled. 
Special  studies  of  particular  parts  or  classes  of  animals  have 
so  rapidly  developed,  that  the  history  of  Zoology  during  the 
last  fifty  years  is  the  history  of  many  sciences.3 


I. 

STRUCTURAL  ZOOLOGY, 


COMPARATIVE   ZOOLOGY. 


CHAPTER  I. 

MINERALS   AND   ORGANIZED   BODIES   DISTINGUISHED. 

Nature  may  be  separated  into  two  great  kingdoms — 
that  of  mere  dead  matter,  and  that  of  matter  under  the 
influence  of  life.4  These  differ  in  the  following  points : 

( 1 )  Composition. — While  most  of  the  chemical  elements 
are  found  in  different  living  beings,  by  far  the  greater 
part  of  their  substance  is  composed  of  three  or  four — car- 
bon, oxygen,  and  hydrogen  ;  or  these  three  with  the  addi- 
tion of  nitrogen.  Next  to  these  elements,  sulphur  and 
phosphorus  are  most  widely  distributed,  though  always 
found  in  very  small  quantities.  The  organic  compounds 
belong  to  the  carbon  series,  and  contain  three,  four,  or 
five  elements.  The  former  class,  comprising  starch,  sugar, 
fat,  etc.,  are  relatively  stable.  The  latter,  possessing  the 
three  elements  named,  with  nitrogen  and  sulphur  or  phos- 
phorus, are  very  complex,  containing  a  very  large  number 
of  atoms  to  the  molecule,  and  are  usually  unstable.  Here 
belong  albumen,  myosin,  chondrin,  etc.,  the  constituents 
of  the  living  tissues.  The  formula  for  albumen  is  said  to 
be  C72H112N18SO22,  or  some  multiple  of  this  formula. 
These  compounds  also  contain  more  or  less  water,  and 
usually  exist  in  a  jelly-like  condition,  neither  solid  nor 
fluid.  With  these  colloid  substances  alone  is  life  associ- 
ated. Only  these  can  undergo  the  rapid  decomposition 


20  COMPARATIVE  ZOOLOGY. 

and  recoinposition  necessary  to  the  manifestation  of  the 
vital  phenomena. 

(2)  Structure. — Minerals  are  homogeneous,  while  organ- 
ized bodies  are  usually  heterogeneous ;  i.  e.,  composed  of 
different  parts,  called  tissues  and  organs,  having  peculiar 
uses  and  definite  relations  to  one  another.     The  tissues 
and  organs,  again,  are  heterogeneous,  consisting  mainly  of 
microscopic  cells,  structures  developed  only  by  vital  ac- 
tion.    All  the  parts  of  an  organism  are  mutually  depend- 
ent, and  reciprocally  means  and  ends,  while  each  part  of  a 
mineral  exists  for  itself.     The  smallest  fragment  of  mar- 
ble is  as  much  marble  as  a  mountain-mass ;  but  the  frag- 
ment of  a  plant  or  animal  is  not  an  individual. 

(3)  Size  and  Shape. — Living  bodies  gradually  acquire  de- 
terminate dimensions;  so  do  minerals  in  their  perfect  or 
crystal  condition.      But  uncrystallized,  inorganic  bodies 
have  an  indefinite  bulk.     Most  minerals  are  amorphous; 
crystals  have  regular  forms,  bounded,  as  a  rule,  by  plane 
surfaces  and  straight  lines ;  plants  and  animals  are  cir- 
cumscribed by  curved  surfaces,  and  rarely  assume  accurate 
geometrical  forms.6 

(4)  Phenomena. — Minerals  remain  internally  at  rest,  and 
increase  by  external  additions,  if  they  grow  at  all.     Liv- 
ing beings  are  constantly  changing  the  matter  of  which 
they  are  composed,  and  grow  by  taking  new  matter  into 
themselves  and  placing  it  among  the  particles  already 
present.     Organized  bodies,  moreover,  pass  through  a  cy- 
cle of  changes — growth,  development,  reproduction,  and 
death.     These  phenomena  are  characteristic  of  living  as 
opposed  to  inorganic  bodies.    All  living  bodies  grow  from 
within,  constantly  give  up  old  matter  and  replace  it  by 
new,  reproduce  their  kind,  and  die;  and  no  inorganic 
body  shows  any  of  these  phenomena. 


PLANTS  AND  ANIMALS  DISTINGUISHED.  21 


CHAPTER  II. 

PLANTS   AND   ANIMALS   DISTINGUISHED. 

IT  may  seem  an  easy  matter  to  draw  a  line  between 
plants  and  animals.  Who  cannot  tell  a  Cow  from  a  Cab- 
bage ?  Who  would  confound  a  Coral  with  a  Mushroom  ? 
Yet  it  is  impossible  to  assign  any  absolute,  distinctive 
character  which  will  divide  the  one  mode  of  life  from 
the  other.  The  difficulty  of  defining  an  animal  increases 
with  our  knowledge  of  its  nature.  Linnaeus  defined  it  in 
three  words ;  a  century  later,  Owen  declared  that  a  defi- 
nition of  plants  which  would  exclude  all  animals,  or  of 
animals  which  would  not  let  in  a  single  plant,  was  impos- 
sible. Each  different  character  used  in  drawing  the  boun- 
dary will  bisect  the  debatable  ground  in  a  different  lati- 
tude of  the  organic  world.  Between  the  higher  animals 
and  higher  plants  the  difference  is  apparent;  but  when 
we  reflect  how  many  characters  the  two  have  in  common, 
and  especially  when  we  descend  to  the  lower  and  minuter 
forms,  we  discover  that  the  two  "kingdoms"  touch,  and 
even  dissolve  into,  each  other.  This  border-land  has  been 
as  hotly  contested  among  naturalists  as  many  a  disputed 
frontier  between  adjacent  nations.  Its  inhabitants  have 
been  taken  and  retaken  several  times  by  botanists  and 
zoologists ;  for  they  have  characters  that  lead  on  the  one 
side  to  plants,  and  on  the  other  to  animals.  To  solve  the 
difficulty,  some  eminent  naturalists,  as  Hackel  and  Owen, 
propose  a  fourth  "  kingdom,"  to  receive  those  living  be- 
ings which  are  organic,  but  not  distinctly  vegetable  or 
animal.  But  a  greater  difficulty  arises  in  attempting  to 
fix  its  precise  limits. 


22  COMPARATIVE  ZOOLOGY. 

The  drift  of  modern  research  points  to  this :  that  there 
are  but  two  kingdoms  of  nature,  the  mineral  and  the  or- 
ganized, and  these  closely  linked  together;  that  the  lat- 
ter must  be  taken  as  one  whole,  from  which  two  great 
branches  rise  and  diverge.  "  There  is  at  bottom  but  one 
life,  which  is  the  whole  life  of  some  creatures,  and  the 
common  basis  of  the  life  of  all ;  a  life  of  simplest  moving 
and  feeling,  of  feeding  and  breathing,  of  producing  its 
kind  and  lasting  its  day:  a  life  which,  so  far  as  we  at 
present  know,  has  no  need  of  such  parts  as  we  call  organs. 
Upon  this  general  foundation  are  built  up  the  manifold 
special  characters  of  animal  and  vegetable  existence  ;  but 
the  tendency,  the  endeavor,  so  to  speak,  of  the  plant  is 
one,  of  the  animal  is  another,  and  the  unlikeness  between 
them  widens  the  higher  the  building  is  carried  up.  As 
we  pass  along  the  series  of  either  [branch]  from  low  to 
high,  the  plant  becomes  more  vegetative,  the  animal  more 
animal." ' 

Defining  animals  and  plants  by  their  prominent  char- 
acteristics, we  may  say  that  a  living  being  which  has  cell- 
walls  of  cellulose,  and  by  deoxidation  and- synthesis  of  its 
simple  food-stuffs  produces  the  complicated  organic  sub- 
stances, is  a  plant ;  while  a  living  being  which  has  albu- 
minous tissues,  and  by  oxidation  and  analysis  reduces  its 
complicated  food-stuffs  to  a  simpler  form,  is  an  animal. 
But  both  definitions  are  defective,  including  too  many 
forms,  and  excluding  forms  that  properly  belong  to  the 
respective  kingdoms.  No  definition  is  possible  which 
shall  include  all  animals  and  exclude  all  plants,  or  vice 
versa. 

(D  Origin. — Both  branches  of  the  tree  of  life  start  alike : 
the  lowest  of  plants  and  animals,  as  Protococcus  and  Gre- 
garina,  consist  of  a  single  cell.  In  fact,  the  cycle  of  life 
in  all  living  beings,  high  or  low,  begins  in  a  small,  round 
particle  of  matter — in  plants  called  an  ovule,  in  animals 


PLANTS  AND  ANIMALS  DISTINGUISHED.  23 

an  ovum.  This  cell  contains  a  serai-fluid,  called  proto- 
plasm, similar  in  composition  and  in  function.  In  the 
very  simplest  forms  the  protoplasm  is  not  enclosed  by  a 
membrane,  but  generally  there  is  a  cell-wall.  In  plants, 
with  few  exceptions,  this  wall  is  of  cellulose,  a  substance 
akin  to  starch ;  in  animals,  with  few'  exceptions,  the  wall 
is  a  pellicle  of  firmer  protoplasm,  i.  e.,  albuminous. 

(2)  Composition. — Modern  research  has  broken  down  the 
partition  between  plants  and  animals,  so  far  as  chemical 
nature  is  concerned.    The  vegetable  fabric  and  secretions 
may  be  ternary  or  binary  compounds;  but  the  essential 
living  parts  of  plants,  as  of  animals,  are  quaternary,  con- 
sisting of  four  elements — carbon,  hydrogen,  oxygen,  and 
nitrogen.     Cellulose  (woody  fibre),  starch,  arid  chlorophyl 
(green  coloring  matter)  are  eminently  vegetable  products, 
but  not  distinctive;  for  cellulose  is  wanting  in  some  plants, 

•as  some  Fungi,  and  present  in  some  animals,  as  Tunicates; 
starch,  under  the  name  of  glycogen,  is  found  in  the  liver 
and  brains  of  Mammals,  and  chlorophyl  gives  color  to  the 
fresh  -  water  Polyp.  Still,  it  holds  good,  generally,  that 
plants  consist  mainly  of  cellulose,  dextrine,  and  starch; 
while  animals  are  mainly  made  up  of  albumen,  fibrine, 
and  gelatine ;  that  nitrogen  is  more  abundant  in  animal 
tissues,  while  in  plants  carbon  is  predominant. 

(3)  Form. — No  outline  can  be  drawn  which  shall  be  com- 
mon to  all  animals  or  all  plants.     The  lowest  members  of 
both  have  no  fixed  shape.     The  spores  of  Confervas  can 
hardly  be  distinguished  from  animalcules ;  the  compound 
and  fixed  animals,  Sea-mat  and  Sea-moss  (Polyzoa),  and 
Corals,  often  resemble  vegetable  forms,  although  in  struct- 
ure widely  removed  from  plants.     Similar  conditions  of 
life  are  here  accompanied  by  an  external  likeness.     In 
free-living  animals  this  resemblance  is  not  found. 

(4)  Structure. — A  plant  is  the  multiplication  of  the  unit 
— a  cell  with  a  cellulose  wall.     Some  simple  animals  have 


24:  COMPARATIVE  ZOOLOGY. 

a  similar  simple  cellular  structure ;  and  all  animal  tissues, 
while  forming,  are  cellular.  But  this  character,  which  is 
permanent  in  plants,  is  generally  transitory  in  animals. 
In  the  more  highly  organized  tissues  the  cells  are  so  united 
as  partly  or  wholly  to  lose  their  individuality,  and  the 
characteristic  part  of  the  tissue  is  the  intercellular  sub- 
stance, while  the  cells  themselves  are  small  and  unimpor- 
tant, or  else  the  cells  are  melted  together  and  lose  their 
dividing  walls,  as  in  striped  muscles  and  in  nerves.  Ex- 
cepting the  lowest  forms,  animals  are  more  composite  than 
plants,  i.  e.,  their  organs  are  more  complex  and  numerous, 
and  more  specially  devoted  to  particular  purposes.  Rep- 
etition of  similar  parts  is  a  characteristic  of  plants ;  and 
when  found  in  animals,  as  the  Angle-worm,  is  called  vege- 
tative repetition.  Differentiation  and  specialization  are 
characteristic  of  animals.  Most  animals,  moreover,  have 
fore-and-aft  polarity;  in  contrast,  plants  are  up-and-down 
structures,  though  in  this  respect  they  are  imitated  by 
radiated  animals,  like  the  Star-fish.  Plants  are  continually 
receiving  additional  members ;  most  animals  soon  become 
perfect. 

(5)  Physiology. — In  their  modes  of  nutrition,  plants  and 
animals  stand  widest  apart.  A  plant  in  the  seed  and  an 
animal  in  the  egg  exist  in  similar  conditions:  in  both 
cases  a  mass  of  organic  matter  accompanies  the  germ. 
When  this  supply  of  food  is  exhausted,  both  seek  nourish- 
ment from  without.  But  here  analogy  ends:  the  plant 
feeds  on  mineral  matter,  the  animal  on  organic.  Plants 
have  the  power  to  form  chlorophyl,  the  green  coloring 
matter  of  leaves,  which  uses  the  force  of  the  sunlight  to 
form  starch  out  of  the  inorganic  substances — carbon-di- 
oxide and  water.  They  are  able  also  to  form  albuminoid 
matter  out  of  inorganic  substances.  A  very  few  animals 
which  have  a  substance  identical  with  or  allied  to  chloro- 
phyl have  the  same  power,7  but  in  general  animals  are  de- 


PLANTS   AND  ANIMALS  DISTINGUISHED.  25 

pendent  for  their  food  on  the  compounds  put  together  in 
plants.  Colorless  plants,  possessing  no  chlorophyl,  feed, 
like  animals,  on  organic  compounds.  No  living  being  is 
able  to  combine  the  simple  elements — carbon,  oxygen,  hy- 
drogen, and  nitrogen — into  organic  compounds. 

The  food  of  plants  is  gaseous  (carbon  dioxide  and  am- 
monia) or  liquid  (water),  that  of  animals  usually  more  or 
less  solid.  The  plant,  then,  absorbs  these  foods  through 
its  outer  surface,  while  the  animal  takes  its  nourishment 
in  larger  or  smaller  masses,  and  digests  it  in  a  special  cav- 
ity. A  few  exceptions,  however,  occur  on  both  sides. 
Certain  moulds  seem  to  swallow  their  food,  and  certain 
animals,  as  the  tape-worm,  have  no  digestive  tract. 

Plants  are  ordinarily  fixed,  their  food  is  brought  to 
them,  and  a  large  share  of  their  work,  the  formation  of 
organic  compounds,  is  done  by  the  force  of  the  sunlight; 
while  animals  are  usually  locomotive,  must  seek  their 
food,  and  are  unable  to  utilize  the  general  forces  of  nature 
as  the  plant  does.  The  plant  is  thus  able  to  grow  much 
more  than  the  animal,  as  very  little  of  the  nourishment 
received  is  used  to  repair  waste,  while  in  most  animals  the 
time  soon  comes  when  waste  and  repair  are  approximately 
equal.  But  in  both  all  work  done  is  paid  for  by  waste  of 
substance  already  formed. 

In  combining  carbon  dioxide  and  water  to  form  starch 
the  plant  sets  oxygen  free  (6(CO2)  +  5(H2O)  =  C6H10O5  + 
6(O2)) :  in  oxidizing  starch  or  other  food  the  animal  uses 
oxygen  and  sets  carbon  dioxide  free.  The  green  plant  in 
the  sunlight,  then,  gives  off  oxygen  and  uses  carbon  diox- 
ide, while  plants  which  have  no  chlorophyl,  at  all  times, 
and  all  plants  in  the  darkness,  use  oxygen  and  give  off 
carbon  dioxide,  like  an  animal.  Every  plant  begins  life 
like  an  animal — a  consumer,  not  a  producer :  not  till  the 
young  shoot  rises  above  the  soil,  and  unfolds  itself  to  the 
light  of  the  sun,  at  the  touch  of  whose  mystic  rays  chlo- 


26  COMPARATIVE  ZOOLOGY. 

rophyl  is  created,  does  real,  constructive  vegetation  begin ; 
then  its  mode  of  life  is  reversed — carbon  is  retained  and 
oxygen  set  free. 

Most  plants,  and  many  animals,  multiply  by  budding 
and  division;  on  both  we  practise  grafting;  in  both  the 
cycle  of  life  comes  round  again  to  the  ovule  or  ovum. 
Do  annuals  flower  but  to  die?  Insects  lay  their  eggs  in 
their  old  age. 

Both  animals  and  plants  have  sensibility.  This  is  one 
of  the  fundamental  physiological  properties  of  proto- 
plasm. But  in  plants  the  protoplasm  is  scattered  and 
buried  in  rigid  structures :  feeling  is,  therefore,  dull.  In 
animals,  the  protoplasm  is  concentrated  into  special  or- 
gans, and  so  feeling,  like  electricity  rammed  into  Leyden 
jars,  goes  off  with  a  flash.8  Plants  never  possess  conscious- 
ness or  volition,  as  the  higher  animals  do. 

The  self-motion  of  animals  and  the  rooted  state  of  plants 
is  a  very  general  distinction ;  but  it  fails  where  we  need  it 
most.  It  is  a  characteristic  of  living  things  to  move.  The 
protoplasm  of  all  organisms  is  unceasingly  active.9  Be- 
sides this  internal  movement,  myriads  of  plants,  as  well 
as  animals,  are  locomotive.  Rambling  Diatoms,  writhing 
Oscillaria,  and  the  agile  spores  of  Cryptogams  crowd  our 
waters,  their  instruments  of  motion  (cilia)  being  of  the 
very  same  character  as  in  microscopic  animals;  while 
Sponges,  Corals,  Oysters,  and  Barnacles  are  stationary. 
A  contractile  vesicle  is  not  exclusively  an  animal  prop- 
erty, for  the  fresh  -  water  Yolvox  and  Gonium  have  it. 
The  act  of  muscular  contraction  in  the  highest  animal  is 
due  to  the  same  kind  of  change  in  the  form  of  the  cells  of 
the  ultimate  fibrillae  as  that  which  produces  the  sensible 
motions  of  plants.  The  ciliary  movements  of  animals 
and  of  microscopic  plants  are  precisely  similar,  and  in 
neither  case  indicate  consciousness  or  self  -  determining 
power. 


RELATION  BETWEEN   MINERALS,  PLANTS,  ETC.        27 

Plants,  as  well  as  animals,  need  a  season  of  repose. 
Both  have  their  epidemics.  On  both,  narcotic  and  acrid 
poisons  produce  analogous  results.  Are  some  animals 
warm-blooded?  In  germination  and  flowering,  plants 
evolve  heat — the  stamens  of  the  Arum,  e.  g.,  showing  a 
rise  of  20°.  In  a  sense,  an  Oak  has  just  as  much  heat  as 
an  Elephant,  only  the  miserly  tree  locks  up  the  sunlight 
in  solid  carbon. 

At  present,  any  boundary  of  the  Animal  Kingdom  is 
arbitrary.  "  Probably  life  is  essentially  the  same  in  the 
two  kingdoms ;  and  to  vegetable  life,  faculties  are  super- 
added  in  the  lower  animals,  some  of  which  are,  here  and 
there,  not  indistinctly  foreshadowed  in  plants."  "  It  must 
be  said  that  there  are  organisms  which  at  one  period  of 
their  life  exhibit  an  aggregate  of  phenomena  such  as  to 
justify  us  in  speaking  of  them  as  animals,  while  at  another 
they  appear  to  be  as  distinctly  vegetable.10 


CHAPTER  III. 

RELATION   BETWEEN   MINERALS,  PLANTS,  AND   ANIMALS. 

THERE  are  no  independent  members  of  creation :  all 
things  touch  upon  one  another.  The  matter  of  the  living 
world  is  identical  with  that  of  the  inorganic.  The  plant, 
feeding  on  the  minerals,  carbon  dioxide,  water,  and  am- 
monia, builds  them  up  into  complex  organic  compounds, 
as  starch,  sugar,  gum,  cellulose,  albumen,  fibrine,  caseine, 
and  gluten.  When  the  plant  is  eaten  by  the  animal,  these 
substances  are  used  for  building  up  tissues,  repairing 
waste,  laid  up  in  reserve  as  glycogen  and  fat,  or  oxi- 
dized in  the  blood  to  produce  heat.  The  albuminoids  are 
essential  for  the  formation  of  tissues,  like  muscle,  nerve, 


28  COMPARATIVE  ZOOLOGY. 

cartilage ;  but  the  ternary  compounds  help  in  repairing 
waste,  while  both  produce  heat.  When  oxidized,  whether 
for  work  or  warmth,  these  complex  compounds  break  up 
into  the  simple  compounds — water,  carbon  dioxide,  and 
(ultimately)  ammonia,  and  as  such  are  returned  to  earth 
and  air  from  the  animal.  Both  plant  and  animal  end 
their  life  by  going  back  to  the  mineral  world:  and  thus 
the  circle  is  complete — from  dust  to  dust.  Carbonate  of 
ammonia  and  water,  a  blade  of  grass  and  a  horse,  are  but 
the  same  elements  differently  combined  and  arranged. 
Plants  compress  the  forces  of  inorganic  nature  into  chem- 
ical compounds  ;  animals  liberate  them.  Plants  produce ; 
animals  consume.  The  work  of  plants  is  synthesis,  a 
building-up ;  the  work  of  animals  is  analysis,  or  destruc- 
tion. The  tendency  in  plants  is  deoxidation;  the  tenden- 
cy in  animals  is  oxidation.  Without  plants,  animals  would 
perish;  without  animals,  plants  had  no  need  to  be.  There 
is  no  plant  which  may  not  serve  as  food  to  some  animal. 


CHAPTEK  IY. 

LIFE. 

ALL  forces  are  known  by  the  phenomena  which  they 
cause.  So  long  as  the  animal  and  plant  were  supposed  to 
exist  in  opposition  to  ordinary  physical  forces  or  indepen- 
dently of  them,  a  vital  force  or  principle  was  postulated 
by  which  the  work  of  the  body  was  performed.  It  is  now 
known  that  most,  if  not  all,  of  the  phenomena  manifested 
by  a  living  body  are  due  to  one  or  more  of  the  ordinary 
physical  forces  —  heat,  chemical  affinity,  electricity,  etc. 
There  is  no  work  done  which  demands  a  vital  force. 

The  common  modern  view  is  that  vitality  is  simply  a 


LIFE.  29 

collective  name  for  the  sum  of  the  phenomena  displayed 
by  living  beings.  It  is  neither  a  force  nor  a  thing  at  all, 
but  is  an  abstraction,  like  goodness  or  sweetness ;  or,  to 
use  Huxley's  expression,  to  speak  of  vitality  is  as  if  one 
should  speak  of  the  horologity  of  a  clock,  meaning  its 
time-keeping  properties. 

A  third  theory  is  still  possible.  The  combination  of 
elements  into  organic  cells,  the  arrangement  of  these  cells 
into  tissues,  the  grouping  of  these  tissues  into  organs,  and 
the  marshalling  of  these  organs  into  plans  of  structure, 
call  for  some  further  shaping,  controlling  power  to  effect 
such  wonderful  co-ordination.  Moreover,  the  manifesta- 
tion of  feeling  and  consciousness  is  a  mystery  which  no 
physical  hypothesis  has  cleared  up.  The  simplest  vital 
phenomenon  has  in  it  something  over  and  above  the  known 
forces  of  the  laboratory.11  If  the  vital  machine  is  given, 
it  works  by  physical  forces;  but  to  produce  it  and  keep 
it  in  order  needs,  so  far  as  we  now  know,  more  than  mere 
physical  force.  To  this  controlling  power  we  may  apply 
the  name  vitality. 

Life  is  exhibited  only  under  certain  conditions.  One 
condition  is  the  presence  of  a  physical  basis  called  proto- 
plasm. This  substance  is  found  in  all  living  bodies,  and, 
so  far  as  we  know,  is  similar  in  all  —  a  viscid,  transpar- 
ent, homogeneous,  or  minutely  granular,  albuminoid  mat- 
ter. Life  is.  inseparable  from  this  protoplasm;  but  it  is 
dormant  unless  excited  by  some  external  stimulants,  such 
as  heat,  light,  electricity,  food,  water,  and  oxygen.  Thus, 
a  certain  temperature  is  essential  to  growth  and  motion ; 
taste  is  induced  by  chemical  action,  and  sight  by  luminous 
vibrations. 

The  essential  manifestations  of  animal  life  may  be  re- 
duced to  three:  contractility;  sensibility r,  or  the  peculiar 
power  of  receiving  and  transmitting  impressions ;  and  the 
power  of  assimilating  food.  All  these  powers  are  pos- 


30  COMPARATIVE  ZOOLOGY. 

sessed  by  protoplasm,  and  so  by  all  animals:  all  move, 
feel,  and  grow.  But  some  of  the  lowest  forms  are  with- 
out the  slightest  trace  of  organs ;  they  seem  to  be  as  per- 
fectly homogeneous  and  structureless  as  a  drop  of  jelly. 
They  could  not  be  more  simple.  They  are  devoid  of 
muscles,  nerves,  and  stomach;  yet  they  have  all  the  fun- 
damental attributes  of  life — moving,  feeling,  and  eating. 
It  has  been  supposed  that  the  muscular  and  nervous  mat- 
ter is  diffused  in  a  molecular  form ;  but  all  we  can  say  is, 
that  the  highest  power  of  the  microscope  reveals  no  organ- 
ized structure  whatever — i.  0.,  there  are  no  parts  set  apart 
for  a  particular  purpose,  but  a  fragment  is  as  good  as  the 
whole  to  perform  all  the  functions  of  life.  The  animal 
series,  therefore,  begins  with  forms  that  feel  without 
nerves,  move  without  muscles,  and  digest  without  a  stom- 
ach :  in  other  words,  life  is  the  cause  of  organization,  not 
the  result  of  it.  Animals  do  not  live  because  they  are  or- 
ganized, but  are  organized  because  they  are  alive. 


CHAPTER  Y. 

ORGANIZATION. 

have  seen  that  the  simplest  life  is  a  formless  speck 
of  protoplasm,  without  distinctions  of  structure,  and  there- 
fore without  distinctions  of  function,  all  parts  serving  all 
purposes  —  mouth,  stomach,  limb,  and  lung  —  indiscrimi- 
nately. There  is  no  separate  digestive  cavity,  no  separate 
respiratory,  muscular,  .or  nervous  systems.  Every  part 
will  successively  feed,  feel,  move,  and  breathe.  Just  as  in 
the  earliest  state  of  society  all  do  everything,  each  does 
all.  Every  man  is  his  own  tailor,  architect,  and  lawyer. 
But  in  the  progress  of  social  development  the  principle  of 


ORGANIZATION.  31 

the  division  of  labor  emerges.  First  comes  a  distinction 
between  the  governing  and  governed  classes ;  then  follow 
and  multiply  the  various  civil,  military,  ecclesiastical,  and 
industrial  occupations. 

In  like  manner,  as  we  advance  in  the  animal  series,  we 
find  the  body  more  and  more  heterogeneous  and  complex 
by  a  process  of  differentiation,  i.  e.,  setting  apart  certain 
portions  of  the  body  for  special  duty.  In  the  lowest 
forms,  the  work  of  life  is  carried  on  by  very  simple  appara- 
tus." But  in  the  higher  organisms  every  function  is  per- 
formed by  a  special  organ.  For  example,  contractility, 
at  first  the  property  of  the  entire  animal,  becomes  centred 
in  muscular  tissue;  respiration,  which  in  simple  beings 
is  effected  by  the  whole  surface,  is  specialized  in  lungs 
or  gills ;  sensibility,  from  being  common  to  the  whole  or- 
ganism, is  handed  over  to  the  nerves.  An  animal,  then, 
whose  body,  instead  of  being  uniform  throughout,  is  made 
up  of  different  parts  for  the  performance  of  particular 
functions,  is  said  to  be  organized.  And  the  term  is  as  ap- 
plicable to  the  slightly  differentiated  cell  as  to  complex 
Man.  Organization  is  expressed  by  single  cells,  or  by 
their  combination  into  tissues  and  organs. 

1.  Cells. — A  cell  is  the  simplest  form  of  organized  life. 
In  general,  it  is  a  microscopic  globule,  consisting  of  a  del- 
icate membrane  enclosing  a  minute  por- 
tion of  protoplasm.  The  very  simplest 
kinds  are  without  granules  or  signs  of 
circulation;  but  usually  the  protoplasm 
is  granular,  and  contains  a  defined  sep- 
arate mass  called  the  nucleus,  within 
which  are  sometimes  seen  one  or  two, 

,  ,      ,  ,  ,  ,    Fro.  1.— Parts  of  a  Cell : 

rarely  more,  dark,  round  specks,  named     a,  v, y, ceii-waii ;  p,  uu- 
nudeoli.     The  enveloping  membrane  is     cleus;  "• uucleolu9' 
extremely  thin  and  transparent,  and  structureless:  it  is 
only  an  excretion  of  dead  matter  acting  as  a  boundary  to 


32  COMPARATIVE  ZOOLOGY. 

the  cell-contents.18  The  nucleus  is  generally  attached  to 
the  inside  of  the  membrane,  and  is  the  centre  of  activity. 

Cells  vary  greatly  in  size,  but  are  generally  invisible  to 
the  naked  eye,  ranging  from  --J-g-  to  T-JTUTTO  of  an  inch  in 
diameter.  About  4000  of  the  smallest  would  be  necessary 
to  cover  the  dot  of  this  letter  i.  The  natural  form  of  iso- 
lated cells  is  spherical;  but  when  they  crowd  each  other, 
as  seen  in  bone,  cartilage,  and  muscle,  their  outlines  be- 
come angular,  either  hexagonal  or  irregular. 

Within  the  narrow  boundary  of  a  simple  sphere,  the 
cell-membrane,  are  exhibited  all  the  essential  phenomena 
of  life  —  growth,  development,  and  reproduction.  The 
physiology  of  these  minute  organisms  is  of  peculiar  inter- 
est, since  all  animal  structure  is  but  the  multiplication  of 
the  cell  as  a  unit,  and  the  whole  life  of  an  animal  is  that 
of  the  cells  which  compose  it:  in  them  and  by  them  all 
its  vital  processes  are  carried  on.14 

The  structure  of  a  cell  can  be  seen  in  blood-corpuscles, 
by  diluting  with  a  weak  (J-  per  cent.)  solution  of  salt  a 
drop  of  blood  from  a  Frog,  and  placing  it  under  the  mi- 
croscope. (See  Fig.  63.) 

2.  Tissues.— There  are  organisms  of  the  lowest  grade 
(as  Gregarina)  which  consist  of  a  single  cell,  living  for  and 
by  itself.  In  this  case,  the  animal  and  cell  are  identical: 
the  Gregarina  has  as  much  individuality  as  the  Elephant. 
But  all  animals,  save  these  unicellular  beings,  are  mainly 
aggregations  of  cells :  for  the  various  parts  of  a  body  are 
not  only  separable  by  the  knife  into  bones,  muscles,  nerves, 
etc.,  but  these  are  susceptible  of  a  finer  analysis  by  the 
microscope,  which  shows  that  they  arise  from  the  devel- 
opment and  union  of  cells.  These  cellular  fabrics,  called 
tissues,  differ  from  one  another  both  chemically  and  struct- 
urally, but  agree  in  being  permeable  to  liquids  —  a  prop- 
erty which  secures  the  flexibility  of  the  organs  so  essential 
to  animal  life.  Every  part  of  the  human  body,  for  exam- 


ORGANIZATION.  33 

pie,  is  moist:  even  the  hairs,  nails,  and  cuticle  contain 
water.  The  contents  as  well  as  the  shape  of  the  cells  are 
usually  modified  according  to  the  tissue  which  they  form  : 
thus,  we  find  cells  containing  earthy  matter,  iron,  fat,  mu- 
cus, etc. 

In  plants,  the  cell  always  retains  the  characters  of  the 
cell;  but  in  animals  (after  the  embryonic  period)  the  cell 
usually  undergoes  such  modifications  that  the  cellular  form 
disappears.  The  cells  are  connected  together  or  enveloped 
by  an  intercellular  substance  (blastema),  which  may  be 
watery,  soft,  and  gelatinous,  firmer  and  tenacious,  still 
more  solid  and  hyaline,  or  hard  and  opaque.  In  the  fluids 
of  the  body,  as  the  blood,  the  cells  are  separate ;  i.  e.9  the 
blastema  is  fluid.  But  in  the  solid  tissues  the  cells  coa- 
lesce, being  simply  connected,  as  in  the  epidermis,  or  united 
into  fibres  and  tubes. 

In  the  lowest  forms  of  life,  and  in  all  the  higher  ani- 
mals in  their  embryonic  state,  the  cells  of  which  they  are 
composed  are  not  transformed  into  differentiated  tissues: 
definite  tissues  make  their  first  appearance  in  the  Sponges, 
and  they  differ  from  one  another  more  and  more  widely 
as  we  ascend  the  scale  of  being.  In  other  words,  the  bod- 
ies of  the  lower  and  the  immature  animals  are  more  uni- 
form in  composition  than  the  higher  or  adult  forms.  In 
the  Vertebrates  only  are  all  the  following  tissues  found 
represented : 

(1)  Epithelial  Tissue. — This  is  the  simplest  form  of  cellu- 
lar structure.  It  covers  all  the  free  surfaces  of  the  body, 
internal  and  external,  so  that  an  animal  may  be  said  to  be 
contained  between  the  walls  of  a  double  bag.  That  which 
is  internal,  lining  the  mouth,  windpipe,  lungs,  blood-ves- 
sels, gullet,  stomach,  intestines — in  fact,  every  cavity  and 
canal  —  is  called  epithelium.  It  is  a  very  delicate  skin, 
formed  of  flat  or  cylindrical  cells,  and  in  some  parts  (as  in 
the  wind-pipe  of  air-breathing  animals,  and  along  the  gills 

3 


COMPARATIVE  ZOOLOGY. 


of  the  Oyster)  is  covered  with  cilia,  or  minute  hairs,  about 
sinnr  of  an  mcn  l°ng>  which  are  incessantly  moving.  Con- 
tinuous with  this  in- 
ner lining  of  the 
body  (as  seen  on  the 
lip),  and  covering 
the  outside,  is  the 
epidermis,  or  cuti- 
cle. It  is  the  outer 
layer  of  the  "skin," 
which  we  can  re- 

Fia2.— Various  kinds  of  Epithelium  Cells:  a,  colum-  move  DJ  a  blister, 
nar,  from  small  intestine;  3,  a  single  cell,  showing  j  •  TIT  Vorjpc  in 
nucleus;  ft,  ciliated,  from  one  of  the  small  air-  ' 

tubes;  (f,  the  same,  from  the  windpipe,  with  single   thickness    from    —- 1  — 
cell  magnified  about  200  times;  c,  squamous,  from 

eyelid  of  a  calf,  showing  changes  of  form,  from  the    of    an     inch    Oil     tlie 
deep  to  superficial  cells,  1  being  the  scurf.  ,        , 

cheek  to  TV  on  the 

sole  of  the  foot.  It  is  constantly  wearing  off  at  the  sur- 
face, and  as  constantly  growing  in  the  deeper  portion ;  and 
in  the  process  of  growth  and  passage  outward,  the  cells 
change  from  the  spherical  form  to  dead  horny  scales  (seen 
in  scurf  and  dandruff).  In  the  lower  layer  of  the  cuticle 
we  find  the  pigment  cells,  characteristic  of  colored  races. 
Neither  the  epidermis  nor  the  corresponding  tissue  within 
(epithelium)  has  any  blood-vessels  or  nerves.  The  epithe- 
lial tissue,  then,  is  simply  a  superficial  covering,  bloodless 
and  insensible,  protecting  the  more  delicate  parts  under- 
neath. Hairs,  horns,  hoofs,  nails,  claws,  corns,  beaks,  scales, 
tortoise-shell,  the  wings  of  Insects,  etc.,  are  modifications 
of  the  epidermis. 

The  next  three  sorts  of  tissue  are  characterized  by  a 
great  development  of  the  intercellular  substance,  while 
the  cells  themselves  are  very  slightly  modified. 

(2)  Connective  Tissue. — This  is  the  most  extensive  tissue 
in  animals,  as  it  is  the  great  connecting  medium  by  which 
the  different  parts  are  held  together.  Could  it  be  taken 


ORGANIZATION. 


35 


out  entire,  it  would  be  a  complete  mould  of  all  the  organs. 
It  surrounds  the  bones,  muscles,  blood-vessels,  nerves,  and 
glands,  and  is  the  substance 
of  the  ligaments,  tendons, 
"true  skin,"  mucous  mem- 
brane, etc.  It  varies  in 
character,  being  soft,  ten- 
der, and  elastic,  or  dense, 
tough,  and  generally  un- 
yielding. In  the  former 
state,  it  consists  of  innu- 
merable fine  white  and  yel- 
low fibres,  which  interlace 

in     all     directions,    leaving    FIG.  3,-Connective  Tissue,  showing  areolar 

irregular  spaces,  and  form- 
ing a  loose,  spongy,  moist  web.     In  the  latter,  the  fibres 


Fie.  4 — Connective  Tissue  from  human  peritoneum;  highly  magnified;  a,  blood- 
vessel. 


36 


COMPARATIVE   ZOOLOGY. 


are  condensed  into  sheets  or  parallel  cords,  having  a  wavy, 
glistening  appearance.  Such  structures  are  the  fasciae  and 
tendons.  Connective  tissue  is  not  very  sensitive.  It  con- 
tains gelatine — the  matter  which  tans  when  hide  is  made 
into  leather.  In  this  tissue  the  intercellular  substances 
take  the  form  of  fibres.  The  white  fibres  are  inelas- 
tic, and  from  40;u0  to  YTTTS-ZT  of  an  inch  in  diameter. 
They  are  best  seen  in  the  tendons.  The  yellow  fibres  are 
elastic,  curled  at  the  ends,  very  long, 
and  from  -^nhnr  to  Winr  of  an  incn  i11 
diameter.  They  are  shown  in  the 
hinge-ligament  of  an  Oyster.  Connec- 
tive tissue  appears  areolar,  i.  e.9  shows 
interspaces,  only  under  the  microscope. 

Diagram:   a,   cartilage        (3)  Cartilaginous  Tissue. — This  tissue, 
cell;  ft,  cell  about  to  di-  .      ,     „    . 

vide  ;c,  cell  divided  iu to  known  also  as  "  gristle,  is  composed 
The' space ^etweeuathe  °f  ce^8  imbedded  in  a  granular  or  hy- 
^SEdStoS:  aline  substance,  which  is  dense,  elastic, 
stance;  highly  magui-  bluish  white,  and  translucent.  It  is 
found  where  strength,  elasticity,  and 
insensibility  are  wanted,  as  at  the 
joints.  It  also  takes  the  place  of  the 
long  bones  in  the  embryo.  When 
cartilage  is  mixed  with  connective  tis- 
sue, as  in  the  ear,  it  is  called  fibro-car- 
tilage. 

(4)  Osseous  Tissue.— This  hard,  opaque 
tissue,  called  "  bone,"  differs  from  the 
former  two  in  having  the  intercellular 
spaces  or  meshes  filled  with  phosphate 
of  lime  and  other  earths,  instead  of  a 
a  hyaline  or  fibrous  substance.     It  may 
FiG.6.-owifyiug  carti-  ^e  caned  petrified  tissue — the  quantity 

lage,  X  10;  a,  cartilage 

cells,  passing  into  com-  of  earthy  matter,  and  therefore  the  brit- 

pact  bone,  c,  and  then  .  ..1,1 

spongy  bone,  e.  tleness  of  the  bone,  increasing  with  the 


ORGANIZATION. 


37 


age  of  the  animal.  If  a  chicken-bone  be  left  in  dilute 
muriatic  acid  several  days,  it  may  be  tied  into  a  knot,  since 
the  acid  has  dissolved 
the  lime,  leaving  noth- 
ing but  cartilage  and 
connective  tissue.  If  a 
bone  be  burned,  it  be- 
comes light,  porous,  and 
brittle,  the  lime  alone 
remaining.16 

Bone  is  a  very  vas- 
cular tissue;  that  is,  it 
is  traversed  by  minute 
blood-vessels  and  nerves,  _ 

7    FIG.  7. — Transverse  section  of  a  Bone  (Human 
which     paSS     through     a         Femur),  x  50,  showing  Haversian  canals. 

net-work  of  tubes,  called  Haversian  canals.  The  canals 
average  -nnnr  of  an  inch,  being  finest  near  the  surface  of 
the  bone,  and  larger  further  in,  where  they  form  a  cancel- 
lated or  spongy  structure,  and  finally  merge  (in  the  long 

bones)  into  the  central 
cavity,  containing  the 
marrow.  Under  the 
microscope,  each  canal 
appears  to  be  the  cen- 
tre of  a  multitude  of 
lamina?,  or  plates,  ar- 
ranged around  it.  Ly- 
ing between  these  plates 
are  little  cavities,  called 
lacunae,  from  which  ra- 
diate exceedingly  fine 

.-Frontal  Bone  of  Human  Skull  under  the   pOl'68,       Or       Canoliculi. 
microscope,  showing  lacuni  and  canaliculi.         These       represent       the 

original  cells  of  the  bone,  and  differ  in  shape  and  size  in 
different  animals. 


38 


COMPARATIVE  ZOOLOGY. 


True  bone  is  found  only  in  Vertebrates,  or  back-boned 
animals. 

(5)  Dental  Tissue. — Like  bone,  a  tooth  is  a  combination 
of  earthy  and  animal  matter.  It  may  be  called  petrified 
skin.  In  the  higher  animals,  it  consists  of  three  parts : 
dentine,  forming  the  body  of  the  tooth,  and  always  pres- 
ent; enamel,  capping  the  crown;  and  cement,  covering  the 
fangs  (Fig.  31).  The  last  is  true  bone,  or  osseous  tissue. 


FIO.  9.— Highly  magnified  section  of  Dentine  and  Cement,  from  the  fang  of  a  Human 
Molar:  a,  b,  marks  of  the  original  dentinal  pulp;  d,  dentiual  tubes,  terminating 
in  the  very  sensitive,  modified  layer,  g ;  h,  cement. 

Dentine  resembles  bone,  but  differs  in  having  neither  la- 
cunae nor  (save  in  Shark's  teeth)  canaliculi.  It  shows,  in 
place  of  the  former,  innumerable  parallel  tubes,  reaching 
from  the  outside  to  the  pulp-cavity  within.  The  "  ivory  " 
of  Elephants  consists  of  dentine.  Enamel  is  the  hardest 
substance  in  the  body,  and  is  composed  of  minute  six-sided 
fibres,  set  closely  together.  It  is  want- 
ing in  the  teeth  of  most  Fishes,  Snakes, 
Sloths,  Armadillos,  Sperm-whales,  etc. 
True  dental  tissue  is  confined  to 
Vertebrates. 

(6)  Adipose  Tissue. — Certain  cells  be- 
come greatly  enlarged  and  filled  with 
fat.  so  that  the  original  protoplasm  oc- 
cupies a  very  small  part  of  the  space 
within  the  cell-membrane.  These  cells 
FIG.  lo— Adipose  Tissue,  a;  are  united  into  masses  by  connective 

with  fibres  of  connective     .  .  .  . 

tissue, b.  tissue,  in  the  skin  (as  in  the  "blub- 


raw^i»H 

x<® 


ORGANIZATION.  30 

ber"  of  whales),  between  the  muscles  (as  in  "streaky" 
meat),  or  in  the  abdominal  cavity,  in  the  ornentum,  mes- 
entery, or  about  the  kidneys.  The  marrow  of  bones  is  an 
example.  Globules  of  fat  occur  in  many  Molluscs  and 
Insects;  but  true  adipose  tissue  is  found  only  in  back- 
boned animals,  particularly  the  herbivorous.  In  the  aver- 
age Man,  it  constitutes  about  -^V  part  of  his  weight,  and  a 
single  Whale  has  yielded  120  tons  of  oil.  The  fat  of 
animals  has  the  different  names  of  oil,  lard,  tallow,  suet, 
spermaceti,  etc.  It  is  a  reserve  of  nutriment  in  excess  of 
consumption,  serving  also  as  a  packing  material,  and  as 
a  protection  against  cold. 

(7>  Muscular  Tissue. — If  we  examine  a  piece  of  lean  meat, 
we  find  it  is  made  up  of  a  number  of  fasciculi,  or  bundles 
of  fibres,  placed  side  by 
side,  and  bound  together 
by  connective  tissue.  The 
microscope  informs  us 
that  each  fibre  is  itself  a 
bundle  of  smaller  fibres; 
and  when  one  of  these  is 
more  closely  examined, 
it  is  found  to  be  enclosed 
in  a  delicate,  glossy  tube, 
called  the  sarcolemma. 
This  tube  is  filled  with 

Fio.  11.—  Striated  Muscular  Fibre  (of  the  Pig), 
very        minute,       parallel       x  200.    The  constituent  fibres  are  seen  at  a; 

fibrils,  averaging   ^-1^     cis a  fasciculus' or buudle- 

of  an  inch   in    diameter,  and   having  a   striated   aspect. 

Tissue  of  this  description  constitutes  all  ordinary  muscle, 

or  "  lean  meat,"  and  is  marked  by  regular  cross-lines,  or 

striae. 

Besides  this  striated  muscular  tissue,  there  exist,  in  the 
coats  of  the  stomach,  intestines,  blood-vessels,  and  some  oth- 
er parts  of  Vertebrates,  smooth  muscular  fibres,  or  mem- 


COMPARATIVE   ZOOLOGY. 


branes,  which  show  a  nucleus  under  the  microscope,  and 
do  not  break  up  into  fibrils  (Fig.  122).  The  gizzards  of 
fowls  exhibit  this  form. 

All  muscle  has  the  property  of  shorten- 
ing itself  when  excited  ;  but  the  contraction 
of  the  striated  kind  is  under  the  control  of 
the  will,  while  the  movement  of  the  smooth 
fibres  is  involuntary.18  Muscles  are  well  sup- 
plied with  arteries,  veins,  and  nerves  ;  but 
the  color  is  due  to  a  peculiar  pigment,  not 
to  the  blood. 

Muscular  tissue  is  found  in  all  animals 
from  the  Coral  to  Man. 

(  8  )  Nervous  Tissue.  —  Nervous  matter  exists 
under  three  forms  :  First  —  the  cellular,  con- 

IG.  12.  -striated  *™t{nS  of  »™leated  cells,  varying  from  ^Vrr 
Mnscuinr  Fibres,  to  -j^-g-  of  an  inch  in  diameter,  and  found  in 

from  the  heart  of  ' 

Man,  divided  by  the  nerve-centres  (Fig.  132),  the  gray  por- 


^  tne  brain,  spinal  cord,  and  other  gan- 
cieated  portions.  g}ja>  gecond  —  tliefibrous,  consisting  of  pale, 
flat,  extremely  fine  filaments.  They  abound  in  the  sympa- 
thetic nerves,  and  are  the  only  nerves  found  in  the  Inverte- 
brates. Third  —  the  tubular.  These  are  much 
larger  than  the  fibrous,  the  coarsest  being 
-oW  °f  an  inch  in  diameter.  They  consist 
of  tubes  enclosing  a  transparent  fibre  and  a 
fatty  substance  called  the  nerve-  marrow.17 
The  delicate  tube  itself  is  called  neurilem- 
ma,  analogous  to  the  sarcolernma  of  mus-  Fl°j  ^  " 
cular  tissue.  Nerve  -tubes  are  found  only 
in  back  -boned  animals,  in  the  white  sub- 
stance of  the  brain,  spinal  cord,  and  in  the 
nerves. 

A  bundle  of  fibrous  or  tubular  nervous  matter,  sur- 
rounded by  connective  tissue,  constitutes  a  nerve. 


sheath,  or  neuri- 
lemma;  2,  med- 
ullary substance 
of  Schwanu  ;  3, 
axis  cylinder,  or 
primitive  band. 


ORGANIZATION. 


41 


FIG.  14. — A  Gauglioii  of  the  Sympathetic  Nerve  of  a  Mouse. 

3.  Organs,  and  their  Functions. — Animals,  like  Plants, 
grow,  feel,  and  move ;  these  three  are  the  capital  facts  of 
every  organism.  Besides  these  there  may  be  some  pecul- 
iar phenomena,  as  motion  and  will. 

Life  is  manifested  in  certain  special  operations,  called 
functions,  performed  by  certain  special  parts,  called  or- 
gans. Thus,  the  stomach  is  an  organ,  whose  function  is 
digestion.  A  single  organ  may  manifest  vitality,  but  it 
does  not  (save  in  the  very  lowest  forms)  show  forth  the 
whole  life  of  the  animal.  For,  in  being  set  apart  for  a 
special  purpose,  an  organ  takes  upon  itself,  so  to  speak,  to 
do  something  for  the  benefit  of  the  whole  animal,  in  return 
for  which  it  is  absolved  from  doing  many  things.  The 
stomach  is  not  called  upon  to  circulate  or  purify  the  blood. 

There  may  be  functions  without  special  organs,  as  the 
Amoeba  digests,  respires,  moves,  and  reproduces  by  its 
general  mass.  But,  as  we  ascend  the  scale  of  animal  life, 
we  pass  from  the  simple  to  the  complex :  groups  of  cells 
or  tissues,  instead  of  being  repetitions  of  each  other,  take 
on  a  difference,  and  become  distinguished  as  special  parts 
with  specific  duties.  The  higher  the  rank  of  the  animal, 
the  more  complicated  the  organs.  The  more  complicated 
the  structure,  the  more  complicated  the  functions.  But  in 


42  COMPARATIVE  ZOOLOGY. 

all  animals,  the  functions  are  performed  under  conditions 
essentially  the  same.  Thus,  respiration  in  the  Sponge,  the 
Fish,  and  in  Man  has  one  object  and  one  means,  though 
the  methods  differ.  A  function,  therefore,  is  a  group  of 
similar  phenomena  effected  by  analogous  structures/ 

The  life  of  an  animal  consists  in  the  accumulation  and 
expenditure  of  force.  )  The  tissues  are  storehouses  of 
power,  which,  as  they  waste,  is  given  off  in  various  forms. 
Thus,  the  nervous  tissue  generates  nerve-force ;  the  mus- 
cles, motion.  If  we  contemplate  the  phenomena  presented 
by  a  Dog,  the  most  obvious  fact  is  his  power  of  moving 
from  place  to  place,  a  power  produced  by  the  interplay  of 
muscles  and  bones.  We  observe,  also,  that  his  motions 
are  neither  mechanical  nor  irregular;  there  is  method  in 
his  movement.  He  has  the  power  of  willing,  seeing,  hear- 
ing, feeling,  etc. ;  and  these  functions  are  accomplished  by 
a  delicate  apparatus  of  nerves. 

But  the  Dog  does  not  exhibit  perpetual  motion. '  Sooner 
or  later  he  becomes  exhausted,  and  rest  is  necessary.  Sleep 
gives  only  temporary  relief.  In  every  exercise  of  the 
muscles  and  nerves  there  is  a  consumption  or  waste  of 
their  substance.  The  blood  restores  the  organs,  but  in 
time  the  blood  itself  needs  renewal.  If  not  renewed,  the 
animal  becomes  emaciated,  for  the  whole  body  is  laid  un- 
der contribution  to  furnish  a  supply.  Hence  the  feelings 
of  hunger  and  thirst,  impelling  the  creature  to  seek  food. 
Only  this  will  maintain  the  balance  between  waste  and 
repair.  We  notice,  therefore,  an  entirely  different  set  of 
functions,  involving,  however,  the  use  of  motion  and  will. 
The  Dog  seizes  a  piece  of  meat,  grinds  it  between  its 
teeth,  sends  it  into  the  stomach,  where  it  is  digested,  and 
then  into  the  intestine,  where  it  is  further  changed;  there 
the  nourishing  part  is  absorbed,  and  carried  to  the  heart, 
which  propels  it  through  tubes,  called  blood-vessels,  all 
over  the  body.  In  this  process  of  digestion,  certain  fluids 


ORGANIZATION.  43 

are  required,  as  saliva,  gastric  juice,  and  bile :  these  are 
secreted  by  special  organs,  called  glands.  Moreover,  since 
not  all  the  food  eaten  is  fitted  to  make  blood,  and  as  the 
blood  itself,  in  going  around  the  body,  acts  like  a  scaven- 
ger, picking  up  worn-out  particles,  we  have  another  func- 
tion, that  of  excretion,  or  removal  of  useless  matter  from 
the  system.  The  kidneys  and  lungs  do  much  of  this;  but 
the  lungs  do  something  else.  They  expose  the  blood  to 
the  air,  and  introduce  oxygen,  which,  we  shall  find,  is 
essential  to  the  life  of  every  animal. 

These  centripetal  and  centrifugal  movements  in  the 
body — throwing  in  and  throwing  out — are  so  related  and 
involved,  especially  in  the  lower  forms,  that  they  cannot 
be  sharply  defined  and  classified.  It  has  been  said  that 
every  Dog  has  two  lives  —  a  vegetative  and  an  animal. 
The  former  includes  the  processes  of  digestion,  circulation, 
respiration,  secretion,  etc.,  which  are  common  to  all  life; 
the  functions  of  the  other,  as  motion,  sensation,  and  will, 
are  peculiar  to  animals.  The  heart  is  the  centre  of  the 
vegetative  life,  and  the  brain  is  the  centre  of  the  animal 
life.  The  aim  of  the  vegetative  organs  is  to  nourish  the 
individual,  and  reproduce  its  kind;  the  organs  of  locomo- 
tion and  sense  establish  relations  between  the  individual 
and  the  world  without.  The  former  maintain  life;  the 
others  express  it.  The  former  develop,  and  afterwards 
sustain,  the  latter.  The  vegetative  organs,  however,  are 
not  independent  of  the  animal;  for  without  muscles  and 
nerves  we  could  not  procure,  masticate,  and  digest  food. 
The  closer  the  connection  and  dependence  between  these 
two  sets  of  organs,  the  higher  the  rank.18 

All  the  apparatus  and  phenomena  of  life  may  be  in- 
cluded under  the  heads  of 

NUTRITION, 

MOTION, 

SENSATION. 


f 


44  COMPARATIVE  ZOOLOGY. 

These  three  are  possessed  by  all  animals,  but  in  a  vari- 
ety of  ways.  No  two  species  have  exactly  the  same  mech- 
anism and  method  of  life.  We  must  learn  to  distinguish 
,  between  what  is  vital  and  what  is  only  accessory.  That 
only  is  essential  to  life  which  is  common  to  all  forms  of 
life.  Our  brains,  stomachs,  livers,  hands,  and  feet  are 
luxuries.  They  are  necessary  to  make  us  human,  but  not 
living,  beings'.  Half  of  our  body  is  taken  up  with  a  com- 
plicated system  of  digestion ;  but  the  Amoeba  has  neither 
mouth  nor  stomach.  We  have  an  elaborate  apparatus  of 
motion;  the  Oyster  cannot  stir  an  inch. 

Nutrition,  Motion,  and  Sensation  indicate  three  steps 
up  the  grade  of  life.  Thus,  the  first  is  the  prominent 
function  in  the  Coral,  which  simply  "  vegetates,"  the  pow- 
ers of  moving  and  feeling  being  very  feeble.  In  the 
higher  Insect,  as  the  Bee,  there  is  great  activity  with  sim- 
ple organs  of  nutrition.  In  the  still  higher  Mammal,  as 
Man,  there  is  less  power  of  locomotion,  though  the  most 
perfect  nutritive  system ;  but  both  functions  are  subordi- 
nate to  sensation,  which  is  the  crowning  development. 

In  studying  the  comparative  anatomy  and  physiology 
of  the  animal  kingdom,  our  plan  will  be  to  trace  the  vari- 
ous organs  and  functions,  from  their  simplest  expression 
upward  to  the  highest  complexity.  Thus  Nutrition  will 
begin  with  absorption,  which  is  the  simplest  method  of 
taking  food;  going  higher,  we  find  digestion,  but  in  no 
particular  spot  in  the  body;  next,  we  see  it  confined  to  a 
tube ;  then  to  a  tube  with  a  sac,  or  stomach ;  and,  finally, 
we  reach  the  complex  arrangement  of  the  higher  animals. 


NUTRITION.  45 


CHAPTER  VI. 

NUTKITION. 

Nutrition  is  the  earliest  and  most  constant  of  vital  op- 
erations. So  prominent  is  the  nutritive  apparatus,  that 
an  animal  has  been  likened  to  a  moving  sac,  organized  to 
convert  foreign  matter  into  its  own  likeness,  to  which  the 
complex  organs  of  animal  life  are  but  auxiliaries.  Thus, 
the  bones  and  muscles  are  levers  and  cords  to  carry  the 
body  about,  while  the  nervous  system  directs  its  motions 
in  quest  of  food. 

The  objects  of  nutrition  are  growth,  repair,  and  propa- 
gation. The  first  object  of  life  is  to  grow,  for  no  animal 
is  born  finished.  Some  animals,  like  plants,  grow  as  long 
as  they  live;19  but  the  majority  soon  attain  a  fixed  size. 
In  all  animals,  however,  without  exception,  food  is  wanted 
for  another  purpose  than  growth,  namely,  to  repair  the 
waste  which  is  constantly  going  on.  For  every  exercise 
of  the  muscles  and  nerves  involves  the  death  and  decay 
of  those  tissues,  as  shown  by  the  excretions.  The  amount 
of  matter  expelled  from  the  body,  and  the  amount  of  nour- 
ishment needed  to  make  good  the  loss,  increase  with  the 
activity  of  the  animal.  The  supply  must  equal  the  de- 
mand, in  order  to  maintain  the  life  of  the  individual ;  and 
as  an  organism  can  make  nothing,  it  must  seek  it  from 
without.  Not  only  the  muscles  and  nerves  are  wasted  by 
use,  but  every  organ  in  the  body  ;  so  that  the  whole  struct- 
ure needs  constant  renewal.  An  animal  begins  to  die  the 
moment  it  begins  to  live.  The  function  of  nutrition, 
therefore,  is  constructive,  while  motion  and  sensation  are 
destructive. 


46  COMPARATIVE   ZOOLOGY. 

Another  source  of  demand  for  food  is  the  production  of 
germs,  to  propagate  the  race,  and  the  nourishment  of  such 
offspring  in  the  egg  and  infantile  state.  This  reproduc- 
tion and  development  of  parts  which  can  maintain  an  in- 
dependent existence  is  a  vegetative  phenomenon  (for  plants 
have  it),  and  is  a  part  of  the  general  process  of  Nutrition. 
But  it  will  be  more  convenient  to  consider  it  hereafter 
(chapters  xix.,  xx.).  Still  another  necessity  for  aliment 
among  the  higher  animals  is  the  maintenance  of  bodily 
heat.  This  will  be  treated  under  the  head  of  Respiration. 

For  the  present,  we  will  study  Nutrition,  as  manifested 
in  maintaining  the  life  of  an  adult  individual. 

In  all  animals,  this  process  essentially  consists  in  the  in- 
troduction of  food,  its  conversion  into  tissue,  its  oxidation, 
and  the  removal  of  worn-out  material. 

\.  The  food  must  be  procured,  and  swallowed.  (Inges- 
tion.) 

2.  The  food  must  be  dissolved,  and  the  nutritious  parts 
separated  into  a  fluid.     (Digestion.) 

3.  The  nutritive  fluid  must  be  carefully  taken  up,  and 
then  distributed  all  over  the  body.     (Absorption  and  Cir- 
culation.) 

4.  The  tissues  must  repair  their  parts  wasted  by  use, 
by  transforming  particles  of  blood  into  living  matter  like 
themselves.     (Assimilation.) 

5.  Certain  matters  must  be  strained  from  the  blood, 
some  to  serve  a  purpose,  others  to  be  cast  out  of  the  sys- 
tem.    (Secretion  and  Excretion.) 

6.  In  order  to  produce  work  and  heat,  the  food  must  be 
oxidized,  either  in  the  blood  or  in  the  tissues,  after  assimi- 
lation.    The  necessary  oxygen  is  obtained  through  expos- 
ure of  the  blood  to  the  air  in  the  lungs.     (Respiration  in 
part.) 

7.  The  waste  products  of  this  oxidation  taken  up  by 
the  blood  must  be  got  rid  of;  some  from  the  lungs  (car- 


THE  FOOD  OF  ANIMALS.  47 

bon  dioxide,  water),  some  from  the  kidneys  (water,  urea, 
mainly),  some  from  the  skin  (water,  salines).  (Respira- 
tion in  part,  Excretion.) 

The  mechanism  to  accomplish  all  this  in  the  lowest 
forms  of  life  is  exceedingly  simple,  a  single  cavity  and 
surface  performing  all  the  functions.  But  in  the  major- 
ity of  animals  the  apparatus  is  very  complicated:  there  is 
a  set  of  organs  for  the  prehension  of  food ;  another,  for 
digestion ;  a  third,  for  absorption ;  a  fourth,  for  distribu- 
tion ;  and  a  fifth,  for  purification. 


CHAPTER  VII. 

THE     FOOD    OF     ANIMALS. 

THE  term  food  includes  all  substances  which  contribute 
to  nutrition,  whether  they  simply  assist  in  the  process,  or 
are  actually  appropriated,  and  become  tissue.  With  the 
food  is  usually  combined  more  or  less  indigestible  matter, 
which  is  separated  in  digestion. 

Food  is  derived  from  the  mineral,  vegetable,  and  animal 
kingdoms.  Water  and  salt,  for  example,  are  inorganic. 
The  former  is  the  most  abundant,  and  a  very  essential 
article  of  food.  Most  of  the  lower  forms  of  aquatic  life 
seem  to  live  by  drinking:  their  real  nourishment,  how- 
ever, is  present  in  the  water  in  the  state  of  solution.  The 
Earthworm,  some  Beetles,  and  certain  savage  tribes  of 
Men  swallow  earth;  but  this,  likewise,  is  for  the  organic 
matter  which  the  earth  contains.  As  no  animal  is  pro- 
duced immediately  from  inorganic  matter,  so  no  animal 
can  be  sustained  by  it. 

Nutritious  or  tissue-forming  food  comes  from  the  or- 
ganic world,  and  is  albuminous,  as  the  lean  meat  of  ani- 


48  COMPARATIVE  ZOOLOGY. 

mals  and  the  gluten  of  wheat;  oleaginous,  as  animal  fat 
and  vegetable  oil ;  or  saccharine,  as  starch  and  sugar.  The 
first  is  the  essential  food-stuff;  no  substance  can  serve 
permanently  for  food — that  is,  can  permanently  prevent 
loss  of  weight  in  the  body — unless  it  contains  albuminous 
matter.  As  stated  before,  all  the  living  tissues  are  albu- 
minous, and  therefore  albuminous  food  is  required  to  sup- 
ply their  waste.  Albumen  contains  nitrogen,  which  is 
necessary  to  the  formation  of  tissue;  fats  and  sugars  are 
rich  in  carbon,  and  therefore  serve  to  maintain  the  heat 
of  the  body,  and  to  repair  part  of  the  waste  of  tissues. 
Warm -blooded  animals  feed  largely  on  farinaceous  or 
starchy  substances,  which  in  digestion  are  converted  into 
sugar.  But  any  animal,  of  the  higher  orders  certainly, 
whether  herbivorous  or  carnivorous,  would  starve,  if  fed 
on  pure  albumen,  oil,  or  sugar.  Nature  insists  upon  a 
mixed  diet;  and  so  we  find  in  all  the  staple  articles  of 
food,  as  milk,  meat,  and  bread,  at  least  two  of  these  prin- 
ciples present.  As  a  rule,  the  nutritive  principles  in  veg- 
etables are  less  abundant  than  in  animal  food,  and  the 
indigestible  residue  is  consequently  greater.  The  nutri- 
ment in  flesh  increases  as  we  ascend  the  animal  scale; 
thus,  Oysters  are  less  nourishing  than  Fish;  Fish,  less  than 
Fowl ;  and  Fowl,  less  than  the  flesh  of  Quadrupeds. 

Many  animals,  as  most  Insects  and  Mammals,  live  solely 
on  vegetable  food,  and  some  species  are  restricted  to  par- 
ticular plants,  as  the  Silk-worm  to  the  white  mulberry. 
But  the  majority  of  animals  feed  on  one  another;  such 
are  hosts  of  the  microscopic  forms,  and  nearly  all  the  ra- 
diated species,  marine  Mollusks,  Crustaceans,  Beetles,  Flies, 
Spiders,  Fishes,  Amphibians,  Reptiles,  Birds,  and  clawed 
Quadrupeds. 

A  few,  as  Man  himself,  are  omnivorous,  i.  e.,  are  main- 
tained on  a  mixture  of  animal  and  vegetable  food.  The 
use  of  fire  in  the  preparation  of  food  is  peculiar  to  Man, 


HOW   ANIMALS   EAT.  49 

who  has  been  called  "  the  cooking  animal."  A  few  of  the 
strictly  herbivorous  and  carnivorous  animals  have  shown 
a  capacity  for  changing  their  diet.  Thus,  the  Hoise  and 
Cow  may  be  brought  to  eat  fish  and  flesh ;  the  Sea-birds 
can  be  habituated  to  grain  ;  Cats  are  fond  of  alligator- 
pears  ;  and  Dogs  take  naturally  to  the  plantain.  Certain 
animals,  in  passing  from  the  young  to  the  mature  state, 
make  a  remarkable  change  of  food.  Thus,  the  Tadpole 
feeds  upon  vegetable  matter;  but  when  it  becomes  a  Frog 
it  lives  on  Insects. 

Many  tribes,  especially  of  Reptiles  and  Insects,  are  able 
to  go  without  food  for  months,  or  even  years.  Insects  in 
the  larval,  or  caterpillar,  state  are  very  voracious;  but 
upon  reaching  the  perfect,  or  winged,  state,  they  eat  little 
— some  species  taking  no  food  at  all,  the  mouth  being  act- 
ually closed.  The  males  of  some  Rotifers  and  other  tribes 
take  no  food  from  the  time  of  leaving  the  egg  until  death. 

In  general,  the  greater  the  facility  with  which  an  animal 
obtains  its  food,  the  more  dependent  is  it  upon  a  constant 
supply.  Thus,  carnivores  endure  abstinence  better  than" 
herbivores,  and  wild  animals  than  domesticated  ones. 


CHAPTER  VIII. 

HOW     ANIMALS     EAT. 

1.  The  Prehension  of  Food. —  (l)  Liquids.— The  sim- 
plest' method  of  taking  nourishment  is  by  absorption 
through  the  skin.  The  Tape -worm,  for  example,  has 
neither  month  nor  stomach,  but  imbibes  the  digested  food 
of  the  animal  it  infests.  Many  other  animals,  especially 
Insects,  live  upon  liquid  food,  but  obtain  it  by  suction 
through  a  special  orifice  or  tube.  Thus,  we  find  a  mouth, 

4 


50  COMPARATIVE  ZOOLOGY. 

or  sucker,  furnished  with  teeth  for  lancing  the  skin  of  an- 
imals, as  in  the  Leech;  a  bristle-like  tube  fitted  for  pierc- 
ing, as  in  the  Mosquito;  a  sharp  sucker  armed  with  barbs, 
to  fix  it  securely  during  the  act  of  sucking,  as  in  the 
Louse ;  and  a  long,  flexible  proboscis,  as  in  the  Butterfly. 
Bees  have  a  hairy,  channelled  tongue,  and  Flies  have  one 
terminating  in  a  large  fleshy  knob,  with  or  without  little 
"  knives  "  at  the  base  for  cutting  the  skin  :  both  lap,  rather 
than  suck,  their  food. 

Most  animals  drink  by  suction,  as  the  Ox;  and  a  few 
by  lapping,  as  the  Dog;  the  Elephant  pumps  the  water 
up  with  its  trunk,  and  then  pours  it  into  its  throat;  and 
Birds  (excepting  Doves)  fill  the  beak,  and  then,  raising 
the  head,  allow  the  water  to  run  down. 

Many  aquatic  animals,  whose  food  consists  of  small  par- 
ticles diffused  through  the  water,  have  an  apparatus  for 
creating  currents,  so  as  to  bring  such  particles  within  their 
reach.  This  is  particularly  true  of  low,  fixed  forms,  which 
are  unable  to  go  in  search  of  their  food.  Thus,  the  Sponge 
draws  nourishment  from  the  water,  which  is  made  to  cir- 
culate through  the  system  of  canals  traversing  its  body 
by  the  vibration  of  minute  hairs,  or  cilia,  lining  parts  of 
the  canals  (Fig.  189).  The  microscopic  Infusoria  have 
cilia  surrounding  the  mouth,  with  which  they  draw  or 
drive  into  the  body  little  currents  containing  nutritious 
particles.  Bivalve  mollusks,  as  the  Oyster  and  Clam,  are 
likewise  dependent  upon  this  method  of  procuring  food, 
the  gills  being  fringed  with  cilia.  So  the  singular  fish, 
Amphioxus  (the  only  example  among  Vertebrates),  em- 
ploys ciliary  action  to  obtain  the  minute  .organisms  on 
which  it  feeds.  The  Greenland  Whale  has  a  mode  of  iri- 
gestion  somewhat  unique,  gulping  great  volumes  of  water 
into  its  mouth,  and  then  straining  out,  through  its  whale- 
bone sieve,  the  small  animals  which  the  water  may  con- 
tain (Fig.  343). 


HOW    ANIMALS   EAT.  51 

(2)  Solids. — When  the  food  is  in  solid  masses,  whether 
floating  in  water  or  not,  the  animal  is  usually  provided 
with  prehensile  appendages  for 
taking  hold  of  it.  The  jelly- 
like  Amoeba  has  neither  mouth 
nor  stomach,  but  extemporizes 
them,  seizing  its  food  by  means 
of  its  soft  bod}7.  The  food  then 
passes  through  the  outer  wall  ^*,  v/ 

into  the  softer  interior,  where  it  FlG.15._ARhiz0p0d(/ZotoZ,aren,to), 
is  digested.  The  waste  particles  with  P^eudopodia  extended,  x  so. 
are  passed  out  in  a  similar  way.  In  the  Foraminifers, 
thread-like  projections  of  the  body  are  thrown  out  (pseu- 
dopodia)  which  adhere  to  the  prey.  The  soft  jelly-like 
substance  of  the  body  then  flows  down  the  pseudopodium, 
collects  about  the  food,  and  digests  it  (Fig.  15). 
V  A  higher  type  is  seen  in  Polyps  and  Jelly-fishes,  which 
have  hollow  tentacles  around  the  entrance  to  the  stomach 
(Fig.  193).  These  tentacles  are  contractile,  and,  moreover, 
are  covered  with  an  immense  number  of  minute  sacs,  in 
which  a  highly  elastic  filament  is  coiled  up  spirally  (lasso- 
cells,  nettle-cells).  When  the  tentacles  are  touched  by  a 
passing  animal,  the}r  seize  it,  and  at  the  same  moment 
throw  out  their  myriad  filaments,  like  so  many  lassos, 
which  penetrate  the  skin  of  the  victim,  and  probablj7  also 
emit  a  fluid,  which  paralyzes  it ;  the  mou.th,  meanwhile, 
expands  to  an  extraordinary  size,  and  the  creature  is  soon 
engulfed  in  the  digestive  bag. 

In  the  next  stage,  we  find  no  tentacles,  but  the  food  is 
brought  to  the  mouth  by  the  flexible  lobes  of  the  body, 
commonly  called  "arms,"  which  are  covered  with  hun- 
dreds of  minute  suckers;  and  if  the  prey,^is  an  Oyster,  is 
too  large  to  be  swallowed,  the  stomach  protrudes,  like  a 
proboscis,  and  sucks  it  out  of  its  shell.  This  is  seen  in 
the  Star-fish  (Fig.  126). 


52 


COMPARATIVE  ZOOLOGY. 


A  great  advance  is  shown  by  the  Sea-urchin,  whose 
mouth  is  provided  with  five  sharp  teeth,  set  in  as  many 
jaws,  and  capable  of  being  projected  so  as  to  grasp,  as  well 
as  to  masticate,  its  food  (Figs.  214,  28). 

In  Mollusks  having  a  single  shell,  as  the  Snail,  the  chief 
organ  of  prehension  is  a  strap-like  tongue,  covered  with 
minute  recurved  teeth,  or  spines,  with  which  the  animal 

rasps  its  food,  while  the  upper  lip 
is  armed  with  a  sharp,  horny 
plate  (Fig.  29).  In  many  marine 
species,  as  the  Whelk,  the  tongue 
is  situated  at  the  end  of  a  retrac- 
tile proboscis,  qr  muscular  tube. 
In  the  Cuttle-fish,  we  see  the  sud- 
den development  of  an  elaborate 
system  of  prehensile  organs.  Be- 
sides a  spinous  tongue,  it  has  a 
pair  of  hard  mandibles,  resem- 
bling the  beak  of  a  Parrot,  and 
working  vertically  ;  and  around 
the  mouth  are  eight  or  ten  pow- 

PIG.  W'-SnctonrB  on  the  Tentacles        f    j  furnished  with  llUtner- 

of  a  Cuttle-fish  :  a,  hollow  axis  of 

the  arm,  containing  nerve  and  ar-   QUS  CUD-Hke  SUCkei'S.  So  perfect  is 
tery;  c,  cellular  tissue;  d,  radiat-  11        «  ,• 

ing  fibres;  h,  raised   margin  of    the  adllCSlOU  OI  tllCSC  SUCKCrS,  that 
the  disk  around  the  aperture/,  g,    .,     .  v      u 

which  contains  a  retractile  mem-   it    IS    easier  to  tear  away  a    111110 


brane,  or  "piston,"  i. 


t() 


i  The  Earth-worm  swallows  earthy 
matter  and  decaying  leaves,  which 
it  secures  with  its  lips,  the  up- 
per one  being  prolonged.  Other 
worms  (as  Nereis)  are  so  construct- 
ed that  the  gullet,  which  is  fre- 
quently armed  with  teeth  and  for- 
ceps, can  be  turned  inside  out,  to  FIG.  IT.  -Nereis  -head,  with  ex- 

£  i  •     £  •    •  tended  proboscis:  J.  jaws  •  T. 

form  a  proboSCIS  for  Seizing  prey.         tentacles;  //,  head  ;  E\  eyes. 


HOW   ANIMALS  EAT.  53 

The  Arthropoda  exhibit  a  great  variety  of  means  for 
procuring  nourishment,  in  addition  to  the  suctorial  con- 
trivances already  mentioned,  the  innumerable  modifica- 
tions of  the  mouth  corresponding  to  the  diversity  of  food. 
Millepedes,  Caterpillars,  and  Grubs  have  a  pair  of  horny 
jaws  moving  horizontally.  The  Centipede  has  a  second 
pair  of  jaws,  which  are  really  modified  feet,  terminated 
by  curved  fangs  containing  a  poison-duct.  The  Horse- 
shoe Crab  uses  its  feet  for  prehension,  and  the  thighs,  or 
basal  joints,  of  its  legs  to  masticate  the  food  and  force  it 
into  the  stomach.  The  first  six  pair  of  legs  in  the  Lob- 
ster and  Crab  are  likewise  appropriated  to  conveying  food 
into  the  mouth,  the  sixth  being  enormously  developed, 
and  furnished  with  powerful 
pincers.  Scorpions  have  a 
similar  pair  of  claws  for  pre- 
hension, and  also  a  pair  of 
small  forceps  for  holding 
the  food  in  contact  with  the 

mOUth.        In    their    relatives,    FIG.  IS.— One  of  the  Fangs,  or  Perforated 

the  Spiders,  the   claws   are  Mandible,,  of  the  spider, 

wanting,  and  the  forceps  end  in  a  fang,  or  hook,  which  is 
perforated  to  convey  venom.20 

\,The  biting  Insects,  as  Beetles  and  Locusts, 'have  two 
pairs  of  horny  jaws,  which  open  sidewise,  one  above  and 
the  other  below  the  oral  orifice.  The  upper  pair  are  called 
mandibles;  the  lower,  maxillae.  The  former  are  armed 
with  sharp  teeth,  or  with  cutting  edges,  and  sometimes 
are  fitted,  like  the  molars  of  quadrupeds,  to  grind  the 
food.  The  maxillae  are  usually  composed  of  several  parts, 
some  of  which  serve  to  hold  the  food,  or  to  help  in  divid- 
ing it,  while  others  (palpi)  are  sensory.  There  is  generally 
present  a  third  pair  of  jaws  —  the  labium  —  which  are 
united  in  the  middle  line,  and  serve  as  a  lower  lip.  They 
also  bear  palpi.  The  Mantis  seizes  its  prey  with  its  long 


54:  COMPARATIVE  ZOOLOGY. 

fore-legs,  crushes  it  between  its  thighs,  which  are  armed 
with  spines,  and  then  delivers  it  up  to  the  jaws  for  masti- 
cation. All  Arthropods  move  their  jaws  horizontally. 

The  back-boned  animals  generallj7  apprehend  food  by 
means  of  their  jaws,  of  which  there  are  two,  moving  ver- 
tically. The  toothless  Sturgeon  draws  in  its  prey  by  pow- 
erful suction.  The  Hag-fish  has  a  single  tooth,  which  it 
plunges  into  the  sides  of  its  victim,  and,  thus  securing  a 
firm  hold,  bores  its  way  into  the  flesh  by  means  of  its  saw- 
like  tongue.  But  Fishes  are  usually  well  provided  with 
teeth,  which,  being  sharp  and  curving  inward,  are  strictly 
prehensile.  The  fins  and  tongue  are  not  prehensile.  A 
mouth  with  horny  jaws,  as  in  the  Turtles,  or  bristling  with 
teeth,  as  in  the  Crocodile,  is  the  only  means  possessed  by 
nearly  all  Amphibians  and  Reptiles  for  securing  food. 
The  Toad,  Frog,  and  Chameleon  capture  insects  by  dart- 
ing out  the  tongue,  which  is  tipped  with  glutinous  saliva. 
The  constricting  serpents  (Boas)  crush  their  prey  in  their 
coils  before  swallowing;  and  the  venomous  Snakes  have 
a  poison-fang.  No  reptile  has  prehensile  lips.  All  Birds 
use  their  toothless  beaks  in  procuring  food,  but  birds  of 
prey  also  seize  with  their  talons,  and  Woodpeckers,  Hum- 
mers, and  Parrots  with  their  tongues.  The  beak  varies 
greatly  in  shape,  being  a  hook  in  the  Eagle,  a  probe  in  the 
Woodpecker,  and  a  shovel  in  the  Duck. 

Among  the  Quadrupeds  we  find  a  few  special  contriv- 
ances, as  the  trunk  of  the  Elephant,  and  the  long  tongues 
of  the  Giraffe  and  Ant-eater;  but,  as  a  rule,  the  teeth  are 
the  chief  organs  of  prehension,  always  aided  more  or  less 
by  the  lips.  Ruminants,  like  the  Ox,  having  hoofs  on 
their  feet,  and  no  upper  front  teeth,  employ  the  lips  and 
tongue.  Such  as  can  stand  erect  on  the  hind-legs,  as  the 
Squirrel,  Bear,  and  Kangaroo,  use  the  front  limbs  for  hold- 
ing the  food  and  bringing  it  to  the  mouth,  but  never  one 
limb  alone.  The  clawed  animals,  like  the  Cat  and  Lion, 


HOW   ANIMALS  EAT. 


55 


make  use  of  their  feet  in  securing  prey,  all  four  limbs  be- 
ing furnished  with  curved  retractile  claws ;  but  the  food 
is  conveyed  into  the  mouth  by 
the  movement  of  the  head  and 
jaws.  Man  and  the  Monkeys  em- 
ploy the  hand  in  bringing  food 
to  the  mouth,  and  the  lips  and 
tongue  in  taking  it  into  the  cavi- 
ty. The  thumb  on  the  human 
hand  is  longer  and  more  perfect 
than  that  of  the  Apes  and  Mon- 
keys ;  but  the  foot  of  the  latter 
is  also  prehensile. 
\l  2.  The  Mouths  of  Animals. 
—In  the  Parasites,  as  the  Tape- 
worm, which  absorb  nourishment 
through  the  skin,  and  Insects,  as 

the  May-fly  and  Bot-fly,  which  do    FIG.  19. -Arm  of  the  Thnmbless 
„.,     .  .         .        ,      ,  Monkey  (A  teles). 

all  their  eating  in  the  larval  state, 

the  mouth  is  either  wanting  or  rudimentary.  The  Amoeba, 
also,  has  no  mouth  proper,  its  food  passing  through  the 
firmer  outside  part  of  the  bit  of  protoplasm  which  consti- 
tutes its  body.  Mouth  and  anus  are  thus  extemporized, 
the  opening  closing  as  soon  as  the  food  or  excrement  has 
passed  through. 

In  the  Infusoria  the  mouth  is  a  round  or  oval  opening 
leading  through  the  cuticle  and  outer  layer  of  protoplasm 
to  the  interior  of  the  single  cell  which  makes  their  body. 
It  is  usually  bordered  with  cilia,  and  situated  on  the  side 
or  at  one  end  of  the  animal. 

An  elliptical  or  quadrangular  orifice,  surrounded  with 
tentacles,  and  leading  directly  to  the  stomach,  is  the  ordi- 
nary mouth  of  the  Polyps  and  Jelly-fishes,  In  those 
which  are  fixed-,  as  the  Actinia,  Coral,  and  Hydra,  the 
mouth  looks  upward :  in  those  which  freely  move  about, 


56  COMPARATIVE  ZOOLOGY. 

as  the  Jelly-fish,  it  is  generally  underneath,  the  position  of 
the  animal  being  reversed.  In  some,  the  margin,  or  lip, 
is  protruded  like  a  proboscis ;  and  in  all  it  is  exceedingly 
dilatable. 

The  mouth  of  the  Star-fish  and  Sea-urchin  is  a  simple 
round  aperture,  followed  by  a  very  short  throat.  In  the 
Star-fish,  it  is  enclosed  by  a  ring  of  hard  tubercles  and  a 
membrane.  In  the  Sea-urchin,  it  is  surrounded  by  a  mus- 
cular membrane  and  minute  tentacles,  and  is  armed  with 
five  sharp  teeth,  set  in  as  many  jaws,  resembling  little 
conical  wedges  (Fig.  28). 

-<^j^mong  the  headless  Mollusks,  the  oral  apparatus  is  very 
simple,  being  inferior  to  that  of  some  of  the  radiated  ani- 
mals. In  the  Oyster  and  Bivalves  generally,  the  mouth 
is  an  unarmed  slit — a  mere  inlet  to  the  oesophagus,  situ- 
ated in  a  kind  of  hood  formed  by  the  union  of  the  gills 
at  their  origin,  and  between  two  pairs  of  delicate  lips. 
These  lips  make  a  furrow,  along  which  pass  the  particles 
of  food  drawn  in  by  the  cilia. 

Of  the  higher  Mollusks,  the  little  Clio  (one  of  the  Ptero- 
pods)  has  a  triangular  mouth,  with  two  jaws  armed  with 
sharp  horny  teeth,  and  a  tongue  covered  with  spiny  hook- 
lets  all  directed  backward.  Some  Univalves  have  a  sim- 
ple flesh}7  tube.  Others,  as  the  Whelk,  have  an  extensible 
proboscis,  which  unfolds  itself,  like  the  finger  of  a  glove, 
and  carries  within  it  a  rasp-like  tongue,  which  can  bore 

into  the  hardest  shells.  Such 
as  feed  on  vegetable  matter, 
as  the  Snail,  have  no  probos- 
cis, but  on  the  roof  of  the 
of  the  Common'  siuiii  mouth  a  curved  horny  plate 

(Helix  albolabris).  fifcted  t()  ^  j^^  ^  which 

are  pressed  against  it  by  the  lips,  and  on  the  floor  of  the 
mouth  a  small  tongue  covered  with  delicate  teeth.  As  fast 
as  the  tongue  is  worn 'off  by  use,  it  grows  out  from  the  root. 


HOW  ANIMALS  EAT.  57 

The  mouth  of  the  Cuttle-fish  is  the  most  elevated  type 
below  that  of  the  Fishes.  A  broad  circular  lip  nearly 
conceals  a  pair  of  strong  horny  mandibles,  not  unlike  the 
beak  of  a  parrot,  but  reversed,  the  upper  mandible  being 
the  shorter  of  the  two,  and  the  jaws,  which  are  cartilagi- 
nous, are  imbedded  in  a  mass  of  muscles,  and  move  ver- 
tically. Between  them  is  a  fleshy  tongue  covered  with 
teeth. 

The  parasitic  Worms,  living  within  or  on  the  outside 
of  other  animals,  generally  have  a  sucker  at  one  end  or 
underneath,  serving  simply  for  attachment,  and  another 
which  is  perforated.  The  latter  is  a  true  suctorial  mouth, 
being  the  sole  inlet  of  food.  It  is  often  surrounded  with 
booklets  or  teeth,  which  serve  both  to  scarify  the  victim 
and  secure  a  firm  hold.  In  the  Leech,  the  mouth  is  a 
triangular  opening  with  thick  lips,  the  upper  one  pro- 
longed, and  with  three  jaws.  In  many  Worms  it  is  a 
fleshy  tube,  which  can  be  drawn  iu  or  extended,  like  the 
eye -stalks  of  the  Snail,  and  contains  a  dental  apparatus 
inside  (Fig.  17). 

Millepedes  and  Centipedes  have  two  lateral  jaws  and  a 
four-lobed  lip. 

In  Lobsters  and  Crabs  the  mouth  is  situated  underneath 
the  head,  and  consists  of  a  soft  upper  lip,  then  a  pair  of 
upper  jaws  provided  with  a  short  feeler,  below  which  is  a 
thin  bifid  lower  lip  ;  then  follow  two  pairs  of  membranous 
under  jaws,  which  are  lobed  and  hairy ;  and  next,  three 
pairs  of  foot-jaws  (Fig.  250).  The  Horse-shoe  Crab  has 
no  special  jaws,  the  thighs  answering  the  purpose.  The 
Barnacle  has  a  prominent  mouth,  with  three  pairs  of  rudi- 
mentary jaws. 

N.With  few  exceptions,  the  mouths  of  Insects  in  the  lar- 
val state  are  fitted  only  for  biting,  the  two  jaws  being 
horny  shears.  But  in  the  winged,  or  perfect,  state,  Insects 
may  be  divided  into  the  masticating  (as  the  Beetle)  and 


58 


COMPARATIVE  ZOOLOGY. 


PIG.  21 — Mouth  of  a  Locust  dissected:  1,  labrnm,  or  upper  lip;  2,  mandibles;  3, 
jaws;  4,  labinm,  or  lower  lip;  5,  tongue.  The  appendages  to  the  maxillae  and 
lower  lip  are  palpi. 

the  suctorial  (as  the  Butterfly).  In  the  former  group,  the 
oral  apparatus  consists  of  two  pairs  of  horny  jaws  (inandi- 
bles  and  maxillce),  which  work  horizontally  between  an 
upper  (Idbrum)  and  an  under  (labium)  lip.  The  maxillae 
and  under  lip  carry  sensitive  jointed  feelers  (palpi).  The 
front  edge  of  the  labium  is  commonly  known  as  the  tongue 
(ligula)?1  In  such  a  mouth,  the  mandibles  are  the  most 
important  parts;  but  in  passing  to  the  suctorial  Insects, 
we  find  that  the  mandibles  are  secondary  to  the  maxillae 
and  labium,  which  are  the  only  means  of  taking  food.  In 


HOW  ANIMALS  EAT.  59 

the  Bee  tribe,  we  have  a  transi- 
tion between  the  biting  and  the 
sucking  Insects — the  mandibles 
"supply  the  place  of  trowels, 
spades,  pickaxes,  saws,  scissors, 
and  knives,"  while  the  maxillae 
are  developed  into  a  sheath  to 
enclose  the  long,  slender,  hairy 
tongue  which  laps  up  the  sweets 
of  flowers.  In  the  suctorial  But- 
terfly, the  lips,  mandibles,  and 
palpi  are  reduced  to  rudiments, 
while  the  maxillae  are  the  only 
useful  oral  organs.  These  ar  • 
excessively  lengthened  into  a 
proboscis,  their  edges  locking  FI«.  22.— Head  of  n  wild  Bee  (An- 

thophora  retuna),  front  view:   a, 

by  means  ot  minute  teeth,  so  as     compound  eyes;  &,  ciypeus;  c, 

P  i  i     ,1  1         three  simple  eyes;  d,  antennae;  e, 

to  form  a  central  canal,  through  ,.,„„„„.  ;,  ln,,,,dibie8;  f,mnzin»; 
which  the  liquid  food  is  pumped 
up  into  the  mouth.  Seen  un- 
der  the  microscope,  the  proboscis  is  made  up  of  innumer- 
able rings  interlaced  with  spiral  muscular  fibres.  The 

proboscis  of  the  Fly 
is  a  modified  lower 
lip ;  that  of  the  Bugs 
and  Mosquitos,  fitted 
both  for  piercing  and 
suction,  is  formed  by 
the  union  of  four 
bristles,  which  are 
the  mandibles  and 
maxillae  strangely  al- 
tered, and  encased  in 
the  labiurn  when  not 

FIG.  23.— Proboscis  of  a  Butterfly.  in  US6. 


60 


COMPARATIVE  ZOOLOGY. 


As  most  of  the  Arachnids  live  by  suc- 
tion, the  jaws  are  seldom  used  for  masti- 
cation. In  the  Scorpion,  the  apparent 
representatives  of  the  mandibles  of  an 
Insect  are  transformed  into  a  pair  of 
small  forceps,  and  the  palpi,  so  small  in 
Insects,  are  developed  into  formidable 

PIG.  24.— Mouth  of  the       i  i      ,  i        /•  ,  i  i 

H«>r«j-fly(7'u&a»M«Kn-  claws  i  both  of  these  organs  are  prehen- 


sile.    In  Spiders,  the  so-called  mandi- 


eola):  a,  antennae;  m, 
mandibles;  mx,  max- 
illae; mp,  maxillary  bles,  which  move  more  or  less  vertically, 

'    palpi;    Ib,  labrnm;    I,  '  J.' 

labium,  or  tongue.  end  in  a  fang;  and  the  club-like  palpi, 
often  resembling  legs,  have 
nothing  to  do  with  inges- 
tion  or  locomotion.  Both 
Scorpions  and  Spiders  have 
a  soft  upper  lip,  and  a 
groove  within  the  mouth, 
which  serves  as  a  canal 
while  sucking  their  prey. 
The  tongue  is  external,  and 
situated  between  a  pair  of 
diminutive  maxillae. 

In  the  Ascidians  the  first, 
part  of  the  alimentary  canal 
is  enormously  enlarged  and 
modified  to  serve  as  a  gill- 
sac.  At  the  bottom  of  this 
sac,  and  far  removed  from 
its  external  opening,  lies 
the  entrance  to  the  diges- 
tive tract  proper.  Into  it 

the  particles  of  food  enter-  FlG.  25._Ululei.  su.-r«ce  or  Male  Spider:  a, 
ing  with  the  water  are  con-     c>  P™"""-^;  &,  <eeth  <>„  interior  mar- 

gin  of  mandible,  e;  f,  labium;  g,  thorax-, 

(Fig.  279).  >*,  limbs;  <,  abdomen;  I,  spinnerets;  m, 

m,  »     -T7-  maxillary    palpus;    d,   dilated    terminal 

The    mouth    of   Verte-    joint. 


HOW  ANIMALS  EAT.  GI 

brates  is  a  cavity  with  a  fixed  roof  (the  hard  palate)  and 
a  movable  floor  (the  tongue  and  lower  jaw),  having  a  trans- 
verse opening  in  front,28  and  a  narrow  outlet  behind,  lead- 
ing to  the  gullet.  Save  in  Birds  and  some  others,  the 
cavity  is  closed  in  front  with  lips,  and  the  margins  of  the 
jaws  are  set  with  teeth. 

In  Fishes  the  mouth  is  the  common  entry  to  both  the 
digestive  and  respiratory  organs;  it  is,  therefore,  large, 
and  complicated  by  a  mechanism  for  regulating  the  tran- 
sit of  the  food  to  the  stomach  and  the  aerated  water  to  the 
gills.  The  slits  leading  to  the  gills  are  provided  with 
rows  of  processes  which,  like  a  sieve,  prevent  the  entrance 
of  food,  arid  with  valves  to  keep  the  water,  after  it  has  en- 
tered the  gills,  from  returning  to  the  mouth.  So  that  the 
mouths  of  Fishes  may  be  said  to  be  armed  at  both  ends 
with  teeth-bearing  jaws.  A  few  Fishes,  as  the  Sturgeon, 
are  toothless ;  but,  as  a  class,  they  have  an  extraordinary 
dental  apparatus — not  only  the  upper  and  lower  jaws,  but 
even  the  palate,  tongue,  and  throat  being  sometimes  stud- 
ded with  teeth.  Every  part  of  the  mouth  is  evidently 
designed  for  prehension  and  mastication.  Lips  are  usu- 
ally present ;  but  the  tongue  is  often  absent,  or  very  small, 
and  as  often  aids  respiration  as  ingestion. 

Amphibians  and  Reptiles  have  a  wide  mouth  ;  even  the 
insect-feeding  Toads  and  the  Serpents  can  stretch  theirs 
enormously.  True  fleshy  lips  are  wanting;  hence  the 
savage  aspect  of  the  grinning  Crocodile.  With  some  ex- 
ceptions, as  Toads  and  Turtles,  the  jaws  are  armed  with 
teeth.  Turtles  are  provided  with  horny  beaks.  The 
tongue  is  rarely  absent,  but  is  generally  too  thick  and 
short  to  be  of  much  use.  In  the  Toad  and  Frog  it  is  sin- 
gularly extensile :  rooted  in  front  and  free  behind,  it  is 
shot  from  the  mouth  with  such  rapidity  that  the  insect  is 
seized  and  swallowed  more  quickly  than  the  eye  can  fol- 
low. The  Chameleon's  tongue  is  also  extensile.  Snakes 


COMPARATIVE  ZOOLOGY. 


FIG.  26. — Mouth  of  the  Crocodile:  rf,  tongue;  ?,  gla'uds;  /,  inferior,  and  g,  superior, 
valve,  separating  the  cavity  of  the  mouth  from  the  throat,  h. 

have  a  slender  forked  tongue,  consisting  of  a  pair  of  mus- 
cular cylinders,  which  is  solely  an  instrument  of  touch. 

Birds  are  without  lips  or  teeth,  the  jaws  being  covered 
with  horn  forming  a  beak.  This  varies  greatly  in  shape, 
being  extremely  wide  in  the  Whippoorwill,  remarkably 
long  in  the  Pelican,  stout  in  the  Eagle,  and  slender  in  the 
Hummer.  It  is  hardest  in  those  that  tear  or  bruise  their 
food,  and  softest  in  water-birds.  The  tongue  is  also  cov- 
ered with  a  horny  sheath,  and  generally  spinous,  its  chief 
function  being  to  secure  the  food  when  in  the  mouth. 
It  is  proportionally  largest  and  most  fleshy  in  the  Parrots. 

The  main  characteristics  of  the  mammalian  mouth  are 
flesh  lips  and  mobile  cheeks.23  In  the  duck-billed  Mon- 
otrernes  lips  are  wanting,  and  in  the  Porpoises  they  are 
barely  represented.  But  in  the  herbivorous  quadrupeds 
they,  with  the  tongue,  are  the  chief  organs  of  prehension  ; 
in  the  carnivorous  tribes  they  are  thin  and  retractile; 
while  in  the  Whale  the  upper  lip  falls  down  like  a  cur- 
tain, overlapping  the  lower  jaw  several  feet.  As  a  rule, 
the  mouth  is  terminal ;  but  in  the  Elephant,  Tapir,  Hog, 


HOW  ANIMALS  EAT. 


C3 


and  Shrew,  the  upper  lip  blends  with  the  nose  to  form  a 
proboscis,  or  snout.  The  mouth  is  comparatively  small 
in  the  Elephant  and  in  gnawing  animals  like  the  Squir- 
rel, wide  in  the  Carnivores,  short  in  the  Sloth,  and  long  in 
the  Ant-eater.  Teeth  are  usually  present,  but  vary  in 
form  and  number  with  the  habits  of  the  animal.  The 
Ant-eater  is  toothless,  and  the  Greenland  Whale  has  a 
sieve  made  of  horny  plates.  The 
tongue  conforms  in  size  and  shape 
with  the  lower  jaw,  and  is  a  muscu- 
lar, sensitive  organ,  which  serves 
many  purposes,  assisting  in  the 
prehension,  mastication,  and  swal- 
lowing of  food,  besides  being  an 
organ  of  taste,  touch,  and  speech. 
Its  surface  is  covered  with  minute 
prominences,  called  papillce,  which 
are  arranged  in  lines  with  mathe- 
matical precision.  In  the  Cats, 
these  are  developed  into  recurved  Flo  2T._IIllman  Tongne  nml 

SDilieS,  which    the    animal   USeS    in       J^cent  parts:  a,lingunl  papillae: 

ft,    papillae    forming    V-shnped 

Cleaning    bones    and    Combing    its       lines;  d,  fungiform  papillae;  e, 

...  filiform    papillae;    <j,   epiglottis; 

fill*.        Similar    paplll83     OCCUr     O11       m,   uvula,    or   conical    process, 

the  roof  and  sides  of  the  month     ^f  L^;  T,-^ 
of  the  Ox  and  other  Ruminants.     ^J£j^l3RrS 

In  some  animals,  as  the  Hamster  lower  jaw. 
and  Gopher,  the  cheeks  are  developed  into  pouches  in 
which  the  food  may  be  carried.  These  may  be  lined  with 
hair.  The  tongue  is  remarkably  long  in  the  Ant-eater 
and  Giraffe,  and  almost  immovable  in  the  Gnawers,  Ele- 
phants, and  Whales. 

3.  The  Teeth  of  Animals. — Nearly  all  animals  have 
certain  hard  parts  within  the  mouth  for  the  prehension  or 
trituration  of  solid  food.  If  these  are  wanting,  the  legs 
are  often  armed  with  spines,  or  pincers,  to  serve  the  same 


64:  COMPARATIVE  ZOOLOGY. 

purpose,  as  in  the  Horse -shoe  Crab;  or  the  stomach  is 
lined  with  "gastric  teeth,"  as  in  some  marine  Snails;  or 
the  deficiency  is  supplied  by  a  muscular  gizzard,  as  in 
Birds,  Ant-eaters,  and  some  Insects.  Even  the  Lobster 
and  Crab,  in  addition  to  their  complicated  oral  organs, 
have  the  stomach  furnished  with  a  powerful  set  of  teeth. 
The  Sea-urchin  is  the  first  of  animals,  and  almost 
the  only  one  below  Worms  and  Mollusks,  which  exhibits 

anything  like  a 
dental  apparatus. 
Five  calcareous 
teeth,  having  a 
wedge  -  shaped 
apex,  each  set  in 
a  triangular  pyr- 
amid, or  "jaw," 
are  moved  upon 
each  other  by  a 

FIG. 28.— Echinus  bisected,  showing  masticating  apparatus.  Complex  arrail  o"e- 

ment  of  levers  and  muscles.  Instead  of  moving  up  and 
down,  as  in  Vertebrates,  or  from  right  to  left,  as  in  Ar- 
thropods, they  converge  towards  the  centre,  and  the  food 
passes  between  ten  grinding  surfaces. 

The  Rotifers  (a  group  of  minute  Worms)  have  a  curi- 
ous pair  of  horny  jaws.  That  which  answers  to  the  lower 
jaw  is  fixed,  and  called  the  "  anvil."  The  upper  jaw  con- 
sists of  two  pieces  called  "hammers,"  which  are  sharply 
notched,  and  beat  upon  the  "anvil"  between  them  (Fig. 
219). 

The  horny-toothed  mandibles  of  Insects,  already  men- 
tioned, are  prehensile,  and  also  serve  to  divide  the  food. 

The  three  little  white  ridges  in  the  mouth  of  the  Leech 
are  the  convex  edges  of  horny  semicircles,  each  bordered 
by  a  row  of  nearly  a  hundred  hard,  sharp  teeth.  When 
the  mouth,  or  sucker,  is  applied  to  the  skin,  a  sawing 


HOW  ANIMALS  EAT. 


65 


movement  is  given 
to  the  horny  ridges, 
so  that  the  "bite" 
of  the  Leech  is  real- 
ly a  saw-cut. 
The  dentition  of 


\*£  dufsisn 


B 


FIG.  2W.— Teeth  and  Masticatory  Apparatus  of  Gastero- 
the  Univalve  .Mol-  pods:  Af  portion  of  odontophore,  or"  tongne,"  of  Pel- 
utina,  enlarged  ;  B,  portion  of  odontophore  of  Whelk 
(Kuf-cinum  undatitrn),  magnified  —  the  entire  tongue 
has  100  rows  of  teeth  ;  C.  head  and  odontophore  of  Lira- 
pet  (Patella  vulgata) ;  D,  portion  of  same,  greatly  mag- 
nified, to  show  the  transverse  rows  of  siliceous  teeth. 


lusks,  or  the  Snails, 

is  generally  lingual, 

i.  £.,  it  consists  of 

microscopic  teeth,  usually  siliceous  and  amber -colored, 

planted  in  rows  on  the  tongue. 
The  teeth  are,  in  fact,  the  ser- 
rated edges  of  minute  plates. 
The  number  of  these  plates  va- 
ries greatly;  the  garden  Slug 
has  160  rows,  with  180  teeth 
in  each  row. 

All  living  Birds,  and  some 
other  Vertebrates,  as  Ant-eat- 
_  ers,24  Turtles,  Tortoises,  Toads, 

;and  Sturgeons,  have  no  teeth. 
Their  place  is  often  supplied 
by  a  horny  beak,  a  muscular 
gizzard,  or  both  structures. 
In  a  few  Vertebrates,  horny 
plates  take  the  place  of  teeth, 
as  the  Duck  Mole  (Ornitho- 
rftynchus)  and  Whalebone 
Whale.  In  the  former,  the 
plates  consist  of  closely  set  ver- 

FIG.  30.— Section  of  one  half  of  the  Up-  ,•      1111          ,     i  ,1        i    , 

per  Jaw  of  a  Whale  (Balcenoptera),  tlCal  hollOW  tubes  ;  in  the  lat- 
showiug  baleen -plates:  a,  superior  *pr  *up  Kalppn  nr  wlialaHnnA 
maxillary  bone;  ft,  ligamentous  gum  -'  IJ  3D>  ° 

attaching  the  horny  body  of  the  ba-  plates,  triangular  in  shape,  and 

leen-plate,  c;  d,  fringe  of  bristles;  e,  *   .         7 

smaller  plates.  fringed  on  the  inner  side,  hang 

5 


66  COMPARATIVE  ZOOLOGY. 

in  rows  from  the  gums  of  the  upper  jaw.    In  some  Whales 

there  are  about  300  plates  on  each  side.25 

True  teeth,  consisting  mainly  of  a  hard,  calcareous  sub- 

stance called  dentine,  are  found  only  in  back-boned  ani- 

mals. They  are  distinct  from  the  skeleton,  and  differ 
from  bone  in  containing  more  min- 
e  eral  matter,  and  in  not  showing, 
under  the  microscope,  any  minute 
cavities,  called  lacunae.  A  typical 
tooth,  as  found  in  Man,  consists  of 
a  central  mass  of  dentine,  capped 
with  enamel  and  surrounded  on 
the  fang  with  cement.  The  first 
tissue  is  always  present,  while  the 
others  may  be  absent.  It  is  a  mixt- 
ure of  animal  and  mineral  matter 

FIG.  31.—  Section  of  Human  Mo-  . 

lar,    enlarged:    k,   crown;    n,  disposed   111   the  form  of  extremely 


tubes  and  cells,  so  minute  as  to 
cavity-  prevent  the  admission  of  the  red 

particles  of  blood.  One  modification  of  it  is  ivory,  seen 
in  the  tusks  of  Elephants.  Enamel  is  the  hardest  tissue 
of  the  body,  and  contains  not  more  than  two  per  cent,  of 
animal  matter.  It  consists  of  six-sided  fibres  set  side  by 
side,  at  right  angles  to  the  surfaces  of  the  dentine.  Ce- 
ment closely  resembles  bone,  and  is  present  only  in  the 
teeth  of  the  higher  animals. 

Teeth  are  usually  confined  to  the  jaws  ;  but  the  num- 
ber, size,  form,  structure,  position,  and  mode  of  attachment 
vary  with  the  food  and  habits  of  the  animal.  As  a  rule, 
animals  developing  large  numbers  of  teeth  in  the  back 
part  of  the  mouth  are  inferior  to  those  having  fewer  teeth, 
and  those  nearer  the  lips.  The  teeth  of  Mammals  only 
have  fangs. 

The  teetli  of  Fishes  present  the  greatest  variety.  In 
number,  they  range  from  zero  to  hundreds.  The  Hag- 


PIOW  ANIMALS  EAT. 


67 


fish  (Myxine)  has  a  single  tooth  on  the  roof  of  the  mouth, 
and  two  serrated  plates  on  the  tongue;  while  the  mouth 
of  the  Pike  is  crowded  with  teeth.  In  some  we  find 
teeth  short  and  blunt,  in  the  shape  of  cubes,  or  prisms, 
arranged  like  mosaic  work.  Such  pavement-teeth  (seen 
in  some  Rays)  are  fitted  for  grinding  sea-weed  and  crush- 
ing shell-fish.  But  the  cone 
is  the  most  common  form  : 
sometimes  so  slender  and  close 
as  to  resemble  plush,  as  in  the 
Perch  ;  or  of  large  size,  and 
flattened  like  a  spear  -  head 
with  serrated  edges,  as  in  the 
Shark;  but  more  often  like  the  _ 

FIG.  32.—  Jaws  an  a  Pavement-teeth  of  a 

canines  of  Mammals,  curved  Ray 


inward  to  fit  them  for  grappling.  In  the  Shark,  the 
teeth  are  confined  to  the  fore-part  of  the  mouth;  in  the 
Carp,  they  are  all  situated  on  the  bones  of  the  throat;  in 
the  Parrot-fish,  they  occupy  both  back  and  front;  but  in 
most  Fishes  the  teeth  are  developed  also  on  the  roof,  or 
palate,  and,  in  fact,  on  nearly  every  bone  in  the  mouth. 
They  seldom  appear  (as  in  the  Salmon)  on  the  upper  max- 
illary. As  to  mode  of  attachment,  the  teeth  are  generally 
anchylosed  (fastened  by  bony  matter)  to  the  bones  which 
support  them,  or  simply  bound  by  ligaments,  as  in  the 
Shark.  In  a  few  Fishes,  the  teeth  consist  of  flexible  car- 
tilage ;  but  almost  invariably  they  are  composed  of  some 
kind  of  dentine,  enamel  and  cement  being  absent. 

Of  Amphibians  and  Reptiles,  Toads,  Turtles,  and  Tor- 
toises are  toothless;  Frogs  have  teeth  in  the  upper  jaw 
only  ;  Snakes  have  a  more  complete  set,  but  Saurians  pos- 
sess the  most  perfect  dentition.  The  number  is  not  fixed 
even  in  the  same  species:  in  the  Alligator  it  varies  from 
72  to  88.  The  teeth  are  limited  to  the  jawbones  in  the 
higher  forms  (Saurians);  but  in  others,  as  the  Serpents, 


68  COMPARATIVE  ZOOLOGY. 

they  are  planted  also  in  the  roof  of  the  month.  With 
few  exceptions,  they  are  conical  and  curved  (Fig.  33).  In 
the  Serpents  they  are  longest  and  sharpest;  and  the  ven- 
omous species  have  two  or  more  fangs  in  the  upper  jaw. 

These  fangs  contain  a  canal, 
through  which  the  poison 
is  forced  by  muscles  which 
compress  the  gland.  The 
bones  to  which  they  are  at- 
tached are  movable,  and  the 
FIG.  33.— Poison  Apparatus  of  the  Rattle-  fangs  ordinarily  lie  flat  upon 

snake:   or,  gland,  with  duct,  leading  to  ,1  ,                     ,              •,  , 

the  fangV/;  m,  elevator  muscles  of  the  the  gums,    bl.lt    are    brought 

jaw,  which  in  contracting,  compress  the  j     t  vertical     position     in 

gland  ;  «,  salivary  glands  on  the  edge  of  r 

the  jaws ;  n,  nostril.  the  act  of  striking.     As  a 

rule,  the  teeth  of  Reptiles  are  simply  soldered  to  the  bone 
which  supports  them,  or  lodged  in  a  groove;  but  those  of 
Crocodiles  are  set  in  sockets.  Reptilian  teeth  are  made 
of  dentine  and  a  thin  layer  of  cement,  to  which  is  added 
in  most  Saurians  a  coat  of  enamel  on  the  crown. 

In  the  majority  of  Mammals,  the  teeth  are  limited  in 
number  and  definite  in  their  forms.  The  number  ranges 
from  1  in  the  Narwhal  (but  the  longest  tooth  in  the  king- 
dom) to  220  in  the  Dolphin.  The  average  is  32,  occur- 
ring in  Ruminants,  Apes,  and  Man ;  but  44  (as  in  the 
Hog  and  Mole)  is  called  the  typical  or  normal  number, 
and  this  number  is  exceeded  only  in  the  lower  groups. 
When  very  numerous,  the  teeth  are  of  the  Reptilian  type, 
small,  pointed,  and  of  nearly  equal  size,  as  in  the  Porpoise. 
In  the  higher  Mammals,  the  teeth  are  comparatively  few, 
and  differ  so  much  in  size,  shape,  and  use,  that  they  can 
be  classed  into  incisors,  canines,  premolars,  and  molars. 
Such  a  dental  series  exhibits  a  double  purpose,  prehension 
and  mastication.  The  chisel-shaped  front  teeth  are  fitted 
for  cutting  the  food,  and  hence  called  incisors.  These 
vary  in  number  :  the  Lion  has  six  in  each  jaw;  the  Squir- 


HOW   ANIMALS  EAT.  69 

rel  has  two  in  each  jaw,  but  remarkably  developed ;  the 
Ox  has  none  in  the  upper  jaw,  and  the  Elephant  none  in 
the  lower ;  while  the  Sloth  has  none  at  all.26  The  canines, 
so  called  because  so  prominent  in  the  Dog,  are  conical, 
and,  except  in  Man,  longer  than  the  other  teeth.  They 
are  designed  for  seizing  and  tearing;  and  they  are  the 
most  formidable  weapons  of  the  wild  carnivores.  There 


FIG.  34.— Skull  of  the  Babirusa,  or  Malayan  Hog,  showing  growth  and  curvature  of 

the  canines. 

are  never  more  than  four.  They  are  wanting  in  all  Ro- 
dents,  and  in  nearly  all  herbivorous  quadrupeds.  The 
molars,  or  grinders,  vary  greatly  in  shape,  but  closely  cor- 
respond with  the  structure  and  habits  of  the  animal,  so 
that  a  single  tooth  is  sufficient  to  indicate  the  mode  of 
life  and  to  identify  the  species.27  In  the  Ruminants,  Ro- 
dents, Horses,  and  Elephants,  the  summits  of  the  molars 
are  flat,  like  mill-stones,  with  transverse  or  curving  ridges 


70  COMPARATIVE  ZOOLOGY. 

of  enamel.  In  the  Cats  and  Dogs,  they  are  narrow  and 
sharp,  passing  by  each  other  like  the  blades  of  scissors, 
and  therefore  cutting,  rather  than  grinding,  the  food. 
The  more  purely  carnivorous  the  species,  and  the  more 
it  feeds  upon  living  prey,  the  fewer  the  molars.  In  ani- 
mals living  on  mixed  diet,  as  the  Hog  and  Man,  the 
crowns  have  blunt  tubercles.  Premolars,  or  bicuspids, 
are  those  which  were  preceded  by  milk-teeth;  the  true, 
or  back,  molars  had  no  predecessors. 

The  dentition  of  Mammals  is  expressed  by  a  formula, 
which  is  a  combination  of  initial  letters  and  figures  in 


FIG.  35. — Teeth  of  the  right  lower  jaw  of  adult  male  Chimpanzee  (Troglodytes  niger), 
natural  size.    The  molar  series  does  not  form  a  curve,  as  in  Man. 

fractional  form,  to  show  the  number  and  kind  of  teeth 
on  each  side  of  both  jaws.     Thus,  the  formula  for  Man 

is-  i  2~2'  c  l~l-  v  2~2'  m  8"8-°.9 

155  •     *'5  2  —  2  '       '  1  —  1  '  JrJ  2  —  2  '         '  3  —  3  —  "^' 

The  teeth  of  Mammals  are  always  restricted  to  the 
margins  of  the  jaws,  and  form  a  single  row  in  each.  But 
they  rarely  form  an  unbroken  series.28  The  teeth  im- 
planted in  the  premaxillary  bone,  and  in  the  correspond- 
ing part  of  the  lower  jaw,  whatever  their  number,  are  in- 
cisors. The  first  tootli  behind  the  premaxillary,  if  sharp 
and  projecting,  is  a  canine. 

Each  tooth  lias  its  particular  bony  socket.29    The  molars 


HOW  ANIMALS  EAT.  71 

may  be  still  further  strengthened  by  having  two  or  more 
diverging  fangs,  or  roots,  a  feature  peculiar  to  this  class. 
The  incisors  and  canines  have  but  one  fang;  and  those 
that  are  perpetually  growing,  as  the  incisors  of  Rodents 
and  Elephants,  have  none  at  all.  The  teeth  of  flesh-eat- 
ing Mammals  usually  consist  of  hard  dentine,  surrounded 
on  the  root  with  cement  and  capped  with  enamel.  In  the 
herbivorous  tribes,  they  are  very  complex,  the  enamel  and 
cement  being  inflected  into  the  dentine,  forming  folds, 
as  in  the  molar  of  the  Ox,  or  plates,  as  in  the  compound 
tooth  of  the  Elephant.  This  arrangement  of  these  tissues, 
which  differ  in  hardness,  secures  a  surface  with  prominent 


FIG.  36.— Upper  Molar  Tooth  of  Indian  Elephant  (Elephas  Indicus),  showing  trans- 
verse arrangement  of  dentine,  d,  with  festooned  border  of  enamel  plates,  e;  c, 
cemeiit ;  one-third  natural  size. 

ridges,  well  adapted  for  grinding.  The  cutting  teeth  of 
the  Rodents  consist  of  dentine,  with  a  plate  of  enamel  on 
the  anterior  surface,  and  the  unequal  wear  preserves  a 
chisel-like  edge.  Enamel  is  sometimes  wanting,  as  in  the 
molars  of  the  Sloth  and  the  tusks  of  the  Elephant. 

In  Fishes  and  Reptiles,  there  is  an  almost  unlimited 
succession  of  teeth;  but  Mammalian  teeth  are  cast  and 
renewed  but  once  in  life. 

Vertebrates  use  their  teeth  for  the  prehension  of  food, 
as  weapons  of  offence  or  defence,  as  aids  in  locomotion, 
and  as  instruments  for  uprooting  or  cutting  down  trees. 
But  in  the  higher  class  they  are  principally  adapted  for 
dividing  or  grinding  the  food.30  While  in  nearly  all  other 


72  COMPARATIVE  ZOOLOGY. 

Vertebrates  the  food  is  bolted  entire,  Mammals  masticate 
it  before  swallowing.  Mastication,  is  more  essential  in  the 
digestion  of  vegetable  than  of  animal  food  ;  and  hence  we 
find  the  dental  apparatus  most  efficient  in  the  herbivorous 
quadrupeds.  The  food  is  most  perfectly  reduced  by  the 
Rodents. 

Teeth,  as  we  shall  see,  are  appendages  of  the  skin,  not 
of  the  skeleton,  and,  like  other  superficial  organs,  are  es- 
pecially liable  to  be  modified  in  accordance  with  the  hab- 
its of  the  creature.  They  are,  therefore,  of  great  zoologi- 
cal value ;  for,  such  is  the  harmony  between  them  and 
their  uses,  the  naturalist  can  predict  the  food  and  general 
structure  of  an  animal  from  a  sight  of  the  teeth  alone. 
For  the  same  reason,  they  form  important  guides  in  the 
classification  of  animals;  while  their  durability  renders 
them  available  to  the  paleontologist  in  the  determination 
of  the  nature  and  affinities  of  extinct  species,  of  which 
they  are  often  the  sole  remains.  Even  the  structure  is 
so  peculiar  that  a  fragment  will  sometimes  suffice. 

4.  Deglutition,  or  How  Animals  Swallow. — In  the 
lowest  forms  of  life,  the  mouth  is  but  an  aperture  opening 
immediately  into  the  body-cavity,  and  the  food  is  drawn 
in  by  ciliary  currents.  But  in  the  majority  of  animals,  a 
muscular  tube,  called  the  gullet,  or  oesophagus,  intervenes 
between  the  mouth  and  stomach,  the  circular  fibres  of 
which  contract,  in  a  wave-like  manner,  from  above  down- 
ward, propelling  the  morsel  into  the  stomach.31  In  the 
higher  Mollusks,  Arthropods,  and  Vertebrates,  deglutition 
is  generally  assisted  by  the  tongue,  which  presses  the  food 
backward,  and  by  a  glairy  juice,  called  saliva,  which  facil- 
itates its  passage  through  the  gullet.32  Vertebrates  have 
a  cavity  behind  the  mouth,  called  the  throat,  or  pharynx, 
which  may  be  considered  as  a  funnel  to  the  oesophagus." 
In  air-breathers,  it  has  openings  leading  to  the  windpipe, 
nose,  and  ears.  In  Man,  as  in  Mammals  generally,  the 


HOW  ANIMALS  EAT.  73 

process  of  deglutition  is  in  this  wise :  the  food,  masticated 
by  the  teeth  and  lubricated  by  the  saliva,  is  forced  by  the 
tongue  and  cheeks  into  the  pharynx  ;  the  soft  palate  keep- 
ing it  out  of  the  nasal  aperture,  and  the  valve-like  epiglot- 
tis falling  down  to  form  a  bridge  over  the  opening  to  the 
windpipe.  The  moment  the  pharynx  receives  the  food, 
it  is  firmly  grasped,  and,  the  muscular  fibres  contracting 
above  it  and  left  lax  below  it,  it  is  rapidly  thrust  into  the 
oesophagus.  Here,  a  similar  movement  (the  peristaltic) 
strips  the  food  into  the  stomach.34  The  rapidity  of  these 
contractions  transmitted  along  the  oesophagus  may  be  ob- 
served in  the  neck  of  a  Horse  while  drinking. 

Deglutition  in  the  Serpents  is  painfully  slow,  and  some- 
what peculiar.  For  how  is  an  animal,  without  limbs  or 
molars,  to  swallow  its  prey,  which  is  often  much  larger 
than  its  own  body  ?  The  Boa-constrictor,  e.  g.,  seizes  the 


35 

Fia.  ST.— Skull  of  Boa-constrictor:  1,  frontal;  2,  prefrontal ;  4,  postfrontal ;  5,  basi- 
occipital;  6,  sphenoid;  7,  parietal;  12,  squamosal;  13,  prootic;  17,  premax- 
illary;  18,  maxillary;  20,  nasal;  24,  transverse;  25,  internal  pterygoid;  34,  den- 
tary,  lower  jaw;  35,  angular ;  36,  articular ;  a,  quadrate;  s,  prenasal;  v,  petrosal. 

head  of  its  victim  with  its  sharp  recurving  teeth,  and 
crushes  the  body  with  its  overlapping  coils.  Then,  slow- 
ly uncoiling,  and  covering  the  carcass  with  a  slimy  mu- 
cus, it  thrusts  the  head  into  its  mouth  by  main  force,  the 
mouth  stretching  marvellously,  the  skull  being  loosely  put 


74  COMPARATIVE  ZOOLOGY. 

together.  One  jaw  is  then  unfixed,  and  the  teeth  with- 
drawn by  being  pushed  forward,  when  they  are  again 
fastened  farther  back  upon  the  animal.  The  other  jaw 
is  then  protruded  and  refastened ;  and  thus,  by  successive 
movements,  the  prey  is  slowly  and  spirally  drawn  into 
the  wide  gullet. 


CHAPTER  IX. 

THE    ALIMENTARY    CANAL. 

The  Alimentary  Canal  is  the  great  route  by  which 
nutritive  matter  reaches  the  interior  of  the  body.  It  is 
the  most  universal  organ  in  the  animal  kingdom,  and  the 
rest  are  secondary  or  subservient  to  it.  In  the  higher  an- 
imals, it  consists  of  a  mouth,  pharynx,  gullet,  stomach, 
and  intestine. 

It  is  a  general  law,  that  food  can  be  introduced  into 
the  living  system  only  in  a  fluid  state.  While  plants  send 
forth  their  roots  to  seek  nourishment  from  without,  ani- 
mals, which  may  be  likened  to  plants  turned  outside  in, 
have  their  roots  (called  absorbents)  directed  inward  along 
the  walls  of  a  central  tube  or  cavity.  This  cavity  is  for 
the  reception  and  preparation  of  the  food,  so  that  animals 
may  be  said  to  carry  their  soil  about  with  them.  The 
necessity  for  such  a  cavity  arises  not  only  from  the  fact 
that  the  food,  which  is  usually  solid,  must  be  dissolved,  so 
as  to  make  its  way  through  the  delicate  walls  of  the  cav- 
ity into  the  system,  but  also  from  the  occurrence  of  inter- 
vals between  the  periods  of  eating,  and  the  consequent 
need  of  a  reservoir.  For  animals,  unlike  plants,  are  thrown 
upon  their  own  wits  to  procure  food. 

The  Protozoa,  as  the  Amoeba  and  Infusoria,  can  hardly 


THE  ALIMENTARY   CANAL. 


75 


be  said  to  have  a  digestive  canal.  The  animal  is  here 
composed  of  a  single  cell,  in  which  the  food  is  digested. 
The  jelly-like  Amoeba  passes  the  food  through  the  firmer 
outer  layer  (ectosarc)  into  the  more  fluid  inner  part  (endo- 
sarc),  where  it  is  digested.  The  Infusoria,  which  have  a 
cuticle,  and  so  a  more  definite  form,  possess  a  mouth,  or 
opening,  into  the  interior  of  their  cell-body,  and  at  least 
a  definite  place  where  the  excrement  is  passed  out.  But 
we  cannot  call  this  cell-cavity  a  digestive  tract. 

In  the  higher  animals,  the  alimentary  canal  is  a  contin- 
uation of  the  skin,  which  is  reflected  inward,  as  we  turn 
the  finger  of  a  glove.35  We  find  every  grade  of  this  re- 
flection, from  the  sac  of  the  Hydra  to  the  long  intestinal 
tube  of  the  Ox.  So  that  food  in  the  stomach  is  still  out- 
side of  the  true  body. 

The  simplest  form  of  such  a  digestive  tract  is  seen  in 
the  Hydra  (Fig.  191).  Here  the  body  is  a  simple  bag, 
whose  walls  are  composed  of  two  layers  of  cells  (ectoderm 
and  endoderm).  A 
mouth  leads  into  the 
cavity,  and  serves  as 
well  for  the  outlet  of 
matter  not  wanted. 
The  endodermal  cells 
furnish  the  juices  by 
which  the  food  is  di- 
gested and  absorb  the 
nutritious  portions  of 
it.  There  is  no  rad- 
ical difference,  how- 
ever, between  the  two 

lavors  of  pplk    for  tliP  FlG'  38--Dissected  Actinia:  a,  the  thick  opaque  skin 

l£V  l'         p*  '-tJllb,  it  consisting  of  ectoderm,  lined  with  muscular  fibres ; 

Hydra  has  been  turn-  c' the  tllbalar  tentacles  communicating  with  the  in- 

•   .       t  terspaces ;    k,  between    the  membranous  vertical 

ed    inside    OUt,   When  folds;  #,  #',  orifices  in  the  walls  allowing  passage 

,        ,.                             ,  of  respiratory  water  from  one  compartment  to  an- 

tlie  lOrmer  ectoderm  other;  d,  mouth  leading  to  gastric  cavity,  e. 


76  COMPARATIVE  ZOOLOGY. 

has  digested  the  food  and  the  former  endoderra  has  taken 
on  the  functions  of  the  outer  layer.  The  Polyps  have 
also  but  one  external  opening ;  but  from  this  hangs  down 
a  short  tube,  open  at  both  ends,  reaching  about  half-way 
to  the  bottom  of  the  body-cavity.  Such  an  arrangement 
would  be  represented  by  a  bottle  with  its  neck  turned 
inward.  In  this  suspended  sac,  which  is  somewhat  con- 
stricted at  the  extremities,  digestion  takes  place ;  but  the 
product  passes  freely  into  all  the  surrounding  chambers, 
along  with  the  water  for  respiration.  The  Medusae,  or 
Jelly-fishes,  preserve  the  same  type  of  a  digestive  appara- 
tus ;  but  the  sac  is  cut  off  from  the  general  cavity,  and 
numerous  canals  radiate  from  it  to  a  circular  canal  near 
the  margin  of  the  disk.  In  the  Star-fishes  (Fig.  126),  we 
find  a  great  advance.  The  sac-like  stomach  sends  off  two 
glandular  branches  to  each  arm,  which  doubtless  furnish 
a  fluid  to  aid  in  digestion  (so-called  hepatic  coeca).  There 
is  also  an  anus  present  in  some  forms,  but  it  hardly  serves 
to  pass  off  the  waste  matter. 

L-  Thus  far  we  have  seen  but  one  opening  to  the  digestive 
cavity,  rejected  portions  returning  by  the  same  road  by 
which  they  enter.  But  a  true  alimentary  canal  should 
have  an  anal  aperture  distinct  from  the  oral.  The  sim- 
plest form  of  such  a  canal  is  exhibited  by  the  Sponge,  in 
its  system  of  absorbent  pores  for  the  entrance  of  liquid, 
and  of  several  main  channels  for  its  discharge.  The 
apparatus,  however,  is  not  marked  off  from  the  general 
cavity  of  the  body,  and  digestion  is  not  distinct  from  cir- 
culation.36 

The  Sea-urchin  presents  us  with  an  important  advance 
— one  cavity  with  two  orifices;  and  the  complicated  ap- 
paratus of  higher  animals  is  but  the  development  of  this 
type.  This  alimentary  canal  begins  in  a  mouth  well  pro- 
vided with  teeth  and  muscles,  and  extends  spirally  to  its 
outlet,  which  generally  opens  on  the  upper,  or  opposite, 


THE  ALIMENTARY  CANAL. 


77 


surface.  Moreover,  while  in  some  of  the  Worms  the  canal 
is  a  simple  tube  running  through  the  axis  of  the  cylindri- 
cal body  from  oral  ori- 
fice to  anal  aperture,  the 
canal  of  the  Sea-urchin 
shows  a  distinction  of 
parts, foreshadowing  the 
pharynx,  gullet,  stom- 
ach, and  intestines.  Both 
mouth  and  vent  have 
muscles  for  constriction 
and  expansion;  and,  as 

tho  vpnt  k  on  thp  mini-  Fie.  39._Diagrammatic  Section  of  a  Sea-nrchin 

(Echinus):  a,  month ;  b,  oesophagus;  c,  stom- 

mit  of  the  shell,  and  the 
latter  is  covered  with 
spines,  the  ejected  par- 
ticles are  seized  by  del- 
icate forks  (pedicella- 
rice),  and  passed  on  from 
one  to  the  other  down 
the  side  of  the  body,  till  they  are  dropped  off  into  the 
water.37 

The  Worms  present  us  with  a  great  range  of  structure 
in  the  digestive  tract.  It  is  sometimes  almost  as  simple 
as  that  of  the  Hydra — a  mere  sac.  The  Earth-worm  has 
a  tube  running  straight  through  the  body,  divided  into 
pharynx,  oesophagus,  crop,  gizzard,  and  sacculated  intes- 
tine. The  Leech  has  large  sacs  on  each  side  of  the  intes 
tine.  The  Sea- worms  have  the  pharynx  armed  with  teeth, 
and  some  have  glandular  cceca  attached  to  the  intestine. 
The  plan  is  that  of  a  straight  tube  extending  from  mouth 
to  anus.  In  Myriapods  and  larvse  of  Insects,  the  same 
general  plan  is  continued,  the  canal  passing  in  a  straight 
line  from  one  extremity  to  the  other,  but  showing  a  divis- 
ion into  gullet,  stomach,  and  intestine/8  Crustacea,  like 


ach  ;  (f,  intestine:  /,  madreporitbrm  tubercle; 
(j,  stone-canal;  h,  ambnlacral  ring;  fc,  Polian 
vesicles,  which  are  probably  reservoirs  of  fluid; 
m,  ambnlacral  tube;  o,  anus;  jo,  ambulacra, 
with  their  contractile  vesicles;  r,  nervous  ring 
around  the  gullet;  s,  t\vo  nervous  trunks,  the 
right  terminating,  at  anal  pole,  in  a  small  gan- 
glion ;  t,  blood-vascular  rings  connected  by  v, 
the  contractile  heart ;  w,  two  arterial  trunks  ra- 
diatir.g  from  the  anal  ring;  x,  an  ovary  open- 
ing at  the  anal  pole  in  a  genital  plate,  y;  z, 
spines,  with  their  tubercles. 


78 


COMPARATIVE  ZOOLOGY. 


the  Lobster,  have  a  short  gullet  leading  to  a  large  cav- 
ity, situated  in  the  front  of  the  animal,  which  is  a  giz- 
zard, rather  than 
stomach,  as  it  has 
thick  muscular 
walls  armed  with 
teeth.  A  well- 
marked  constric- 
tion separates  this 
organ  from  the  in- 
testine. The  liver 
is  highly  devel- 
oped; instead  of 
numerous  folli- 
cles, there  is  a 
large  bilaterally 
symmetrical  or- 
gan, divided  into 
three  lobes  on  each 
side,  pouring  its 
secretion  into  the 
upper  part  of  the 
intestine,  which  is 
the  true  stomach. 
J'Among  Insects, 
there  is  great  vari- 
ation in  the  form 
and  length  of  the 

PIG.  40.—  Anatomy  of  a  Caterpillar:  cj,  h,  oesophagus;  h,  i     mi       /?   -n 

i,  stomach  ;  k,  hepatic  vessels ;  I,  m,  intestine ;  q,  r,  sal-  Canal.    1  lie  lOllOW- 

ivary  glands;  p,  salivary  duct;  a,  6,  c,  longitudinal  •         _nrf.Q  __n       p_ 

tracheal  trunks;  d,  e,  air-tubes  distributed  to  the  vis-  11J&  P*11 1&  tcin  &en' 

cera;   /,  fat-mass;    v,  x,  y,  silk-secretors ;   z,  their  ex-  grally    be      distil.l- 
cretory  ducts,  terminating  in  t,  the  spinneret,  or  fu-  * 

wins.  guished :     gullet, 

crop,  gizzard,  stomach, and  large  and  small  intestines,  with 
many  glandular  appendages.  The  crop,  gizzard,  and  large 
intestine  are  sometimes  absent,  especially  in  the  carnivorous 


THE  ALIMENTARY   CANAL. 


79 


species.     In  Bees,  the  crop  is  called  the  "honey -bag." 
The  gizzard  is  found  in  Insects  having  mandibles,  and  is 


FIG.  41. — Alimentary  canal  of  a  Beetle : 
<i,  pharynx;  &,  gullet,  leading  to  crop, 
«,-,  gizzard,  d,  and  stomach,  e;  /,  deli- 
cate urinary  tubes ;  g,  intestine ;  h, 
other  secreting  organs. 


FIG.  42.  —  Alimentary  Canal  of  the  Bee 
(Apis  mellifica) :  a,  gullet ;  &,  crop ;  c,  d, 
stomach  ;  e,  small  intestine  ;  /,  large  in- 
testine ;  g,  anal  orifice ;  h,  urinary  ves- 
sels ;  ?',  auxiliary  glands. 


frequently  lined  with  rows  of  horny  teeth,  which  are  spe- 
cially developed  in  Grasshoppers,  Crickets,  and  Locusts. 
The  intestines  are  remarkable  for  their  convolutions.  In- 
sects have  no  true  liver ;  but  its  functions  are  performed 
by  little  cell-masses  on  the  inside  of  the  stomach.39 

The  alimentary  canal  of  Spiders  is  short  and  straight, 
the  pharynx  and  gullet  being  very  minute.  The  stomach 
is  characterized  by  sending  out  tubular  prolongations,  and 


n    I'      I"  I'"  s       n  n 

FIG  43.— Anatomy  of  a  Sphinx  Moth:  n,  nervous  cord  ;  n',  brain  sending  off  nerves 
to  the  legs,  I',  I",  I'",  and  for  the  wings  at  n" ;  k,  dorsal  vessel,  or  heart ;  c,  crop; 
«,  stomach ;  i,  intestines ;  o,  reproductive  organs ;  o',  oviduct ;  8-20,  segments. 


80 


COMPARATIVE  ZOOLOGY. 


the  intestines  end  in  a  large  bladder-like  expansion.  Scor- 
pions have  no  stomachal  cavity — a  straight  intestine  passes 
directly  through  the  body. 

In  bivalve  Mollusks,  like  the  Clam,  the  month  opens 
into  a  short  oesophagus  which  leads  into  the  stomach, 
which  lies  imbedded  in  a  large  liver,  and  the  intestine, 
describing  a  few  turns,  passes  directly  through  the  heart.40 
In  the  univalve  Molhisks,  like  the  Snail,  the  gullet  is  long, 
and  frequently  expands  into  a  crop ;  the  stomach  is  often 
double,  the  anterior  being  a  gizzard  provided  with  teeth 
for  mastication ;  the  intestine  passes  through  the  liver, 
and  ends  in  the  fore-part  of  the  bod}7,  usually  on  the  right 
side. 

,  The  highest  Mollusks,  as  the  Cuttle-fish  and  Nautilus, 
exhibit  a  marked  advance.  A  mouth  with  powerful  man- 
dibies  leads  to  a  long  gullet,  which  ends  in  a  strong  mus- 
cular gizzard  resembling  that  of  a  fowl.41  Below  this  is  a 
cavity,  which  is  either  a  stomach  or  duodenum  ;  it  receives 

the  bile  from  a 
large  liver.  The 
intestine  is  a  tube 
of  uniform  size, 
which,  after  one  or 
two  slight  curves, 
bends  up,and  opens 
into  the  "funnel" 
near  the  mouth. 

Fishes  have  a 
simple,  short,  and 
wide  alimentary 
canal.  The  stom- 
ach is  separated 

FIG.  44.— Alimentary  Caunl  of  the  Oyster:  a,  stomach  frorn   the    intestine 
laid  open ;  d,  liver ;  b,  c,  d,f,  convolutions  of  the  intes- 
tine ;  g,  anal  aperture;  n,  o,  auricle  and  ventricle;  I,  by    a   narrOW    "  PY~ 
m,  adductor  muscle;  h,  k, lobes  of  month  divided  to  ,       .     „  .« 
show  the  venous  canals  at  the  base  of  the  gills.  lOHC         Orince,      Or 


THE   ALIMENTARY  CANAL. 


81 


Fio.  45. —  Anatomy  of  a  Gasteropod  (Snait):  a,  month  ;  &,  foot;  c,  anus;  d,  lung^ 
e,  stomach,  covered  above  by  the  salivary  glands  ;  /,  intestine ;  g,  liver ;  /t,  heart ; 
i,  aorta;  j,  gastric  artery;  Z,  hepatic  artery;  k,  artery  of  the  foot;  w,  abdominal 
cavity,  supplying  the  place  of  a  venous  sinus ;  n,  irregular  canal  communicating 
with  the  abdominal  cavity,  and  carrying  the  blood  to  the  lung;  o,  vessel  carry- 
ing blood  from  the  lung  to  the  heart. 

valve,  but  is  not  so  clearly  distinguished  from  the  gullet, 
so  that  regurgitation  is  easy.4*     Indeed,  it  is  common  for 


— q 


8  I  k  r  b 

FIG.  46 Anatomy  of  a  Lamellibranch  (Mactra) :  a,  shell ;  b,  mantle  ;  c,  tentacles,  or 

lips;  rf,  mouth;  e,  nerves;  /,  muscles;  g,  anterior,  and  n,  posterior  ganglion ;  h, 
liver;  t,  heart:  k,  stomach  ;  I,  intestine  passing  through  the  heart;  w,  kidney;  o, 
anal  end  of  the  intestine;  p,  exhalent,  and  g,  iuhalent  respiratory  tubes,  or  si- 
phons ;  r,  gills ;  «,  foot. 

6 


82 


COMPAKATIVE  ZOOLOGY. 


Fishes  to  disgorge  the  indigestible  parts  of  their  food,  and 
some,  as  the  Carp,  send  the  food  back  to  the  pharynx  to 
be  masticated.  The  stomach  is  usually  bent,  like  a  si- 
phon ;  but  the  intestine  is  nearly  straight,  and  without 
any  marked  distinction  into  small  and  large.  Its  append- 
ages are  a  large  liver  and  a  rudimentary  pancreas. 

In  the  Amphibians,  as  the  Frogs,  the  digestive  appara- 
tus is  very  similar  to  that  of  Fishes  ;  but  the  two  kinds 

of  intestines  can  be  more  readily 
distinguished.  The  He  ptiles  gen- 
erally have  a  long,  wide  gullet, 
which  passes  insensibly  into  the 
stomach,  and  a  short  intestine 
(about  twice  the  length  of  the 
body)  very  distinctly  divided  into 
small  and  large  by  a  constric- 
tion.43 The  vegetable  -feed  ing 
Tortoises  have  a  comparatively 
long  intestinal  tube  ;  and  the 
Serpents  have  a  slender  stomach, 
but  little  wider  than  the  rest  of 
Fi».  47.—  Anatomy  of  a  cephaiopod  the  alimentary  canal. 

(diagram):  a,  tentacles;  b,  masti-         m.  .         „     ,        ~  ,., 

catory  apparatus;  c,  eye;  d,  sali-         Hie  Stomach  OI  the  CrOCOdlle 

BSZa^T«  is  more  cot"Plex  than  any  hith- 

A,  stomach;  i,  in-  erto   mentjoned.      It   resembles 

testme  ;    k,   aims;    6,   funnel;    m, 

ink-bag;  «,  ovary;  o,  oviduct:  p,  that  of  the  Cllttle-fisll,  but  offei'S 

liver  ;  r,  gill  contained  in  the  bran-  ...                           ..  . 

chial  chamber  ;  «,  branchial  heart  ;  a   Still   mOl'6    Striking   analogy   to 

t,  systemic  heart;,,  mantle.  Qf    &     Bird?having 


very  thick  walls,  and  the  muscular  fibres  radiating  pre- 
cisely in  the  same  manner,  so  that,  in  this  respect,  the 
Crocodile  may  be  considered  the  connecting  link  between 
Reptiles  and  Birds."  In  Crocodiles  also  the  duodenum, 
with  which  the  intestine  begins,  is  first  distinctly  denned. 
Into  this  part  of  the  intestine  the  liver  and  pancreas,  or 
sweet-bread,  pour  their  secretions.  Furthermore,  in  the 


THE  ALIMENTARY  CANAL. 


83 


lower  animals,  the  intestines  lie  more  or  less  loose  in  the 
abdomen  ;  but  in  the  Crocodile,  and  likewise  in  Birds  and 
Mammals,  they  are  supported  by  a  membrane  called  mes- 
entery. 


FIG.  48.— Anatomy  of  the  Carp :  br,  branchiae,  or  gill-openings ;  c,  heart ;  /,  liver;  tm, 
vn',  swimming-bladder;  ci,  intestinal  canal;  o,  oyarium ;  u,  ureter;  a,  anus;  o', 
genital  opening;  «',  opening  of  ureter.  The  side-view  shows  the  disposition  of 
the  muscles  iu  vertical  flakes. 


84 


COMPARATIVE  ZOOLOGY. 


In  Birds,  the  length  of  the  alimentary  canal  varies  with 
their  diet,  being  greatest  in  those  living  on  grain  and  fruit. 
The  gullet  corresponds  in  length  with  the  neck,  which  is 
longest  in  the  long-legged  tribes,  and  in  width  with  the 
food.  In  those  that  swallow  large  fish  entire,  the  gullet 
is  dilatable,  as  in  Snakes.  In  nearly  all  Birds,  the  food  is 
delayed  in  some  cavity  before  digestion  :  thus,  the  Pelican 
has  a  bag  under  the  lower  jaw,  and  the  Cormorant  has  a 

capacious  gullet, 
where  they  store 
up  fishes;  while 
those  that  gorge 
themselves  at  in- 
tervals, as  the 
Vulture,  or  feed 
on  seeds  and 
grains, as  the  Tur- 
key, have  a  pouch, 
called  the  crop, 
developed  near 
the  lower  end  of 
the  gullet.45  The 
Ostrich,  Goose, 
Swan,  most  of 
the  Waders,  and 
the  fruit  or  in- 
sect eating  Birds, 
which  find  their  food  in  tolerable  abundance,  and  take  it 
in  small  quantities,  have  no  such  reservoir.  Pigeons  have 
a  double  crop.  » 

In  all  Birds,  the  food  passes  from  the  gullet  into  the 
proventriculus,  or  stomach  proper,  where  it  is  mixed  with 
a  "gastric  juice"  secreted  from  glands  on  the  surface. 
Thence  it  goes  into  the  gizzard,  an  oval  sac  of  highly 
muscular  texture,  and  lined  with  a  tough,  horny  skin.4' 


FIG.  49.— Stomach  of  the  Crocodile:  «,  muscular  fibres  ra- 
diating from  a  ceutral  tendon,  b;  d,  commencement  of 
duodenum  ;  c,  oesophagus ;  /,  intestine. 


THE   ALIMENTARY   CANAL. 


85 


The  gizzard  is  most  highly  developed,  and  of  a  deep-red 
color,  in  the  Scratchers  and  flat-billed  Swimmers  (as  Fowls 
and  Swans);  but  comparatively  thin  and  feeble  in  Birds 
of  Prey  (as  the  Eagle). 
The  gizzard  is  follow- 
ed by  the  intestines, 
which  are  longer  than 
those  of  Reptiles :  the 
small  intestine  begins 
with  a  loop  (the  duo- 
denum), and  is  folded 
several  times  upon  it- 
self ;  the  large  intestine 
is  short  and  straight, 
terminating  in  the  sole 
outlet  of  the  body,  the 
cloaca.  A  liver  and 
pancreas  are  always 
attached  to  the  upper 
part  of  the  small  in- 
testine. 

The  alimentary  ca- 
nal in  Mammals  is 
clearly  separated  into 
four  distinct  cavities: 
the  pharynx,  or  throat; 
the  oesophagus,  or  gul- 
let ;  the  stomach  ;  and 
the  intestines. 

The  pharynx  1S  more    FIG.  50. —Digestive  Apparatus  of  the  Fowl:  1, 

,         ,  .          tongue;  2,  pharynx;  3,  5,  oesophagus;   4,  crop; 

Complicated      than      in       6,  proventnculns ;  7,  gizzard  ;  8, 9, 10,  duodenum  ; 

"RirHs        Tr  i«  a  fnnnpl         11,12,  small  intestine  ;  13,  two  caeca  (analogue  of 

the  colon  of  mammals) ;  14,  their  insertion  into 

shaped       ba^1        having       the  5ntestinal  tube;  15,  rectum;  1C,  cloaca;  17, 
®       anus ;  18,  mesentery  ;  19,  20,  left  and  right  lobes 

Seven     Openings     lead-       of  liver;  21,  gall-bladder ;  22,  insertion  of  pan- 

creatic and  biliary  ducts;  23,  pancreas;  24,  lung; 
ing  into  it!    tWO  from       as,  ovary;  26,  oviduct. 


80 


COMPARATIVE   ZOOLOGY. 


the  nostrils,  and  two  from 
the  ears;  one  from  the 
windpipe,  guarded  by 
the  epiglottis;  one  from 
the  mouth,  with  a  fleshy 
curtain  called  the  sof  t pal- 
ate ;  and  one  from  the 
oesophagus.  It  is  the  nat- 
ural passage  for  food  be- 
tween the  mouth  and  the 
oesophagus,  arid  of  air  be- 
tween the  nostrils  and 
windpipe.  Like  the 
mouth,  it  is  lined  with  a 
soft  mucous  membrane. 

The  oesophagus  is  a 
long  and  narrow  tube, 
formed  of  two  muscular 
layers :  in  the  outside  one, 
the  fibres  run  length- 
wise ;  in  the  other,  they 
are  circular.  It  is  lined 
with  mucous  membrane. 
While  in  all  Fishes,  Rep- 
tiles, and  Birds  the  ven- 
tral chamber  is  one,  in 
Mammals  it  is  divided, 
by  a  partition  called  the 
diaphragm,  into  two  cav- 
ities —  the  thorax,  con- 
taining the  heart,  lungs, 

PIG.  51.—  Digestive  Apparatus  of  Man  (diagram):  1,  tongue;  2,  pharynx;  3,  oesopha- 
gus; 4,  soft  palate;  5,  larynx;  6,  palate;  7,  epiglottis;  8,  thyroid  cartilage;  9, 
beginning  of  spinal  marrow;  10,  11,  12,  vertebra,  with  spinous  processes;  13, 
cardiac  orifice  of  stomach;  14,  left  end  of  stomach  ;  IS,  pyloric  valve;  19,  20,  21, 
duodenum;  22,  gall-bladder ;  27,  duct  from  pancreas;  28,  29,  jejunum  of  intestine; 
30.  ileum ;  34,  coecum  :  36,  37,  38,  colon,  or  large  intestine  ;  40.  rectum. 


THE   ALIMENTARY   CANAL. 


87 


etc. ;    and  the  abdomen,  containing  the  stomach,  intes- 
tines, etc.     The  oesophagus  passes  through  a  slit  in  the 


FIG.  52. — Ideal  Section  of  a  Mammalian  Vertebrate:  A,  pectoral,  or  fore  limb;  B, 
pelvic,  or  hind  limb:  a,  mouth;  b,  cerebrum;  c,  cerebellum;  rf,  nope ;  e,  eye;  /, 
ear;  g,  oesophagus;  h,  stomach  ;  i,  intestine;  j,  diaphragm,  or  midriff;  k,  rectum, 
or  termination  of  intestine;  I,  anus;  m,  liver;  w,  spleen;  o,  kidney;  p,  sympa- 
thetic system  of  nerves  ;  g,  pancreas ;  r,  urinary  bladder;  s,  spinal  cord;  u,  ure- 
ter ;  v,  vertebral  column  ;  ic,  heart ;  x,  lung ;  ?/,  trachea,  or  windpipe  ;  z,  epi- 
glottis. 

diaphragm,  and   almost   immediately   expands   into   the 
stomach. 

In  the  majority  of  Mammals,  the  stomach  is  a  muscular 
bag  of  an  irregular  oval  shape,  lying  obliquely  across  the 
abdomen.  In  the  Flesh-eaters,  whose  food  is  easy  of  solu- 
tion, the  stomach  is  usually  simple,  and  lies  nearly  in  the 
course  of  the  alimentary  ca- 
nal ;  but  in  proportion  as  the 
food  departs  more  widely 
in  its  composition  from  the 
body  itself,  and  is  therefore 
more  difficult  to  digest,  we 
find  the  stomach  increasing 
in  size  and  complexity,  and 
turned  aside  from  the  gen- 
eral course  of  the  canal,  so  as 
to  retain  the  food  a  longer 
time, 
ing,  into  the  oasophagus  is  called  cardiac;  the  outlet,  or 


.  FIG.  53.—  Section  of  Horse's  Stomach. ;  A, 

The    inlet,    Or    Open-        left  sac;  Bright  sac;  C,  duodenum. 


88 


COMPARATIVE  ZOOLOGY. 


PIG.  54.-stomach  «>f  the 
Porpoise:  c,  cardiac;  p, 

pyloric. 


opening,  leading  into  the  intestines  is  called  pyloric.  In 
the  Carnivores,  Apes,  and  most  odd-toed  quadrupeds,  the 
stomach  resembles  that  of  Man.  That 
of  the  toothless  Ant-eater  has  the 
lower  part  turned  into  a  kind  of  giz- 
zard for  crushing  its  food.  The  Ele- 
phant's is  subdivided  by  numerous 
folds.  In  the  Horse,  it  is  constricted 
in  the^  middle  ;  and  in  the  Rodents, 
Porpoises,  and  Kangaroos,  the  con- 

r  .'  .  => 

stnction  is  carried  so  far  as  to  make 
two  or  three  sections.  But  animals  that  chew  the  cud 
(Ruminants)  have  the  most  complex  stomach.  It  is  di- 
vided into  four  peculiar  chambers  :  First,  the  paunch 
(rumen),  the  largest 
of  all,  receives  the 
half-  masticated  food 
when  first  swallowed. 
The  inner  surface  is 
covered  with  papillae, 
except  in  the  Camel, 
which  has  large  cells 

for  Storing  Up  water.  FIG.  55.—  Stomach  of  the  Lion:  c,  cardiac  orifice,  or 
From  this,  the  food  entrance  of  o^phagnB^pyloric. 

passes  into  the  honev-comb  stomach  (reticulum),  so  named 
from  its  structure.  Liquids  swallowed  usually  go  directly 
to  this  cavity,  without  passing  through  the  paunch,  arid 


Fio.  56. — Complex  Stomach  of  a  Ruminant :  a,  gullet ;  6,  rumen,  or  paunch  ;  c,  reticn- 
lum  ;  rf,  psalterinm,  or  manyplies;  e,  abomasus;  /,  pylorus  leading  to  duodenum. 


THE  ALIMENTARY  CANAL. 


80 


hence  it  is  sometimes  called  the  water -bag.  Here  the 
food  is  made  into  little  balls,  and  returned  to  the  mouth 
to  undergo  a  thorough  mastication.  When  finally  swal- 
lowed, it  is  directed,  by  a  groove  from  the  oesophagus,  to 
the  third,  and  smallest,  cavity,  the  manyplies  (psalterium), 
named  from  its  numerous  folds,  which  form  a  strainer  to 
keep  back  any  undivided  food;  and  thence  it  passes  into 
the  true  stomach  (abom,asus\  from  which,  in  the  calf,  the 
rennet  is  procured  for  curdling  milk  in  the  manufacture 
of  cheese.  This  fourth  cavity 
is  like  the  human  stomach  in 
form  and  function,  and  is  the 
only  part  which  secretes  gastric 
juice.  The  rumen  and  reticu- 
lum  are  rather  dilatations  of  the 
oesophagus  than  parts  of  the 
stomach  itself;  while  the  latter 
is  divided  by  constriction  into 
two  chambers,  the  psalterium 
and  abomasus,  as  in  many  other 
animals. 

In  structure,  the  stomach  re- 
sembles the  oesophagus.  The 
smooth  outside  coat  (perito- 
neum) is  a  reflection  of  the 
membrane  which  lines  the  whole 
abdomen.  The  middle,  or  mus- 
cular, coat  consists  of  three  lay- 
ers of  fibres,  running  length-  or  serous, coat 
wise  around  and  obliquely.  The  successive  contraction  and 
relaxing  of  these  fibres  produce  the  worm-like  motion  of 
the  stomach,  called  peristaltic.  The  innermost,  or  mucous, 
membrane,  is  soft,  velvety,  of  a  reddish-gray  color  in  Man, 
and  filled  with  multitudes  of  glands,  which  secrete  the 
gastric  juice.  The  human  stomach,  when  distended,  wilJ 


FIG.  5T.  —Vertical  Section  of  the 
Coats  of  the  Stomach:  1,  surface 
of  mucous  membrane,  and  mouths 
of  gastric  follicles;  2,  gastric  tubu- 
li,  or  follicles  ;  3,  dense  connective 
tissue;  4,  submucous  tissue;  5, 
transverse  muscular  fibre ;  6,  longi- 
tudinal muscular  fibre  ;  7,  fibrous, 


90 


COMPARATIVE  ZOOLOGY. 


hold  about  five  pints  ;  that  of  the  Kangaroo  is  as  long 
as  its  body. 

The  intestinal  canal  in  Mammals  begins  at  the  pyloric 
end  of  the  stomach,  where  there  is  a  kind  of  valve  or  cir- 
cular muscle.  Like  the  stomach,  it  varies  greatly,  accord- 
ing to  the  nature  of  the  food.  It  is  generally  longest  in 
the  Vegetable-feeders,  and  shortest  in  the  Flesh-feeders. 
The  greater  length  in  the  former  is  due  to  the  fact  that 
vegetable  food  requires  a  longer 
time  for  digestion,  and  that  a  great- 
er bulk  of  such  food  is  required  to 
obtain  a  given  quantity  of  nutri- 
ment. The  intestines  measure  150 
feet  in  a  full-grown  Ox,  while  they 
are  but  three  times  the  length  of 
the  body  in  the  Lion,  and  six  times 
in  Man.  Save  in  some  lower 
forms,  as  the  Whales,  there  are 
two  main  divisions,  the  "  small  " 
and  "large"  intestines,  at  the 
junction  of  which  is  a  valve.  The 
former  is  the  longer  of  the  two, 
and  in  it  digestion  is  completed, 
and  from  it  absorption  takes  place. 
FIG.  58.—  section  of  the  waii  of  The  large  intestine  is  a  temporary 

the  Human  Intestine  (ileum),  . 

X  50  :  a,  villi;  band  d,  glands;  lodging-place    for    the    USeleSS    part 


tndinai  muscles. 


°f  the  f°°d>  ™tn  ifc  is 

from  tne  j^y.  The  beginning  of 
the  small  intestine  is  called  the  duodenum,  into  which 
the  ducts  from  the  liver  and  pancreas  open.  The  intes- 
tinal canal  has  the  same  structure  as  the  stomach,  and  by 
a  peristaltic  motion  its  contents  are  propelled  downward. 
The  inside  surface  of  the  small  intestine  is  covered  with 
a  host  of  thread-like  processes  (villi),  resembling  the  pile 
of  velvet. 


HOW  ANIMALS  DIGEST.  91 

In  taking  this  general  survey  of  the  succession  of  forms 
which  the  digestive  apparatus  presents  among  the  princi- 
pal groups  of  animals,  we  cannot  fail  to  trace  a  gradual 
specialization.  First,  a  simple  sac,  one  orifice  serving  as 
inlet  for  food  and  outlet  for  indigestible  matter;  next,  a 
short  tube,  with  walls  of  its  own  suspended  in  the  body- 
cavity ;  then  a  canal  passing  through  the  body,  and,  there- 
fore, having  both  rnouth  and  vent;  next,  an  apparatus  for 
mastication,  and  a  swelling  of  the  central  part  of  the  canal 
into  a  stomach,  having  the  special  endowment  of  secreting 
gastric  juice ;  then  a  distinction  between  the  small  and 
large  intestine,  the  former  thickly  set  with  villi,  and  re- 
ceiving the  secretions  of  large  glands.  We  also  notice 
that  food,  the  means  of  obtaining  it,  the  instruments  for 
mastication,  and  the  size  and  complexity  of  the  aliment- 
ary canal,  are  closely  related. 


CHAPTEK  X. 

HOW   ANIMALS   DIGEST. 

The  object  of  the  digestive  process  is  the  reduction 
of  food  into  such  a  state  that  it  can  be  absorbed  into  the 
system.  For  this  purpose,  if  solid,  it  is  dissolved;  for 
fluidity  is  a  primary  condition,  but  not  the  only  one. 
Many  soluble  substances  have  to  undergo  a  chemical 
change  before  they  can  form  parts  of  the  living  body. 
If  albumen  or  sugar  be  injected  into  the  veins,  it  will  not 
be  assimilated,  but  be  cast  out  unaltered. 

To  produce  these  two  essential  changes,  solution  and 
transmutation,  two  agencies  are  used  —  one  mechanical, 
the  other  chemical.  The  former  is  not  always  needed, 
for  many  animals  find  their  food  already  dissolved,  as  the 


92  COMPARATIVE  ZOOLOGY. 

Butterfly;  but  solid  substances,  to  facilitate  their  solu- 
tion, are  ground  or  torn  into  pieces  by  teeth,  as  in  Man; 
by  jaws,  as  in  the  Lobster;  or  by  a  gizzard,  as  in  the 
Turkey. 

The  chemical  preparation  of  food  is  indispensable.47  It 
is  accomplished  by  one  or  more  solvent  fluids  secreted  in 
the  alimentary  canal.  The  most  important,  and  one  al- 
ways present,  is  the  gastric  juice,  the  secretion  of  which 
is  restricted  to  the  stomach,  when  that  cavity  exists.  In 
the  higher  animals,  numerous  glands  pour  additional  flu- 
ids into  the  digestive  tube,  as  saliva  into  the  upper  part 
or  mouth,  and  bile  and  pancreatic  juice  into  the  upper 
part  of  the  intestine.  In  fact,  the  mucous  membrane, 
which  lines  the  alimentary  canal  throughout,  abounds  with 
secreting  glands  or  cells. 

The  Digestive  Process  is  substantially  the  same  in  all 
animals,  but  it  is  carried  further  in  the  more  highly  de- 
veloped forms.  In  the  Infusoria,  the  food  is  acted  upon 
by  some  secretion  from  the  walls  of  the  body-cavity,  the 
exact  nature  of  which  is  unknown.  In  the  Star-fish  and 
Sea-urchin,  we  find  two  solvents — a  gastric  juice,  and 
another  resembling  bile;  but  the  two  appear  to  mingle  in 
the  stomach.  Mollusks  and  Arthropods  show  a  clear 
distinction  between  the  stomach  and  intestine,  and  the 
contents  of  the  liver  are  poured  into  the  latter.  There 
are,  therefore,  two  stages  in  the  digestive  act:  first,  the 
food  is  dissolved  by  the  gastric  juice  in  the  stomach,  form- 
ing chyme  •  secondly,  the  chyme,  upon  entering  the  intes- 
tine, is  changed  into  chyle  by  the  action  of  the  bile,  and 
is  then  ready  to  be  absorbed  into  the  system. 

In  Vertebrates,  a  third  solvent  is  added,  the  pancreatic 
juice,  which  aids  the  bile  in  completing  digestion.  But 
Mammals  and  Insects  have  a  still  more  perfect  and  elab- 
orate process;  for  in  them  the  saliva  of  the  mouth  acts 
chemically  upon  the  food;  while  the  saliva  in  many  other 


HOW   ANIMALS   DIGEST. 


93 


animals  has  no  other  office,  so  far  as  we  know,  than  to 
moisten  the  food  for  swallowing. 

Taking  Man  as  an  example,  let  us  note  the  main  facts 
in  the  process.  During  mastication,  by  which  the  relative 
surface  is  increased,  the  food  is  mixed  with  saliva,  which 
moistens  the  food,48  and  turns  part  of  the  starch  into 
grape-sugar.  Passed  into  the  stomach,  the  food  meets  the 
gastric  juice.  This  is  acid,  and,  first,  stops  the  action  of 
the  saliva;  secondly,  by  means  of  the  pepsin  which  it  con- 
tains, and  the  acid,  it  dissolves  the  albumen,  fibrine,  and 
such  constituents  of  the  food.  This  solution  of  albumi- 
noids is  called  a  peptone,  and  is  especially  distinguished 
from  other  such  solutions  by  its  diffusibility — i.  e.,  the  ease 
with  which  it  passes  through  a  membrane.  These  pep- 
tones, with  the  sugars  of  the  food,  whether  original  or  the 
product  of  the  action  of  the  saliva,  are  absorbed  from  the 
stomach.  The  food,  while  in  the  stomach,  is  kept  in  con- 
tinual motion,  and,  after  a  time,  is  discharged  in  gushes 
into  the  intestine.  The  name  chyme  is  given  to  the  pulpy 
mass  of  food  in  the  stomach.  In  the  intestine  the  chyme 
meets  three  fluids — bile,  pancreatic  juice,  and  intestinal 
juice.  All  of  these  are  alkaline,  and  at  once  give  the  acid 
chyme  an  alkaline  reaction.  This  change  permits  the 
action  of  the  saliva  to  recom- 
mence, which  is  aided  by  the 
pancreatic  and  intestinal  juices. 
The  pancreatic  juice  has  much 
more  important  functions.  It 
changes  albuminoid  food  into 
peptones,  and  probably  breaks 
up  the  fats  into  very  small  par- 
ticles, which  are  suspended  in 
the  fluid  chyle.  This  forms  an  FIG.  59.— chyle  corpuscles,  x  500. 
emulsion,  like  milk,  and  causes  the  chyle  to  appear  whit- 
ish. The  bile  has  important  functions,  but  little  under- 


94:  COMPARATIVE  ZOOLOGY. 

stood.  It  saponifies  part  of  the  fats,  so  that  they  are  dis- 
solved, and  prevents  the  food  from  decomposing  during 
the  process  of  digestion  and  absorption.  The  chyle  is 
slowly  driven  through  the  small  intestine  by  the  creep- 
ing, peristaltic  motion  of  its  walls,49  the  nutritious  portion 
being  taken  up  by  the  absorbents,  as  described  in  the  next 
chapter,  while  the  undigested  part  remaining  is  discharged 
from  the  large  intestine.60 


CHAPTER  XL 

THE     ABSORBENT     SYSTEM. 

THE  nutritive  matter  (chyle),  prepared  by  the  digestive 
process,  is  still  outside  of  the  organism.  How  shall  it 
enter  the  living  tissue  ? 

In  animals,  like  the  Infusoria  and  Polyps,  whose  digest- 
ive department  is  not  separated  from  the  body-cavity,  the 
food,  as  soon  as  dissolved,  mingles  freely  with  the  tissues 
and  organs  it  has  to  nourish.  In  the  higher  Invertebrates 
having  an  alimentary  canal,  the  chyle  passes,  by  simple 
transudation,  through  the  walls  of  the  canal  directly  into 
the  soft  tissues,  as  in  Insects,  or  is  absorbed  from  the  canal 
by  veins  in  contact  with  it,  as  in  Sea-urchins,  Mollusks, 
Worms,  and  Crustaceans,  and  then  distributed  through 
the  body. 

In  Vertebrates  only  do  we  find  a  special  absorbent  sys- 
tem. Three  sets  of  vessels  are  concerned  in  the  general 
process  by  which  fresh  material  is  taken  up  and  added  to 
the  blood :  Capillaries,  Lacteals,  arid  Lymphatics. 
Only  the  two  former  draw  material  from  the  alimentary 
canal. 

It  is  a  general  law  that  the  food  is  absorbed  as  fast  as 


THE  ABSORBENT  SYSTEM.  95 

it  is  dissolved,  and,  therefore,  there  is  a  constant  loss  in 
the  passage  down  the  canal.  In  the  mouth  and  oasoph- 
agus,  the  absorption  is  slight;  but  much  of  that  which 
has  yielded  to  the  gastric  juice,  with  most  of  the  water,  is 
greedily  absorbed  by  the  capillaries  of  the  stomach,  and 
made  to  join  the  current  of  blood  which  is  rushing  to  the 
liver.  Absorption  by  the  capillaries  also  takes  place  from 
the  skin  and  lungs.  Medicinal  or  poisonous  gases  and 
liquids  are  readily  introduced  into  the  system  by  these 
channels. 

We  have  seen  that  the  oily  part  of  the  food  passes  un- 
changed from  the  stomach  into  the  small  intestine,  where, 
acted  upon  by  the  pancreatic  juice,  it  is  cut  up  into  ex- 
tremely minute  particles,  and  that  the  undigested  albumi- 
noids and  starches  are  digest-  .fe- 
ed in  the  intestine.  Two 
kinds  of  absorbents  are  pres- 
ent in  the  intestine,  lacteals 
and  blood -capillaries.  Both 
the  lymphatic  and  blood  sys- 
tems send  vessels  into  the 
velvety  villi61  with  which  the 
intestine  is  lined.  The  blood- 

.,,.,.  ,       ,  Fro.  60. — Lacteal  System  of  Mammal :  a. 

Capillaries  lie  towards  the  OUt-      descending   aorta,  or  principal  artery  ; 

fiiHp    of    thp     villns     and     flip      6>  thoracic  duct;  c'  on'«in  of  lacteal 

vessels,^  in  the  walls  of  the  intestine, 

lacteal     in     the     Centre.        The       d>'   e'  mesentery,  or  membrane  attach- 

ing  the  intestine  to  walls  of  the  body; 
albuminoids     and    SUgarS    are      /.lacteal,  or  mesenteric,  glands. 

chiefly  absorbed  by  the  blood-vessels  and  go  to  the  liver. 
The  fats  pass  on  into  the  lacteals,  which  receive  their 
name  from  the  milky  appearance  of  the  chyle.  These 
lacteals  unite  into  larger  trunks,  which  lie  in  the  mesen- 
tery (or  membrane  which  suspends  the  intestine  from  the 
back  wall  of  the  abdomen),  and  these  pour  their  contents 
into  one  large  vessel,  the  thoracic  duct,  lying  along  the 
backbone,  and  joining  the  jugular  vein  in  the  neck. 


96 


COMPARATIVE  ZOOLOGY. 


The-  lacteals  are  only  a  special  part  of  the  great  lym- 
phatic system,  which  absorbs  and  carries  to  the  thoracic 

duct  matter  from  all  parts 
of  the  body.62  The  lymph 
is  a  transparent  fluid  having 
many  white  blood  corpus- 
cles. It  is,  in  fact,  blood, 
minus  the  red  corpuscles, 
while  chyle  is  the  same  fluid 
rendered  milky  by  numer- 
ous fat  -  globules.  During 
the  intervals  of  digestion, 
the  lacteals  carry  ordinary 
lymph.  This  fluid  is  the 
overflow  of  the  blood  —  the 
plasma  and  white  corpus- 
cles which  escape  from  the 
blood  capillaries,  and  are  not 
needed  by  the  tissues  in 
which  they  are.  This  sur- 
plus overflow  is  returned  to 
the  blood  by  the  lymphatics. 
The  current  is  kept  up  by 
the  movements  of  the  body, 
an(j  jn  mariy  Vertebrates,  as 


FIG.  61.— Principal  Lymphatics  of  the  Un- 
man Body:  a,  union  of  left  jugular  and 
subclavian  veins;  &,  thoracic  duct;  c,  Fl'OgS  and  FisllCS,  by  lymph 

hearts. 


The   oval  bodies 


receptaculum  chyli 
are  glands. 

Like  the  roots  of  Plants,  the  absorbent  vessels  do  not 
commence  with  open  mouths;  but  the  fluid  which  enters 
them  must  traverse  the  membrane  which  covers  their  mi- 
nute extremities.  This  membrane  is,  however,  porous, 
and  the  fluids  pass  through  it  by  the  forces  of  filtration 
and  diffusion.  How  the  fat  gets  into  the  lacteals  is  not 
yet  well  understood,  but  the  lacteals  are  themselves  rhyth- 
mically contractile,68  and  force  the  absorbed  chyle  tow- 


THE  BLOOD  OF  ANIMALS.  97 

ards  the  heart.     The  valves  of  the  lymphatics  prevent  its 
return. 


CHAPTER  XII. 

THE    BLOOD    OF    ANIMALS. 

The  Blood  is  that  fluid  which  carries  to  the  living  tis- 
sues the  materials  necessary  to  their  growth  and  repair, 
and  removes  their  waste  and  worn-out  material.  The 
great  bulk  of  the  body  is  occupied  with  apparatus  for  the 
preparation  and  circulation  of  this  vital  fluid. 

The  blood  of  the  lower  animals  (Invertebrates)  differs 
so  widely  from  that  of  Man  and  other  Vertebrates,  that 
the  former  were  long  supposed  to  be  without  blood.  In 
them  the  blood 'is  commonly  colorless ;  but  it  has  a  bluish 
cast  in  Crustaceans;  reddish,  yellowish,  or  greenish,  in 
Worms ;  and  reddish,  greenish,  or  brownish,  in  Jelly- 
tishes.  The  red  liquid  which  appears  when  the  head  of 
a  Fly  is  crushed  is  not  blood,  but  comes  from  the  eyes. 
In  Vertebrates,  the  blood  is  red,  excepting  the  white- 
blooded  fish,  Amphioxus.™ 

As  a  rule,  the  more  simple  the  fabric  of  the  body,  the 
more  simple  the  nutritive  fluid.  In  unicellular  animals 
(as  Protozoa),  in  those  whose  cells  are  comparatively  inde- 
pendent (as  Sponges),  and  in  small  and  lowly  organized 
animals  (like  Hydra),  there  is  no  special  circulating  fluid. 
Each  cell  feeds  itself  either  directly  from  particles  of 
food,  or  from  the  products  of  digestion.  In  Polyps  and 
Jelly-fishes,  the  blood  is  scarcely  different  from  the  prod- 
ucts of  digestion,  although  a  few  blood-corpuscles  are  pres- 
ent. But  in  the  more  highly  organized  Invertebrates  the 
blood  is  a  distinct  tissue,  coagulating,  and  containing 
white  corpuscles.  The  blood  of  the  Vertebrates,  appar- 

7 


COMPARATIVE  ZOOLOGY. 


ently  a  clear,  homogeneous  fluid,  really  consists  of  minute 
grains,  or  globules,  of  organic  matter  floating  in  water. 

If  the  blood  of  a  Frog 
be  poured  on  a  filter  of 
blotting-paper,  a  trans- 
parent fluid  (calledplas- 
ma)  will  pass  through, 
leaving  red  particles,  re- 
fa  sembling  sand,  on  the 
upper  surface.  Under 
the  microscope,  these 
particles  prove  to  be 
cells,  or  flattened  disks 
(called  corpuscles),  con- 

Fio.  62.—  Red  Blood-corpuscles  of  Man:  a,  shows    v  * 

circular  contour;  6,  a  biconcave  section;  c,  a    taining  a  nucleus  j  SOIHC 
group  in  chains.  T      ,  1,1 

are  colorless,  and  others 

red.  The  red  disks  have  a  tendency  to  run  together  into 
piles ;  the  colorless  ones  remain  single.  Meanwhile,  the 
plasma  separates  into  two  parts  by  coagulating;  that  is, 
minute  fibres  form,  consisting  of  fibrine,  leaving  a  pale 
yellowish  fluid,  called  serum.**  Had  the  blood  not  been 
filtered,  the  corpuscles  and  fibrine  would  have  mingled, 
forming  a  jelly-like  mass,  known  as  clot.  Further,  the 
serum  will  coagulate  if  heated,  dividing  into  hardened 
albumen  and  a  watery  fluid,  called  serosity,  which  contains 
the  soluble  salts  of  the  blood. 

These  several  parts  may  be  expressed  thus : 

(colored   ) 

(colorless  V  ^^^-clot. 

(fibrine— 7" 

iserum      \  albumen' 

(  serosity= water  and  salts. 

If  now  we  examine  the  nutritive  fluid  of  the  simplest 
animals,  we  find  only  a  watery  fluid  containing  granules, 
In  Radiates  and  the  Worms  and  Mollusks,  there  is  a  sim- 
ilar fluid,  with  the  addition  of  a  few  white  corpuscles.  But 


(  Corpuscles 
Blood  ] 

(  Plasma 


THE  BLOOD  OF  ANIMALS. 


99 


there  is  little  fibrine,  and,  therefore,  it  coagulates  feebly  or 
not  at  all.  In  the  Arthropods  and  higher  Mollusks,  the 
circulating  fluid  contains 
colorless  nucleated  cells, 
and  coagulates.56  InVer- 
tebrates,  there  are,  in  ad- 
dition to  the  plasma  and 
white  corpuscles  of  In- 
vertebrates, red  corpus- 
cles, to  which  their  blood 
owes  its  peculiar  hue. 
In  Fishes,  Amphibians, 
Keptiles,  and  Birds,  i.  e., 
all  oviparous  Vertebrates, 

these    red   COrpUSCleS   are   Fio.63.-NuCleatedBlood-cellSofaFrog,x  250. 

nucleated;  but  in  those  of  Mammals,  no  nucleus  has  been 

discovered.57 

All  blood -corpuscles  are  microscopic.     The  white  are 

more  uniform  in  size  than  the  red ;  and  generally  smaller 
(except  in  Mammals),  being  about 
Winr  °f  an  incn  *n  diameter.  The 
red  corpuscles  are  largest  in  Amphib- 
ians (those  of  Proteus  being  the  ex- 
treme, or  T|¥  of  an  inch),  next  in 
Fishes,  then  Birds  and  Mammals.  The 
smallest  known  are  those  of  the  Musk- 

FIG. 64. -Elliptical  Corpus-  deer.     In  Mammals,  the  size   agrees 

cle  of  the  Frog,  showing        ..v,i          .  /.  ,1  •         i         , 

a  white  prominence  at  the  with  the  size  of  the  animal  only  with- 
in a  natural  order;  but  in  Birds  the 
correspondence  holds  good  throughout  the  class,  the  larg- 
est being  found  in  the  Ostrich,  and  the  smallest  in  the 
Humming-bird.  In  Man,  they  measure  -g-^VTr  of  an  inch, 
so  that  it  would  take  40,000  to  cover  the  head  of  a 
pin. 

As  to  shape,  the  colorless  corpuscles  are  ordinarily  glob- 


100 


COMPARATIVE   ZOOLOGY. 


ular,  or  sac-like,  in  all  animals;  but  they  are  constantly 
changing.  The  form  of  the  red  disks  is  more  permanent, 
although  they  are  soft  and  elastic,  so  that  they  squeeze 


FIG.  65.— Comparative  Size  and  Shape  of  the  red  Corpuscles  of  various  Animals. 

through  very  narrow  passages.  They  are  oval,  circular, 
or  angular,  in  Fishes;  oval  in  Reptiles,  Birds,  and  the 
Camel  tribe ;  and  circular  in  the  rest  of  Mammals.  They 
are  double-convex  when  nucleated,  and  double-concave 
when  circular  and  not  nucleated. 

Blood  is  always  heavier  than  water;  but  is  thinner  in 
cold-blooded  than  in  warm-blooded  animals,  in  herbivores 
than  in  carnivores.  The  blood  of  Birds,  which  is  the  hot- 
test known,  being  10°  higher  than  Man's,  is  richest  in  red 
corpuscles.  In  Man,  they  constitute  about  one  half  the 
mass  of  blood.  The  white  globules  are  far  less  numerous 
than  the  red;  they  are  relatively  more  abundant  in  venous 
than  arterial  blood,  in  the  sickly  and  ill-fed  than  in  the 
healthy  and  vigorous,  in  the  lower  Vertebrates  than  in 
Birds  and  Mammals.  Their  number  is  subject  to  great 


T11IJ   BLOOD 


101 


variations,  increasing  rapidly  after  a  meal,  and  falling  as 
rapidly. 

There  is  less  blood  in  cold-blooded  than  in  warm-blood- 
ed animals ;  and  the  larger  the  animal,  the  greater  is  the 


FIG.  06.— Capillary  Circulation  in  the  Web  of  a  Frog's  Foot,  X  100:  n,  6,  small  veins  5 
d,  capillaries  in  which  the  oval  corpuscles  are  seen  to  follow  one  another  in  sin- 
gle series ;  c,  pigment-cells  in  the  skin. 

proportion  of  blood  to  the  body.  Man  has  about  a  gallon 
and  a  half,  equal  to  one  thirteenth  of  his  weight.  The 
heart  of  the  Greenland  Whale  is  a  yard  in  diameter. 

The  main  Office  of  the  Blood  is  to  supply  nourish- 
ment to,  and  take  away  waste  matters  from,  all  parts  of 
the  body.  It  is  at  once  purveyor  and  scavenger.  In  its 
circulation,  it  passes,  while  in  the  arterial  half  of  the  cap- 
illaries, within  an  infinitesimal  distance  of  the  various  tis- 
sues. The  plasma,  carrying  the  nutritive  matter  needed, 
exudes  through  the  walls  of  the  capillary  tubes  ;  the  tissue 
assimilates  or  makes  like  to  itself  whatever  is  suitable  for 
its  growth  and  repair;  and  the  lymphatics  (the  escape- 


102  COMPARATIVE  ZOOLOGY. 

pipes)  take  up  any  surplus,  and  return  it  to  the  blood. 
At  the  same  time,  the  venous  part  of  the  capillary  net- 
work absorbs  the  waste  products  of  the  tissues,  expelling 
the  gases  by  the  lungs,  and  the  solid  matters  by  the  skin 
and  kidneys.  The  special  function  of  the  several  constit- 
uents of  the  blood  is  not  wholly  known.  The  colorless 
corpuscles  in  Vertebrates  are  supposed  to  be  the  source  of 
the  red  disks.  The  latter  are  the  carriers  of  oxygen, 
which  is  taken  up  by  their  red  matter  (haemoglobin)  in 
the  lungs,  and  given  up  to  the  tissues.  The  same  office  is 
performed  by  the  blue  coloring  -  matter  (hsemocyamn)  in 
the  blood  of  certain  Invertebrates,  as  the  Squid  and  Lob- 
ster. The  carbon  dioxide  is  taken  up  by  the  plasma. 

Like  the  solid  tissues,  the  blood,  which  is  in  reality  a 
liquid  tissue,  is  subject  to  waste  and  renewal,  to  growth 
and  decay.  The  loss  is  repaired  from  the  products  of 
digestion,  carried  to  the  blood  by  the  lacteals,  or  absorbed 
directly  by  the  capillaries  of  the  digestive  tract.  The 
white  corpuscles  are  probably  prepared  in  many  parts  of 
the  body,  especially  the  liver,  spleen,  and  lymphatic  glands. 
In  the  lower  organisms,  the  nutritive  food  is  prepared  by 
contact  with  the  tissues,  without  passing  through  special 
organs.  Lymph  differs  from  blood  chiefly  in  containing 
less  albumen  and  fibrine,  and  no  red  disks.  Chyle  is 
lymph  loaded  with  fat  globules,  and  is  found  in  the  lac- 
teals  and  vessels  connected  with  them  during  the  absorp- 
tion of  food  containing  fat. 


THE  CIRCULATION  OF  THE  BLOOD.  103 


CHAPTER  XIII. 

THE   CIRCULATION   OF   THE   BLOOD. 

The  Blood  is  kept  in  continual  motion  in  order  to 
nourish  and  purify  the  body  and  itself.  For  as  life  means 
work,  and  work  brings  waste,  there  is  constant  need  of 
fresh  material  to  make  good  the  loss  in  every  part  of  the 
system,  and  of  the  removal  of  matter  which  is  no  longer 
fit  for  use. 

In  the  very  lowest  animals,  where  every  part  of  the 
structure  is  equally  capable 
of  absorbing  the  digested 
food  and  is  in  contact  with 
it,  there  is  no  occasion  for 
any  circulation,  although 
in  them  even  the  blood  is 
not  allowed  to  stagnate. 
But  in  proportion  as  the 
power  of  absorption  is  con- 
fined to  certain  parts,  the 
more  is  the  need  and  the 
greater  the  complexity  of 
an  apparatus  for  convey- 
ing the  nutritive  fluid  to 
the  various  tissues. 

In  nearly  all  animals, 
the  nutritive  fluid  is  con- 
veyed to  the  various  parts 
of  the  body  by  a  system 
of  tubes,  called  Hood-ves- 

.  FIG.  67.  —Venous  Valves.    They  usually  oc- 

JLhe     higher     forms  cur  in  pairs,  as  represented. 


104 


COMPARATIVE   ZOOLOGY. 


have  two  sets — arteries  and  veins,  in  which  the  blood 
moves  in  opposite  directions,  the  former  carrying  blood 
from  a  central  reservoir  or  heart, 
the  latter  taking  it  to  the  heart. 
In  the  Vertebrates,  the  walls  of 
these  tubes  are  made  of  three 
coats,  or  layers,  of  tissue,  the  arte- 
ries being  elastic,  like  rubber,  and 
many  of  the  veins  being  furnished 
with  valves.66  The  great  artery 
coming  out  of  the  heart  is  called 
aorta,  and  the  grand  venous  trunk, 
entering  the  heart  on  the  opposite 
side,  is  called  vena  cava.  Both 
sets  divide  and  subdivide  until 
their  branches  are  finer  than  hairs; 
and  joining  these  finest  arteries 
and  finest  veins  are  intermediate 
microscopic  tubes,  called  capilla- 
ries (in  Man  about  -g-^Vrr  °f  an  inch 
2  in  diameter).69  In  these  only,  so 
seeu  m  th«  muscles  of  a  Dog.  thin  and  Delicate  are  their  walls, 
does  the  blood  come  in  Contact  with  the  tissues  or  the  air. 
In  those  Vertebrates  which  have  lungs  there  are  two 
sets  of  capillaries,  since  there  are  two  circulations — the 
systemic,  from  the  heart  around  the  system  to  the  heart 
again,  and  the  pulmonary,  from  the  heart  through  the 
respiratory  organ  back  to  the  heart.  This  double  course 
may  be  illustrated  by  the  figure  8.  In  gill-bearing  animals 
there  are  capillaries  in  the  gills,  but  not  a  double  circu- 
lation. 

There  is  no  true  system  of  blood-vessels  below  the 
Star-fish,  The  simplest  provision  for  the  distribution  of 
the  products  of  digestion  is  shown  by  the  Jelly-fish,  whose 
stomach  sends  off  radiating  tubes  (Fig.  197). 


THE  CIRCULATION  OF  THE  BLOOD.  1Q5 

The  first  Approach  to  a  Circulatory  System  is  made 
by  the  Star-fish  and  the  Sea-urchin.  A  vein  runs  along 
the  whole  length  of  the  alimentary  tube,  to  absorb  the 
chyle,  and  forms  a  circle  around  each  end  of  the  tube. 
These  circular  vessels  send  off  branches  to  various  parts 
of  the  body;  but  as  they  are  not  connected  by  a  net-work 
of  capillaries,  there  can  be  no  circuit  (Fig.  39). 

A  higher  type  is  exhibited  by  the  Insects.  If  we  ex- 
amine the  back  of  any  thin-skinned  Caterpillar,  a  long 
pulsating  tube  is  seen  running  beneath 
the  skin  from  one  end  of  the  body  to 
the  other.  This  dorsal  vessel,  or  heart, 
as  it  is  called,  is  open  at  both  ends,  and 
divided  by  valves  into  compartments, 
permitting  the  blood  to  go  forward, 
but  not  backward.  Each  compartment 
communicates  by  a  pair  of  slits,  guard- 
ed by  valves,  with  the  body  -cavity,  so 
that  fluids  may  enter,  but  cannot  es- 
cape. "Circulation"  is  very  simple. 
We  have  seen  that  the  chyle  exudes 
through  the  walls  of  the  alimentary  ca- 
nal directly  into  the  cavity  of  the  abdo- 
men, where  it  mingles  with  the  blood 
already  there.  This  mixed  fluid  is 
drawn  into  the  dorsal  tube  through  the  FiG.69.-p«rtoftheDor- 

0  sal  Vessel,  or  Heart,  of 

valvular  openings  as  it  expands;   and     a  cockchafer  bisected  : 

.,  ,.  n    .-,          .  j  i  a,   b,  muscular   walls; 

upon  its  contraction,  all  the  side-valves     <*,  vaives  between  the 


are  closed,  and  the  fluid  is  forced  tow- 

ards  the  head.     Passing  out  at  the  front     orifices  communicating 

g  °  with  the  general  cavity 

opening,  it  is  again  diffused  among  and     of  the  abdomen. 
between  the  tissues  of  the  body.     The  blood,  therefore, 
does  not  describe  a  circle  in  definite  channels  so  as  to  re- 
turn constantly  to  its  point  of  departure. 

Many  worms  (as  the  Earthworm)  have  a  pulsating  tube 


106 


COMPARATIVE  ZOOLOGY. 


extending  from  tail  to  head  above  the  alimentary  canal, 
a  similar  tube  on  the  ventral  side  through  which  the  blood 
returns,  and  cross-tubes  in  every  segment.  In  the  Lob- 
ster and  Crab,  Spider  and  Scorpion,  the  dorsal  tube  sends 


PIG.  70. — Circulation  in  a  Lobster:  ct,  heart;  6,  artery  for  the  eyes;  c,  artery  for  an- 
tennae; d,  hepatic  artery;  ?,  superior  ubdomiual  artery;  /,  sternal  artery;  g,  ve- 
nous sinuses  transmitting  blood  from  the  body  to  the  branchiae,  h,  whence  Jt 
returns  to  the  heart  by  the  brauchio-cardiac  vessels,  i. 

off  a  system  of  arteries  (not  found  in  Insects) ;  but  the 
blood,  as  it  leaves  these  tubes,  escapes  into  the  general 
cavity,  as  in  other  Arthropoda.  The  Lobster  and  Crab, 
however,  show  a  great  advance  in  the  concentration  of 
the  propelling  power  into  a  short  muscular  sac. 

A  third  development  of  the  circulatory  system  is  fur- 
nished by  the  Mollusks.  Comparatively  sluggish,  they 
need  a  powerful  force-pump  in  the  form  of  a  compact 
heart.  In  the  Oyster  and  Snail  (Figs.  44, 45),  we  find  such 
an  organ  having  two  cavities — an  auricle  and  a  ventricle, 
one  for  receiving,  and  the  other  for  distributing,  the  blood. 
The  auricle  injects  the  blood  into  the  ventricle,  which 
propels  it  by  the  arteries  to  the  various  organs.  Thence 
it  passes,  not  immediately  to  the  veins,  as  in  higher  ani- 
mals, but  into  the  spaces  around  the  alimentary  canal.  A 
part  of  this  is  carried  by  vessels  to  the  gills  or  lung,  and 
then  returned  with  the  unpurified  portion  to  the  auricle. 
The  whole  of  the  blood,  therefore,  does  not  make  a  com- 
plete circuit.  The  Clam  has  a  similar  heart,  but  with  two 
auricles. 


THE  CIRCULATION  OF  THE  BLOOD. 


g  •— 


A  still  higher  form  is  seen  in  the  Cuttle-fish,  the  high- 
est of  the  Invertebrates.  This  animal  has  a  central  heart, 
with  a  ventricle  and  two  auricles, 
and,  in  addition,  the  veins  which 
collect  the  blood  from  the  system 
to  send  it  back  to  the  heart  by 
the  way  of  the  gills  are  furnished 
with  two  branchial  hearts,  which 
accelerate  the  circulation  through 
those  organs.  Many  of  the  arte- 
ries and  veins  are  joined  by  cap- 
illaries, but  not  all ;  so  that  in 
no  invertebrate  animal  is  the 
blood  returned  to  the  heart  by  a 
continuousclosed  system  of  blood- 
vessels. 

As  a  rule,  in  all  animals  hav- 
ing any  circulation  at  all,  the  cur- 
rent always  takes  one  direction. 
This  is  generally  necessitated  by 
valves.  But  a  curious  exception 
is  presented  by  the  Ascidians, 
whose  tubular  heart  is  valveless, 
and  the  contractions  occur  alter- 
nately at  one  end  and  then  the 
other;  so  that  the  blood  oscil- 
lates to  and  fro,  and  a  given  ves- 
sel is  at  one  time  a  vein  and  at 
another  an  artery.  In  this  re- 
spect it  resembles  the  foetal  heart 
of  higher  animals  (Fig.  279). 

In  Vertebrates  only  is  the  cir- 
culating current  strictly  confined 
to  the  blood-vessels;  in  no  case  does  it  escape  into  the 
general  cavity  of  the  body.     In  other  respects,  there  is 


Fio.  71.— Circulating  Apparatus  in 
the  Fish :  a,  branchial  artery  ;  &, 
arterial  bulb ;  c,  ventricle  ;  d,  au- 
'ricle ;  e,  venous  sinus ;  /,  portal 
vein  ;  <;,  intestine  ;  ft,  vena  cava ; 
t,  branchial  vessels ;  A,  dorsal  ar- 
tery, or  aorta ;  Z,  kidneys ;  m, 
dorsal  artery. 


108 


COMPARATIVE  ZOOLOGY. 


FIG.  7'2.— Diagniin  of  a  single  Heart:    (/, 
auricle;  e,  ventricle;  c,  veins  leading  to 


no  great  advance  in  the  apparatus  of  the  lowest  Verte- 
brates over  that  of  the  highest  Mollnsks.  The  heart  of 

Fishes,  as  in  the  Oyster,  has 
two  cavities,  but  its  position 
is  reversed.  Instead  of  driv- 
ing arterial  blood  over  the 
body,  it  receives  the  return- 
ing, or  venous,  blood,  and 
sends  it  to  the  gills.  Re- 
collected from  the  gills,  the 
blood  is  passed  into  a  large 
artery,  or  aorta,  along  the 
back,  which  distributes  it  by 
a  complex  system  of  capil- 
laries among  the  tissues. 

anrlcle ;  a,  aorta,  or  main  artery.  Thege  capillaries  unite  with 

the  ends  of  the  veins  which  pass  the  blood  into  the  auri- 
cle60 (Fig.  48). 

In  Amphibians  and  in  Reptiles  generally  (as  Frogs, 
Snakes,  Lizards,  and  Turtles),  the  heart  has  three  cavities 
—two  auricles  and  one  ventricle.  The  venous  blood  from 
the  body  is  received  into  the  right  auricle,  and  the  puri- 
fied blood  from  the  lungs  into  the  left.  Both  throw  their 
contents  into  the  ventricle,  which  pumps  the  mixed  blood 
in  two  directions — partly  to  the  lungs,  and  partly  around 
the  system.  Circulation  is,  therefore,  incomplete,  since 
the  whole  current  does  not  pass  through  the  Inngs,  and 
three  kinds  of  blood  are  found  in  the  body — arterial,  ve- 
nous, and  mixed.  In  many  animals,  however,  arrange- 
ments exist  which  nearly  separate  the  venous  from  the 
arterial  blood. 

The  ventricle  of  Reptiles  is  partially  divided  by  a  par- 
tition. In  the  Crocodile,  the  division  is  complete,  so  that 
there  are  really  four  cavities — two  auricles,  and  two  ven- 
tricles. But  both  ventricles  send  off  aortas  which  cross 


THE  CIRCULATION   OF  THE   BLOOD. 


109 


one  another,  and  at  that  point  a  small  aperture  brings  the 
two  into  communication.  The  venous  and  arterial  cur- 
rents are,  therefore,  mixed, 
but  not  within  the  heart,  as 
in  the  other  Reptiles,  nor  so 
extensively.  In  the  structure 
of  the  heart,  as  well  as  in  that 
of  the  gizzard,  Crocodiles  ap- 
proach the  Birds. 

The  Highest  Form  of  the 
Circulating  System  is  pos- 
sessed by  the  warm-blooded 
Vertebrates,  Birds  and  Mam-  FIG.  73.— Heart  of  the  uugoug,  n  four- 

,  1VT  ,  j?    i  i       j       chambered  heart,  the  parts  being  more 

ma,ls.       oNot    a    drop    OI    blOOd       separated  than  in  higher  animals:  E, 

pan    mflkp    tliP    pi  mi  it    of    tllP       right  veutricle'  L,  left  ventricle ;  D, 

right   auricle;   F,  pulmonary  artery; 

body  without  passing  through     K> left  auricle  >  A>  aorta- 
the  lungs,  the  circulation  to  and  from  those  organs  being 
as  perfect  as  the  distribution  of  arterial  blood.     The  heart 
/     0       *       *  consists    of    four    cavities  —  a 

right  auricle  and  ventricle,  and 
a  left  auricle  and  ventricle.  In 
other  words,  it  is  a  hollow  mus- 
cle divided  internally  by  a  ver- 
tical partition  into  two  distinct 
chambers,  each  of  which  is 
again  divided  by  a  valve  into 
an  auricle  and  a  ventricle.  The 
work  of  the  right  auricle  and 
'entride  is  to  receive  the  blood 
i  from  the  ™ns,and  send  it  to 

ry  veins;/,  superior  vena  cava;  .7,    the  luilgS  I    while  the  Other  tWO 

pulmonary  arteries ;  h,  aorta ;  k,  left 

auricle;  I,  mitral  valve;  m,  left  ven-    receive      the      blOOd     from      the 

lungs,  and  propel  it  over  the 

body.     The  left  ventricle  has  more  to  do  than  any  other 
cavity.     The  two  auricles  contract  at  the  same  instant; 


110 


COMPARATIVE  ZOOLOGY. 


so  also  do  the  ventricles.  The  course 
of  the  current  in  Birds  and  Mammals 
is  as  follows  :  the  venous  blood 
brought  from  the  system  is  discharged 
by  two  or  three  large  trunks"  into 
the  right  auricle,  which  immediately 
forces  it  past  a  valve e2  into  the  right 
ventricle.  The  ventricle  then  con- 
tracts, and  the  blood  rushes  through 
the  pulmonary  artery  past  its  semi- 
lunar  valves  into  the  lungs,  where  it 
is  changed  from  venous  to  arterial, 
FIG.  75. —  Plan  of  circuia-  returning  by  the  pulmonary  veins  to 

tion  in  Fishes:   a,  auri-      ,         ,    ,.  .   ,  mi  .  . 

cie-  6,  ventricle;  e, bran-  the  leit  auricle.  Ihis  sends  it  past 
^rtfi^td  the  mitral  valves  into  the  left  ventri- 
from  the  gills,  d,  and  c]e  wnicn  drives  it  past  the  semilunar 

uniting  in  the  aorta,  /;  g, 

venacava.  valves  into  the  aorta,  and  thence,  by 

its  ramifying  arteries  and  capillaries,  into  all  parts  of  the 
body  except  the  lungs. 
From  the  capillaries, 
the  blood,  now  changed 
from  arterial  to  venous, 
is  gathered  by  the  veins, 
and  conveyed  back  to 
the  heart. 

The  Rate  of  the 
Blood  -  current  gener- 
ally increases  with  the 
activity  of  the  animal, 
being  most  rapid  in 
Birds.63  In  Insects, 

however   it  IR  rnm-nara  FlG- ™— A,  Plan  of  Circulation  in  Amphibia  and 

Cr,  11               mpara-  Reptiles.  B>  Plan  of  circulation  in  Birds  mid 

tivelv  slow*    but  this  is  Mammals:    a,  right   auricle   receiving  venous 

*  blood  from  the  system  :  b,  left  auricle  receiving 

because  the  air  is  taken  arterial  blood  from  the  lungs;  c,  e',  ventricles; 

,,        ,         .           .  d,  e,  f,  systemic  artery,  vein,  and  capillaries;  .7, 

to" the  blOOd — the  Whole  pulmonary  artery ;  h,k,  vein  and  capillaries. 


HOW  ANIMALS  BREATHE.  HI 

body  being  bathed  in  air,  so  that  the  blood  lias  no  need 
to  hasten  to  a  special  organ.  However,  activity  nearly 
doubles  the  rate  of  pulsation  in  a  Bee.  The  motion  in 
the  arteries  is  several  times  faster  than  in  the  veins,  but 
diminishes  as  the  distance  from  the  heart  increases.  In 
the  carotid  of  the  Horse,  the  blood  moves  12J  inches  per 
second;  in  that  of  Man,  16;  in  the  capillaries  of  Man,  1 
to  2  inches  per  minute ;  in  those  of  a  Frog,  1. 

The  Cause  of  the  Blood-current  may  be  cilia,  or  the 
contractions  of  the  body,  or  pulsating  tubes  or  hearts.  In 
the  higher  animals,  the  impulse  of  the  heart  is  not  the 
sole  means :  it  is  aided  by  the  contractions  of  the  arteries 
themselves,  the  movements  of  the  chest  in  respiration,  and 
the  attraction  of  the  tissues  for  the  arterial  blood  in  the 
capillaries.  In  the  Chick,  the  blood  moves  before  the 
heart  begins  to  beat;  and  if  the  heart  of  an  animal  be 
suddenly  taken  out,  the  motion  in  the  capillaries  will 
continue  as  before.  It  has  been  estimated  that  the  force 
which  the  human  heart  expends  in  twenty-four  hours  is 
about  equivalent  to  lifting  217  tons  one  foot. 


CHAPTER  XIV. 

HOW    ANIMALS    BREATHE. 

Arterial  Blood,  in  passing  through  the  system,  both 
loses  and  gains  certain  substances.  It  loses  constructive 
material  and  oxygen  to  the  tissues.  These  losses  are  made 
good  from  the  digestive  tract  and  breathing  organ.  It 
gains  also  certain  waste  materials  from  the  tissues,  which 
must  be  got  rid  of.  Of  these  waste  products,  one,  carbon 
dioxide,  is  gaseous,  and  is  passed  off  from  the  same  organ 
as  that  where  the  oxygen  is  taken  in.  This  exchange  of 


112  COMPARATIVE  ZOOLOGY. 

gases  between  the  animal  and  its  surroundings  is  called 
Respiration. 

The  First  Object  of  Respiration  is  to  convert  venous 
into  arterial  blood.  It  is  done  by  bringing  it  to  the  sur- 
face, so  that  carbon  dioxide  may  be  exhaled  and  oxygen 
absorbed.  The  apparatus  for  this  purpose  is  analogous  to 
the  one  used  for  circulation.  In  the  lowest  animals,  the 
two  are  combined.  But  in  the  highest,  each  is  essentially 
a  pump,  distributing  a  fluid  (in  one  case  air,  in  the  other 
blood)  through  a  series  of  tubes  to  a  system  of  cells  or 
capillaries.  They  are  also  closely  related  to  each  other: 
the  more  perfect  the  circulation,  the  more  careful  the  pro- 
vision made  for  respiration. 

Respiration  is  performed  either  in  air  or  in  water. 
So  that  all  animals  may  be  classed  as  air-breathers  or 
water -breather s.  The  latter  are,  of  course,  aquatic,  and 
seek  the  air  which  is  dissolved  in  the  water.  Land-snails, 
Myriapods,  Spiders,  Insects,  Reptiles,  Birds,  arid  Mam- 
mals breathe  air  directly ;  the  rest,  with  few  exceptions, 
receive  it  through  the  medium  of  water.  In  the  former 
case,  the  organ  is  internal;  in  the  latter,  it  is  more  or  less 
on  the  outside.  But  however  varied  the  organs  —  tubes, 
gills,  or  lungs — they  are  all  constructed  on  the  same  prin- 
ciple— a  thin  membrane  separating  the  blood  from  the 
atmosphere. 

( 1 )  Sponges,  Infusoria,  and  Polyps  have  no  separate  respir- 
atory apparatus,  but  absorb  air,  as  well  as  food,  from  the 
currents  of  water  passing  through  them. 

In  the  Star-fish,  Sea-urchin,  and  the  like,  we  find  the 
first  distinct  respiratory  organs,  although  none  are  exclu- 
sively devoted  to  respiration.  There  are  two  sets  of  ca- 
nals— one  carrying  the  nutrient  fluid,  and  the  other,  radi- 
ating from  a  ring  around  the  mouth,  distributing  aerated 
water,  used  for  locomotion  as  well  as  respiration.  This 
may  be  called  the  "water-pipe  system."  Besides  this, 


HOW  ANIMALS  BREATHE. 


113 


there  are  numerous  gill-like  fringes,  which 
probably  aid  in  respiration  (Fig.  39). 

Fresh-water  Worms,  like  the  Leech  and 
Earth  -  worm,  breathe  by  the  skin.  The 
body  is  always  covered  by  a  viscid  fluid, 
which  has  the  property  of  absorbing  air. 
The  air  is,  therefore,  brought  into  immedi- 
ate contact  with  the  soft  skin,  underneath 
which  lies  a  dense  net -work  of  blood-ves- 
sels. 

But  most  water -breathing  animals  have 
gills.  The  simplest  form  is  seen  in  Marine 
Worms :  delicate  veins  projecting  through 
the  skin  make  a  series  of  arborescent  tufts 
ulong  the  side  of  the  body;  as  these  float 
in  the  water,  the  blood  is  purified.64  Bi- 
valve Mollusks  have  four  flat  gills,  consist- 
ing of  delicate  membranes  filled  with  blood- 
vessels and  covered  with  cilia.  In  the  Oys-  FIG  7T_Lob.worm 
ter,  these  ribbon-like  folds  are  exposed  to 

the  water  when 
the  shell  opens; 
but  in  the  Clam, 
the  mantle  en- 
closes  them,  forming  a  tube, 
called  siphon,  through  which 
the  water  is  driven  by  the 
cilia.  The  aquatic  Gastero- 
pods  (Univalves)  have  either? 
tufts,  like  the  Worms,  or  comb- 
IG.  78.—  Diagrammatic  Section  of  a  like  ciliated  gills  in  a  cavity 

Lamellibranch  (Anodon):  cr,  lobes  of  i     i  .     j    ,-,       i         ,     .  i  •   -i     ,1 

mantle;  6,  gills,  showing  transverse  behind  the  head,  to  which   the 

partitions;  c,  ventricle  of  heart;  rf,  Wofpr  ,'«  arjrnirrprl  hv  a  sinhrm 
auricles;  e,  pericardium;  /,  g,  kid-  "J  a  S1P" 

neys;    ft,  venons  sinus;   k,  foot ;  A,  The    Cuttle-fish    has   flat    gills 
branchial,  or  pallia],  chamber;   B, 

chamber.  covered  by  the  mantle ;  but  the 

8 


rum),  a  dorsibran- 
chiate,  showing 
the  tufts  of  capil- 
laries, or  external 
gills.  The  large 
head  is  without 
eyes  or  jaws. 


114 


COMPARATIVE  ZOOLOGY. 


water  is  drawn  in  by  muscular  contractions  instead  of  by 
cilia.  The  end  of  the  siphon  through  which  it  is  ejected 
is  called  the  funnel.  The  gills  of  Lobsters  and  Crabs  are 
placed  in  cavities  covered  by  the  sides  of  the  shell  (cara- 
pace); and  the  water  is  brought  in  from  behind  by  the 
action  of  a  scoop-shaped  process  attached  to  one  of  the 
jaws,  which  constantly  bales  the  water  out  at  the  front. 

The  perfection  of  apparatus  for  aquatic  respiration  is 
seen  in  .Fishes.  The  gills  are  comb-like  fringes  supported 
on  four  or  five  bony  or  cartilaginous  arches,  and  contain 
myriads  of  microscopic  capillaries,  the  object  being  to  ex- 
pose the  venous  blood  in  a  state  of  minute  subdivision 
to  streams  of  water.  The  gills  are  always  covered.  In 
bony  fishes  they  are  attached  to  the  hinder  side  of  bony 
arches,  all  covered  by  a  flap  of  the  skin,  supported  by 
bones  (the  gill-cover,  or  operculum),  and  the  water  escapes 
from  the  opening  left  at  its  hinder  edge.  In  Sharks,  the 
gills  are  placed  in  pouches  which  open  separately  (Figs. 
164  and  287).  The  act  of  "breathing  water"  resembles 
swallowing,  only  the  water  passes  the  gills  instead  of  en- 
tering the  gullet. 

(2)  Air-breathers  have 
trachece,  or  lungs.  The 
former  consist  of  two 
principal  tubes,  which 
pass  from  one  end  of 
the  body  to  the  other, 
opening  on  the  surface 
by  apertures,  called  spir- 
acles, resembling  a  row 
of  button  -  holes  along 
the  sides  of  the  thorax 
and  abdomen,  arid  rami- 

FiG.  79._Spiracle  of  an  Insect,  x  75.  f  y .  fig  throngll  the  gmall- 

est  and  most  delicate  organs,  so  that  the  air  may  follow 


HOW  ANIMALS  BREATHE. 


115 


the  blood  wherever  it  circulates.     To  keep  the  pipes  ever 

open,  and  at  the  same  time  leave  them  flexible,  they  are 

provided  with  an  elastic  spiral  thread,  like 

the  rubber  tube  of  a  drop-light.     Respira- 

tion  is  performed  by  the  movements  of 

the  abdomen,  as  may  be  seen  in  the  Bee 

when  at  rest.     This  "air-pipe  system,"  as 

it  may  be  termed,  is  best  developed  in  In- 

sects. 

The  "nerves"  of  an  Insect's  wing  con- 
sist  of  a  tube  within  a  tube:  the  inner  one 
is  a  trachea  carrying  air,  and  the  outer  one, 
sheathing  it,  is  a  blood-vessel.  So  perfect 
is  the  aeration  of  the  whole  body,  from  brain  to  feet, 
the  blood  is  oxygenated  at  the  moment  when,  and  on  the 
spot  where,  it  is  carbonized;  only  one  kind  of  fluid  is, 
h 


w  8ft  _Tracheal 
Tube  <>fau  insect, 

highly  magnified, 

showing    elastic 
8piral  threa<L 


FIG.  81. — Ideal  Section  of  a  Bee:  a,  alimentary  canal;  h,  dorsal  vessel;  f,  trachea; 
n,  nervous  cord. 

therefore,  circulating  —  arterial.  It  is  difficult  to  drown 
an  Insect,  as  the  water  cannot  enter  the  pores ;  but  if  a 
drop  of  oil  be  applied  to  the  abdomen,  it  falls  dead  at 
once,  being  suffocated.  The  largest  spiracle  is  usually 


116 


COMPARATIVE  ZOOLOGY. 


found  on  the  thorax,  as  un- 
der the  wing  of  a  Moth: 
such  may  be  strangled  by 
pinching  the  thorax. 

In  Millipedes  and  Centi- 
pedes, the  spiracles  open 
into  little  sacs  connected 
together  by  tubes  ;  in  Spi- 
ders and  Scorpions,  the 
spiracles,  usually  four  in 
P.O.  82,-section  through  a  bronchial  tube,  number,  are  the  mouths  of 

Lung  of  a  Bird,  magnified  :  a,  the  cavity;  sacs  without  the  tubes,  and 

6,  its  lining  membrane  supporting  blood-     ...  ., 

vessels  ;  c,  perforations  at  the  orifices  of  the    interior    of    the 

the   lobnlar    passages,  d;   e.  interlobular  •,  -,    .  /»    -,  -. 

spaces,  containing  the  terminal  branches  gathered  into  loldS. 

of  the  pulmonary  vessels  supplying  the  GninU  Ti9V£>   r\n(*    «m'raplp    or 

capillary  plexus,/,  to  the  meshes  of  which  Snails  '16>  Ol 

the  air  gets  access  by  the  lobular  passages,  aperture,  On  the  left  side  of 

the  neck,  leading  to  a  large  cavity,  or  sac,  lined  with  fine 
blood-vessels.  These  sacs  represent  the  primitive  idea  of 
a  lung,  which  is  but  an  infolding  of  the  skin,  divided  up 
into  cells,  and  covered  with  capillary  veins.65 


Sac    IS 


PIG.  83.— Part  of  a  transverse  section  of  a  Pig's  Bronchial  Twig,  X  240:  a,  outer 
fibrous  layer;  &,  muscular  layer;  c,  inner  fibrous  layer;  d,  epithelial  layer  with 
cilia;  /,  one  of  the  neighboring  alveoli. 


HOW   ANIMALS   BREATHE. 


117 


Like  the  alimentary  canal,  the  lungs  of  an  animal  are 
really  an  inflected  portion  of  the  outer  surface;  so  that 
breathing  by  the  skin  and  breathing  by  lungs  are  one  in 
principle.  Indeed,  in  many  animals,  especially  Frogs,  res- 
piration is  carried  on  by  both  lungs  and  skin. 

The  lungs  of  Vertebrates  are  deriveoLfrom  the  front 
part  of  the  alimentary  canal.  In  some  Fishes,  air  is  swal- 
lowed, which  passes  the  whole  length  of  the  digestive 
tract,  and  is  expelled  from  the  anus.  Here 
the  whole  canal  serves  for  respiration.  In 
Reptiles,  Birds,  and  Mammals  the  hinder 
part  of  the  intestine  develops  an  outgrowth 
(the  allantois)  during  embryo -life  which 
serves  as  the  embryo's  breathing  organ  (Figs. 
170, 171). 

All  Vertebrates  have  two  kinds  of  respir- 
atory organs  in  the  course  of  their  life. 
Fishes  have  gills;  their  lung  (the  air-blad- 
der) rarely  serves  as  a  functional  respiratory 
organ,  and  is  sometimes  wanting.  Amphibi- 
ans have  gills  while  in  the  larval  state.  Some 
keep  them  throughout  life;  but  all  develop 
functional  lungs,  and  also  breathe  by  means 
of  the  skin. 

In  the  remaining  Vertebrates,  the  allantois 
is  the  breathing  organ  of  the  embryo,  and 
the  lung  is  the  breathing  organ  of  the  adult. 
The  skin  is  of  small  or  no  importance  in 
respiration. 

The  lungs  of  Vertebrates  are  elastic  mem- 

.  FIG.   84.  —  Lungs 

branous  sacs,  divided  more  or  less  into  cells     of  a  snake:  a, 

to  increase  the  surface.     Upon  the  walls  of 

the  cells  are  spread  the  capillary  blood-ves- 

sels.     The  smaller  the  cells,  the  greater  the     nary  veiu;  the 

£  £  i  •    i     xi        1.1       j    •         lung,  B,i8  nidi- 

extent  of  surface   upon  which  the  blood  is     mentnry. 


118 


COMPARATIVE  ZOOLOGY. 


exposed  to  the  influence  of  the  air,  and,  therefore,  the 
more  active  the  respiration  and  the  purer  the  blood.  The 
lungs  are  relatively  largest  in  Reptiles,  and  smallest  in 
Mammals.  But  in  the  cold-blooded  Amphibians  and  Rep- 
tiles, the  air-cells  are  few  and  large ;  in  the  warm-blooded 
Birds  and  Mammals,  they  are  exceedingly  numerous  and 
minute.66  In  Birds  and  Mammals,  the  blood  in  the  capil- 
laries is  exposed  to  the  air  on  all  sides ;  in  the  Reptiles, 
on  one  only.  Respiration  is  most  perfect  in  Birds ;  they 
require,  relatively  to  their  weights,  more  air  than  Mam- 
mals or  Reptiles,  and  most  quickly  die  for  lack  of  it.  In 
Birds,  respiration  is  not  confined  to  the  lungs;  but,  as  in 
Insects,  extends  through  a  great  part  of  the  body.  Air- 
sacs  connected  with  the  lungs  exist  in  the  abdomen  and 
under  the  skin  of  the  neck,  wings,  and  legs.  Even  the 
bones  are  hollow  for  this  purpose ;  so  that  if  the  wind- 


FIQ.  85.— Lungs  of  a  Frog:  a,  hyoid 
apparatus ;  b,  cartilaginous  ring  at 
root  of  the  lungs;  c,  pulmonary 
vessels ;  d,  pulmonary  sacs,  having 
this  peculiarity  common  to  all  cold- 
blooded air-breathers,  that  the  tra- 
chea does  not  divide  into  bronchial 
branches,  but  terminates  abruptly 
by  orifices  which  open  at  once  into 
the  general  cavity.  A  cartilaginous 
net-work  divides  the  space  into  lit- 
tle sacs,  on  the  walls  of  which  the 
capillaries  are  spread. 


FIG.  86. —Distribution  of  Air-tubes  in  Mam- 
malian Lungs  :  a,  larynx;  b,  trachea;  c,  d, 
left  and  right  bronchial  tubes ;  e,  /,  g,  the 
ramifications.  In  Man  the  subdivision  con- 
tinues until  the  ultimate  tubes  are  one  twen- 
ty-fifth of  an  inch  in  diameter.  Each  lobule 
represents  in  miniature  the  structure  of  the 
entire  lung  of  a  Frog. 


HOW  ANIMALS  BREATHE. 


119 


pipe  be  tied,  and  an  opening  be  made  in  the  wing-bone, 
the  bird  will  continue  to  respire.  The  right  lung  is  usu- 
ally the  larger ;  in  some  Snakes,  the  left  is  wanting  en- 
tirely. In  most  Vertebrates,  lungs  are  freely  suspended ; 
in  Birds,  they  are  fastened  to  the  back. 

The  lungs  communicate  with  the  atmosphere  by  means 
of  the  trachea,  or  windpipe,  formed  of  a  series  of  cartilag- 
inous rings,  which  keep  it  constantly  open.  It  begins  in 
the  back  part  of  the  month,  opening  into  the  pharynx  by 
a  slit,  called  the  glottis,  which,  in  Mammals,  is  protected 
by  the  valve -like  epiglottis.  The  trachea  passes  along 
the  neck  in  front  of 
the  oesophagus,  and 
divides  into  two 
branches,  or  bronchi, 
one  for  each  lung. 
In  Birds  and  Mam- 
mals, the  bronchial 
tubes,  after  entering 
the  lungs,  subdivide 
again  into  minute 
ramifications. 

Vertebrates  are  the  FlG-  8*--skeleton  of  a  Fr°fr 

only  animals  that  breathe  through  the  mouth  or  nos- 
trils. Frogs,  having  no  ribs,  and  Turtles,  whose  ribs  are 
soldered  together  into  a  shield,  are  compelled  to  swallow 
the  air.  Snakes,  Lizards,  and  Crocodiles  draw  it  into  the 
lungs  by  the  play  of  the  ribs.67  Birds,  unlike  other  ani- 
mals, do  not  inhale  the  air  by  an  active  effort ;  for  that  is 
done  by  the  springing-back  of  the  breast-bone  and  ribs  to 
their  natural  position.  To  expel  the  air,  the  breast-bone 
is  drawn  down  towards  the  back-bone  by  muscles,  which 
compresses  the  lungs. 

Mammals  alone  have  a  perfect  thorax — i.  e.,  a  closed 
cavity  for  the  heart  and  lungs,  with  movable  walls  (breast 


120 


COMPARATIVE  ZOOLOGY. 


bone  and  ribs)  and  a  diaphragm,  or  muscular  partition, 
separating  it  from  the  abdomen.68  Inspiration  (or  filling 
the  lungs)  and  expiration  (or  emptying  the  lungs)  are 
both  accomplished  by  muscular  exertion ;  the  former,  by 
raising  the  ribs  and  lowering  the  diaphragm,  which  en-, 

large  the  capacity  of  the 
chest,  and  the  air  rushes 
in  to  prevent  a  vacuum ; 
the  latter,  by  the  ascent  of 
the  diaphragm  and  the  de- 
.— "&  scent  of  the  ribs. 

As  a  rule,  the  more  ac- 
tive and  more  muscular  an 
animal,  the  greater  the  de- 
mand for  oxygen.  Thus, 
warm-blooded  animals  live 
fast,  and  their  rapidly  de- 
caying tissues  call  for  rapid 
respiration ;  while  in  the 
cold-blooded  creatures  the 
waste  is  comparatively 
slow.  Respiration  is  most 
active  in  Birds,  and  least 
in  water-breathing  animals. 
The  sluggish  Toad  respires 
more  slowly  than  the  busy 
Bee,  the  Mollusk  more  slowly  than  the  Fish.  But  respi- 
rations, like  beats  of  the  heart,  are  fewer  in  large  Mam- 
mals than  in  small  ones.  An  average  Man  inhales  about 
300-400  cubic  feet  of  air  per  day  of  rest,  and  much  more 
when  at  work. 

Another  result  of  respiration,  besides  the  purification 
of  the  blood,  is  the  production  of  heat.  The  chemical 
combination  of  the  oxygen  in  the  air  with  the  carbon  in 
the  tissues  is  a  true  combustion  ;  and,  therefore,  the  more 


PIG.  88. — Human  Thorax:  a,  vertebral  col- 
umn ;  &,  &',  ribs,  the  lower  ones  false  ;  c, 
clavicle;  e,  intercostal  muscles,  removed 
on  the  left  side  to  show  the  diaphragm,  d; 
f,  pillars  of  the  diaphragm  attached  to  the 
lumbar  vertebrae ;  g,  muscles  for  elevating 
the  ribs  ;  h,  sternum. 


SECRETION  AND  EXCRETION.  121 

active  the  animal  and  its  breathing,  the  higher  its  temper- 
ature. Birds  and  Mammals  have  a  constant  temperature, 
which  is  usually  higher  than  that  of  the  atmosphere  (108° 
and  100°  F.  respectively).  They  are  therefore  called  con- 
stant-temper atured  or  warm-blooded.  Other  animals  do 
not  vary  greatly  in  temperature  from  that  of  their  sur- 
roundings, and  are  called  changeable-temperatured  or  cold- 
Hooded.  Still,  their  temperature  does  not  agree  exactly 
with  that  of  the  air  or  water.  The  Bee  is  from  3°  to  10°, 
and  the  Earth-worm  and  Snail  from  1£°  to  2°,  higher  than 
the  air.  The  mean  temperature  of  the  Carp  and  Toad  is 
51°;  of  Man,  98°;  Dog,  99°;  Cat,  101°;  Squirrel,  105°; 
Swallow,  111°. 


CHAPTER  XY. 

SECRETION   AND    EXCRETION. 

IN  the  circulation  of  the  blood,  not  only  are  the  nutrient 
materials  deposited  within  the  body  in  the  form  of  tissue, 
but  certain  special  fluids  are  separated  and  conveyed  to 
the  external  or  internal  surfaces  of  the  body.  These  flu- 
ids are  of  two  kinds :  some,  like  saliva,  gastric  juice,  bile, 
milk,  etc.,  are  for  useful  purposes ;  others,  like  sweat  and 
urine,  are  expelled  from  the  system  as  useless  or  injurious. 
The  separation  of  the  former  is  called  secretion;  the  re- 
moval of  the  latter  is  excretion.  Both  processes  are  sub- 
stantially alike. 

In  the  lower  forms,  there  are  no  special  organs,  but  se- 
cretion and  excretion  take  place  from  the  general  surface. 
The  simplest  form  of  a  secreting  organ  closely  resembles 
that  of  a  respiratory  organ,  a  thin  membrane  separating 
the  blood  from  the  cavity  into  which  the  secretion  is  to 


122 


COMPARATIVE  ZOOLOGY. 


be  poured.  Usually,  however,  the  cells  of  the  membrane 
manufacture  the  secretion  from  materials  furnished  by  the 
blood.  Even  in  the  higher  animals,  there  are  such  secret- 
ing membranes.  The  membranes  lining  the  nose  and  ali- 
mentary canal  and  enclosing 
the  lungs,  heart,  and  joints, 
secrete  lubricating  fluids. 

The  infolding  of  such  a 
membrane  into  little  sacs  or 
short  tubes  (follicles},  each 
having  its  own  outlet,  is  the 
type  of  all  secreting  and  ex- 
creting organs.  The  lower 
tribes  have  nothing  higher, 
and  the  apparatus  for  pre- 
paring the  gastric  fluid  at- 
tains no  further  develop- 
ment even  in  Man.  When 

FIG.  S9.-Three  plans  of  secreting  Mem-  a  cluster  Of  tllCSC  f ollicleS,  Ol' 
branes.    The  heavy  line  represents  the 

areolar-vascular  layer;  the  next  line  is  saCS,  discharge  their  Contents 

the  basement,  or  limiting  membrane;  ,  .. 

and  the  dotted  line  the  epithelial  layer:  by    One     Common     QUCt,    WC 

a  shows  increase  of  surface  by  simple  \  7         ?        p    ,       i      ,  r 

plaited  or  fringed  projections ;   6,  five  haVe  a  fa™*-       Bttt  whether 

modes  of  increase  by  recesses,  forming  membrane,  f  ollicle.  Or  gland, 
simple  glands,  or  follicles;  c,  two  forms 

of  compound  glands.  the  organ  is  covered  with  a 

net-work  of  blood-vessels,  and  lined  witli  epithelial  cells, 
which  are  the  real  agents  in  the  process. 

The  chief  Secreting  Organs  are  the  salivary  glands, 
gastric  follicles^  pancreas,  and  liver,  all  situated  along  the 
digestive  tract. 

1.  The  salivary  glands,  which  open  into  the  mouth,  se- 
crete saliva.  They  exist  in  nearly  all  Vertebrates,  higher 
Mollusks,  and  Insects,  and  are  most  largely  developed  in 
such  as  live  on  vegetable  food.  The  saliva  serves  to  lu- 
bricate or  dissolve  the  food  for  swallowing,  and,  in  some 
Mammals,  aids  also  in  digestion  of  starch.8" 


SECRETION  AND  EXCRETION. 


123 


2.  The  gastric  follicles  are  minute  tubes  in  the  walls  of 
the  stomach  secreting  gastric  juice.  They  are  found  in 
all  Vertebrates,  and  in  the  higher  Mol- 
lusks  and  Arthropods.  In  the  lower 
forms,  a  simple  membrane  lined  with 
cells  serves  the  same  purpose.  Under 
the  microscope,  the  soft  mucous  mem- 
brane of  the  human  stomach  presents  a 
honey-comb  appearance,  caused  by  nu- 
merous depressions  or  cells.  At  the  bot- 
tom of  these  depressions  are  clusters  of 
spots,  which  are  the  orifices  of  the  tubu- 
lar follicles.  The  follicles  are  about  -^ 
of  an  inch  in  diameter,  and  number  mill- 


ons. 


3.  The  pancreas,  or  "  sweetbread,"  so 

.         .  -    ,.  FIG.  90.-Follicles  from  the 

important  in  the  process  01  digestion,    stomach  of  a  Dog,  x 


when  present,  exists  only  in  the  Yerte- 

brates,  and  perhaps  in  the  higher  Mol-   inmnnr  epithelium. 

Insks.     In  its  structure  and  its  secretion  it  closely  resem- 

bles the  salivary  glands.     In  the  Cuttle-fish,  it  is  repre- 

sented by  a  sac;  in  Fish- 
es, by  a  group  of  follicles. 
It  is  proportionally  larg- 
est in  Birds  whose  sali- 
vary glands  are  deficient. 
The  pancreatic  juice  en- 
ters the  duodenum. 

4.  A  liver  in  some  form 
is  found  in  all  animals 
having  a  distinct  diges- 
tive cavity.  In  Mollusks 

an(j  YertebrateS,  it  IS  the 

largest  gland  in  the  body. 
The  higher  the   animal,  the  more   compact   the   organ. 


Fio.91.-PancreasofMan,f>;  0,  gall-bladder  ; 
*,  cystic  duct;  c,  duct  from  the  liver;  p,  py- 

loric  valve;  e,  ;,  duodenum. 


124 


COMPARATIVE  ZOOLOGY. 


Thus,  in  Polyps  it  is  represented  by  yellowish  cells  lining 
the  stomach ;  in  Insects,  by  cells  in  the  wall  of  the  stom- 
ach ;  in  Mollusks,  by  a  cluster  of  sacs,  or  follicles,  forming 
a  loose  compound  gland.  In  Vertebrates,  the  liver  is  well 
defined,  and  composed  of  a  multitude  of  lobules  (which 
give  it  a  granular  appearance)  arranged  on  the  capillary 
veins,  like  grapes  on  a  stem,  and  containing  nucleated 
secreting  cells.  It  is  of  variable  shape,  but  usually  two, 
three,  or  five  lobed,  and  is  centrally  situated — in  Mam- 
mals, just  below  the  diaphragm.  In  most  Vertebrates, 
there  is  an  appendage  to  the  liver,  called  the  gaUMadder, 
which  is  simply  a  reservoir  for  the  bile  when  not  wanted. 
The  so-called  liver  of  Invertebrates  is  probably  more 


p,O(  92.— Liver  of  the  Dog,  F,  F;  D,  duodenum  and  intestines:  P,  pancreas;  r, 
'spleen ;  e,  stomach ;  /,  rectum ;  R,  right  kidney ;  B,  gall-bladder ;  eh,  cystic 
duct;  F,  lobe  of  liver  dissected  to  show  distribution  of  portal  vein,  VP,  nnd 
hepatic  vein,  vh;  d,  diaphragm;  VC,  vena  cavn;  C,  heart. 


SECRETION  AND  EXCRETION.  125 

like  the  pancreas  of  Vertebrates  in  function,  as  its  secre- 
tion digests  starches  and  albuminoids.  The  liver  of  Ver- 
tebrates is  both  a  secretory  and  an  excretory  organ.  The 
bile  performs  an  important,  although  ill-understood,  func- 
tion in  digestion,  and  also  contains  some  waste  products. 
The  gland  also  serves  to  form  sugar  from  part  of  the 
digested  food,  and  may  well  be  called  a  chemical  work- 
shop for  the  bod}7.  In  animals  of  slow  respiration,  as 
Crustaceans,  Mollusks,  Fishes,  and  Reptiles,  fat  accumu- 
lates in  the  liver.  " Cod-liver  oil"  is  an  example. 

The  great  Excreting  Organs  are  the  lungs,  the  kid- 
neys, and  the  skin;  and  the  substances  which  they  re- 
move from  the  system — carbonic  acid,  water,  and  urea — 
are  the  products  of  decomposition,  or  organic  matter  on 
its  way  back  to  the  mineral  kingdom.70  Different  as  these 
organs  appear,  they  are  constructed  upon  the  same  prin- 
ciple :  each  consisting  of  a  very  thin  sheet  of  tissue  sepa- 
rating the  blood  to  be  purified  from  the  atmosphere,  and 
straining  out,  as  it  were,  the  noxious  matters.  All,  more- 
over, excrete  the  same  substances,  but  in  very  different 
proportions :  the  lungs  exhale  carbon  dioxide  and  water, 
with  a  trace  of  urea ;  the  kidneys  expel  water,  urea,  and 
a  little  carbon  dioxide  ;  while  the  skin  partakes  of  the  nat- 
ure of  both,  for  it  is  not  only  respiratory,  especially  among 
the  lower  animals,  but  it  performs  part  of  the  work  of  the 
kidneys  when  they  are  diseased. 

1.  The  lungs  (and  likewise  gills)  are  mainly  excretory 
organs.  The  oxygen  they  impart  sweeps  with  the  blood 
through  every  part  of  the  body,  and  unites  with  the  tis- 
sues and  with  some  elements  of  the  blood.  Thus  are  pro- 
duced heat  and  work,  whether  muscular,  nervous,  secre- 
tory,  etc.  As  a  result  of  this  oxidation,  carbon  dioxide, 
water,  and  urea  or  a  similar  substance,  are  poured  into  the 
blood.  The  carbon  dioxide  and  part  of  the  water  are 
passed  off  from  the  respiratory  organs.  This  process  is 


126 


COMPARATIVE  ZOOLOGY. 


more  immediately  necessary  to  life  than  any  other :  the 

arrest  of  respiration  is  fatal. 

2.  While  the  lungs  (and  skin  also, 
to  a  slight  degree)  are  sources  of 
gain  as  well  as  loss  to  the  blood,  the 
kidneys  are  purely  excretory  organs. 
Their  main  function  is  to  eliminate 
the  solid  products  of  decay  which 
cannot  pass  out  by  the  lungs.  In 
Mammals,  they  are  discharged  in 
solution ;  but  from  other  animals 
which  drink  little  the  excretion  is 
more  or  less  solid.  In  Insects,  the 
kidneys  are  groups  of  tubes ;  in  the 

FIG.  93.-sect.uu  «f  Human  h%her  Mollusks,  they  are  represeiit- 

Kidtiey,  showing  the  tubu-   ec[  by  spongy  maSS6S  of  follicles  I   ill 
lar  portion,  3,  grouped  into  J       r        &</ 

cones;  7,  the  ureter,  or  out-   V  ertebrates,  they  are  well-developed 

let  of  the  secretion.  i        j  •  i_  i 

glands,  two  in  number,  and  consist- 
ing of  closely  packed  tubes. 

3.  The  skin  of  the  soft-skinned  animals,  particularly  of 
Amphibians  and  Mammals,  is  covered  with  minute  pores, 
which  are  the  ends  of  as  many  delicate  tubes  that  lie 
coiled  up  into  a  knot  within  the  true  skin.  These  are 
the  sweat-glands,  which  excrete  water,  and  with  it  certain 
salts  and  gases. 

Besides  these  secretions-and  excretions,  there  are  others, 
contined  to  particular  animals,  and  designed  for  special 
purposes:  such  are  the  oily  matters  secreted  from  the 
skin  of  quadrupeds  for  lubricating  the  hair  and  keeping 
the  skin  flexible ;  the  tears  of  Reptiles,  Birds,  and  Mam- 
mals ;  the  milk  of  Mammals ;  the  ink  of  the  Cuttle-fish ; 
the  poison  of  Jelly-fishes,  Insects,  and  Snakes;  and  the 
silk  of  Spiders  and  Caterpillars. 


THE  SKIN  AND  SKELETON.  127 


CHAPTER  XVI. 

THE    SKIN   AND    SKELETON. 

The  Skin,  or  Integument,  is  that  layer  of  tissue  which 
covers  the  outer  surface  of  the  body.  The  term  Skeleton 
is  applied  to  the  hard  parts  of  the  body,  whether  external 
or  internal,  which  serve  as  a  framework  or  protection  to 
the  softer  organs,  and  afford  points  of  attachment  to  mus- 
cles. If  external,  as  the  crust  of  the  Lobster,  it  is  called 
Exoskeleton ;  if  internal,  as  the  bones  of  Man,  it  is  called 
Endoskeleton.  The  former  is  a  modification  of  the  skin ; 
the  latter,  a  hardening  of  the  deeper  tissues. 

1.  The  Skin. — In  the  lowest  forms  of  life,  as  Amoeba, 
there  is  no  skin.  The  jelly  of  which  they  are  composed 
is  firmer  outside  than  inside,  but  no  membrane  is  present. 
In  Infusoria,  there  is  a  very  thin  cuticle  covering  the  ani- 
mal. They  have  thus  a  definite  form,  while  the  Amoebae 
continually  change.  Sponges  and  Hydras  also  have  no 
true  skin.  But  in  Polyps,  the  outside  layer  of  the  animal 
is  separated  into  two  portions — ecderon  and  enderon71— 
which  may  be  regarded  as  partly  equivalent  to  epidermis 
and  dermis  in  the  higher  animals.  These  two  layers  are, 
then,  generally  present.  The  outer  is  cellular,  the  latter 
fibrous,  and  may  contain  muscular  fibres,  blood-vessels, 
nerves,  touch-organs,  and  glands.  It  thus  becomes  very 
complicated  in  some  animals. 

In  Worms  and  Arthropods,  the  cellular  layer,  here 
called  hypodermis,  excretes  a  structureless  cuticle,  which 
may  become  very  thick,  as  in  the  tail  of  the  Horseshoe 
Crab,  or  may  be  hardened  by  deposition  of  lime-salts,  as 
in  many  Crustacea.  The  loose  skin,  called  the  mantle. 


128  COMPARATIVE   ZOOLOGY. 

which  envelopes  the  body  of  the  Mollusk  corresponds  to 
the  true  skin  of  higher  animals.  The  border  of  the  man- 
tle is  surrounded  with  a  delicate  fringe,  and,  moreover, 
contains  minute  glands,  which  secrete  the  shell  and  the 
coloring  matter  by  which  it  is  adorned.  The  Tunicates 
have  a  leathery  epidermis,  remarkable  for  containing,  in- 
stead of  lime,  a  substance  resembling  vegetable  cellulose. 

In  Mammals,  whose  skin  is  most  fully  developed,  the 
dermis  is  a  sheet  of  tough  elastic  tissue,  consisting  of  in- 
terlacing fibres,  and  containing  blood-vessels,  lymphatics, 
sweat-glands,  and  nerves.  It  is  the  part  converted  into 
leather  when  hides  are  tanned,  and  attains  the  extreme 
thickness  of  three  inches  in  the  Rhinoceros.  The  upper 
surface  in  parts  of  the  body  is  covered  with  a  vast  num- 
ber of  minute  projections,  called  papillce,  each  containing 
the  termination  of  a  nerve;  these  are  the  essential  agents 
in  the  sense  of  touch.72 '  They  are  best  seen  on  the  tongue 
of  an  Ox  or  Cat,  and  on  the  human  fingers,  where  they 
are  arranged  in  rows. 

Covering  this  sensitive  layer,  and  accurately  moulded 
to  all  its  furrows  and  ridges,  lies  the  bloodless  and  nerve- 
less epidermis.  It  is  that  part  of  the  skin  which  is  raised 
in  a  blister.  It  is  thickest  where  there  is  most  pressure 
or  hard  usage :  on  the  back  of  the  Camel  it  attains  un- 
usual thickness.  The  lower  portion  of  the  epidermis 
(called  rete  mucosum)  is  comparatively  soft,  and  consists 
of  nucleated  cells  containing  pigment-granules,  on  which 
the  color  of  the  animal  depends.  Towards  the  surface 
the  cells  become  flattened,  and  finally,  on  the  outside,  are 
changed  to  horny  scales  (Fig.  2,  c). 

These  scales,  in  the  higher  animals,  are  constantly  wear- 
ing off  in  the  form  of  scurf,  and  as  constantly  being 
renewed  from  below.  In  Lizards  and  Serpents,  the  old 
epidermis  is  cast  entire,  being  stripped  off  from  the  head 
to  the  tail;  in  the  Toad,  it  comes  off  in  two  pieces;  in  the 


THE  SKIN   AND   SKELETON. 


129 


FIG.  94.— Section  of  Skin  from  Horse's  Nostril:  E,  epidermis;  D,  dermi* ;  1,  horny 
layer  of  epidermis ;  2,  rete  mucosum ;  3,  papillary  layer  of  dermis ;  4,  excretory 
duct  of  a  sudoriparous,  or  sweat,  gland;  5,  glomerule,  or  convoluted  tube  of  the 
same ;  C,  hair  follicle  ;  7,  sebaceous  gland  ;  8,  internal  sheath  of  the  hair  follicle  ; 
9,  bulb  of  the  hair ;  10,  mass  of  adipose  tissue. 

Frog,  in  shreds ;  in  Fishes  and  some  Mollusks,  in  the  form 
of  slime.  However  modified  the  epidermis,  or  whatever 
its  appendages,  the  like  process  of  removal  goes  on.  Mam- 
mals shed  their  hair ;  Birds,  their  feathers ;  and  Crabs, 
their  shells.  When  the  loss  is  periodical,  it  is  termed 
moulting. 

2.  The  Skeletons.  —  ( l )  The  Exoskeieton  is  developed 
by  the  hardening  of  the  skin, 'and,  with  very  few  excep- 
tions, is  the  only  kind  of  skeleton  possessed  by  inverte- 
brate animals.  The  usual  forms  are  coral,  shells,  crusts, 
scales,  plates,  hairs,  and  feathers.  It  is  horny  or  calca- 
reous; while  the  endoskeleton  is  generally  a  deposit  of 
earthy  material  within  the  body,  and  is  nearly  confined 
to  the  Vertebrates.  The  exoskeleton  may  be  of  two  kinds 
— dermal  and  epidermal. 

The  microscopic  particles  of  living  jelly,  called  Polycis- 
tina  and  Foraminifera,  possess  siliceous  and  calcareous 
shells  of  the  most  beautiful  patterns.  The  Sponge  has  a 

9 


130 


COMPARATIVE  ZOOLOGY. 


skeleton  of  horny  fibres,  which  is  the  sponge  of  commerce. 
Coral  is  the  solid  framework  of  certain  Polyps.  There 
are  two  kinds:  one  represented  by  the  common  white 
coral,  which  is  a  calcareous  secretion  within  the  body  of 


FIG.  95.— 1,  Vertical  Section,  and,  2,  Transverse  Section,  of  a  sclerodermic  Corallite : 
a,  mouth;  &,  tentacles;  c,  stomach;  d,  intermesenteric  chamber;  e,  mesentery; 
/,  septnm ;  g,  endoderm ;  h,  epitheca ;  k,  theca,  or  outer  wall ;  m,  columella ;  nt 
short  partitions;  p,  tabula,  or  transverse  partition;  r,  sclerobase;  s,  ccenenchy- 
ma,  or  common  substance  connecting  neighboring  corallites ;  t,  ectoderm ;  x, 
pali,  or  imperfect  partitions. 

the  Polyp,  in  the  form  of  a  cylinder,  with  partitions  ra- 
diating towards  a  centre  (scleroderm) ;  the  other,  repre- 
sented by  the  solid  red  coral  of  jewelry,  is  a  central  axis 
deposited  by  a  group  of  Polyps  on  the  outside  (sdero- 

lase).  The  first 
sort  is  a  dermal,  the 
latter  an  epider- 
mal, exoskeleton. 

The  skeleton  of 
the  Star-fish  is  a 
leathery  skin  stud- 
ded with  calcare- 
ous particles  and 
plates.  The  Sea- 
urchin  is  covered 
with  an  inflexible 

FIG.  96.— Shell  of  Sea-urchin  (Cidaris)  without  its  spines.      •,     ,,        /.      ,    , 

and  beautiful  construction.     The  shell  is  really  a  calcified 


THE   SKIN  AND   SKELETON. 


131 


skin,  being  a  net- work  of  fibrous  tissue  and  earthy  matter. 
It  varies  in  shape  from  a  sphere  to  a  disk,  and  consists 
of  hundreds  of  angular  pieces  accurately  fitted  together, 
like  mosaic-work.  These  form  ten  zones,  like  the  ribs  of 
a  melon,  five  broad  ones  alternating  with  five  narrower 


FIG.  97.— Structure  of  Sea-urchins'  Spines:  1,  a,  spine  of  Cidaria  cut  longitudinally; 
£,  s,  ball-and-socket  joint ;  p,  pedicellarise ;  2, 3,  transverse  sections  of  spines  of 
Cidaris  and  Echinus.^ 

ones.  The  former  (called  interambulacra)  are  covered 
with  tubercles  bearing  movable  spines.  The  narrow 
zones  (called  ambulacra,  as  they  are  likened  to  walks 
through  a  forest)  are  pierced  with  small  holes,  through 
which  the  animal  sends  out  fleshy  sucker-feet. 

The  skin  of  the  Crab  and  Lobster  is  hardened  by  cal- 
careous deposit  into  a  "crust,"  or  shell;73  but,  instead  of 
forming  one  piece,  it  is  divided  into  a  series  of  segments, 
which  move  on  each  other.  The  number  of  these  seg- 
ments, or  rings,  is  usually  twenty-one — to  the  head,  tho- 
rax, and  abdomen,  seven  each.  In  the  adult,  however, 
the  rings  of  the  head  and  thorax  are  often  soldered  to- 
gether into  one  shield,  called  cephalo-thorax ;  and  in  the 
Horseshoe  Crab  the  abdominal  rings  are  also  united.  The 
shell  of  Crustaceans  is  periodically  cast  off,  for  the  ani- 
mals continue  to  grow  even  after  they  have  reached  their 


132 


COMPARATIVE  ZOOLOGY. 


mature  form.  This  moulting  is  a  very  remarkable  opera- 
tion. How  the  Lobster  can  draw  its  legs  from  their  cases 

without  unjointing 
or  splitting  them 
was  long  a  puz- 
zle. The  flesh  be- 
comes soft,  and  is 
drawn  through  the 
joints,  the  wounds 
thus  caused  quickly 
healing.  The  cast- 
off  skeleton  is  a  per- 
fect copy  of  the  an- 
imal, retaining  in 
their  places  the  del- 
icate coverings  of 
the  eyes  and  anten- 
nae, and  even  the 

FIG.  98.— Diagram  of  nn  Insect:  A,  head  bearing  the  Ijnincr  membrane  of 
eyes  aud  antennae;  B,  prothorax,  carrying  the  first 

pair  of  legs;  C,  mesothorax,  carrying  the  second  the  Stomach  With  its 
pair  of  legs  and  first  pair  of  wings ;  D,  carrying  the  , 

third  pair  of  legs  and  second  pair  of  wings;  E,  ab-  teeth, 
domen,  with  ovipositor,  F;  1,  coxa,  or  hip;   2,  tro-         nni         -i  , 

chanter ;  3,  femur,  or  thigh ;  4,  tibia,  or  shank ;  5,  tar-  •  UJ 

BUB,  or  foot ;  6,  claw.  of      Insects       differs 

from  that  of  Crustaceans  in  consisting  mainly  of  a  horny 
substance  called  chitine  and  in  containing  no  lime.  The 
head,  thorax,  and  abdomen  are  distinct,  and  usually  con- 
sist of  fourteen  visible  segments — one  for  the  head,  three 
for  the  thorax  (called  prothorax,  mesothorax,  and  metaiho- 
rax\  and  ten  for  the  abdomen.  The  antennae,  or  feelers, 
legs,  and  wings,  as  well  as  hairs,  spines,  and  scales,  are  ap- 
pendages of  the  skeleton.  As  Insects  grow  only  during 
the  larval,  or  caterpillar,  state,  moulting  is  confined  to  that 
period.  These  skeletons  are  epidermal,  deposited  in  suc- 
cessive layers,  from  the  inside,  and  are,  therefore,  capable 
of  but  slight  enlargement  when  once  formed. 


THE   SKIN  AND   SKELETON.  133 

The  shells  of  Mollusks  are  well-known  examples  of  exo~ 
skeletons.  The  mantle,  or  loose  skin,  of  these  animals  se- 
cretes calcareous  earth  in  successive  layers,  converting  the 
epidermis  into  a  "  shell." 74  So  various  and  characteristic 
is  the  microscopic  character  of  shells,  that  a  fragment  is 
sometimes  sufficient  to  determine  the  group  to  which  it 
belongs.  Many  shells  resemble  that  of  the  Fresh-water 
Mussel  (Unio),  which  is  composed  of  three  parts:  the  ex- 
ternal brown  epidermis,  of  horny  texture ;  then  the  pris- 
matic portion,  consisting  of  minute  columns  set  perpen- 
dicularly to  the  surface;  and  the  internal  nacreous  layer, 
or  "  mother-of-pearl,"  made  up  of  exceedingly  thin  plates. 
The  pearly  lustre  of  the  last  is  due  to  light  falling  upon 
the  outcropping  edges  of  wavy  laminae.75  In  many  cases, 
the  prismatic  and  nacreous  layers  are  traversed  by  minute 
tubes.  Another  typical  shell-structure  is  seen  in  the  com- 
mon Cone,  a  section  of  which  shows  three  layers,  besides 
the  epidermis,  consisting  of  minute  plates  set  at  different 
angles.  The  Nautilus  is  composed  of  two  distinct  layers : 
the  outer  one  having  the  fracture  of  broken  china;  the 
inner  one,  nacreous. 

Most  living  shells  are  made  of  one  piece,  as  the  Snail ; 
these  are  called  "  univalves."  Others,  as  the  Clam,  con- 
sist of  two  parts,  and  are  called  "  bivalves."  In  either 
case,  a  valve  may  be  regarded  as  a  hollow  cone,  growing 
in  a  spiral  form.  The  ribs,  ridges,  or  spines  on  the  out- 
side of  a  shell  mark  the  successive  periods  of  growth,  and, 
therefore,  correspond  to  the  age  of  the  animal.  The 
figures  on  the  following  page  show  the  principal  parts 
of  the  ordinary  bivalves  and  univalves.  The  valves  of  a 
bivalve  are  generally  equal,  and  the  umbones,  or  beaks,  a 
little  in  front  of  the  centre.  The  valves  are  bound  to- 
gether by  a  ligature  near  the  umbones,  and  often,  also,  by 
means  of  a  "  hinge  "  formed  by  the  "  teeth  "  of  one  valve 
interlocking  into  cavities  in  the  other.  The  aperture  of 


134 


COMPARATIVE  ZOOLOGY. 


a  univalve  is  frequently  closed  by  a  horny  or  calcareous 

plate,  called  "  operculurn,"  which  the  animal  carries  on  its 

back,  and  which  is  a  part  of  the  exo- 

skeleton.     The  shells  of  Mollusks 

are  epidermal,  and  are,  therefore, 

dead  and  incapable  of  true  repair. 

When  broken,  they  can  be  mended 


FIG.  99.—  Left  Vaive  of  ai>ivalveMollnsk(C«/«/t<Tea    FIG.  100.  —  Section   of  a  Spiral 


chione) :  h,  hinge  ligament ;  u,  umbo ;  £,  lunule ; 
c,  cardinal,  and  t,  t',  lateral  teeth ;  a,  a',  impres- 
sions of  the  anterior  and  posterior  adductor  mus- 
cles ;  p,  pallial  impression  ;  s,  sinus,  occupied  by 
the  retractor  of  the  siphous. 


Univalve  (Triton  corrugatus) : 
a,  apex;  b,  spire;  c,  suture; 
d,  posterior  canal;  e.  outer 
lip  of  the  aperture ;  /,  ante- 
rior canal. 


only  by  the  animal  pouring  out  lime  to  cement  the  parts 
together.  They  cannot  grow  together,  like  a  broken  bone. 

Imbedded  in  the  back  of  the  Cuttle-fish  is  a  very  light 
spongy  "bone,"  which,  as  already  observed, i^  a  secretion 
from  the  skin,  and  therefore  belongs  to  the  exoskeleton. 
It  has  no  resemblance  to  true  bone,  but  is  formed,  like 
shells,  of  a  number  of  calcareous  plates.  Nevertheless, 
the  Cuttle-fish  does  exhibit  traces  of  an  endoskeleton: 
these  are  plates  of  cartilage,  one  of  which  surrounds  the 
brain,  and  hence  may  be  called  a  skull.  To  this  cartilage, 
not  to  the  "  cuttle-bone,"  the  muscles  are  attached. 

In  Vertebrates,  the  exoskeleton  is  subordinate  to  the 
endoskeleton,  and  is  feebly  developed  in  comparison.  It 


THE   SKIN   AND   SKELETON. 


135 


is  represented  by  a  great  variety  of  appendages  to  the 
skin,  which  are  mainly  organs  for  protection,  not  for  sup- 
port. Some  are  horny 
developments  of  the  ep- 
idermis, such  as  hairs, 
feathers,  nails,  claws, 
hoofs,  horns,  and  the 
scales  of  Reptiles;  oth- 
ers arise  from  the  hard- 
ening of  the  dermis  by 
calcareous  matter,  as  the 

i         £  -n-  -U        .LI,     u  FIG.  101.— Skeletal  Architecture  in  the  Armadil- 

SCalCS  Ot  £  ISheS,  the  bony      ,0>  showing  lhe  relation  of  the  carapax  to  the 
plates  Of  Crocodiles  and     vertebral  column. 

Turtles,  and  the  shield  of  the  Armadillo. 

The  scales  of  Fishes  (and  likewise  the  spines  of  their 
vertical  fins)  lie  imbedded  in  the  overlapping  folds  of  the 
skin,  and  are  covered  with  a  thin,  slimy  epidermis.  The 
scales  of  the  bony  Fishes  (Perch,  Salmon,  etc.)  consist  of 


FIG.  102.— Diagrammatic  Section  of  the  Skin  of  a  Fish  (Ca?p) :  a,  d*rm,  showing  lam- 
inated structure  with  vertical  fibres,  6;  c,  gristly  layer;  e,  laminated  layer,  with 
calcareous  granules ;  d,  superficial  portion  developing  into  scales  ;  /,  scale-pit. 

two  layers,  slightly  calcareous,  and  marked  by  concentric 
and  radiating  lines.  Those  of  the  Shark  have  the  structure 
of  teeth,  while  the  scutes,  or  plates,  of  the  Crocodiles, 
Turtles,  and  Armadillos  are  of  true  bone. 

The  scales  of  Snakes  and  Lizards  are  horny  epidermal 
plates  covering  the  overlapping  folds  of  the  true  skin. 
In  some  Turtles  these  plates  are  of  great  size,  and  are 
called  "tortoise-shell;"  they  cover  the  scutes.  The  scales 
on  the  legs  of  Birds,  and  on  the  tail  of  the  Beaver  and 
Rat,  have  the  same  structure.  Nails  are  flattened  horny 
plates  developed  from  the  upper  surface  of  the  fingers 


136 


COMPARATIVE  ZOOLOGY. 


12 


Pro.  103.— Vertical  Section  of  the  Forefoot  of  the  Horse 
(middle  digit):  1,  2,  4,  proximal,  middle,  and  distal, 
or  ungual,  phalanges ;  3,  sesamoid,  or  nut-bone ;  5, 
6,  7,  tendons ;  9,  elastic  tissue ;  8,  10,  internal  and 
external  floor  of  the  hoof;  11, 12,  internal  and  exter- 
nal walls. 


and  toes.  Claws 
are  sharp  conical 
nails,  being  devel- 
oped from  the  sides 
as  well  as  upper 
surface;  and  hoofs 
are  blunt  cylin- 
drical claws.  Hol- 
low horns,  as  of  the 
Ox,  may  be  likened 
to  claws  sheathing 
a  bony  core.  The 
horn  of  the  Rhinoc- 
eros is  a  solid  mass 
of  epidermal  fibres. 
"Whalebone,"  the 
rattles  of  the  Rattlesnake,  and  the 
beaks  of  Turtles  and  Birds,  are  like- 
wise epidermal. 

Hairs,  the  characteristic  clothing 
of  Mammals,  are  elongated  horny 
cones,  composed  of  "pith"  and 
"crust."  The  latter  is  an  outer 
layer  of  minute  overlapping  scales, 
which  are  directed  towards  the 
point,  so  that  rubbing  a  human 
hair  or  fibre  of  wool  between  the 
thumb  and  finger  pushes  the  root- 
end  away.  The  root  is  bulbous, 
and  is  contained  in  a  minute  de- 
pression, or  sac,  formed  by  an  in-  Fi&.io4.-secti^ftheRootand 
folding  of  the  skin.  Hairs  are usn-  ^'^ ££* ^'™» 

ally     Set     obliquely    into     the     Skin.  dermic  scales,  the  inner  layer, 

_.  ,       ,  .„  -,   -r-r     -,       ,  c»  forming  the  outer  covering 

Porcupines  quills  and  Hedgehogs  of  the  shaft,  being  imbricated; 

,  i  .   .  the  root  consists  of  angular 

spines  make  an  easy  transition  to     ceils  loaded  with  pigment. 


THE  SKIN  AND  SKELETON. 


137 


feathers,  which  differ  from  hairs  only  in  splitting  np  into 
numerous  laminae.  They  are  the  most  complicated  of  all 
the  modifications  of  the  epidermis. 
They  consist  of  a  "  quill "  (answer- 
ing to  the  bulb  of  a  hair),  and  a 
"shaft,"  supporting  the  "vane," 
which  is  made  up  of  "  barbs,"  "  bar- 
bules,"  and  interlocking  "  process- 
es." The  quill  alone  is  hollow,  and 
has  an  orifice  at  each  end.  Thus 
feather  is  moulded  on  a  papilla,  the 
shaft  lying  in  a  groove  on  one  side 
of  it,  and  the  vane  wrapped  around 
it.  When  the  feather  emerges  from 
the  skin,  it  unfolds  itself.  Thus 
shaft  and  vanes  together  resemble 
the  quill  split  down  one  side  and 
spread  out. 

The  teeth  of  Mollusks,  Worms, 
and  Arthropods  are  also  epidermal 
structures.  Those  of  Vertebrates  are 
mixed  in  their  origin,  the  dentine  be- 
ing derived  from  the  dermis  and  the 
enamel  from  the  epidermis.  In  all 
cases  teeth  belong  to  the  exoskeleton. 

(2)  The  Endoskeleton,  as  we  have 
seen,  is  represented  in  the  Cuttle- 
fish. With  this  and  some  other 
exceptions,  it  is  peculiar  to  Verte- 
brates. In  the  Cuttle-fish,  and  some  Fishes,  as  the  Stur- 
geon and  Shark,  it  consists  of  cartilage ;  but  in  all  others 
(when  adult)  it  is  bone  or  osseous  tissue.  Yet  there  is  a 
diversity  in  the  composition  of  bony  skeletons ;  that  of 
fresh-water  Fishes  contains  the  least  earthy  matter,  and 
that  of  Birds  the  most.  Hence  the  density  and  ivory- 


FIG.  105.— Parts  of  a  Fent  her : 
a,  quill,  or  barrel;  6,  shaft;  c, 
vane,  or  beard;  d,  accessory 
plume,  or  down ;  e,  f,  lower 
and  upper  umbilicus,  or  ori- 
fice, leading  to  the  interior 
of  the  quill. 


138  COMPARATIVE  ZOOLOGY. 

whiteness  of  the  bones  of  the  latter.  Unlike  the  shells  of 
Mollusks  and  the  crust  of  the  Lobster,  which  grow  by  the 
addition  of  layers  to  their  borders,  bones  are  moist,  living 
parts,  penetrated  by  blood-vessels  and  nerves,  and  covered 
with  a  tough  membrane,  called  periosteum,  for  the  attach- 
ment of  muscles. 

The  surface  of  bones  is  compact ;  but  the  interior  may 
be  solid  or  spongy  (as  the  bones  of  Fishes,  Turtles,  Sloths, 
and  Whales),  or  hollow  (as  the  long  bones  of  Birds  and 
the  active  quadrupeds).  There  are  also  cavities  (called 
"sinuses")  between  the  inner  and  outer  walls  of  the  skull, 
as  is  remarkably  shown  by  the  Elephant.  The  cavities  in 
the  long  bones  of  quadrupeds  are  filled  with  marrow ; 
those  in  the  long  bones  of  Birds  and  in  skulls  contain  air. 

The  number  of  bones  not  only  differs  in  different  ani- 
mals, but  varies  with  the  age  of  an  individual.  In  very 
early  life  there  are  no  bones  at  all;  and  ossification,  or 
the  conversion  of  cartilage  into  bone,  is  not  completed 
until  maturity.  This  process  begins  at  a  multitude  of 
points,  and  theoretically  there  are  as  many  bones  in  a 
skeleton  as  centres  of  ossification.  But  the  actual  number 
is  usually  much  less — a  result  of  the  tendency  of  these 
centres  to  coalesce.  Thus,  the  thigh-bone  in  youth  is 
composed  of  five  distinct  portions,  which  gradually  unite. 
So  in  the  lower  Vertebrates  many  parts  remain  distinct 
which  in  the  higher  are  joined  into  one.  The  occiput  or 
back-bone  of  Man's  skull  is  the  union  of  four  bones,  which 
are  seen  separate  in  the  skull  of  the  Fish,  or  of  a  baby. 

A  complete  skeleton,  made  up  of  all  the  pieces  which 
might  enter  into  its  composition,  does  not  exist.  Every 
Vertebrate  has  some  deficiency.  All,  except  Amphioxus, 
have  a  skull  and  back-bone;  but  in  the  development  of 
the  various  parts,  and  especially  of  the  appendages,  there 
is  endless  variety.  Fishes  possess  a  great  number  of  skull- 
bone.%  but  have  no  fingers  and  toes.  The  Snake  has  plenty 


THE   SKIN  AND   SKELETON. 


139 


of  ribs  and  tail,  but  no  breast-bone ;  the  Frog  has  a  breast- 
bone, but  neither  tail  nor  ribs.  As  the  skeleton  of  a  Fish 
is  too  complicated  for  the  primary  student,  we  will  select 
for  illustration  the  skeleton  of  a  Lion — the  type  of  quad- 


rupeds.     It  should  be  remembered,  however,  that  all  Ver- 
tebrates are  formed  on  one  plan. 

In  the  lowest  Vertebrate,  Amphioxus,  the  only  skeleton 
is  a  cartilaginous  rod  running  from  head  to  tail.  There  is 
no  skull,  nor  ribs,  nor  limbs.  In  the  cartilaginous  Fishes, 


140 


COMPARATIVE  ZOOLOGY. 


the  backbone  is  only  partially  ossified.  But  usually  it 
consists  of  a  number  of  separate  bones,  called  vertebrae,  ar- 
ranged along  the  axis  of  the  body.  They  range  in  number 
from  10  in  the  Frog  to  305  in  the  Boa-constrictor.  The 
skull,  with  its  appendages,  and  the  vertebrae,  with  the  ribs 
and  sternum,  make  up  the  axial  skeleton.  The  shoulder 
and  pelvic  girdles  and  the  skeleton  of  the  limbs  constitute 
the  appendicular  skeleton. 

A  typical  vertebra  consists  of  a  number  of  bony  pieces 
so  arranged  as  to  form  two  arches,  or  hoops,  connected  by 


FIG.  107. — Vertebrae — A,  cervical ;  B,  dorsal ;  2,  centrum  •  4,  transverse  process,  con- 
taining foramen,  a,  for  artery;  5,  articular  process;  3,  spiuous  process,  or  neural 
spine  ;  1,  neural  canal ;  6,  facets  for  head  of  rib,  the  tubercle  of  the  rib  fitting  in 
a  facet  on  the  process,  4 ;  6,  laminae,  or  neurapophyses. 

a  central  bone,  or  centrum.'16  The  upper  hoop  is  called 
the  neural  arch,  because  it  encircles  the  spinal  marrow ; 
the  lower  hoop  is  called  the  haemal  arch,  because  it  en- 
closes the  heart  and  the  great  central  blood-vessels.  An 
actual  vertebra,  however,  is  subject  to  so  many  modifica- 
tions, that  it  deviates  more  or  less  from  this  ideal  type. 
Selecting  one  from  the  middle  of  the  back  for  an  exam- 
ple, we  see  that  the  centrum  sends  off  from  its  dorsal  side 
two  branches,  or  processes,  called  neurapophyses.  These 
meet  to  form  the  neural  arch,  under  which  is  the  neural 
canal,  and  above  which  is  a  process  called  the  neural 
spine.  On  the  anterior  and  posterior  edges  of  the  arch 
are  smooth  surfaces,  or  zygapophyses,  which  in  the  natural 
state  are  covered  with  cartilage,  and  come  in  contact  with 


THE  SKIN  AND  SKELETON.  141 

the  corresponding  surfaces  of  the  preceding  and  succeed- 
ing vertebrae.  The  bases  of  the  arch  are  notched  in  front 
and  behind,  so  that  when  two  vertebrae  are  put  together  a 
round  opening  (intervertebral  foramen)  appears  between 
the  pair,  giving  passage  to  the  nerves  issuing  from  the 
spinal  cord.  From  the  sides  of  the  arch,  blunt  transverse 
processes  project  outward  and  backward,  called  diapophy- 
ses.  Such  are  the  main  elements  in  a  representative  ver- 
tebra. The  haemal  arch  is  not  formed  by  any  part  of  the 
vertebra,  but  by  the  ribs  and  breast-bone.  Theoretically, 
however,  the  ribs  are  considered  as  elongated  processes 
from  the  centrum  (pleurapophyses),  and  in  a  few  cases  a 
hcemal  spine  is  developed  corresponding  to  the  neural 
spine. 

The  vertebrae  are  united  together  by  ligaments,  but 
chiefly  by  a  very  tough,  dense,  and  elastic  substance  be- 
tween the  centra.  The  neural  arches  form  a  continuous 
canal  which  contains  and  protects  the  spinal  cord ;  hence 
the  vertebral  column  is  called  the  neuroskeleton.  The 
column  is  always  more  or  less  curved ;  but  the  beautiful 
sigmoid  curvature  is  peculiar  to  Man.  The  vertebrae 
gradually  increase  in  size  from  the  head  towards  the  end 
of  the  trunk,  and  then  diminish  to  the  end  of  the  tail. 
The  neural  arch  and  centrum  are  seldom  wanting;  the 
first  vertebra  in  the  neck  has  no  centrum,  and  the  last  in 
the  tail  is  all  centrum.  The  vertebrae  of  the  extremities 
(head  and  tail)  depart  most  widely  from  the  typical  form. 

The  vertebral  column  in  Fishes  and  Snakes  is  divisible 
into  three  regions  —  head,  trunk,  and  tail.  But  in  the 
higher  animals  there  are  six  kinds  of  vertebrae :  cranial, 
cervical,  dorsal,  lumbar,  sacral,  and  caudal. 

The  cranial  vertebra  form  the  skull."  They  are  greatly 
modified,  as  the  neural  arches  are  expanded  to  enclose  the 
brain.  The  number  of  distinct  bones  composing  the  skull 
is  greatest  in  Fishes,  and  least  in  Birds :  this  arises  partly 


^COMPARATIVE  ZOOLOGY. 


THE  SKIN  AND  SKELETON.  143 


BONES  OF  THE  MAMMALIAN  SKULL  * 


BRAIN-CASE. 


\ASAL. 


LAC  HRYMAL.  SQUAMOSAL. 


NOSE. 


ETHMOID. 


SUPRA  OCCIPITAL. 


ORBITOSPHENOID.  EYE.  ALISPHENOID.    PERI-  EAR.  OTIC.     EXOCCIPITAL. 

MALAR.  TYMPANIC. 

PRESPHENOID.  BASISPHENOID.  BASIOCCIPITAL. 


VOMER.  HYOID  ARCH. 

PREMAXILLA.        MAXILLA.        PALATINE.        PTERYGOID. 
LOWER  JAW,  OR  MANDIBLE. 


THE  SKULL  OF  THE  DOG. 

Fio.  108.— Under  surface.  FIG.  109.— Upper  surface.  FIG.  110.— Longitudinal  ver- 
tical section ;  one-half  natural  size :  SO,  supraoccipital ;  ExO,  exoccipital ;  BO, 
basioecipital ;  IP,  interparietal ;  Pa,  parietal ;  Fr,  frontal ;  Sq,  squamosal ;  Ma, 
malar;  L,  lachrymal ;  MX,  maxilla  ;  PMx,  premaxilla ;  ^a,  nasal ;  MT,  maxillo- 
turbinal:  ET,  ethmoturbinal ;  ME,  ossitied  portion  of  the  mesethmoid;  CE,  cri- 
briform, or  sieve-like,  plate  of  the  ethmoturbinal ;  VO,  vomer ;  PS,  presphenoid ; 
OS,  orbitosphenoid ;  AS,  alisphenoid ;  BS,  basisphenoid ;  PI,  palatine;  Pt, 
pterygoid  ;  Per,  periotic  ;  Ty,  tympanic  bnlla  ;  an,  anterior  narial  aperture ;  ap, 
or  apf,  anterior  palatine  foramen ;  ppf,  posterior  palatine  foramen ;  to,  infra- 
orbital  foramen ;  pof,  postorbital  process  of  frontal  bone  ;  op,  optic  foramen  ;  sf, 
sphenoidal  fissure ;  ft;  foramen  rotnndum,  and  anterior  opening  of  alisphenoid 
canal;  as,  posterior  opening  of  alisphenoid  canal ;  fo,  foramen  ovale  ;  Jim,  fora- 
men lacerum  medium;  of,  glenoid  fossa;  gp,  postglenoid  process;  pgf,  post- 
glenoid  foramen  ;  earn,  external  auditory  meatus ;  sm,  stylomastoid  foramen ; 
flp,  foramen  lacerum  posterius  ;  cf,  coudylar  foramen  ;  pp,  paroccipital  process ; 
oc,  occipital  coudyle ;  fm,  foramen  magnum ;  a,  angular  process ;  s,  eymphyeis  of 
the  mandible  where  it  unites  with  the  left  ramns ;  id,  inferior  dental  canal ;  cd, 
condyle ;  cp,  coronoid  process ;  the  *  indicates  the  part  of  the  cranium  to  which 
the  condyle  is  articulated  when  the  mandible  is  in  place ;  the  upper  border  in 
which  the  teeth  are  implanted  is  called  alveolar;  sh,  eh,  ch,  6ft,  th,  hyoidean  ap- 
paratus, or  os  linguae,  supporting  the  tongue.  In  the  skulls  of  old  animals, 
there  are  three  ridges:  occipital,  behind;  sagittal, median,  on  the  upper  surface; 
and  super  orbital,  across  the  frontal,  in  the  region  of  the  eyebrows.  The  last  is 
highly  developed  in  the  Gorilla  and  other  Apes. 


*  In  this  diagram,  modified  from  Huxley's,  the  italicized  bones  are  single ;  the 
rest  are  double.  Those  in  the  line  of  the  Ethmoid  form  the  Cranio -facial  Axis; 
these,  with  the  other  sphenoids  and  occipitals,  are  developed  in  cartilage ;  the  rest 
are  membrane  bones.  In  the  Human  skull,  the  four  occipitals  coalesce  into  one. 


144 


COMPARATIVE  ZOOLOGY. 


from  the  fact  that  the  bones  remain  separate  in  the  for- 
mer case,  while  those  of  the  chick  become  united  together 
(anchylosed)  in  the  full-grown  Bird ;  but  many  bones  are 
present  in  the  Fish  which  have  no  representatives  in  the 
Bird.  The  skull  consists  of  the  brain-case  and  the  face. 
The  principal  parts  of  the  skull,  as  shown  in  the  Dog's, 
are:  1.  The  occipital  bones  behind,  enclosing  a  large  hole, 
or  foramen  magnum,  on  each  side  of  which  are  rounded 
prominences,  called  condyles,  by  which  the  skull  articulates 
with  the  first  cervical  vertebra.  2.  The  parietal.  3.  The 
frontal.  These  three  form  the  main  walls  of  the  brain. 
4.  The  sphenoid,  on  the  floor  of  the  skull  in  front  of  the 
occipital,  and  consisting  of  six  pieces.  5.  The  temporal, 
in  which  is  situated  the  ear.  In  Man  this  is  one  bone; 
but  in  most  animals  there  are  three  or  more — thepe^iotic, 
tympanic,  and  squamosal.  6.  The  malar,  or  "  cheek-bone," 
which  sends  back  a  process  to  meet  one  from  the  squamo- 
sal,  forming  the  zygomatic  arch.  7.  The  nasal,  or  roof  of 


PIG.  111. —Skull  of  the  Horse:  1,  premaxillary  bone;  2,  upper  incisors;  3,  upper 
canines;  4,  superior  maxillary;  5,  infrnorbital  foramen;  6,  superior  maxillary 
spine;  7,  nasal  bones;  8,  lachrymal;  9,  orbital  cavity;  10,  lachrymal  fossa;  11, 
malar;  12,  upper  molars;  13,  frontal;  15,  zygomatic  arch;  16,  parietal;  IT,  oc- 
cipital protuberance;  18,  occipital  crest;  19,  occipital  condyles;  20,  styloid  proc- 
esses; 21,  petrous  bone;  22,  basilar  process;  23,  condyle  of  inferior  maxillary; 
24,  parietal  crest;  25,  inferior  maxillary;  26,  lower  molars;  27,  anterior  maxillary 
foramen ;  28,  lower  canines ;  29,  lower  iucieors. 


THE  SKIN  AND  SKELETON.  145 

the  nose.  8.  The  maxilla;  that  part  of  the  upper  jaw  iu 
which  the  canines,  premolars,  and  molars  are  lodged.  9. 
The  premaxilla,  in  which  the  upper  incisors  are  situated. 
10.  The  palatine,  which,  with  the  maxillary  bones,  forms 
the  roof  of  the  mouth.  There  are  two  appendages  to  the 
skull :  the  mandible,  or  lower  jaw,  whose  condyles,  or 
rounded  extremities,  fit  into  a  cavity  (the  glenoid)  in  the 
temporal  bone ;  and  the  hyoid,  situated  at  the  root  of  the 
tongue. 

The  simplest  form  of  the  skull  is  a  cartilaginous  box, 
as  in  Sharks,  enclosing  the  brain  and  supporting  the  car- 
tilaginous jaws  and  gill  arches.  In  higher  Fishes  this  box 
is  overlaid  with  bony  plates  and  partly  ossified.  In  Frogs 
the  skull  is  mainly  bony,  although  a  good  deal  of  the  car- 
tilage remains  inside  the  bones.  In  higher  Vertebrates  the 
cartilage  never  makes  an  entire  box,  and  early  disappears. 

The  cervical  vertebra?,,  or  bones  of  the  neck,  are  peculiar 
in  having  an  orifice  on  each  side  of  the  centrum  for  the 
passage  of  an  artery.  The  first,  called  atlas,  because  it 
supports  the  head,  has  no  centrum,  and  turns  on  the  sec- 
ond, called  axis,  around  a  blunt  process,  called  the  odon- 
toid. The  centra  are  usually  wider  than  deep,  and  the 
neural  spines  very  short,  except  in  the  last  one.  The 
number  of  cervical  vertebrae  ranges  from  1  in  the  Frog 
to  25  in  the  Swan. 

The  dorsal  vertebras,  are  such  as  bear  ribs,  which,  unitino- 

o 

with  the  breast-bone,  or  sternum,  form  a  bony  arch  over 
the  heart  and  lungs,  called  the  thorax.  The  sternum  may 
be  wanting,  as  in  Fishes  and  Snakes,  or  greatly  developed, 
as  in  Birds.  "When  present,  the  first  vertebra  whose  ribs 
are  connected  with  it  is  the  first  dorsal.  The  neural  spines 
of  the  dorsal  series  are 'generally  long,  pointing  backward. 

The  lumbar  vertebrae,  are  the  massive  vertebrae  lying  in 
the  loins  between  the  dorsals  and  the  hip-bones. 

The  sacral  vertebrae,  lie  between  the  hip-bones,  and  are 

10 


146  COMPARATIVE   ZOOLOGY. 

generally  consolidated  into  one  complex  bone,  called  sa- 
crum. 

The  caudal  vertebrae  are  placed  behind  the  sacrum,  and 
form  the  tail.  They  diminish  in  size,  losing  processes  and 
neural  arch,  till  finally  nothing  is  left  but  the  centrum. 
They  number  from  3  or  4  in  Man  to  270  in  the  Shark. 

Besides  the  lower  jaw,  hyoid,  and  ribs,  Vertebrates 
have  other  appendages  to  the  spinal  column — two  pairs 
of  limbs.™  The  fore  limb  is  divided  into  the  pectoral 
arch  (or  shoulder  girdle),  the  arm,  and  the  hand.  The 
arch  is  fastened  to  the  ribs  and  vertebrae  by  powerful 
muscles,  and  consists  of  three  bones,  the  scapula,  or  shoul- 
der-blade, the  coracoid,  and  the  clavicle,  or  collar-bone. 
The  scapula  and  coracoid  are  generally  united  in  Mam- 
mals, the  latter  forming  a  process  of  the  former ;  and  the 
clavicles  are  frequently  wanting,  as  in  the  hoofed  animals. 
The  humerus,  radius,  and  ulna  are  the  bones  of  the  arm, 
the  first  articulating  by  ball-and-socket  joint  with  the 
scapula,  and  by  a  hinge-joint  with  the  radius  and  ulna. 
The  humerus  and  radius  are  always  present,  but  the  ulna 
may  be  absent.  The  bones  of  the  hand  are  divided  into 
those  of  the  carpus,  or  wrist ;  the  metacarpus,  or  palm : 
and  the  phalanges,  or  fingers.  The  fingers,  or  "  digits," 
range  in  number  from  1  to  5. 

The  hind  limb  is  composed  of  the  pelvic  arch  (or  hip- 
bones), the  leg,  and  the  foot.  These  parts  correspond 
closely  with  the  skeleton  of  the  fore  limb.  Like  the 
shoulder,  the  pelvic  arch,  or  os  innominatum,  consists  of 
three  bones — ilium,  ischium,  and  pubis.  The  three  are 
distinct  in  Amphibians,  Reptiles,  and  in  the  young  of 
higher  animals;  but  in  adult  Birds  and  Mammals  they 
become  united  together,  and  are  also  (except  in  Whales) 
solidly  attached  to  the  sacrum.  The  two  pelvic  arches 
and  the  sacrum  thus  soldered  into  one  make  the  pelvis. 
The  leg-bones  consist  of  the  femur,  or  thigh;  the  tibia,  or 


THE  SKIN   AND   SKELETON. 


147 


shin-bone ;  and  the  fibula,  or  splint-bone.  The  rounded 
head  of  the  femur  tits  into  a  cavity  (acetabulum)  in  the 
pelvic  arch,  while  the  lower  end  articulates  with  the  tibia, 
and  sometimes  (as  in  Birds)  with  the  fibula  also.  An  ex- 
tra bone,  t\\Q  patella,  or  knee-pan,  is  hung  in  a  tendon  in 
front  of  the  joint  between  the  femur  and  tibia  of  the  high- 
er animals.  The  foot  is  made  up  of  the  tarsus,  or  ankle  ; 
the  metatarsus,  or  lower  instep ;  and  the  phalanges,  or 
toes.  The  toes  number  from  1  in  the  Horse  to  5  in  Man. 
Certain  parts  of  the  skeleton,  as  of  the  skull,  are  firmly 
joined  together  by  zigzag  edges  or  by  overlapping;  in 
either  case  the  joint  is  called  a  suture.  But  the  great 
majority  of  the  bones  are  intended  to  move  one  upo*n  an- 
other. The  vertebrae  are  locked  together  by  their  proc- 
esses, and  also  by  a  tough  fibrous  substance  between  the 
centra,  so  that  a  slight  motion  only  is  allowed.  The  limbs 
furnish  the  best  examples  of  movable  articulations,  as  the 
ball-and-socket  joint  at  the  shoulder,  and  the  hinge-joint 
at  the  elbow.  The  bones  are  held  together  by  ligaments, 
and,  to  prevent  friction,  the  extremities  are  covered  with 
cartilage,  which  is  constantly  lubricated  with  an  unctuous 
fluid  called  synovia. 

CHEMICAL  COMPOSITION  OF  BONES. 


COB. 

TORTOIBK. 

HAWK. 

MAN. 

Phosphate  of  Lime,  with  trace  of 
Fluate  of  Lime  

57  29 

52  66 

64  39 

59  63 

Carbonate  of  Lime  

4  90 

12  53 

7  03 

7  33 

Phosphate  of  Magnesia  

2.40 

0  82 

0  94 

1.32 

Sulphate,  Carbonate,  and  Chlorate 
of  Soda  

1  10 

0  90 

0  92 

0  69 

Glutine  and  Chondrine  

32  31 

31  75 

25.73 

29.70 

Oil  

2.00 

1  34 

0  99 

1.33 

100.00 

100.00 

100.00 

100.00 

148 


COMPARATIVE  ZOOLOGY. 


THE  SKIN  AND  SKELETON. 


149 


150 


COMPARATIVE  ZOOLOGY. 


FIG.  115.— Skeleton  of  the  Tortoise  (plastron 
sal  vertebrae ;  d,  ribs;  e,  marginal  bones 
coid  ;  &,  coracoid ;  /,  pelvis ;  i,  femur 


removed) :  a,  cervical  vertebrae ;  c,  dor- 
of  the  carapace ;  I,  scapula ;  k,  precora- 
',  tibia  ;  h,  fibula. 


FIG.  116. — Skeleton  of  aVnltnre:  1,  cranium — the  parts  of  which  are  separable  only 
in  the  chick;  2,  cervical  vertebrae ;  3,  dorsal ;  4,  coccygeal,  or  caudal ;  the  lumbar 
and  sacral  are  consolidated;  5,  ribs;  6,  sternum,  or  breast-bone,  extraordinarily 
developed;  7,  furculum,  clavicle,  or  "wish-bone;"  3,  coracoid;  9,  scapula ;  10, 
humeniS'.  11,  ulna,  with  rudimentary  radius;  12,  metacarpals ;  13,  phalanges  of 
the  great  digit  of  the  wing;  19,  thumb;  14,  pelvis;  15,  femur;  16,  tibia-tarsus  and 
fibula,  or  cms;  17,  tarso-metatai>us ;  18,  internal  digit,  or  toe,  formed  of  three 
phalanges ;  the  middle  toe  has  four  phalanges  ;  the  outer,  five ;  and  the  back  toe, 
or  thumb,  two. 


THE  SKIN  AND  SKELETON. 


151 


G    S 


FIG.  117.— Skeleton  of  the  Horse  (Equus  cdballus) :  22,  premaxillary ;  12,  foramen  in 
the  maxillary ;  15,  nasal ;  9,  orbit ;  19,  coronoid  process  of  lower  jaw ;  17,  surface 
of  implantation  for  the  masseter  muscle ;  there  are  seven  cervical  vertebrae,  nine- 
teen dorsal,  D-D;  five  lumbar,  a-e;  five  sacral,  f-l;  and  seventeen  caudal,  p-r; 
51,  scapula,  or  shoulder-blade ;  i,  spine,  or  crest ;  k,  coracoid  process  (acromion 
wanting) ;  1,  first  pair  of  ribs  (clavicle  wanting,  as  in  all  Ungulates) ;  e,  sternum : 
a,  shaft  of  humerus;  6,  deltoid  ridge ;  #,  head  fitting  in  the  glenoid  cavity  of  the 
scapula— near  it  is  a  great  tuberosity  for  the  attachment  of  a  powerful  muscle ; 
jfc,  condyles  ;  54,  radius,  to  which  is  firmly  anchylosed  a  rudimentary  ulna,  55,  the 
olecranon  •  56,  the  seven  bones  of  the  carpus,  or  wrist ;  57,  large  metacarpal,  or 
"  cannon-bone,"  with  two  "  splint-bones ;"  58,  fetlock-joint ;  59,  phalanges  of  the 
developed  digit,  corresponding  to  the  third  finger  in  Man ;  62,  pelvis ;  63,  the 
great  trochanter,  or  prominence  on  the  femur,  65 ;  66,  tibia ;  67,  rudimentary 
fibula;  68,  hock,  or  heel,  falsely  called  kuee;  69,  rnetatarsals. 


152 


COMPARATIVE  ZOOLOGY. 


FIG.  118.— Skeleton  of  the  Cow  (Bos  taurus). 


FIG.  119.— Skeleton  of  an  Elephant  (Elephas  Tndicus). 


THE  SKIN  AND  SKELETON. 


153 


Fio.  120.— Skeleton  of  the  Chimpanzee  (Troglodytes  Niger). 


154:  COMPARATIVE  ZOOLOGY. 


CHAPTER  XVII. 

HOW    ANIMALS    MOVE. 

1.  THE  power  of  animal  motion  is  vested  in  protoplasm, 
cilia,  and  muscles.  The  power  of  contractility  is  one  of 
the  ultimate  physiological  properties  of  protoplasm,  like 
sensibility  and  the  power  of  assimilation.  Protoplasma- 
animals,  like  the  Amoeba  and  Rhizopoda,  move  by  the 
contractility  of  their  protoplasm,  as  also  may  the  germs 
of  higher  animals  upon  the  yolk  of  the  egg.  The  proto- 
plasm may  be  extended  into  projections  c&\]edpseudopodia, 
by  whose  contraction  the  animal  may  mpve  (Fig.  186). 

Infusoria,  and  nearly  all  higher  animals,  possess  cilia 
(Fig.  188).  These  are  microscopic  hairs  (Fig.  2,  b)  which 
have  the  power  of  bending  into  a  sickle-shape  and  straight- 
ening out.  As  they  bend  much  faster  than  they  straight- 
en, and  as  they  all  work  together,  they  can  cause  motion 
of  the  animal,  or  may  serve  to  produce  currents  in  the 
water,  the  animal  remaining  at  rest.  They  are  seen  on 
the  outside  of  Infusoria,  and  of  very  many  embryos  of 
higher  animals,  serving  as  paddles  for  locomotion  ;  they 
fringe  the  gills  of  the  Oyster,  creating  currents  for  respi- 
ration; and  they  line  the  passage  to  our  lungs  to  expel 
the  mucus.  Flagella  (Fig.  189)  are  a-  sort  of  long  cilia, 
which  are  thrown  into  several  curves  when  active,  resem- 
bling a  whip-lash,  whence  their  name.  Both  cilia  and  fla- 
gella  seem  to  be  wanting  in  Arthropods. 

The  cause  of  ciliary  motion  is  unknown.  Their  one- 
sided contraction  is  their  property,  as  the  straight  con- 
traction of  the  muscle-fibre  belongs  to  it.  No  structure 
can,  however,  be  seen  in  them  with  the  microscope.  No 


HOW  ANIMALS  MOVE.  155 

nerves  go  to  them,  yet  they  work  in  concert,  waves  of 
motion  passing  over  a  surface  covered  with  cilia,  as  over 
a  field  of  grain  moved  by  the  wind. 

But  muscular  tissue  is  the  great  motor  agent,  and  exists 
in  all  animals  from  the  Coral  to  Man.79  The  power  of 
contractility,  which  in  the  Amoeba  is  diffused  throughout 
the  body,  is  here  confined  to  bundles  of  highly  elastic 
fibres,  called  muscles.  When  a  muscle  contracts,  it  tends 


FIG.  121—  A  Contracting  Muscle. 

to  bring  its  two  ends  together,  thus  shortening  itself,  at 
the  same  time  increasing  in  thickness.  This  shrinking 
property  is  excited  by  external  stimulants,  such  as  elec- 
tricity, acids,  alkalies,  sudden  heat  or  cold,  anu  even  a 
sharp  blow;  but  the  ordinary  cause  of  contraction  is  an 
influence  from  the  brain  conveyed  by  a  nerve.  The  prop- 
erty, however,  is  independent  of  the  nervous 
system,  for  the  muscle  may  be  directly  stim- 
ulated. The  amount  of  force  with  which  a 
muscle  contracts  depends  on  the  number  of 
its  fibres;  and  the  amount  of  shortening,  on 
their  length. 

As  a  rule,  muscles  are  white  in  cold-blooded 
animals,  and  red  -in  the  warm-blooded.  They 
are  white  in  all  the  Invertebrates,  Fishes, 
Batrachians,  and  Keptiles,  except  Salmon, 
Sturgeon,  and  Shark  ;  and  red  in  Birds  and 
Mammals,  except  in  the  breast  of  the  com-  FlgGt'r 


lllOn  fowl,  and  the  like.80  larFibre,much 

,  .  .  enlarged;    n, 

It  is  also  a  rule,  with  some  exceptions,  that      nucleus. 
the  voluntary  muscles  of  Vertebrates,  and  all  the  muscles 


156  COMPARATIVE  ZOOLOGY. 

of  the  Lobster,  Spider,  and  Insect  tribes,  are  striated ;  while 
the  involuntary  muscles  of  Vertebrates,  and  all  the  muscles 
of  Radiates,  Worms,  and  Mollusks,  are  smooth.  All  mus- 
cles attached  to  internal  bones,  or  to  a  jointed  external 
skeleton,  are  striated.  The  voluntary  muscles  of  Verte- 
brates are  generally  solid,  and  the  involuntary  hollow.81 

This  leads  to  another  classification  of  muscles :  into 
those  which  are  attached  to  solid  parts  within  the  body; 
those  which  are  attached  to  the  skin  or  its  modifications; 
and  those  having  no  attachments,  being  complete  in  them- 
selves. The  last  are  hollow  or  circular  muscles,  enclosing 
a  cavity  or  space,  which  they  reduce  by  contraction.  Ex- 
amples of  such  are  seen  in  the  heart,  blood-vessels,  stom- 
ach, iris  of  the  eye,  and  around  the  mouth.  In  the  lower 
Invertebrates,  the  muscular  system  is  a  net-work  of  longi- 
tudinal, transverse,  and  oblique  fibres  intimately  blended 
with  the  skin,  and  not  divisible  into  separate  muscles.  As 
in  the  walls  of  the  human  stomach,  the  fibres  are  usually 
in  three  distinct  layers.  This  arrangement  is  exhibited  by 
soft-bodied  animals,  like  the  Sea-anemone,  the  Snail,  and 
the  Earth-worm.  Four  thousand  muscles  have  been  count- 
ed in  a  Caterpillar.  There  are  also  "skin-muscles"  in 
the  higher  animals,  as  those  by  which  the  Horse  produces 
a  twitching  of  the  skin  to  shake  off  insects,  and  those  by 
which  the  hairs  of  the  head  and  the  feathers  of  Birds  are 
made  to  stand  on  end.  Invertebrates  whose  skin  is  hard- 
ened into  a  shell  or  crust  have  muscles  attached  to  the 
inside  of  such  a  skeleton.  Thus,  the  Oyster  has  a  mass 
of  parallel  fibres  connecting  its  two  valves ;  while  in  the 
Lobster  and  Bee  fibres  go  from  ring  to  ring,  both  longi- 
tudinally and  spirally.  The  muscles  of  all  Invertebrates 
are  straight  parallel  fibres,  not  in  bundles,  but  distinct, 
and  usually  flat,  thin,  and  soft. 

The  great  majority  of  the  muscles  of  Vertebrates  are 
attached  to  the  bones,  and  such  are  voluntary.  The  fibres, 


HOW  ANIMALS  MOVE.  157 

which  are  coarsest  in  Fishes  (most  of  all  in  the  Kays),  and 
finest  in  Birds,  are  bound  into  bundles  by  connective  tis- 
sue; and  the  muscles  thus  made  up  are  arranged  in  layers 
around  the  skeleton.  Sometimes  their  extremities  are  at- 
tached to  the  bones  (or  rather  to  the  periosteum)  directly ; 
but  generally  by  means  of  white  inelastic  cords,  called 
tendons.  In  Fishes,  the  chief  masses  of  muscle  are  dis- 
posed along  the  sides  of  the  body,  apparently  in  longitu- 
dinal bands,  reaching  from  head  to  tail,  but  really  in  a 
series  of  vertical  flakes,  one  for  each  vertebra.  In  propor- 
tion as  limbs  are  developed,  we  find  the  muscles  concen- 
trated about  the  shoulders  and  hips,  as  in  quadrupeds. 
The  bones  of  the  limbs  are  used  as  levers  in  locomotion, 
the  fulcrum  being  the  end  of  a  bone  with  which  the  mov- 
ing one  is  articulated.  Thus,  in  raising  the  arm,  the  hu- 
merus  is  a  lever  working  upon  the  scapula  as  a  fulcrum. 
The  most  important  muscles  are  called  extensors  and  flex- 
ors. The  latter  are  such  as  bring  a  bone  into  an  angle 
with  its  fulcrum — as  in  bending  the  arm — while  the  for- 
mer straighten  the  limb.  Abductors  draw  a  limb  away 
from  the  middle  line  of  the  body,  or  a  finger  or  toe  away 
from  the  axis  of  the  limb,  while  adductors  bring  them  back. 

2.  Locomotion. — All  animals  have  the  power  of  vol- 
untary motion,  and  all,  at  one  time  or  another,  have  the 
means  of  moving  themselves  from  place  to  place.  Some 
are  free  in  the  embryo-life,  and  fixed  when  adult,  as  the 
Sponge,  Coral,  Crinoid,  and  Oyster.  There  may  be  no 
regular  well-defined  means  of  progression,  as  in  the  Amoe- 
ba, which  extemporizes  arms  to  creep  over  the  surface ; 
or  movement  may  be  accomplished  by  the  contraction  of 
the  whole  body,  as  in  the  Jelly-fish,  which,  pulsating  about 
fifteen  times  in  a  minute,  propels  itself  through  the  water. 
So  the  Worms  and  Snakes  swim  by  the  undulations  of  the 
body. 

But,  as  a  rule,  animals  are  provided  with  special  organi 


158  COMPARATIVE  ZOOLOGY. 

for  locomotion.  These  become  reduced  in  number,  and 
progressively  perfected,  as  we  advance  in  the  scale  of 
rank.  Thus,  the  Inf  usorian  is  covered  with  thousands  of 
hair-like  cilia ;  the  Star-fish  has  hundreds  of  soft,  unjoint- 
ed,  tubular  suckers;  the  Centipede  has  from  30  to  40 
jointed  hollow  legs ;  the  Lobster,  10 ;  the  Spider,  8 ;  and 
the  Insect,  6 ;  the  Quadruped  has  4  solid  limbs  for  loco- 
motion ;  and  Man,  only  2. 

( 1 )  Locomotion  in  Water. — As  only  the  lower  forms  of 
life  are  aquatic,  and  as  the  weight  of  the  body  is  partly 
sustained  by  the  element,  we  must  expect  to  find  the  or- 
gans of  progression  simple  and  feeble.  The  Infusoria 
swim  with  great  rapidity  by  the  incessant  vibrations  of 
the  delicate  filaments,  or  cilia,  on  their  bodies.  The  com- 
mon Squid  on  our  coast  admits  water  into  the  interior  of 
the  body,  and  then  suddenly  forces  it  out  through  a  fun- 
nel, and  thus  moves  backward,  or  forward,  or  around,  ac- 
cording as  the  funnel  is  turned — towards  the  head,  or  tail, 
or  to  one  side.  The  Lobster  has  a  fin  at  the  end  of  its 
tail,  and  propels  itself  backward  by  a  quick  down-stroke 
of  the  abdomen. 

But  Fishes,  whose  bodies  offer  the  least  resistance  to 
progression  through  water,  are  the  most  perfect  swimmers. 
Thus,  the  Salmon  can  go  twenty  miles  an  hour,  and  even 


FIG.  123.— The  Fins  of  a  Fish  (Pike-perch). 

ascend  cataracts.     They  have  fins  of  two  kinds :  those  set 
obliquely  to  the  body,  and  in  pairs ;  and  those  which  are 


HOW  ANIMALS  MOVE.  159 

vertical,  and  single.  The  former,  called  pectoral  and  ven- 
tral fins,  represent  the  fore  and  hind  limbs  of  Quadrupeds. 
The  vertical  fins,  which  are  only  expansions  of  the  skin, 
vary  in  number;  but  in  most  Fishes  there  are  at  least 
three :  the  caudal,  or  tail-fin  ;  the  dorsal,  or  back-fin  ;  and 
the  anal,  situated  on  the  abdomen, 
near  the  tail.  The  chief  locomotive 
agent  is  the  tail,  which  sculls  like  a 
stern-oar ;  the  other  fins  are  mainly 
used  to  balance  and  raise  the  body. 
When  the  two  lobes  of  the  tail  are 
equal,  and  the  vertebral  column  stops 
near  its  base,  as  in  the  Trout,  it  is  said 
to  be  homocercal.  If  the  vertebrae 
extend  into  the  upper  lobe,  making 
it  longer  than  the  lower  one,  as  in 
the  Shark,  the  tail  is  called  hetero- 

7        rr,i       i    ,          •     ,v  re  FIG.  124. -Diagram  illustrat- 

cercal.  The  latter  is  the  more  eilec-  ing  the  locomotion  of  a 
tive  for  varying  the  course;  the 
Shark,  e.  g.,  will  accompany  and 
gambol  around  a  ship  in  full  sail  in  front, 
across  the  Atlantic.  The  Whale  swims  by  striking  the 
water  up  and  down,  instead  of  laterally,  with  a  fin-like 
horizontal  tail.  Many  air-breathing  animals  swim  with 
facility  on  the  surface,  as  the  Water-birds,  having  webbed 
toes,  and  most  of  the  Reptiles  and  Quadrupeds. 

(2)  Locomotion  in  Air. — The  power  of  flight  requires  a 
special  modification  of  structure  and  an  extraordinary 
muscular  effort,  for  air  is  800  times  lighter  than  water. 
Nevertheless,  the  velocity  attainable  by  certain  Birds  is 
greater  than  that  of  any  Fish  or  Quadruped;  the  Hawk 
being  able  to  go  at  the  rate  of  150  miles  an  hour.  The 
bodies  of  Insects  and  Birds  are  made  as  light  as  possible 
by  the  distribution  of  air-sacs  or  air-cavities.82 

The  wings  of  Insects  are  generally  four  in  number; 


160 


COMPARATIVE  ZOOLOGY. 


sometimes  only  two,  as  in  the  Fly.  They  are  moved  by 
muscles  lying  inside  the  thorax.  They  are  simple  expan 
sions  of  the  skin,  or  crust,  being  composed  of  two  delicate 
films  of  the  epidermis  stretched  upon  a  net-work  of  tubes. 
There  are  three  main  varieties:  thin  and  transparent,  as 
in  the  Dragon-fly ;  opaque,  and  covered  with  minute  col- 
ored scales,  which  are  in  reality  flattened  hairs,  as  in  the 
Butterfly ;  and  hard  and  opaque,  as  the  first  pair  (called 
elytra)  of  the  Beetle. 

The  wings  of  Birds,  on  the  other  hand,  are  modified 
fore-limbs,  consisting  of  three  sets  of  feathers  (called  pri- 
mary^ secondary,  and  tertiary),  inserted  on  the  hand,  fore- 
arm, and  arm.  The  muscles  which  give  the  downward 
stroke  of  the  wing  are  fastened  to  the  breast-bone ;  and 
their  power,  in  proportion  to  the  weight  of  the  Bird,  is 
very  great.  Yet  the  Insect  is  even  superior  in  vigor  and 
velocity  of  flight.83  In  ascending,  the  Bird  slightly  rotates 
the  wing,  striking  downward  and  a  little  backward  ;  while 
the  tail  acts  as  a  rudder.  A  short,  rounded,  concave  wing, 
as  in  the  common  Fowl,  is  not  so  well  fitted  for  high  and 
prolonged  flight  as  the  long,  broad,  pointed,  and  flat  wing 


FIG.  125.— Flamingoes  taking  Wing. 

of  the  Eagle.  The  wing  is  folded  by  means  of  an  elastic 
skin  and  muscle  connecting  the  shoulder  and  wrist.  Be- 
sides Insects  and  Birds,  a  few  other  animals  have  the  power 


HOW  ANIMALS  MOVE.  161 

of  flight,  as  Bats,  by  means  of  long-webbed  fingers ;  Fly- 
ing Fishes,  by  large  pectoral  fins.  Flying  Keptiles,  Flying 
Squirrels,  and  the  like,  have  a  membrane  stretched  on  the 
long  ribs,  or  connecting  the  fore  and  hind  limbs,  which  they 
use  as  a  parachute,  enabling  them  to  take  very  long  leaps. 

(3)  Locomotion  on  Solids.  —  This  requires  less  muscular 
effort  than  swimming  or  flying.  The  more  unyielding 
the  basis  of  support,  the  greater  the  amount  of  force  left 
to  move  the  animal  along.  The  simplest  method  is  the 
suctorial,  the  animal  attaching  itself  to  some  fixed  object, 
and  then,  by  contraction,  dragging  the  body  onward.  But 
the  higher  and  more  common  method  is  by  the  use  of 
bones,  or  other  hard  parts,  as  levers. 

The  Star -fish  creeps  by  the  working  of  hundreds  of 
tubular  suckers,  which  are  extended  by  being  filled  with 


FIG.  126.— Diagrammatic  section  of  Star-fish:  a,  month;  &,  stomach;  c,  hepatic  c$e- 
cnm ;  cf,  dorsal  or  aboral  surface ;  e,  ambulacra!  plates ;  /,  ovary  ;  g,  tubular  feet ; 
A,  internal  sacs  for  extending  the  feet. 

fluid  forced  into  them  by  little  sacs.  The  Clam  moves 
by  fixing  and  contracting  a  muscular  appendage,  called 
a  "foot."  The  Snail  has  innumerable  short  muscles  on 
the  under  side  of  its  body,  which,  by  successive  contrac- 
tions, resembling  minute  undulations,  enable  the  animal 
to  glide  forward  apparently  without  effort.  The  Leech 
lias  a  sucker  at  each  end :  fixing  itself  by  the  one  on  its 
tail,  and  then  stretching  the  body,  by  contracting  the  mus- 
cular fibres  which  run  around  it,  the  creature  fastens  its 
mouth  by  suction,  and  draws  forward  the  hinder  parts  by 

11 


162 


COMPARATIVE  ZOOLOGY. 


the  contraction  of  longitudinal  muscles.  The  Earth-worm 
lengthens  and  shortens  itself  in  the  same  way  as  the  Leech, 
but  instead  of  suckers  for  holding  its  position,  it  has  nu- 
merous minute  spines  pointing  backward  ;  while  the  Cat- 
erpillar has  short  legs  for  the  same  purpose.  The  legless 
Serpent  moves  by  means  of  the  scutes,  or  large  scales,  on 
the  under  side  of  the  body,  acted  .upon  by  the  ribs.  In 
a  straight  line,  locomotion  is  slow ;  but  by  curving  the 
body,  laterally  or  vertically,  it  can  glide  or  leap  with  great 
rapidity. 

Most  animals  have  movable  jointed  limbs,  acted  upon 
as  levers  by  numerous  muscles.  The  Centipede  has  forty- 
two  legs,  each  with 
five  joints  and  a  claw. 
The  Crab  has  five 
pairs  of  six -jointed 
legs;  but  the  front 
pair  is  modified  into 
pincers  for  prehen- 
sion. With  the  rest, 
which  end  in  a  sharp 
claw,  the  Crab  moves 
backward,  forward, 
or  sideways.  The 
Spider  has  eight  legs, 
usually  seven -joint- 
ed, and  terminating 

Fie.  127.  — Feet   of  Insects:    A,  Bibio  febi-ilia;    B,   jM  two  claWS  toothed 
House-fly  (Musca  domestica);    C,  Water  -  beetle 

(Dtjtiscm).  like  a  comb,  and  a 

third  which  acts  like  a  thumb.  In  running,  it  moves  the 
first  right  leg,  then  the  fourth  left ;  next,  the  first  left, 
and  then  the  fourth  right ;  then  the  third  right  and  sec- 
ond left  together;  and  lastly,  the  third  left  and  second 
right  together.  The  front  and  hind  pairs  are,  therefore, 
moved  like  those  of  a  quadruped.  The  Insect  has  six 


HOW  ANIMALS  MOVE.  163 

legs,  each  of  five  parts:  the  coxa;  trochanter ;  femur ; 
tibia,  or  shank ;  and  tarsus.  The  last  is  subdivided  usu- 
ally into  five  joints  and  a  pair  of  claws.  Such  as  can 
walk  upside  down,  as  the  Fly,  have,  in  addition,  two  or 
three  pads  between  the  claws.84  These  pads  bear  hairs 
which  secrete  a  sticky  fluid,  by  means  of  which  the  Fly 
adheres  to  the  surface.  While  the  leg-bones  of  Verte- 
brates are  covered  by  the  muscles  which  move  them,  the 
limbs  of  Insects  are  hollow,  and  the  muscles  inside.  The 
fore  legs  are  directed  forward,  and  the  two  hinder  pairs 
backward.  In  motion,  the  fore  and  hind  feet  on  one  side, 
and  the  middle  one  on  the  other,  are  moved  simultane- 
ously, and  then  the  remaining  three. 

The  four-legged  animals  have  essentially  the  same  appa- 
ratus and  method  of  motion.  The  Crocodile  has  an  awk- 
ward gait,  owing  to  the  fact  that  the  limbs  are  short,  and 
placed  far  apart,  so  that  the  muscles  act  at  a  mechanical  dis- 
advantage. The  Tortoise  is  proverbially  slow,  for  a  similar 
reason.  Both  swim  better  than  they  walk.  Lizards  are  light 
and  agile,but  progression  is  aided  by  a  wriggling  of  the  body. 

The  locomotive  organs  of  the  mammalian  quadrupeds 
are  much  more  highly  organized.  The  bones  are  more 
compact ;  the  vertebral  column  is  arched,  and  yet  elastic, 
between  the  shoulder  and  hip,  and  the  limbs  are  placed 
vertically  underneath  the  body.  The  bones  of  the  fore 
limb  are  nearly  in  a  line;  but  those  of  the  hind  limb, 
which  is  mainly  used  to  project  the  body  forward,  are 
more  or  less  inclined  to  one  another,  the  angle  being  most 
marked  in  animals  of  great  speed,  as  the  Horse.  Some 
walk  on  hoofs,  as  the  Ox  (Ungulate) ;  some  on  the  toes, 
as  the  Cat  (Digitigrade) ;  others  on  the  sole,  touching  the 
ground  with  the  heel,  as  the  Bear  (Plantigrade).  In  the 
Pinnigrade  Seal,  half  of  the  fore  limb  is  buried  under  the 
skin,  and  the  hind  limbs  are  turned  backward  to  form  a 
fin  with  the  tail.  The  normal  number  of  toes  is  five;  but 


164 


COMPARATIVE  ZOOLOGY. 


FIG.  128.— Feet  of  Carnivores:  A,  Plantigrade  (Bear);  B,  Pinnigrade   (Seal):  C, 
Digitigrade  (Lion). 

some  may  be  wanting,  so  that  we  have  one-toed  animals 
(as  Horse),  two-toed  (as  Ox),  three-toed  (as  Rhinoceros), 
four-toed  (as  Hippopotamus),  and  five-toed  (as  the  Ele- 
phant). The  Horse  steps  on  what  corresponds  to  the  nail 
of  the  middle  finger ;  and  its  swiftness  is  conditioned  on 
the  solidity  of  the  extremities  of  the  limbs.  Horses  of 
the  greatest  speed  have  the  shoulder-joints  directed  at  a 

considerable  angle  with  the  arm. 

D 


FIG.  129. —Feet  of  Hoofed  Mammals:  A,  Elephant;  B,  Hippopotamus;  C,  Rhinoc- 
eros; D,  Ox;  E,  Horse,  a,  astragalus;  cl,  calcaneum,  or  heel;  s,  uaviculare ;  6, 
cuboides ;  <*,  ct,  cm,  cuneiform  bones ;  the  numbers  indicate  the  digits  in  use. 


HOW  ANIMALS  MOVE. 


165 


The  order  in  which  the  legs  of  Quadrupeds  succeed 
each  other  determines  the  various  modes  of  progression, 
called  the  walk,  trot,  gallop,  and  leap.  Many,  as  the 
Horse,  have  all  these  movements ;  while  some  only  leap, 
as  the  Frog  and  Kangaroo.  In  leaping  animals,  the  hind 
limbs  are  extraordinarily  developed.  In  many  Mammals, 
like  the  Squirrel,  Cat,  and  Dog,  the  fore  legs  are  used  for 
prehension  as  well  as  locomotion.  Monkeys  use  all  four, 


W.  130.— Muscles  of  the  Unman  Leg: 
tartoriut,  or  "tailor's  muscle,"  the 
longest  muscle  in  the  body,  flexes  the 
leg  upon  the  thigh;  rectiis  femoris 
and  vastits  externus  and  internus  ex- 
tend the  leg,  maintaining  an  erect 
posture;  gastrocnemius,  or  "calf," 
used  chiefly  in  walking,  for  raising 
the  heel.  Another  layer  underlies 
these  superficial  muscles. 


PIG.  131.— Muscles  of  an  Insect's  Leg 
(Melolontha  vulgarix):  a,  flexor,  and 
b,  extensor,  of  tibia ;  c,  flexor  of  foot ; 
d,  accessory  muscle ;  e,  extensor  of 
claw;  /,  extensor  of  tarsus.  The 
joints  are  restricted  to  movements 
in  one  plane ;  and  therefore  the  mus- 
cles are  simply  flexors  and  extensors. 
All  the  muscles  are  within  the  skele- 
ton. 


166 


COMPARATIVE  ZOOLOGY. 


and  also  the  tail,  for  locomotion  and  prehension,  keeping 
a  horizontal  attitude;  while  the  Apes,  half  erect,  as  if 
they  were  half-quadruped,  half-biped,  go  shambling  along, 
touching  the  ground  with  the  knuckles  of  one  hand  and 
then  of  the  other.  In  descending  the  scale,  from  the 
most  anthropoid  Ape  to  the  true  Quadruped,  we  find  the 
centre  of  gravity  placed  increasingly  higher  up — that  is, 
farther  forward.  Birds  and  Men  are  the  only  true  bipeds ; 
the  former  standing  on  their  toes,  the  latter  on  the  soles 
of  the  feet.  Terrestrial  Birds  walk  and  run  ;  while  Birds 
of  flight  usually  hop.  The  Ostrich  can  for  a  time  outrun 
the  Arabian  Horse ;  and  the  speed  of  the  Cassowary  ex- 
ceeds that  of  the  swiftest  Greyhound. 


CHAPTER  XYIII. 

THE    NERVOUS    SYSTEM. 

Nervous  Matter  exists  in  the  form  of  cells,  fibres,  or 
tubes.     In  the  cellular  state  it  is  grayish,  and  accumulated 

in  masses,  called 
ganglia,  or  centres, 
which  alone  origi- 
nate nervous  force ; 
the  fibrous  and  tu- 
bular kinds  are  gen- 
erally white,  and 
arranged  in  bun- 
dles, called  nerves, 
which  serve  only  as 
conductors.  Most 
nerves  contain  two 

Fio.  132.  —  Nerve-cells  from  Human  Brain:  A,  associ-   kinds  of  fibres,  like 
ated  with  nerve-tnbes  aud  blood-vessels;  B,  multi-    .  , 

polar  nucleated  cells.  in      structure,      but 


THE  NERVOUS  SYSTEM. 


167 


each  having  its  distinct  office:  one  carries  impressions  re- 
ceived from  the  external  world  to  the  gray  centres,  and 
hence  is  called  an  afferent^  sen- 
sory, nerve ;  the  other  conducts 
an  influence  generated  in  the 
centre  to  the  muscles,  in  obedi- 
ence to  which  they  contract,  and 
hence  it  is  called  an  efferent,  or 
motor,  nerve.  Thus,  when  the 
finger  is  pricked  with  a  pin,  af- 
ferent nerve -fibres  Convey  the  FIG.  133.-Nem>us  System  of  Star- 

impression  to  the  centre -the     ^JSS^SKA 

Spinal    COrd,    which    immediately       each  arm,  ending  in  the  eye. 

transmits  an  order  by  efferent  fibres  to  the  muscles  of  the 
hand  to  contract.  If  the  former  are  cut,  sensation  is  lost, 
but  voluntary  motion  remains ;  if  the  latter  are  cut,  the 
animal  loses  all  control  over  the  muscles,  although  sensi- 
bility is  perfect ;  if  both  are  cut,  the  animal  is  said  to  be 

paralyzed.  The  nerve-fibres  are 
connected  with  nerve-cells  in  the 
central  organs,  and  at  the  outer 
ends  are  connected  with  the  mus- 
cular fibres,  or  with  various  sen- 
sory end -organs  in  the  skin  or 
other  parts  of  the  body.  The 
nature  of  nerve  -  force  is  not 
known.  As  to  the  velocity  of  a 
nervous  impulse,  we  know  it  is 
far  less  than  that  of  electricity  or 
light,  and  that  it  is  more  rapid  in 
FIG.  134. -Nervous  System  of  a  warm-blooded  than  in  2old-blood- 

ed  animals>  beins faster  in  Man 

;  i, lateral;  0, abdominal,  than  in  the  Frog.  In  the  latter 
it  averages  about  85  feet  per  second,  in  the  former  over 
100  feet. 


168 


COMPARATIVE  ZOOLOGY. 


The  very  lowest  animals,  like  the  Amoeba  and  Infuso- 
ria, have  no  nerves,  although  their  protoplasm  has  a  gen- 
eral sensibility.  The  Hydra  has  certain 
cells  which  are,  perhaps,  partly  nervous 
and  partly  muscular  in  function.  The 
Jelly-fish  has  a  nervous  system,  consist- 
ing of  a  net-work  of  threads  and  ganglia 
scattered  all  over  its  disk.  We.  should 
look  for  a  definite  system  of  ganglia  and 
nerves  only  in  those  animals  which  pos- 
sess a  definite  muscular  structure,  and 
show  definitely  co-ordinat- 
ed muscular  movements. 
In  the  Star-fish  we  detect 
the  first  clear  specimen  of 
such  a  system.  It  consists 
PIG.  m-Nervons  Sys-  Of  a  rjn g  around  the  mouth, 

tern  of  Clam:  c,  cere-  e  ' 

braigaugiion;p,ped-  made   of  five   ganglia  of 

al  ganglia ;  ps,  parie-  ,      .  .  ,  ,.      . 

ia;  equal  size,  with  radiating 


from  cerebral  to  pedal  distinguished  by  an  irregu- 

ganglia;ps',commi8-  * 

sure  from  cerebral  to  larly  scattered  nervous  sys- 

parietosplanchnic    ,  m,       ^,          ,          ,, 

ganglia;  oe,  cesopha-  tern.  The  Clam  has  three 
main  pairs  of  connected 
ganglia  —  one  near  the  mouth,  one  in  the 
foot,  and  the  third  in  the  posterior  region, 
near  the  siphons.  In  the  Snail,  these  are 
united  into  a  ring  around  the  gullet,  and 
there  are  other  ganglia  scattered  through 


the  body.     The  same  is  true  of  the  Cuttle-  FIG.  135.—  Nervous 


™   i          i  .1       i        •      •  .-i  ^          -t   •  System  of  aCater- 

nsh,  where  the  brain  is  partly  enclosed  in  a     pii]ar  (spMnx  u- 


cartilaginous  box  (Fig.  151). 

In  the  simpler  worms  there  is  but  a  sin-     head>  gaȣlion- 
gle  ganglion  or  a  single  pair.     The  Earth-worm  has  a  pair 
of  brain-ganglia  lying  above  the  gullet,  and  connected  by 


THE  NERVOUS  SYSTEM. 


169 


two  cords  with  a  ventral  chain  of  ganglia — one  pair,  ap- 
parently a  single  one,  for  each  segment.  In  the  lower 
Arthropods,  such  as  Crustacea,  Centipedes,  and  Larval  In- 
sects, the  arrangement  is  substan-  ^  — g^  -6 
tially  the  same.  In  higher  Insects 
and  Crustacea,  many  of  the  gan- 
glia are  fused  together  in  the  head 
and  thorax,  indicating  a  concen- 
tration of  organs  for  sensation  and 
locomotion. 

In  Vertebrates,  the  nervous 
system  is  more  highly  developed, 
more  complex,  and  more  concen- 
trated than  in  the  lower  forms. 
In  fact,  there  are  some  parts,  as  the 
brain,  to  which  we  find  nothing 
homologous  in  the  Invertebrates ; 
and  while  the  actions  of  the  lat- 
ter are  mainly,  if  not  wholly,  au- 
tomatic, those  of  backboned  ani- 
mals are  voluntary.  Its  position, 
moreover,  is  peculiar,  the  great 
mass  of  the  nervous  matter  being 
accumulated  on  the  dorsal  side, 
and  enclosed  by  the  neural  arches 
of  the  skeleton. 

The  brain  and  spinal  cord  lie 
in  the  cavity  of  the  skull  and 
spinal  column,  wrapped  in  three 
membranes.  Both  consist  of  gray 
and  white  nervous  matter;  but  in 
the  brain  the  gray  is  on  the  out- 
side, and  the  white  within ;  while 
the  white  of  the  spinal  cord  is  external,  and  the  gray  in- 
ternal. Both  are  double,  a  deep  fissure  running  from  the 


FIG.  137. — Human  Brain  and  Spinal 
Cord,  one  fifth  natural  size :  a, 
great  longitudinal  fissure ;  &,  an- 
terior lobe  ;  c,  middle  lobe ;  d, 
medulla  oblongata;  e,  cerebel- 
lum ,  /,  first  spinal  nerve  -,  g, 
brachial  plexus  of  nerves  supply- 
ing the  arms ;  h,  dorsal  nerves ;  t, 
lumbar  nerves ;  *,  sacral  plexus 
of  nerves  for  the  limbs ;  I,  canda 
equiua:  the  figures  indicate  the 
twelve  pairs  of  cranial  nerves,  of 
which  1  is  olfactory,  2  optic,  and 
8  auditory. 


170  COMPARATIVE  ZOOLOGY. 

forehead  backward,  dividing  the  brain  into  two  hemi- 
spheres, and  the  spinal  cord  resembling  two  columns 
welded  together;  even  the  nerves  come  forth  in  pairs  to 
the  right  and  left.  The  brain  is  the  organ  of  sensation 
and  voluntary  motion  ;  the  spinal  cord  is  the  organ  of  in- 
voluntary life  and  motion.  The  brain,  above  the  medulla 
oblongata,  may  be  removed,  and  yet  the  animal,  though  it 
cannot  feel,  will  live  for  a  time,  showing  that  it  is  not  ab- 
solutely essential  to  life ;  in  fact,  the  brain  does  nothing 
in  apoplexy  and  deep  sleep.  All  of  the  cord,  except  that 
part  containing  the  centres  for  respiration  and  circulation, 
may  also  be  destroyed,  without  causing  immediate  death. 

The  Brain  is  that  part  of  the  nervous  system  contained 
in  the  skull.85  It  increases  in  size  and  complexity  as  we 
pass  from  the  Fishes,  by  the  Amphibians,  Keptiles,  and 
Birds,  to  Mammals.  Thus,  the  body  of  the  Cod  is  5000 
times  heavier  than  its  brain — in  fact,  the  brain  weighs  less 
than  the  spinal  cord ;  while  in  Man,  the  brain,  compared 
with  the  body,  is  as  1  to  36,  and  is  40  times  heavier  than 
the  spinal  cord.  The  brains  of  the  Cat  weigh  only  1  oz. ; 
of  the  Dog,  6  oz.  5£  dr. ;  and  of  the  Horse,  22  oz.  15  dr. 
The  only  animals  whose  brains  outweigh  Man's  are  the 
Elephant  and  Whale — the  maximum  weight  of  the  Ele- 
phant's being  10  Ibs.,  and  of  the  Whale's  5  Ibs. ;  while 
the  human  does  not  exceed  4  Ibs.  Yet  the  human  brain 
is  heavier  in  proportion  to  the  body.  But  quality  must 
be  considered  as  well  as  quantity,  else  the  Donkey  will 
outrank  the  Horse,  and  the  Canary-bird,  Man ;  for  their 
brains  are  relatively  heavier. 

The  main  parts  of  the  brain  are  the  cerebrum,  cerebel- 
lum, and  medulla  oblongata. 

The  cerebrum  is  a  mass  of  white  fibrous  matter  covered 
by  a  layer  of  gray  cellular  matter.  In  the  lower  Verte- 
brates, the  exterior  is  smooth;  but  in  most  of  the  Mam- 
mals it  is  convoluted,  or  folded,  to  increase  the  amount  of 


THE  NERVOUS  SYSTEM. 


171 


the  gray  surface.  The  convolutions  multiply  and  deepen 
as  we  ascend  the  scale  of  size  and  intelligence,  being  very 
complex  in  the  Elephant  and  Whale,  Monkey  and  Man. 
As  a  rule,  they  are  proportioned  to  the  intelligence  of  the 
animal ;  yet  the  brains 
of  the  Dog  and  Horse 
are  smoother  than  those 
of  the  Sheep  and  Don- 
key. Evidently  the 
quality  of  the  gray  mat- 
ter must  be  taken  into 
account.  Save  in  the 
bony  Fishes,  the  cere- 
brum is  the  largest  por- 
tion of  the  brain  ;  in 
Man  it  is  over  eight 
times  heavier  than  the 
cerebellum. 

The  cerebellum,  or 
"  little  brain,"  lies  be- 
hind the  cerebrum,  and, 
like  it,  presents  an  ex- 
ternal gray  layer,  with 
a  white  interior.  In 
Mammals,  it  is  likewise 
finely  convoluted,  con- 
si  citi  no-  nf  0-rflV  anrl  Fro- 138.— Brain  of  the  Horse— upper  view,  one 
ing  (  I  gray  an<  half  natural  size :«,  medulla  oblongata ;  6,  lat- 
eral and  middle  lobes  of  cerebellum ;  c,  inter« 
lobular  fissure ;  rf,  cerebral  hemispheres ;  e,  ol- 
factory lobes. 

or  hemispheres.  In  the  rest  of  the  Vertebrates,  the  cere- 
bellum is  nearly  or  quite  smooth ;  and  in  the  lowest  Fish- 
es it  is  merely  a  thin  plate  of  nervous  matter.  In  many 
Vertebrates,  however,  it  is  larger,  compared  with  the  cere- 
brum, than  in  Man,  since  in  Man  the  cerebrum  is  extraor- 
dinarily developed. 


white  laminae,  and   is 
divided  into  two  lobes, 


172 


COMPARATIVE  ZOOLOGY. 


The  medulla  oblongata  is  the  connecting  link  between 
the  cerebrum  and  cerebellum  and  the  spinal  cord.  In 
structure,  it  resembles  the  spinal  cord — the  white  matter 
being  external  and  the  gray  internal.  The  former  lies 
beneath  or  behind  the  brain,  passing  through  the  foramen 
magnum  of  the  skull,  and  merging  imperceptibly  into  the 
cord.  The  latter  is  a  continuous  tract  of  gray  matter  en- 
closed within  strands  of  white  fibres.  It  usually  ends  in 
the  lumbar  region  of  the  vertebral  column,  but  in  Fishes 
it  reaches  to  the  end  of  the  tail.  In  Fishes,  Amphibians, 
and  Reptiles,  the  cord  outweighs  the  brain:  in  Birds  and 
Mammals,  the  brain  is  heavier  than  the  cord.  In  Man, 
it  weighs  about  an  ounce  and  a  half. 

Besides  these  parts,  there  are  also  the  olfactory  and  the 
optic  lobes,  which  give  rise  respectively  to  the  nerves  of 
smell  and  sight. 

The  parts  of  the  brain  are  always  in  pairs ;  but  in  rela- 
tive development  and  po- 
sition they  differ  widely  in 
the  several  classes  of  Ver- 
tebrates. In  Fishes  and 
Reptiles,  they  are  arranged 
in  a  horizontal  line;  in 
Birds  and  Mammals,  the 
axis  of  the  spinal  cord 
bends  to  nearly  a  right  an- 
Braiu  of  g[Q  jn  passing  through  the 

the  Perch,  upper   s 

view:  a,  cerebei-  brain,  so  that  the  lobes  no 

him;     &,   optic       '  .  . 

lobes;  c,  cere-  longer  he  in  a  straight  line. 

ryTbes;°rme-   Iri    Man,  the  fore-brain    is   FIG.  140. -Brain  of  the 

duiia  oblongata.  so  developed  that  it  cov. 
ers  all  the  other  lobes.  In  looking  down 
upon  the  brain  of  a  Perch,  we  see  in 
front  a  pair  of  olfactory  lobes  (which  ventricles;  LOP,  optic 

-..,.,       lobes;    C,  cerebellum: 

send  forth  the  nerves  of  smell),  behind     MO, medulla  obion 


Srh 


Mo 


THE  NERVOUS  SYSTEM. 


173 


them  the  small  cerebral  hemispheres,  then  the  large  optic 
lobes  (in  which  originate  the  nerves  of  sight),  and,  last  of 
all,  the  cerebellum.  Not  till  we  reach  Man  and  the  Apes 
do  we  find  the  cerebrum  so  highly  developed  as  to  overlap 
both  the  olfactory  lobes  in  front  and  the  cerebellum  behind. 

Functions  of  the  Brain. — The  cerebrum  is  the  seat  of  in- 
telligence and  will.  It  has  no  direct  communication  with 
the  outside  world,  receiving  its  consciousness  of  external 
objects  and  events  through  the  spinal  cord  and  the  nerves 
of  special  sense.88 

The  cerebellum  seems  to  preside  over  the  co-ordination 
of  the  muscular  movements.  When  removed,  the  animal 


Off. 


Fro.  141.— A,  C,  npper  and  side  views  of  the  Brain  of  a  Lizard ;  B,  D,  npper  and  side 
views  of  the  Brain  of  a  Turkey :  Olf,  olfactory  lobes ;  Hmp,  cerebral  hemispheres ; 
Pn,  pineal  gland  ;  Mb,  optic  lobes  of  the  middle  brain ;  Cb,  cerebellum ;  MO,  me- 
dulla oblongata ;  ii,  optic  nerves ;  iv  and  in,  nerves  for  the  muscles  of  the  eye ; 
Py,  pituitary  body. 

desires  to  execute  the  mandates  of  the  will,  but  cannot ; 
its  motions  are  irregular,  and  it  acts  as  if  intoxicated.  It 
is  usually  largest  in  animals  capable  of  the  most  compli- 
cated movements;  being  larger  in  the  Ape  than  in  the 
Lion,  in  the  Lion  than  in  the  Ox,  in  Birds  than  in  Rep- 
tiles. The  cerebellum  of  the  Frog  is,  however,  smaller 
than  that  of  Fishes  (Figs.  139, 140).  The  olfactory  and  op 
tic  lobes  receive  the  messages  from  their  respective  nerves, 


174 


COMPARATIVE  ZOOLOGY. 


The  medulla  oblongata  is  Dot  only  the  medium  of  com- 
munication between  the  brain  and  the  spinal  cord,  but  it 


FIG.  142.— Brain  of  the  Cat  (Felis  do- 
mestica):  a,  medulla  oblongata;  &, 
cerebellum;  c,  cerebrum. 


FIG.  143.  —Brain  of  the  Orang-utan, 
upper  surface ;  one  third  natural 
size. 


is  itself  a  nervous  centre :  the  brain  above  and  the  cord 
below  may  be  removed  without  death  to  the  animal,  but 
the  destruction  of  the  medulla  is  fatal.  Of  the  twelve 
pairs  of  nerves  issuing  from  the  contents  of  the  skull  (en- 
cephalon\  ten  come  from  the 
medulla  oblongata.  Among 
these  are  the  nerves  of  hearing 


FIG.  144.— Human  Brain,  side  view:  1, 
medulla  oblongata ;  3,  cerebellum ;  5, 
frontal  convolutions  of  cerebrum. 


FIG.  145. —  Human  Brain,  upper  view, 
one  third  natural  size:  1,  anterior 
lobes  ;  2,  posterior;  3,  great  median 
fissure. 


and  taste,  and  those  that  control  the  lungs  and  heart.    Res- 
piration ceases  immediately  when  the  medulla  is  injured. 


THE  NERVOUS  SYSTEM. 


175 


The  spinal  cord  is  a  centre  for  originating  involuntary 
actions,  and  is  also  a  conductor — propagating  through  its 
central  gray  matter  the  impressions  received  by  the  nerves 
to  the  brain,  and  taking  back  through  its  fibrous  part  the 
impulses  of  the  brain. 
In  Man,  thirty-one  pairs 
of  nerves  arise  from  the 
cord  to  supply  the  whole 
body,  except  the  head. 
Each  nerve  has  an  ante- 
rior and  a  posterior  root. 
The  fibres  of  the  former 
go  to  the  muscles,  and 
hence  carry  the  impulses 
which  cause  muscular 
contraction  (hence  call- 
ed motor  fibres) ;  those 
of  the  posterior  root  con- 
vey sensations  from  the 
exterior  to  the  central 
organs  (sensory).  The 
fibres  leading  from  the 
brain  to  the  cord  cross 

niiP  nnnf-hpr  in   flip  mp     FIG.  146.— Relation  of  the  Sympathetic  and  Spinal 

Nerves :  c,  fissure  of  spinal  cord ;  a,  anterior  of 

dtllla  Oblongata.  SO  that       a  dorsal  8Pinal  nerve  5  Pi  Posterior  root,  with  its 

ganglion;    a',  anterior    branch;    p\  posterior 

if     the      right     Cerebral       branch;  «,  sympathetic;  e,  its  double  junction 
,  ,  i       j  •  -I        by  white  and  gray  filaments. 

hemisphere  be  diseased, 

the  left  side  of  the  body  loses  the  power  of  voluntary 

motion. 

The  sympathetic  nervous  system  is  a  double  chain  of 
ganglia,  lying  along  the  sides  of  the  vertebral  column  in 
the  ventral  cavity.  From  these  ganglia  nerves  are  given 
off,  which,  instead  of  going  to  the  skin  and  muscles,  like  the 
spinal  nerves,  form  net-works  about  those  internal  organs 
over  which  the  will  has  no  control,  as  the  heart,  stomach, 


176  COMPARATIVE  ZOOLOGY. 

and  intestines.     Their  apparent  office  is  to  stimulate  these 
organs  to  constant  activity,  but  is  little  understood. 

1.  The  Senses. 

Sensation  is  the  consciousness  of  impressions  on  the 
sensory  nerves.  These  impressions  produce  some  change 
in  the  brain ;  but  what  that  change  is,  is  a  darkness  on 
which  no  hypothesis  throws  light.  Obviously,  we  feel 
o-nly  the  condition  of  our  nervous  system,  not  the  objects 
which  excite  that  condition.87 

All  animals  possess  a  general  sensibility  diffused  over 
the  greater  part  of  the  body.88  This  sensibility,  like  as- 
similation and  contractility,  is  one  of  the  primary  physio- 
logical properties  of  protoplasm.  But,  besides  this  (save 
in  the  very  lowest  forms),  they  are  endowed  with  special 
nerves  for  receiving  the  impressions  of  light,  sound,  etc. 
These  nerves  of  sense,  as  they  are  called,  although  struct- 
urally alike,  transmit  different  sensations :  thus,  the  Ear  can- 
not recognize  light,  and  the  Eye  cannot  distinguish  sounds. 
In  the  Vertebrates,  the  organs  of  sight,  hearing,  and  smell 
are  situated  in  pairs  on  each  side  of  the  head ;  that  of 
taste,  in  the  mucous  membrane  covering  the  tongue; 
while  the  sense  of  touch  is  diffused  over  the  skin.  Sight 
and  hearing  are  stimulated,  each  by  one  agent  only ; 
while  touch,  taste,  and  smell  may  be  excited  by  various 
substances.  The  agents  awakening  sight,  hearing,  and 
touch  are  physical ;  those  causing  taste  and  smell  are 
chemical.  Animals  differ  widely  in  the  numbers  and 
keenness  of  their  senses.  But  there  is  no  sense  in  any 
one  which  does  not  exist  in  some  other. 

Touch  is  the  simplest  and  the  most  general  sense;  no  an- 
imal is  without  it,  at  least  in  the  form  of  general  sensibility. 
It  is  likewise  the  most  positive  and  certain  of  the  senses. 
In  the  Sea-anemone,  Snail,  and  Insect,  it  is  most  acute  in 
the  "  feelers"  (tentacles,  horns,  and  antennae),89  in  the  Oys- 


THE  NERVOUS  SYSTEM. 


177 


Fio.  147.— Antennae  of  Various  Insects. 


ter,  the  edge  of  the  mantle  is  most  sensitive ;  in  Fishes, 
the  lips ;  in  Snakes,  the  tongue ;  in  Birds,  the  beak  and 
under  side  of  the  toes;  in 
Quadrupeds,  the  lips  and 
tongue ;  and  in  Monkeys 
and  Man,  the  lips  and  the 
tips  of  the  tongue  and  fin- 
gers. In  the  most  sensitive 
parts  of  Birds  and  Mam- 
mals, the  true  skin  is  raised 
up  into  multitudes  of  mi- 
nute elevations,  called  pa- 
pillce,  containing  loops  of 
capillaries  and  nerve-filaments.  There  is  a  correspondence 
between  the  delicacy  of  touch  and  the  development  of  in- 
telligence. The  Cat  and  Dog  are  more  sagacious  than 
hoofed  animals.  The  Elephant  and  Parrot  are  remark- 
ably intelligent,  and  are  as  celebrated  for  their  tactual 
power. 

Taste  is  more  refined  than  touch,  since  it  gives  a 
knowledge  of  properties  which  cannot  be  felt.  It  is  al- 
ways placed  at  the  entrance  to  the  digestive  canal>  as  its 
chief  purpose  is  to  guide  animals  in  their  choice  of  food. 
ISTo  special  organ  of  taste  can  be  de- 
tected in  the  Invertebrates,  although 
all  seem>  to  exercise  a  faculty  in  se- 
lecting their  food.  Even  in  Fishes, 
Amphibians,  Reptiles,  and  Birds  this 

Fio.  US.— .PapliUB  of  Human 

Palm,  x  35,  the  cuticle  be-  sense  is  very  obtuse,  for  they  bolt 
their  food.  But  the  higher  Verte- 
brates have  it  well  developed.  It  is  confined  to  the 
tongue,  and  is  most  delicate  at  the  root.90  A  state  of 
solution  and  an  actual  contact  of  the  fluid  are  necessary 
conditions. 

Smell  is  the  perception  of  odors,  i.  e.,  certain  substances 

12 


178  COMPARATIVE  ZOOLOGY. 

in  the  gaseous  state.  Many  Invertebrates  have  this  sense : 
Snails,  e.  g.,  seem  to  be  guided  to  their  food  by  its  scent, 
and  Flies  soon  find  a  piece  of  meat.  In  the  latter  the 
organ  is  probably  located  on  the  antennse.  In  Verte- 
brates, it  is  placed  at  the  entrance 
to  the  respiratory  tube,  in  the  upper 
region  of  the  nose.  There  the  olfac- 
tory nerves,  which  issue  from  the  olfac- 
tory lobe  of  the  brain,  and  pass  through 
the  ethmoid  bone,  or  roof  of  the  nasal 
cavity,  are  distributed  over  a  moist 
cavity,  mucous  membrane.  The  odorous  sub- 

stance, in  a  gaseous  or  finely  divided  state,  is  dissolved  in 
the  mucus  covering  this  membrane.  In  Fishes  and  Rep- 
tiles generally,  this  organ  is  feebly  developed ;  Sharks, 
however,  gather  from  a  great  distance  around  a  carcass. 
In  the  Porpoises  and  Whales  it  is  nearly  or  entirely 
wanting.  Among  Birds,  Waders  have  the  largest  olfac- 
tory nerves.  It  is  most  acute  in  the  carnivorous  Quad- 
rupeds, and  in  some  wild  herbivores,  as  the  Deer.  In 
Man  it  is  less  delicate,  but  has  a  wider  range  than  in  any 
brute. 

Hearing  is  the  perception  of  sound.  The  simplest 
form  of  the  organ  is  a  sac  filled  with  fluid,  in  which  float 
the  soft  and  delicate  ends  of  the  auditory  nerve.  The 
vibrations  of  the  fluid  are  usually  strengthened  by  the 
presence  of  minute  hard  granules,  call- 
ed otoliths.  Most  Invertebrates  have 
no  higher  apparatus  than  this ;  and  it 
is  probable  that  they  can  distinguish 
one  noise  from  another,  but  neither 

'  FIG.  150.— Ear  of  a  Mol- 

pitch  nor  intensity.     The  organ  is  gen-      lusk  (q/cfas),  greatly eu- 
erally  double,  but  not  always  located 
in  the  head.     In  the  Clam,  it  is  found  at  the  base  of  the 
foot ;  some  Grasshoppers  have  it  in  the  fore-legs ;  and  in 


THE  NERVOUS  SYSTEM. 


179 


many  Insects  it  is  on  the  wing.     Lobsters  and  Crabs  have 
the  auditory  sacs  at  the  base  of  the  antennae.91 


FIG.  151.— Brain  and  Auditory  Apparatus  of  the  Cuttle-fish:  a,  &,  brain;  c,  auditory 
apparatus ;  d,  the  cavity  in  which  it  is  lodged ;  «,/,  g,  eyes ;  1, 2,  3,  otoliths. 

A  complex  organ  of  hearing,  located  in  the  head,  exists 
in  all  Vertebrates,  save  the  very  lowest  Fishes.  As  com- 
plete in  Man,  it  consists  of  the  following  parts :  1st.  The 
external  ear  (which  is  peculiar  to  Mammals) ;  the  auditory 
canal,  about  an  inch  long,  lined  with  hairs  and  a  waxy  se- 
cretion, and  closed  at  the 
bottom  by  a  membrane, 
called  tympanum,  or 
"drum  of  the  ear."  2d. 
The  middle  ear,  contain- 
ing three  little  bones  (the 

smallest  in  the  body),  mal-          ^K^BBB  \Mi» 

leus,  incus,  and  stapes,  ar- 
ticulated  together.      The 

Cavity  Communicates  with  FIG.  152.— Section  of  Human  Ear:  a,  external 

,                          ,      .      ,  ear,  with  auditory  canal;  6,  tympanic  cavi- 

the  external   ail'   by   means  ty  containing  the  three  bones;  c,  hammer, 

c\i     tlio     TTncfanliijin      tnKo  and  its  three  mupdes,  d,  e,f;  g,  tympanic 

^i  membrane,  or  head  of  the  drum ;  /»,  Eusta- 

Whicll    Opens    at    the    back  chian  tube  leading  to  the  pharynx  ;  i,  laby- 
rinth, with  semicircular  canals  and  cochlea 

part   of   the  mouth.     3d.     visible. 

The  internal  ear,  or  labyrinth,  an  irregular  cavity  in  the 

solid  part  of  the  temporal  bone,  and  separated  from  the 


180  COMPARATIVE  ZOOLOGY. 

middle  ear  by  a  bony  partition,  which  is  perforated  by 
two  small  holes.  The  labyrinth  consists  of  the  vestibule, 
or  entrance ;  the  semicircular  canals,  or  tubes ;  and  the 
cochlea,  or  spiral  canal.  While  the  other  parts  are  full  of 
air,  the  labyrinth  is  filled  with  a  liquid,  and  in  this  are 
the  ends  of  the  auditory  nerve.  The  vibrations  of  the 
air,  collected  by  the  external  ear,  are  concentrated  upon 
the  tympanum,  and  thence  transmitted  through  the  chain 
of  little  bones  to  the  fluid  in  the  labyrinth. 

Now,  the  essential  organ  of  hearing  is  the  labyrinth, 
which  is,  substantially,  a  bag  filled  with  fluid  and  nerve- 
filaments.  Fishes  generally  have  but  little  more.  In 
Amphibians  and  Reptiles  there  are  added  a  tympanum, 
a  single  bone,  connecting  this  with  the  internal  ear,  the 
cochlea,  and  the  Eustachian  tube;  the  tympanum  being 
external.  Birds  have,  besides,  an  auditory  passage,  open- 
ing on  a  level  with  the  surface  of  the  head,  and  surround- 
ed by  a  circle  of  feathers.  Mammals  only  have  an  exter- 
nal ear.98 

Sight  is  the  perception  of  light.93  In  all  animals  it  de- 
pends upon  the  peculiar  sensitiveness  of  the  optic  organ  to 
the  luminous  vibrations.  In  Yertebrates  the  optic  nerve 
comes  from  the  middle  mass  of  the  brain,  in  Invertebrates 
it  is  derived  from  a  ganglion.  Many  animals  are  utter- 
ly destitute  of  visual  organs,  as  the  Protozoa,  and  the 
lower  Radiates  arid  Mollnsks,  besides  intestinal  Worms 
and  the  blind  Fishes  and  other  cave-animals.  Around  the 
margin  of  the  Jelly-fish  are  colored  spots,  supposed  to  be 
rudimentary  eyes ;  but,  as  a  lens  is  wanting,  there  is  no 
image;  so  that  the  creature  can  merely  distinguish  light 
from  darkness  and  color  without  form.  Such  an  eye  is 
nothing  but  a  collection  of  pigment  granules  on  the  ex- 
pansion of  a  nervous  thread,  and  the  perception  of  light 
is  the  sensation  of  warmth,  the  pigment  absorbing  the 
rays  and  converting  them  into  heat. 


THE  NERVOUS  SYSTEM. 


181 


Going  higher,  we  find  a  lens  introduced  forming  a  dis- 
tinct image.  The  Snail,  for  example,  has  two  simple  eyes, 
called  ocellij  mounted  on  the  tip  of  its  long  tentacles,  con- 
sisting of  a  globular  lens,94 
with  a  transparent  skin 
(cornea)  in  front,  and  a 
colored 
membrane 
(ch  oroid) 
and  a  ner- 
vous n  et- 

FIG.  153.  —  Eye  of    work      (reti- 
Pecten,muchen- 

larged: w.mouth;  na)   behind. 

1.  lens;  r,  retina   rrn       o      n 
and  choroid;n,    The  Scallop 


organs  are  the  only  eyes 
possessed  by  Myriapods, 
Spiders,  Scorpions,  and 
Caterpillars.  Adult  In- 


such  eyes  in  the  edge  of  _ 

J  .  FIG.  154.  —Head  of  a  Snail  bisected,  showing 

its  mailtle  (Fig.  153).   Sucll      structure  of  tentacles:  a,  right  inferior  ten- 

tacle  retracted  within  the  body ;  b,  right  su- 
perior tentacle  fully  protruded  ;  c,  left  supe- 
rior tentacle  partially  inverted ;  d,  left  inferi- 
or tentacle ;  /,  optic  nerve  ;  g,  retractor  mus- 
cle ;  h,  optic  nerve  in  loose  folds ;  i,  retractor 
nmscle  of  head  ;  k,  nerve  and  muscle  of  left 
inferior  tentacle ;  I,  m,  nervous  collar. 

sects  usually  have  three  ocelli  on  the  top  of  the  head. 
But  the  proper  visual  organs  of  Lobsters,  Crabs,  and  In- 
sects are  two  compound  eyes,  perched 
on  pedestals,  or  fixed  on  the  sides  of 
the  head.  They  consist  of  an  immense 
number  of  ocelli  pressed  together  so 
that  they  take  an  angular  form — four- 
sided  in  Crustacea,  six-sided  in  Insects. 
They  form  two  rounded  protuberances 
variously  colored — white,  yellow,  red,  FIG.  155.— Head  of  the  Bee, 
green,  purple,  brown,  or  black.  Under  theThriTeiTo^tem- 
the  microscope,  the  surface  is  seen  to  mata' and  the  anteuuffi- 
be  divided  into  a  host  of  facets,95  each  being  an  ocellus 
complete  in  itself.  Each  cornea  is  convex  on  one  side, 


182 


COMPARATIVE   ZOOLOGY. 


and  either  convex  or  flat  on  the  other,  so  that  it  produces 

a  focus  like  a  lens.  Be- 
hind the  cornea,  or 
lens,  is  the  pigment, 
having  a  minute  aper- 
ture or  "  pupil."  Next 
is  a  conical  tube — one 
for  each  facet  —  with 
sides  and  bottom  lined 
with  pigment.  These 
tubes  converge  to  the 
optic  ganglion,  the 
fibres  of  which  pass 
through  the  tubes  to 
the  cornea.96  Vision 

FiG.15e.-EyeofaBeeile(J/«fofemtfc»):  A,  section ;  ]^T    %UG]1    a    compound 

is  not  a  mosaic; 


1 1 1 


a,  optic  ganglion  ;  b,  secondary  nerves ;  c,  retina ; 

d,  pigment  layer ;  e,  proper  optic  nerves ;  B,  group  QVQ 

of  ocelli;  /,  bulb  of  optic  nerve;  g,  layer  of  pig-     * 

rueiit;  h,  vitreous  humor ;  i,  cornea.  but  each   OCellllS  glVCS 

a  complete  image,  although  a  different  perspective  from 
its  neighbor.  The 
multiplied  images  are 
reduced  to  one  men- 
tal stereoscopic  pict- 
ure, on  the  principle 
of  single  vision  in 
ourselves. 

The    eyes    of 
Cuttle-fish    are 


the 
the 

largest  and  the  most 
perfect  among  Inver- 
tebrates. They  re- 
semble the  eyes  of 
higher  animals  in  hav- 
ing a  crystalline  lens 
with  a  chamber  in 


lower  lid;  c,  conjunctiva,  or  mucous  membrane, 
lining  the  inner  surface ;  d,  external  membrane ;  e, 
sheath  of  optic  nerve;  /,  g,  muscles  for  rolling  the 
eye  up  or  down;  h,  sclerotic;  i,  transparent  cor- 
nea; j,  choroid;  A;,  Z,  ciliary  muscle  for  adjusting 
the  eye  for  distance  ;  m,  iris  and  pupil ;  n,  canal ; 
o,  retina;  s,  vitreous  humor;  t,  crystalline;  »,  au- 
•  terior  chamber;  x,  posterior  chamber. 

front  (open,  however,  to   the   sea- 


THE  NERVOUS  SYSTEM. 


183 


10 


water),  and  a  chamber  behind  it  filled  with  "vitreous 
humor." 

The  eye  of  Vertebrates  is  formed  by  the  infolding  of 
the  skin  to  create  a  lens,  and  an  outgrowth  of  the  brain 
to  make  a  sensitive 
layer;  both  enclosed  in 
a  white  spherical  case 
(sclerotic)  made  of  9 
tough  tissue,  with  a 
transparent  front,  call-  8 
ed  the  cornea.  This 
case  is  kept  in  shape  T 
by  two  fluids — the  thin 
aqueous  hum-or  filling 
the  cavity  just  behind 
the  cornea,  and  the 
ielly-like  vitreous  hu- 
mor occupying  the  lar- 
ger posterior  chamber. 
Between  the  two  hu- 
mors lies  the  double- 
convex  crystalline  lens. 
On  the  front  face  of 
the  lens  is  a  contractile 
circular  curtain  (iris), 
with  a  hole  in  the  cen- 
tre (pupil)',  and  lin- 
ing the  sclerotic  coat 
is  the  choroid  mem- 


Covered  -  with  FlG-  «S.-SectIon  of  the  Human  Retina,  X  400 :  1, 
internal  limiting  membrane;  2,  optic-nerve  fibres; 

dark  pigment.  The  3»  ganglion  cells ;  4,  internal  molecular  layer;  5, 

internal  granules  ;  6,  external  molecular  layer ;  7, 

OptlC     nerve,     entering       externalgranules;8,extemallimitingmembrane; 

at  the  back  of  the  eye     9' layer  of  rod8  and  cone8 ;  10' pigraent  layer> 
through  the  sclerotic  and  choroid  coats,  expands  into  the 
transparent   retina,  which   consists   of  several   layers — • 


COMPARATIVE  ZOOLOGY. 

fibrous,  cellular,  and  granular.  The  most  sensitive  part  is 
the  surface  lying  next  to  the  black  pigment.  And  here 
is  a  peculiarity  of  the  vertebrate  eye :  the  nerve-fibres,  en- 
tering from  behind,  turn  back  and  look  towards  the  bot- 
tom of  the  eye,  so  that  vision  is  directed  backward ;  while 
invertebrate  vision  is  directly  forward.  In  Vertebrates 
only,  the  optic  nerves  cross  each  other  (decussate)  in  pass- 
ing from  the  brain  to  the  eyes ;  so  that  the  right  side  of 
the  brain,  e.  g.,  receives  the  impressions  of  objects  on  the 
left  side  of  the  body.97 

Generally,  the  eyes  of  Vertebrates  are  on  opposite  sides 
of  the  head ;  but  in  the  Flat-fishes  both  are  on  the  same 
side.  Usually,  both  eyes  see  the  same  object  at  once  ;  but 
in  most  Fishes  the  eyes  are  set  so  far  back,  the  fields  of 
vision  are  distinct.  The  cornea  may  be  flat,  and  the  lens 
globular,  as  in  Fishes ;  or  the  cornea  very  convex,  and  the 
lens  flattened,  as  in  Owls.  Purely  aquatic  animals  have 
neither  eyelids  nor  tears,  but  nearly  all  others  (especially 
Birds)  have  three  lids.93  The  pupil  is  usually  round ;  but 
it  may  be  rhomb-shaped,  as  in  Frogs ;  vertically  oval,  as 
in  Crocodiles  and  Cats :  or  transversely  oval,  as  in  Geese, 
Doves,  Horses,  and  Ruminants.  Many  Quadrupeds,  as  the 
Cat,  have  a  membrane  (tapetum)  lining  the  bottom  of  the 
eyeball,  with  a  brilliant  metallic  lustre,  usually  green  or 
pearly :  it  is  this  which  makes  the  eyes  of  such  animals 
luminous  in  the  dark. 

2.  Instinct  and  Intelligence. 

The  simplest  form  of  nervous  excitement  is  mere  sensa- 
tion. Above  this  we  have  sensation  awakening  conscious- 
ness, out  of  which  come  those  voluntary  activities  grouped 
together  under  the  name  of  Instinct;  and,  finally,  Intelli- 
gence. 

The  lowest  forms  of  life  are  completely  under  law,  for 
their  movements  seem  to  be  due  solely  to  their  organiza- 


THE  NERVOUS  SYSTEM.  185 

tion.  They  are  automatons,  or  creatures  of  necessity. 
Such,  also,  are  some  actions  in  the  higher  animals,  as 
breathing,  the  beating  of  the  heart,  the  contractions  of 
the  iris,  and  all  the  first  movements  of  an  infant."  But, 
generally,  the  actions  of  animals  are  not  the  result  of  mere 
bodily  organization. 

The  inferior  orders  are  under  the  control  of  Instinct, 
i.  e.9  an  apparently  untaught  ability  to  perform  actions 
which  are  useful  to  the  animal.100  They  seem  to  be  born 
with  a  measure  of  knowledge  and  skill  (as  Man  is  said  to 
have  innate  ideas),  acquired  neither  by  reason  nor  experi- 
ment. For  what  could  have  led  Bees  to  imagine  that  by 
feeding  a  worker -larva  with  royal  jelly,  instead  of  bee- 
bread,  it  would  turn  out  a  queen,  instead  of  a  neuter? 
In  this  case,  neither  the  habit  nor  the  experience  could  be 
inherited,  for  the  worker -bees  are  sterile.  "We  can  only 
guess  that  the  discovery  has  been  communicated  by  the 
survivors  of  an  older  swarm.  Uniformity  is  another  char- 
acteristic feature  of  instinct.  Different  individuals  of  the 
same  species  execute  precisely  the  same  movements  under 
like  circumstances.  The  career  of  one  Bee  is  the  career 
of  any  other.  We  do  not  find  one  clever  and  another 
stupid.  Honey-combs  are  built. now  as  they  were  before 
the  Christian  era.  The  creatures  of  pure  instinct  appear 
to  be  tied  down,  by  the  constitution  of  their  nervous  sys- 
tem, to  one  line  of  action,  from  which  they  cannot  spon- 
taneously depart.  The  actions  vary  only  as  the  structure 
changes.101  There  is  a  wonderful  fitness  in  what  they  do, 
but  there  is  no  intentional  adaptation  of  means  to  ends. 

All  animals,  from  the  Star-fish  to  Man,  are  guided  more 
or  less  by  instinct;  but  the  best  examples  are  furnished 
by  the  insect-world,  especially  by  the  social  Hymenopters 
(Ants,  Bees,  and  Wasps).  The  Butterfly  carefully  pro- 
vides for  its  young,  which  it  is  destined  never  to  see ; 
many  Insects  feed  on  particular  species  of  plants,  which 


186  COMPARATIVE  ZOOLOGY. 

they  select  with  wonderful  sagacity;  and  Monkeys  avoid 
poisonous  berries;  Bees  and  Squirrels  store  up  food  for 
the  future ;  Bees,  Wasps,  and  Spiders  construct  with  mar- 
vellous precision  ;  and  the  subterranean  chambers  of  Ants 
and  the  dikes  of  the  Beaver  show  engineering  skill ;  while 
Salmon  go  from  the  ocean  up  the  rivers  to  spawn  ;  and 
Birds  of  the  temperate  zones  migrate  with  great  regu- 
larity. 

But  in  the  midst  of  this  automatism  there  are  the  glim- 
merings of  intelligence  and  free-will.  We  see  some  evi- 
dence of  choice  and  of  designed  adaptation.  Pure  in- 
stinct should  be  infallible.  Yet  we  notice  mistakes  that 
remind  us  of  mental  aberrations.  Bees  are  not  so  eco- 
nomical as  has  been  generally  supposed.  A  mathemati- 
cian can  make  five  cells  with  less  wax  than  the  Bee  uses 
for  four ;  while  the  Humble-bee  uses  three  times  as  much 
material  as  the  Hive  bee.  An  exact  hexagonal  cell  does 
not  exist  in  nature.  Flies  lay  eggs  on  the  carrion-plant 
because  it  happens  to  have  the  odor  of  putrid  meat.  The 
domesticated  Beaver  will  build  a  darn  across  its  apartment. 
Birds  frequently  make  mistakes  in  the  construction  and 
location  of  their  nests.  In  fact,  the  process  of  cheating 
animals  relies  on  the  imperfection  of  instinct.  'Nor  are 
the  actions  of  the  brute  creation  always  perfectly  uni- 
form ;  and,  so  far  as  animals  conform  to  circumstances, 
they  act  from  intelligence,  not  instinct.  There  is  proof 
that  some  animals  profit  by  experience.  Birds  do  learn 
to  make  their  nests;  and  the  older  ones  build  the  best. 
Trappers  know  well  that  young  animals  are  more  easily 
caught  than  old  ones.  Birds  brought  up  from  the  egg, 
in  cages,  do  not  make  the  characteristic  nests  of  their 
species ;  nor  do  they  have  the  same  song  peculiar  to  their 
species,  if  they  have  not  heard  it.  Chimney-swallows  cer- 
tainly built  their  nests  differently  in  America  three  hun- 
dred years  ago.  A  Bee  can  make  cells  of  another  shape, 


THE  NERVOUS  SYSTEM.  187 

for  it  sometimes  does;  its  actions,  therefore,  being  elec- 
tive and  conditional,  are  in  a  measure  the  result  of  calcu- 
lation. 

The  mistakes  and  variations  of  instinct  are  indications 
that  animals  have  something  more  —  a  limited  range  of 
that  principle  of  Intelligence  so  luminous  in  Man.  No 
precise  line  can  be  drawn  between  instinctive  and  intel- 
ligent acts ;  all  we  can  say  is,  there  is  more  freedom  of 
choice  in  the  latter  than  the  former;  and  that  some  ani- 
mals are  most  instinctive,  others  most  intelligent.  Thus, 
we  speak  of  the  instinct  of  the  Ant,  Bee,  and  Beaver, 
and  the  intelligence  of  the  Elephant,  Dog,  and  Monkey. 
Instinct  loses  its  peculiar  character  as  intelligence  becomes 
developed.  Ascending  from  the  Worm  and  Oyster  to 
the  Bee,  we  see  the  movements  become  more  complex  in 
character  and  more  special  in  their  objects;  but  instinct 
is  supreme.  Still  ascending,  we  observe  a  gradual  fading- 
away  of  the  instincts,  till  they  become  subordinate  to 
higher  faculties — will  and  reason.  We  can  predict  with 
considerable  certainty  the  actions  of  animals  guided  by 
pure  instinct;  but  in  proportion  as  they  possess  the  power 
of  adapting  means  to  ends,  the  more  variable  their  actions. 
Thus,  the  architecture  of  Birds  is  not  so  uniform  as  that 
of  Insects.102 

We  must  credit  brutes  with  a  certain  amount  of  obser- 
vation and  imitation,  curiosity  and  cunning,  memory  and 
reason.  Animals  have  been  seen  to  pause,  deliberate,  or 
experiment,  and  resolve.  The  Elephant  and  Horse,  Dog 
and  Monkey,  particularly,  participate  in  the  rational  nat- 
ure of  Man,  up  to  a  certain  point.  Thinking  begins  wher- 
ever there  is  an  intentional  adaptation  of  means  to  ends ; 
for  that  involves  the  comparison  and  combination  of  ideas. 
Animals  interchange  ideas:  the  whine  of  a  Dog  at  the 
door  on  a  cold  night  certainly  implies  that  he  wants  to 
be  let  in.  Bees  and  Ants,  it  is  well  known,  confer  by 


188  COMPARATIVE  ZOOLOGY. 

passing  their  antennae.     All  the  higher  animals,  too,  have 
similar  emotions — as  joy,  fear,  love,  and  anger. 

While  instinct  culminates  in  Insects,  the  highest  devel- 
opment of  intelligence  is  presented  in  Man.103  In  Man 
only  does  instinct  cease  to  be  the  controlling  power.  He 
stands  alone  in  having  the  whole  of  his  organization  con- 
formed to  the  demands  of  his  brain;  and  his  intelligent 
acts  are  characterized  by  the  capacity  for  unlimited  prog- 
ress. The  brutes  can  be  improved  by  domestication  ; 
but,  left  to  themselves,  they  soon  relapse  into  their  origi- 
nal wildness.  Civilized  Man  also  goes  back  to  savagery; 
yet  Man  (though  not  all  Men)  has  the  ambition  to  exalt 
his  mental  and  moral  nature.  He  has  a  soul,  or  conscious 
relation  to  the  Infinite,  which  leads  him  to  aspire  after  a 
lofty  ideal.  Only  he  can  form  abstract  ideas.  And, 
finally,  he  is  a  completely  self-determining  agent,  with  a 
prominent  will  and  conscience — the  highest  attribute  of 
the  animal  creation.  In  all  this,  Man  differs  profoundly 
from  the  lower  forms  of  life. 

3.  The  Voices  of  Animals. 

Most  aquatic  animals  are  mute.  Some  Crabs  make 
noises  by  rubbing  their  fore-legs  against  their  carapace ; 
and  many  Fishes  produce  noises  in  various  ways,  mostly 
by  means  of  the  swim-bladder.  Insects  are  the  Inverte- 
brates which  make  the  most  noise.  Their  organs  are  usu- 
ally external,  while  those  of  Vertebrates  are  internal.  In- 
sects of  rapid  flight  generally  make  the  most  noise.  In 
some  the  noise  is  produced  by  friction  (stridulation) ;  in  oth- 
ers, by  the  passage  of  air  through  the  spiracles  (humming). 
The  shrill  notes  of  Crickets  and  Grasshoppers  are  pro- 
duced by  rubbing  the  wings  against  each  other,  or  against 
the  thighs ;  but  the  Cicada,  or  Harvest-fly,  has  a  special 
apparatus — a  tense  membrane  on  the  abdomen,  acted  upon 
by  muscles.  The  buzzing  of  Flies  and  humming  of  Bees 


THE  NERVOUS  SYSTEM.  189 

are  caused,  in  part,  by  the  vibrations  of  the  wings ;  but 
the  true  voice  of  these  Insects  comes  from  the  spiracles 
of  the  thorax. 

Snakes  and  Lizards  have  no  vocal  cords,  and  can  only 
hiss.  Frogs  croak104  and  Crocodiles  roar,  and  the  huge 
Tortoise  of  the  Galapagos  Islands  utters  a  hoarse,  bellow- 
ing noise. 

The  vocal  apparatus  in  Birds  is  situated  at  the  lower 
end  of  the  trachea,  where  it  divides  into  the  two  bron- 
chi.105 It  consists  mainly  of  a  bony  drum,  with  a  cross- 
bone,  having  a  vertical  membrane  attached  to  its  upper 
edge.  The  membrane  is  put.  in  motion  by  currents  of  air 
passing  on  either  side  of  it.  Five  pairs  of  muscles  (in  the 
Songsters)  adjust  the  length  of  the  windpipe  to  the  pitch 
of  the  glottis.  The  various  notes  are  produced  by  differ- 
ences in  the  blast  of  air,  as  well  as  by  changes  in  the  ten- 
sion of  the  membrane.  The  range  of  notes  is  commonly 
within  an  octave.  Birds  of  the  same  family  have  a  simi- 
lar voice.  All  the  Parrots  have  a  harsh  utterance ;  Geese 
and  Ducks  quack;  Crows,  Magpies,  and  Jays  caw;  while 
the  Warblers  differ  in  the  quality,  rather  than  the  kind,  of 
note.106  The  Parrot  and  Mocking-bird  use  the  tongue  in 
imitating  human  sounds.  Some  species  possess  great  com- 
pass of  voice.  The  Bell -bird  can  be  heard  nearly  three 
miles;  and  Livingstone  said  he  could  distinguish  the  voices 
of  the  Ostrich  and  the  Lion  only  by  knowing  that  the  for- 
mer roars  by  day,  and  the  latter  by  night. 

The  vocal  organ  of  Mammals,  unlike  that  of  Birds,  is 
in  the  upper  part  of  the  larynx.  It  consists  of  four  car- 
.tilages,  of  which  the  largest  (the  thyroid)  produces  the 
prominence  in  the  human  throat  known  as  "Adam's  ap- 
ple," and  two  elastic  bands,  called  "  vocal  cords,"  just  be- 
low the  glottis,  or  upper  opening  of  the  windpipe.  The 
various  tones  are  determined  by  the  tension  of  these  cords, 
which  is  effected  by  the  raising  or  lowering  of  the  thyroid 


190  COMPARATIVE  ZOOLOGY. 

cartilage,  to  which  one  end  of  the  cords  is  attached.  The 
will  cannot  influence  the  contraction  of  the  vocalizing 
muscles,  except  in  the  very  act  of  vocalization.  The  vo- 
cal sounds  produced  by  Mammals  may  be 
distinguished  into  the  ordinary  voice,  the 
cry,  and  the  song.  The  second  is  the  sound 
made  by  brutes.  The  Whale,  Porpoise,  Ar- 
madillo, Ant-eater,  Porcupine,  and  Giraffe 
are  generally  silent.  The  Bat's  voice  is 
probably  the  shrillest  sound  audible  to  hu- 
i59.-Human  man  ears>  There  is  little  modulation  in 

Larynx,  seen  in 

profile;  a,  half  brute  utterance.     The  Opossum  purrs,  the 

of     the     hyoid    01      ,  ,    Tr  .        TT 

bone;    «,    tra-  Sloth  and  Kangaroo  moan,  the  Hog  grunts 


°r  squeals,  the  Tapir  whistles,  the  Stag  bel- 
lows, and  the  Elephant  gives  a  hoarse  trump- 
et sound  from  its  trunk  and  a  deep  groan  from  its  throat. 
All  Sheep  have  a  guttural  voice;  all  the  Cows  low,  from 
the  Bison  to  the  Musk-ox;  all  the  Horses  and  Donkeys 
neigh;  all  the  Cats  miau,  from  the  domestic  animal  to  the 
Lion  ;  all  the  Bears  growl  ;  and  all  the  Canine  family  — 
Fox,  Wolf,  and  Dog  —  bark  and  howl.  The  Howling- 
monkeys  and  Gorillas  have  a  large  cavity,  or  sac,  in  the 
throat  for  resonance,  enabling  them  to  utter  a  powerful 
voice;  and  one  of  the  Gibbon  -apes  has  the  remarkable 
power  of  emitting  a  complete  octave  of  musical  notes. 
The  human  voice,  taking  the  male  and  female  together, 
has  a  range  of  nearly  four  octaves.  Man's  power  of  speech, 
or  the  utterance  of  articulate  sounds,  is  due  to  his  intel- 
lectual development  rather  than  to  any  structural  differ- 
ence between  him  and  the  Apes.  Song  is  produced  by 
the  vocal  cords,  speech  by  the  mouth. 


KEFKODUCTION. 


191 


CHAPTER  XIX. 

REPRODUCTION. 

IT  is  a  fundamental  truth  that  every  living  organism 
has  had  its  origin  in  some  pre-existing  organism.  The 
doctrine  of  "spontaneous  generation,"  or  the  supposed 
origination  of  organized  structures  out  of  inorganic  parti- 
cles, or  out  of  dead  organic  matter,  has  not  yet  been  sus- 
tained by  facts. 

Reproduction  is  of  two  kinds  —  sexual  and  asexual. 
All  animals,  probably,  have  the  first  method,  while  a  very 
great  number  of  the 
lower  forms  of  life  have 
the  latter  also. 

Of  asexual  reproduc- 
tion there  are  two  kinds 
-  Self  -  division      and 
Budding. 

Self-division,  the 
simplest  mode  possible, 
is  a  natural  breaking-up 
of  the  body  into  distinct 
surviving  parts.  This 
process  is  sometimes  ex- 
traordinarily rapid,  the 
increase  of  one  animal- 
cule (Paramcecium)  be- 
ing Computed  at  268  FIG.  160.— Reproduction  of  Infusoria  (Vorticel- 

., , .  .  , ,         T ,          Ice  and  others)  by  fission  or  self-division. 

millions  in  a  month.    It 

may  be  either  transverse  or  longitudinal.     Of  the  first 

sort, Figs.  1,2, and  3  (Fig.  160)  are  examples;  of  the  latter, 


192  COMPARATIVE  ZOOLOGY. 

Figs.  4r,  6,  9-13.  This  form  of  reproduction  is,  naturally, 
confined  to  animals  whose  tissues  and  organs  are  simple, 
and  so  can  easily  bear  division,  or  whose  parts  are  so  ar- 
ranged as  to  be  easily  separable  without  serious  injury. 
The  process  is  most  common  in  Protozoa,  Worms,  and 
Polyps. 

Budding  is  separated  by  no  sharp  line  from  Self-divi- 
sion. While  in  the  latter  a  part  of  the  organs  of  the  par- 
ent go  to  the  offspring,  in  the  former  one  or  more  cells 
of  the  original  animal  begin  to  develop  and  multiply  so 
as  to  grow  into  a  new  animal  like  the  parent.  The  proc- 
ess in  animals  is  quite  akin  to  the  same  operation  in 
plants.  The  buds  may  remain  permanently  attached  to 
the  parent-stock,  thus  making  a  colony,  as  in  Corals  and 
Bryozoa  ( continuous  budding ),  or  they  may  be  detached 
at  some  stage  of  growth  (discontinuous  budding).  This 
separation  may  occur  when  the  bud  is  grown  up,  as  in 
Hydra  (Fig.  191),  or  as  in  Plant-lice,  Daphnias  (Fig.  255), 
and  among  other  animals  the  buds  may  be  internal,  and 
detached  when  entirely  undeveloped  and  externally  re- 
sembling an  egg.  They  differ,  however,  entirely  from  a 
true  egg  in  developing  directly,  without  fertilization. 

Sexual  Reproduction  requires  cells  of  two  kinds,  usu- 
ally from  different  animals.  These  are  the  germ-cell  or 
egg,  and  the  sperm-cell.  The  embryo  is  developed  from 
the  union  of  the  two  cells.107 

The  egg  consists  essentially  of  three  parts,  the  germinal 
vesicle,  the  yolk,  and  the  vitelline  membrane,  which  sur- 
rounds both  the  first.  It  is  ordinarily  globular  in  shape. 
Of  the  three  parts,  the  primary  one  is  the  germinal  vesi- 
cle— a  particle  of  protoplasm.  The  yolk  serves  as  food 
for  this,  and  the  membrane  protects  both.  When  a  great 
mass  of  yolk  is  present,  it  is  divisible  into  two  parts— -for- 
mative and  food  yolk.  The  latter  is  of  a  more  oily  nature 
than  the  former,  and  is  usually  not  segmented  with  the 


REPRODUCTION.  193 

egg.  The  structure  of  the  hen's  egg  is  more  complicated. 
The  outside  shell  consists  of  earthy  matter  (lime)  depos- 
ited in  a  net-work  of  animal  matter. 
It  is  minutely  porous,  to  allow  the 
passage  of  vapor  and  air  to  and  fro. 
Lining  the  shell  is  a  double  mem- 
brane (tneinbrana  putaminis)  resem- 
bling delicate  tissue-paper.  At  the 
larger  end,  it  separates  to  enclose  a  FlG.  161.  _^7tical  E,g, 
bubble  of  air  for  the  use  of  the  chick.  or  Cell:  *  viteiiine  mem- 

braue ;  y,  oleaginous  pole  ; 

Next  comes  the  albumen,  or  "  white,       a,  albuminous  poic;  p, 

n  j     -,  .,,  .          Purkinjean,  or  germinal, 

in  spirally  arranged  layers,  within  vesicle ;  «>,  wagnerian,  or 
which  floats  the  yolk.  The  yolk  is  germiua1' dou 
prevented  from  moving  towards  either  end  of  the  egg  by 
two  twisted  cords  of  albumen,  called  chalazce ;  yet  is  al- 
lowed to  rise  towards  one  side,  the  yolk  being  lighter  than 
the  albumen.  The  yolk  is  composed  of  oily  granules 
(about  -5--^-  of  an  inch  in  diameter),  enclosed  in  a  sac,  called 
the  viteiiine  membrane,  and  disposed  in  concentric  layers, 
like  a  set  of  vases  placed  one  within  the  other.  That  part 
of  the  yolk  which  extends  from  the  centre  to  a  white 


Fio.162.  —  Longitudinal  Section  of  Hen's  Egg  before  incubation:  a,  yolk,  showing 
concentric  layers;  a',  its  semi-fluid  centre,  consisting  of  a  white  granular  sub- 
stance—  the  whole  yolk  is  enclosed  in  the  viteTline  meinbrane;  ft,  inner  dense 
part  of  the  albumen  ;  &',  outer,  thinner  part ;  c,  the  chalazae,  or  albumen,  twisted 
by  the  revolutions  of  the  yolk;  rf,  double  shell-membrane,  split  at  the  large  end 
to  form  the  chamber,/;  e,  the  shell ;  h,  the  white  spot,  or  cicatricula. 

13 


194:  COMPARATIVE  ZOOLOGY. 

spot  (cicatricula)  on  the  outside  cannot  be  hardened,  even 
with  the  most  prolonged  boiling.  The  cicatricula,  or  em- 
bryo-spot— the  part  for  which  all  the  rest  was  made — is 
a  thin  disk  of  cellular  structure,  in  which  the  new  life 
first  appears.  This  was  originally  a  simple  cell,  but  de- 
velopment has  gone  some  way  before  the  egg  is  laid.  It 
is  always  on  that  side  which  naturally  turns  uppermost, 
for  the  yolk  can  turn  upon  its  axis ;  it  is,  therefore,  al- 
ways nearest  to  the  external  air  and  to  the  Hen's  body — 
two  conditions  necessary  for  its  development.  There  is 
another  reason  for  this  polarity  of  the  egg:  the  lighter 
and  most  delicate  part  of  the  yolk  is  collected  in  its 
upper  part,  while  the  heavy,  oily  portion  remains  be- 
neath. 

In  most  eggs  the  shell  and  albumen  are  wanting.  When 
the  albumen  is  present,  it  is  commonly  covered  by  a  mem- 
brane only.  In  Sharks,  the  envelope  is  horny;  and  in 
Crocodiles  it  is  calcareous,  as  in  Birds. 

The  egg  of  the  Sponge  has  no  true  vitelline  membrane, 
and  is  not  unlike  an  ordinary  amoeboid  cell.     An  egg  is, 
in  fact,  little  more  than  a  very  large 
cell,  of  which  the  germinal  vesicle  is 
the  nucleus. 

The  size  of  an  egg  depends  mainly 
upon  the  quantity  of  yolk  it  contains ; 
and  to  this  is  proportioned  the  grade  of 
development  which  the  embryo  attains 
when  it  leaves  the  egg.108     In  the  eggs 
FIG.  lea.— Egg  of  sponge;  of  the  Star-fishes,  Worms,  Insects,  Mol- 
n,  nucleus.  jusks  (except  t]ie  Cuttle  -  fishes),  many 

Amphibians,  and  Mammals,  the  yolk  is  very  minute  and 
formative,  i.  e.,  it  is  converted  into  the  parts  of  the  future 
embryo.  In  the  eggs  of  Lobsters,  Crabs,  Spiders,  Cepha- 
lopods,  Fishes,  Reptiles,  and  Birds,  the  yolk  is  large  and 
colored,  and  consists-  of  two  parts  —  the  formative,  or 


REPRODUCTION.  195 

germ-yolk,  immediately  surrounding  the  germinal  vesicle; 
and  the  nutritive,  or  food-yolk,  constituting  the  greater 
part  of  the  mass,  by  which  the  young  animal  in  the  egg- 
life  is  nourished.  In  the  latter  case,  the  young  come  forth 
more  mature  than  where  the  food-yolk  is  wanting. 

As  to  form,  eggs  are  oval  or  elliptical,  as  in  Birds  and 
Crocodiles;  spherical,  as  in  Turtles  and  Wasps;  cylindri- 
cal, as  in  Bees  and  Flies;  or  shaped  like  a  hand-barrow, 
with  tendrils  on  the  corners,  as  in  the  Shark.  The  eggs 


Fro.  164.— Egg  of  a  Shark  (the  external  gills  of  the  embryo  are  not  represented). 

of  some  very  low  forms  are  sculptured  or  covered  with 
hairs  or  prickles. 

The  number  of  eggs  varies  greatly  in  different  animals, 
as  it  is  in  proportion  to  the  risks  during  development. 
Thus,  the  eggs  of  aquatic  tribes,  being  unprotected  by  the 
parent,  and  being  largely  consumed  by  many  animals,  are 
multiplied  to  prevent  extinction.  The  spawn  of  a  single 
Cod  contains  millions  of  eggs ;  that  of  the  Oyster,  6,000,- 
000.  A  Queen-bee,  during  the  five  years  of  her  existence, 
lays  about  a  million  eggs. 

Eggs  are  laid  one  by  one,  as  by  Birds ;  or  in  clusters,  as 
by  Frogs,  Fishes,  and  most  Invertebrates.  The  spawn  of 
the  Sea-snails  consists  of  vast  numbers  of  eggs  adhering 
together  in  masses,  or  in  sacs,  forming  long  strings. 

As  a  rule,  the  higher  the  rank,  the  more  care  animals 


196  COMPARATIVE  ZOOLOGY. 

take  of  their  eggs  and  their  young,  and  the  higher  the 
temperature  needed  for  egg-development.  In  the  major- 
it)7  of  cases,  eggs  are  left  to  themselves.  The  fresh-water 
Mussel  (Unio)  carries  them  within  its  gills,  and  the  Lob- 
ster under  its  tail.  The  eggs  of  many  Spiders  are  envel- 
oped in  a  silken  cocoon,  which  the  mother  guards  with 
jealous  care.  Insects,  as  Flies  and  Moths,  deposit  their 
eggs  where  the  larva,  as  soon  as  born,  can  procure  its  own 
food.  Most  Fishes  allow  their  spawn,  or  roe,  to  float  in 
the  water ;  but  a  few  build  a  kind  of  flat  nest  in  the  sand 
or  mud,  hovering  over  the  eggs  until  they  are  hatched ; 
while  the  Acara  of  the  Amazons  carries  them  in  its 
mouth.  The  Amphibians,  generally,  envelop  their  eggs 
in  a  gelatinous  mass,  which  they  leave  to  the  elements; 
but  the  female  of  the  Surinam  Toad  carries  hers  on  her 
back,  where  they  are  placed  by  the  male.  The  great  Am- 
azon Turtles  lay  their  eggs  in  holes  two  feet  deep,  in  the 
sand;  while  the  Alligators  simply  cover  theirs  with  a  few 
leaves  and  sticks.  Nearly  all  Birds  build  nests,  those  of 
the  Perchers  being  most  elaborate,  as  their  chicks  are  de- 
pendent for  a  time  on  the  parent.109  The  young  of  Mar- 
supials, as  the  Kangaroo,  which  are  born  in  an  extremely 
immature  state,  are  nourished  in  a  pouch  outside  of  the 
body.  But  the  embryo  of  all  other  Mammals  is  devel- 
oped within  the  parent  to  a  more  perfect  condition,  by 
means  of  a  special  organ,  the  placenta.  It  is  a  general 
law,  that  animals  receiving  in  the  embryo  state  the  longest 
and  most  constant  parental  care  ultimately  attain  the  high- 
est grade  of  development. 

The  Protozoa,  which  have  no  true  eggs,  have  a  sort  of 
reproduction  called  conjugation.  In  this  process  two 
Amoebse  unite  into  one  mass,  surround  themselves  with  a 
case,  in  which  they  divide  into  several  parts,  each  portion 
becoming  a  new  Amoeba. 

The  sperm-cells  differ  from  the  egg  in  being  very  small, 


DEVELOPMENT.  197 

usually  motile,  and  in  that  a  large  number  are  usually 
produced  from  a  single  cell  of  the  animal,  while  the  egg 
represents  an  entire  cell.  The  union  of  the  sperm-cell 
with  the  germinal  vesicle  (fertilization)  is  the  first  step 
in  development,  and  without  it  the  egg  will  not  develop. 
But  the  nature  of  the  process  is  unknown. 


CHAPTEK  XX. 

DEVELOPMENT. 

Development  is  the  evolution  of  a  germ  into  a  com- 
plete organism.  The  study  of  the  changes  within  the  egg 
constitutes  the  science  of  Embryology;  the  transforma- 
tions after  the  egg-life  are  called  metamorphoses,  and  in- 
clude growth  and  repair. 

The  process  of  development  is  a  passage  from  the  gen- 
eral to  the  special,  from  the  simple  to  the  complex,  from 
the  homogeneous  to  the  heterogeneous,  by  a  series  of  dif- 
ferentiations. It  brings  out  first  the  profounder  distinc- 
tions, and  afterwards  those  more  external.  That  is,  the 
most  essential  parts  appear  first.  And  not  only  does  de- 
velopment tend  to  make  the  several  organs  of  an  individ- 
ual more  distinct  from  one  another,  but  also  the  individual 
itself  more  distinguished  from  other  individuals  and  from 
the  medium  in  which  it  lives.  With  advancing  develop- 
ment, the  animal,  as  a  rule,  acquires  a  more  specific,  defi- 
nite form,  and  increases  in  weight  and  locomotive  power. 
Life  is  a  tendency  to  individuality. 

The  first  step  in  development,  after  fertilization,  is  the 
segmentation  of  the  egg,  by  a  process  of  self-division.  In 
the  simplest  form,  the  whole  yolk  divides  into  two  parts ; 
these  again  divide,  making  four,  eight,  sixteen,  etc.,  parts, 


198 


COMPARATIVE  ZOOLOGY. 


until  the  whole  yolk  is  subdivided  into  very  small  por- 
tions (cells)  surrounding  a  central  cavity.  This  stage  is 
known  as  the  "  mulberry-mass,"  or  Uastula  (Fig.  165,  c). 


FIG.  165. — First  Stages  in  Segmentation  °f  a  Mammalian  Egg:  A,  first  division  into 
halves,  with  spermatozoa  around  it;  £  and  C,  progressive  subdivision,  ultimate- 
ly transforming  the  vitellus,  or  yolk,  into  a  "  mulberry  mass"  of  globules,  or  em- 
bryo-cells. 

If  the  yolk  is  larger,  relatively  to  the  germinal  vesicle, 
the  process  of  division  may  go  on  more  slowly  in  one  of 
the  two  parts  of  the  egg,  first  formed ;  or  in  very  large 
eggs,  like  those  of  Birds  and  Cuttle-fishes,  only  a  small 
part  of  the  yolk  subdivides. 

In  some  form,  the  process  of  segmentation  is  found  in 
the  eggs  of  all  animals,  as  is  also  the  following  stage. 
This  step  is  the  differentiation  of  the 
single  layer  of  cells  into  two  parts, 
one  for  the  body-wall,  the  other  for 
the  wall  of  the  digestive  tract.     In 
the  typical  example*,  this  is  accom- 
plished by  one  part  of  the  wall  of 
.  i66._ Diagram  of  Gastra-  the  blastula  turning  in,  so  far  as  to 

la  of  a  Worm  (Sagitta):  a,  .1         ,  T      ,     »        .     ,  /• 

primitive  mouth ;  6,  primi-  convert  the  blastula  into  a  sort  of 
XSR&E&  -!  double-walled  cnp,  the  gastrula  (Fig. 

endoderm :  ec,  ectoderm.        166).       One    half    of    the  Wall    of   the 

blastula  is  now  the  outer  wall  of  the  germ,  the  other  half 
that  of  the  digestive  cavity ;  the  original  blastula-cavity 
is  now  the  body-cavity,  and  the  new  cavity  formed  by  the 
infolding  is  the  stomach,  and  its  opening  is  both  mouth 


DEVELOPMENT. 


199 


and  vent  (Figs.  165, 166).  Some  adult  animals  are  little 
more  than  such  a  sac.  Hydra  (Fig.  191),  for  instance,  is 
little  different  from  a  gastrula  with  tentacles,  and  one  of 
its  relatives  wants  even  these  additions. 

Ordinarily,  however,  development  goes  much  further. 
From  the  two  original  layers  arises,  in  various  ways,  a  third 
between  them,  making  the  three  primitive  germ-layers — 
epiblast)  mesoblast,  and  hypoblast.  This  new  layer  is  nec- 
essarily in  the  primitive  body -cavity,  which  it  may  fill 
up ;  or  usually  a  new  body-cavity  is  formed,  in  different 
ways  in  different  groups.  •  In  by  far  the  great  majority 
of  animals  the  digestive  tract  gets  a  new  opening,  which 
usually  becomes  the  mouth  ;  and  the  old  mouth  may 
close,  or  serve  only  the  functions  of  the  vent.  From  this 
point  the  development  of  each  group  must  be  traced  in 
detail. 

Development  of  a  Hen's  Egg.  —  After  the  segmentation 
the  germinal  disk  divides  into  two  layers,  between  which 
a  third  is  soon  formed.  The  upper  layer  (epiblast)  gives 


FIG.  1CT. — Vertical  Sections  of  an  Egg,  showing  progressive  stages  of  development: 
a,  uotochord ;  6,  medullary  furrow,  becoming  a  closed  canal  in  the  last. 

rise  to  the  cuticle,  brain,  spinal  cord,  retina,  crystalline 
lens,  and  internal  ear.  From  the  lower  layer  (hypoblast} 
is  formed  the  epithelium  of  the  digestive  canal.  From 
the  middle  layer  (mesoblast)  come  all  the  other  organs- 
muscles,  nerves,  bones,  etc.  The  mesoblast  thickens  so 
as  to  form  two  parallel  ridges  running  lengthwise  of 
the  germ,  and  leaving  a  groove  between  them  (medul- 
lary furrow  and  ridges).1™  The  ridges  gradually  rise, 
carrying  with  them  the  epiblast,  incline  towards  each  oth- 
er, and  at  last  unite  along  the  back.  So  that  we  have  a 


200  COMPARATIVE  ZOOLOGY. 

tube  of  epiblast  surrounded  by  mesoblast,  which  is  itself 
covered  by  epiblast.  This  tube  becomes  the  brain  and 
spinal  cord,  whose  central  canal,  enlarging  into  the  ven- 
tricles -of  the  brain,  tells  the  story  of  its  original  forma- 
tion. Beneath  the  furrow,  a  delicate  cartilaginous  thread 
appears  (called  notochord)  —  the  predecessor  of  the  back- 
bone. Meanwhile  the  mesoblast  has  divided  into  two 
layers,  except  in  the  middle  of  the  animal,  beneath  the 
spinal  cord,  and  in  the  head.  One  of  these  layers  remains 
attached  to  the  epiblast,  and  with  it  forms  the  body-wall  ; 
the  other  bends  rapidly  downward,  carrying  the  hypoblast 
with  it,  and  forms  the  wall  of  the  intestine.  The  space 
thus  left  between  the  layers  of  the  mesoblast  is  the  body- 
cavity.  At  the  same  time,  the  margin  of  the  germ  ex- 
tends farther  and  farther  over  the  yolk,  till  it  completely 
encloses  it.  So  that  now  we  see  two  cavities  —  a  small 
one,  containing  the  nervous  system  ;  and  a  larger  one  be- 
low, for  the  digestive  organs.  Presently,  numerous  rows 

of  corpuscles  are  seen 

on   ^ie    middle   ^aJer? 
which  are  snbsequent- 
ly  enclosed,  forming  a 
__.  _    ,  .  net-work  of  capillaries, 

FIG.  168.  —  Rudimentary  Hearts,  human  :  1,  venous  • 

trunks  ;  2,  auricle  ;  3,  ventricle  ;  4,  bulbus  arte-    Called  the  Vascular  area. 
riosus.  ,      ,  .      .. 

A  dark  spot  indicates 

the  situation  of  the  heart,  which  is  the  first  distinctly 
bounded  cavity  of  the  circulatory  system.  It  is  a  short 
tube  lying  lengthwise  just  behind  the  head,  with  a  feeble 
pulsation,  causing  the  blood  to  flow  backward  and  for- 
ward. The  tube  is  gradually  bent  together,  until  it  forms 
a  double  cavity,  resembling  the  heart  of  a  Fish.  On  the 
fourth  day  of  incubation,  partitions  begin  to  grow,  divid- 
ing the  cavities  into  the  right  and  left  auricles  and  ven- 
tricles. The  septum  between  the  auricles  is  the  last  to 
be  finished,  being  closed  the  moment  respiration  begins. 


m' 

'^HB 


DEVELOPMENT. 


201 


The  blood-vessels  ramify  in  all  directions  through  the 
yolk,  making  it  a  spongy  mass,  and  all  perform  the  same 
office ;  it  is  not  till  the  fourth  or  fifth  day  that  arteries 
can  be  distinguished  from  veins,  by  being  thicker,  and  by 
carrying  blood  only  from  the  heart.111 


A.  A 

FIG.  169. — Embryo  in  a  Heu's  Egg  daring  the  first  five  days:  A,  hypoblast;  B,  lower 
layer  of  mesoblast ;  C,  upper  layer  of  raesoblast  and  epiblast  united,  in  the  last 
figures  forming  the  amniotic  sac ;  D,  vitelline  membrane ;  e,  thickened  blasto- 
derm, the  first  rudiment  of  the  dorsal  part  (in  the  last  figure  it  marks  the  place 
of  the  lungs);  h,  heart;  a,  6,  its  two  chambers;  ct  aortic  arches;  m,  aorta;  i, 
liver ;  p,  allautois. 


202  COMPARATIVE  ZOOLOGY. 

The  embryo  lies  with  its  face,  or  ventral  surface,  tow- 
ards the  yolk,  the  head  and  tail  curving  towards  each 


FIG.  1?0.—  Hen's  Egg,  more  highly  developed.  The  embryo  is  enveloped  by  the  am- 
nion,  and  has  the  umbilical  vessel,  or  remifcuit  of  the  yolk,  hanging  from  its  un- 
der surface;  while  the  nllantois  turns  upward,  and  spreads  out  over  the  internal 
surface  of  the  shell-membrane.  (From  Daltou's  "  Physiology.") 

other.     Around  the  embryo  on  all  sides  the  epiblast  and 
upper  layer  of  the  inesoblast  rise  like  a  hood  over  the 

back  of  the  embryo  till  they 
form  a  closed  sac,  called  the 
amnion.  It  is  filled  with  a 
thin  liquid,  which  serves  to 
protect  the  embryo.  Mean- 
while, another  important  or- 
gan is  forming  on  the  other 
side.  From  the  hinder  por- 
tion of  the  alimentary  canal 
an  outgrowth  is  formed 

FIG.  171.  -Mammalian  Embryo,  with  al-  wnich    extends    beVOlld     the 
lantois  fully  formed:   1,  umbilical  vesi- 

cle, containing  the  last  of  the  yolk;  2,  wall   of  the   embryo  proper 

amnion;  3,  allautois,  on  which  the  fringes  .  ,  »     •, 

of  the  placenta  are  developing.    (From  ItttO  the  Cavity  OI  the  amni- 


Dalton's  "Physiology.")  Qn  ftnd  gpreads  Qut  Qver 

whole  inner  surface  of  the  shell,  so  that  it  partly  surrounds 
both  embryo  and  inner  layer  of  the  amnion  (amnion  prop- 


DEVELOPMENT.  203 

er).  This  is  the  aUantois.  It  is  full  of  blood-vessels,  and 
it  serves  as  the  respiratory  organ  until  the  chick  picks  the 
shell  and  breathes  by  its  lungs.113  The.chorion  is  the  out- 
ermost part  of  the  allantois,  and  the  placenta  of  Mammals 
is  the  shaggy,  vascular  edge  of  the  chorion. 

The  alimentary  canal  is  at  first  a  straight  tube  closed  at 
both  ends,  the  middle  being  connected  with  the  yolk-bag. 
As  it  grows  faster  than  the  body,  it  is  thrown  into  a  spi- 
ral coil;  and  at  several  points  it  dilates,  to  form  the  crop, 
stomach,  gizzard,  etc.  The  mouth  is  developed  from  an 
infolding  of  the  skin.  The  liver  is  an  outgrowth  from 
the  digestive  tube,  at  first  a  cluster  of  cells,  then  of  folli- 
cles, and  finally  a  true  gland.  The  lungs  are  developed 
on  the  third  day  as  a  minute  bud  from  the  upper  part  of 
the  alimentary  canal,  or  pharynx.  As  they  grow  in  size, 
they  pass  from  a  smooth  to  a  cellular  condition. 

The  skeleton  at  the  beginning  consists,  like  the  noto- 
chord,  of  a  cellular  material,  which  gradually  turns  to  car- 
tilage. Then  minute  canals  containing  blood-vessels  arise, 
and  earthy  matter  (chiefly  phosphate  of  lime)  is  deposited 
between  the  cells.  The  primary  bone  thus  formed  is 
compact:  true  osseous  tissue,  with  canaliculi,  laminae,  and 
Haversian  canals,  is  the  result  of  subsequent  absorption.113 
Certain  bones,  as  those  of  the  face  and  cranium,  are  not 
preceded  by  cartilage,  but  by  connective  tissue:  these  are 
called  membrane  bones.  Ossification,  or  bone-making,  be- 
gins at  numerous  distinct  points,  called  centres ;  and,  the- 
oretically, every  centre  stands  for  a  bone,  so  that  there  are 
as  many  bones  in  a  skeleton  as  centres  of  ossification. 
But  the  actual  number  in  the  adult  animal  is  much  small- 
er, as  many  of  the  centres  coalesce.114  The  development 
of  the  backbone  is  not  from  the  head  or  from  the  tail,  but 
from  a  central  point  midway  between :  there  the  first  ver- 
tebrae appear,  and  from  thence  they  multiply  forward  and 
backward. 


204  COMPARATIVE  ZOOLOGY. 

The  limbs  appear  as  buds  on  the  sides  of  the  body; 
these  lengthen  and  expand  so  as  to  resemble  paddles — 
the  wings  and  legs  looking  precisely  alike ;  and,  finally, 
they  are  divided  each  into  three  segments,  the  last  one 
subdividing  into  digits.  The  feathers  are  developed  from 
the  outside  cells  of  the  epidermis :  first,  a  horny  cone  is 
formed,  which  elongates  and  spreads  out  into  a  vane,  and 
this  splits  up  into  barbs  and  barbules. 

The  muscle-fibres  are  formed  either  by  the  growth  in 
length  of  a  tingle  cell,  or  by  the  coalescence  of  a  row  of 
cells :  the  cell-wall  thus  produces  a  long  tube — the  sarco- 
lemma  of  a  fibre — and  the  granular  contents  arrange  them- 
selves into  linear  series,  to  make  fibrillse. 

Nervous  tissue  is  derived  from  the  multiplication  and 
union  of  embryo-cells.  The  white  fibres  at  first  resemble 
the  gray.  The  brain  and  spinal  marrow  are  developed 
from  the  epiblastic  lining  of  the  medullary  furrow.  Soon 
the  brain,  by  two  constrictions,  divides  into  fore -brain, 
mid-brain,  and  hind -brain.  The  fore- brain  throws  out 
two  lateral  hemispheres  (cerebrum),  and  from  these  pro- 
trude forward  the  two  olfactory  lobes.  From  the  mid- 
dle-brain grow  the  optic  lobes;  and  the  hind -brain  is 
separated  into  cerebellum  and  medulla  oblongata.  The 
essential  parts  of  the  eye,  retina  and  crystalline  lens,  are 
developed,  the  former  as  a  cup-like  outgrowth  from  the 
fore-brain,  the  latter  as  an  ingrowth  of  the  epidermis. 
An  infolding  of  the  epidermis  gives  rise  to  the  essential 
parts  of  the  inner  ear,  and  from  the  same  layer  come  the 
olfactory  rods  of  the  nose  and  the  taste-buds  of  the  tongue. 
So  that  the  central  nervous  system  and  the  essential  parts 
of  most  of  the  sense-organs  have  a  common  origin. 

Modes  of  Development. — The  structure  and  embryology 
of  a  Hen's  egg  exhibit  many  facts  which  are  common 
to  all  animals.  But  every  grand  division  of  the  Animal 
Kingdom  has  its  characteristic  method  of  developing. 


DEVELOPMENT.  205 

Protozoans  differ  from  all  higher  forms  in  having  no 
true  eggs. 

The  egg  of  the  Hydroid,  after  segmentation,  becomes  a 
hollow,  pear-shaped  body,  covered  with  cilia.  Soon  one 
end  is  indented ;  then  the  indentation  deepens  until  it 
reaches  the  interior  and  forms  the  mouth.  The  animal 
fastens  itself  by  the  other  end,  and  the  tentacles  appear 
as  buds.  In  the  Sea-anemone,  the  stomach  is  turned  in, 
and  the  partitions  appear  in  pairs. 

In  the  Oyster,  the  egg  segments  into  two  unequal  parts, 
one  of  which  gives  rise  to  the  digestive  tract  and  its  de- 
rivatives, while  from  the  smaller  part  originate  the  skin, 
gills,  and  shell.  It  is  soon  covered  with  cilia,  by  whose 
help  it  swims  about. 

The  embryo  of  an  Insect  shows  from  the  first  a  right 
and  left  side ;  but  the  first  indication  that  it  is  an  Articu- 
late is  the  development  of  a  series  of  indentations  divid- 
ing the  body  into  successive  rings,  or  joints.  Next,  we 
observe  that  the  back  lies  near  the  centre  of  the  egg,  the 
ventral  side  looking  outward;  i.  <>.,the  embryo  is  doubled 
upon  itself  backward.  And,  finally,  the  appearance  of 
three  pairs  of  legs  proves  that  it  will  be  an  Insect,  rather 
than  a  Worm,  Crustacean,  or  Spider. 

The  Vertebrate  embryo  lies  with  its  stomach  towards 
the  yolk,  reversing  the  position  of  the  Articulate ;  but  the 
grand  characteristic  is  the  medullary  groove,  which  does 
not  exist  in  the  egg  of  any  Invertebrate.  This  feature  is 
connected  with  another,  the  setting  apart  of  two  distinct 
regions  —  the  nervous  and  nutritive.  There  are  three 
modifications  of  Vertebrate  development:  that  of  Fishes 
and  Amphibians,  that  of  True  Keptiles  and  Birds,  and 
that  of  Mammals.  The  amnion  and  allantois  are  wanting 
in  the  first  group ;  while  the  placenta  (which  is  the  allan- 
tois vitally  connected  with  the  parent)  is  peculiar  to  Mam- 
mals. In  Mammals,  the  whole  yolk  is  segmented;  in 


206  COMPARATIVE  ZOOLOGY. 

Birds,  segmentation  is  confined  to  the  small  white  speck 
seen  in  opening  the  shell. 

At  the  outset,  all  animals,  from  the  Sponge  to  Man, 
appear  essentially  alike.  All,  moreover,  undergo  seg- 
mentation, and  most  have  one  form  or  other  of  the 
gastrula  stage.  But  while  Vertebrates  and  Invertebrates 
can  travel  together  on  the  same  road  up  to  this  point, 
here  they  diverge — never  to  meet  again.  For  every  grand 
group  early  shows  that  it  has  a  peculiar  type  of  construc- 
tion. Every  egg  is  from  the  first  impressed  with  the 
power  of  developing  in  one  direction  only,  and  never  does 
it  lose  its  fundamental  characters.  The  germ  of  the  Bee 
is  divided  into  segments,  showing  that  it  belongs  to  the 
Articulates ;  the  germ  of  the  Lion  has  the  medullary 
stripe — the  mark  of  the  coming  Vertebrate.  The  blasto- 
dermic  layer  of  the  Vertebrate  egg  rolls  up  into  two  tubes 
— one  to  hold  the  viscera,  the  other  to  contain  the  nervous 
cord;  while  that  of  the  Invertebrate  egg  forms  only  one 
such  tubular  division.  The  features  which  determine  the 
subkingdom  to  which  an  animal  belongs  are  first  devel- 
oped, then  the  characters  revealing  its  class. 

There  are  differences  also  in  grade  of  development  as 
well  as  type.  For  a  time  there  is  no  essential  difference 
between  a  Fish  and  a  Mammal :  they  have  the  same  ner- 
vous, circulatory,  and  digestive  systems.  There  are  many 
such  cases,  in  which  the  embryo  of  an  animal  represents 
the  permanent  adult  condition  of  some  lower  form.  In 
other  words,  the  higher  species,  in  the  course  of  their  de- 
velopment, offer  likenesses,  or  analogies,  to  finished  lower 
species.  The  human  germ,  at  first,  cannot  be  distinguished 
from  that  of  any  other  animal:  for  aught  we  can  see,  it 
may  turn  out  a  Frog  or  a  Philosopher.  The  appearance 
of  a  medullary  stripe  excludes  it  at  once  from  all  Inverte- 
brates. It  afterwards  has,  for  a  time,  structures  found  in 
the  lower  classes  and  orders  of  Vertebrates  as  permanent 


DEVELOPMENT.  20  T 

organs.  For  a  time,  indeed,  the  human  embryo  so  closely 
resembles  that  of  the  lower  forms  as  to  be  indistinguisha- 
ble from  them ;  but  certain  structures  belonging  to  those 
forms  are  kept  long  after  the  embryo  is  clearly  human.116 
All  the  members  of  a  group  do  not  reach  the  same  degree 
of  perfection,  some  remaining  in  what  corresponds  to  the 
immature  stages  of  the  higher  animals.  Such  may  be 
called  permanently  embryonic  forms. 

Sometimes  an  embryo  develops  an  organ  in  a  rudimen- 
tary condition,  which  is  lost  or  useless  in  the  adult.  Thus, 
the  Greenland  Whale,  when  grown  up,  has  not  a  tooth  in 
its  head,  while  in  the  embryo  life  it  has  teeth  in  both 
jaws;  unborn  Calves  have  canines  and  upper  incisors; 
and  the  female  Dugong  has  tusks  which  never  cut  the 
gum.  The  "splint-bones"  in  the  Horse's  foot  are  unfin- 
ished metatarsals. 

Animals  differ  widely  in  the  degree  of  development 
reached  at  ovulation  and  at  birth.  The  eggs  of  Frogs 
are  laid  when  they  can  hardly  be  said  to  have  become 
fully  formed  as  eggs.  The  eggs  of  Birds  are  laid  when 
segmentation  is  complete,  while  the  eggs  of  Mammals  are 
retained  by  the  parent  till  after  the  egg-stage  is  passed.119 
Ruminants  and  terrestrial  Birds  are  born  with  the  power 
of  sight  and  locomotion.  Most  Carnivores,  Rodents,  and 
perching  Birds  come  into  the  world  blind  and  helpless ; 
while  the  human  infant  is  dependent  for  a  much  longer 
time. 

1.  Metamorphosis. 

Few  animals  come  forth  from  the  egg  in  perfect  condi- 
tion. The  vast  majority  pass  through  a  great  variety  of 
forms  before  reaching  maturity.  These  metamorphoses 
(which  are  merely  periods  of  growth)  are  not  peculiar  to 
Insects,  though  more  apparent  in  them.  Man  himself  is 
developed  on  the  same  general  principles  as  the  Butterfly, 
but  the  transformations  are  concealed  from  view.  The 


208  COMPARATIVE  ZOOLOGY. 

Coral,  when  hatched,  has  six  pairs  of  partitions;  after- 
wards, the  spaces  are  divided  by  six  more  pairs ;  then 
twelve  intermediate  pairs  are  introduced;  next,  twenty- 
four,  and  so  on.  The  embryonic  Star -fish  has  a  long 
body,  with  six  arms  on  a  side,  in  one  end  of  which  the 
young  Star -fish  is  developed.  Soon  the  twelve -armed 
body  is  absorbed,  and  the  young  animal  is  of  age. 
Worms  are  continually  growing  by  the  addition  of  new 
segments.  Nearly  all  Insects  undergo  complete  metamor- 
phosis, i.  e.)  exhibit  four  distinct  stages  of  existence — egg, 
larva,  pupa,  and  imago.  The  worm-like  larva117  may  be 
called  a  locomotive-egg.  It  has  little  resemblance  to  the 
parent  in  structure  or  habits,  eating  and  growing  rapidly. 
Then  it  enters  the  pupa  state,  wrapping  itself  in  a  cocoon, 
or  case,  and  remaining  apparently  dead  till  new  organs 
are  developed;  when  it  escapes  a  perfect  winged  Insect, 


FIG.  172.— Butterfly  in  the  Imago,  Papa,  and  Larva  States. 

or  imago.118  Wings  never  exist  externally  in  the  larva; 
and  some  Insects  which  undergo  no  apparent  metamor- 
phosis, as  Lice,  are  wingless.  The  Grasshopper  develops 
from  the  young  larva  to  the  winged  adult  without  chang- 


DEVELOPMENT. 


209 


ing  its  mode  of  life.  In  the  development  of  the  common 
Crab,  so  different  is  the  outward  form  of  the  newly 
A 


FIG.  173. — Metamorphosis  of  the  Mosquito  (Culex-pipiens) :  A,  boat  of  eggs ;  B,  some 
of  the  eggs  highly  magnified ;  d,  with  lid  open  for  the  escape  of  the  larva,  C ;  D, 
pupa;  E,  larva  magnified,  showing  respiratory  tube,  e,  anal  flue,/,  antennae,  g; 
F,  imago;  a,  antennas;  b,  beak. 

hatched  embryo  from  that  of  the  adult,  that  the  former 
has  been  described  as  a  distinct  species. 

The  most  remarkable  example  of  metamorphosis  among 
Vertebrates  is  furnished  by  the  Amphibians.  A  Tadpole 
—the  larva  of  the  Frog — has  a  tail,  but  no  legs ;  gills,  in- 
stead of  lungs;  a  heart  precisely  like  that  of  the  Fish;  a 
horny  beak  for  eating  vegetable  food,  and  a  spiral  intes- 
tine to  digest  it.  As  it  matures,  the  hinder  legs  show 
themselves,  then  the  front  pair;  the  beak  falls  off;  the 
tail  and  gills  waste  away;  lungs  are  created;  the  diges- 
tive apparatus  is  changed  to  suit  an  animal  diet ;  the  heart 
is  altered  to  the  Keptilian  type  by  the  addition  of  another 
auricle ;  in  fact,  skin,  muscles,  nerves,  bones,  and  blood- 
vessels vanish,  being  absorbed  atom  by  atom,  and  a  new 
set  is  substituted.  Moulting,  or  the  periodical  renewal  of 
epidermal  parts,  as  the  shell  of  the  Lobster,  the  skin  of 


210 


COMPARATIVE  ZOOLOGY. 


the  Toad,  the  scales  of  Snakes,  the  feathers  of  Birds,  and 
the  hair  of  Mammals,  may  be  termed  a  metamorphosis. 


FIG.  17k— Metamorphosis  of  the  Newt. 

The  change  from  milk-teeth  to  a  permanent  set  is  another 
example. 

An  animal  rises  in  organization  as  development  ad- 
vances. Thus,  a  Caterpillar's  life  has  nothing  nobler 
about  it  than  the  ability  to  eat,  while  the  Butterfly  ex- 
pends the  power  garnered  up  by  the  larva  in  a  gay  and 
busy  life.  But  there  are  seeming  reversals  of  this  law. 
Some  mature  animals  appear  lower  in  the  scale  than  their 
young.  The  larval  Cirripede  has  a  pair  of  magnificent 
compound  eyes  and  complex  antennae ;  when  adult,  the 
antennae  are  gone,  and  the  eyes  are  reduced  to  a  single, 
simple,  minute  eye-spot.  So  the  germs  of  the  sedentary 
Sponge  and  Oyster  are  free  and  active.  The  adult  ani- 
mal, however,  is  always  superior  in  alone  possessing  the 
power  of  reproduction.  Such  a  process  is  known  as  retro- 
grade metamorphosis. 

There  are  certain  larval  forms  so  characteristic  of  the 


DEVELOPMENT. 


211 


great  groups  of  the  animal  kingdom  as  to  demand  notice. 
Most  Worms  leave  the  egg  as  a  larva,  called  the  trocho- 
sphere (Fig.  175),  an  oval  larva,  having  mouth 
and  anus,  and  a  circle  of  cilia  anterior  to  the 
mouth.  This  larval  stage  is  common  to  Worms 
with  the  most  diverse  adult  forms  and  habits. 
It  is  also  found  in  all  the  great  groups  of  Mol- 
lusks.  Clams,  Snails,  and  Cuttle-fish  all  have 
the  stage  represented  in  their  history.  The  Mol- 
lusks  usually  pass  through  a  later  stage  called  the  veliger 

(Fig.  176),  in  which 

0 

H* 

"  m 


a  circle  of  cilia  ho- 
mologous to  that  of 
-^  the  trochosphere  is 
borne    by   a    lobed 
expansion  on  the 
head,  called  the  ve- 
or   sail.     The 


Fio.  176  —  Larval  Gu.»tempoJ.a:  A,  /j,  Trochus;  C,  Ter- 
gipes  ;    a,  trochosphere  ;    v,  velum  ;  B,  veliger  ;  d,    ~  .    . 

mouth  ;  /,  foot;  a,  shell;  C,  veliger;  d,  foot;  c,  teiita-   Crustacea,     WlllCll 

cle;&'ear>  exhibit  so   great  a 

range  of  form  in  the  adult  state,  all  pass  through  a  stage 
in  which  they  are  substantially  alike.  Forms  as  different 
in  appearance  as  Barnacles,  Entornostracans,  and  Prawns 
hatch  out  as  Nauplii,  little  oval  animals,  with  a  straight 
intestine,  three  pairs  of  legs,  and  a  simple  eye  (Fig.  177). 
See  Figs.  253,  254,  255,  256.  Fig.  256  represents  the 
Lobster,  which  does  not  hatch  as  a  Nauplius,  but  is  not 
very  unlike  the  Prawn.  These  larval  forms  are  of  great 
interest,  because  they  disclose  the  relationships  of  the 
adult  forms,  as  the  gastrula  stage  hints  at  the  common 
relationships  of  all  animals  above  Protozoa. 

2.  Alternate  Generation. 

Sometimes   a   metamorphosis  extending   over   several 
generations  is  required  to  evolve  the  perfect  animal;  "in 


212 


COMPARATIVE  ZOOLOGY. 


PIG.  177.— Nanplius  of  Entomostracan  (Canthocamptiis).  See  Fig.  255.  A,  first  an- 
tenna ;  An,  second  antenna ;  a,  anus ;  L,  labrum ;  O,  ocellus ;  S,  stomach.  (Prom 
Brooks,  after  Hoek.) 

other  words,  the  parent  may  find  no  resemblance  to  him- 
self in  any  of  his  progeny,  until  he  comes  down  to  the 
great-grandson."  Thus,  the  Jelly-fish,  or  Medusa,  lays 
eggs  which  are  hatched  into  larvae  resembling  Infusoria — 
little  transparent  oval  bodies  covered  with  cilia,  by  which 
they  swim  about  for  a  time  till  they  find  a  resting-place. 
One  of  them,  for  example,  becoming  fixed,  develops  rap- 
idly ;  it  elongates  and  spreads  at  the  upper  end ;  a  mouth 
is  formed,  opening  into  a  digestive  cavity;  and  tentacles 
multiply  till  the  mouth  is  surrounded  by  them.  At  this 
stage  it  resembles  a  Hydra.  Then  slight  wrinkles  appear 
along  the  body,  which  grow  deeper  and  deeper,  till  the- 
animal  looks  like  "a  pine-cone  surmounted  by  a  tuft  of 
tentacles ;"  and  then  like  a  pile  of  saucers  (about  a  dozen 


DEVELOPMENT. 


213 


in  number)  with  scalloped  edges.  Next,  the  pile  breaks 
up  into  separate  segments,  which  are,  in  fact,  so  many  dis- 
tinct animals ;  and  each  turning  over  as  it  is  set  free,  so 
as  to  bring  the  mouth  below,  develops  into  an  adult  Me- 
dusa, becoming  more  and  more  convex,  and  furnished 
with  tentacles,  circular  canals,  and  other  organs  exactly 
like  those  of  the  progenitor  that  laid  the  original  egg. 

Here  we  see  a  Medusa  producing  eggs  which  develop 
into  stationary  forms  resembling  Hydras.     The  Hydras 


FIG.  178 — Alternate  Generation:  a,  6,  c,  ova  of  an  Acaleph  (Chrysaora) ;  d,e,f,  Hy- 
dras ;  0,  h,  Hydras  with  constrictions ;  i,  Hydra  undergoing  fission ;  k,  one  of  the 
separated  segments,  a  free  Medusa. 

then  produce  not  only  Medusae  by  budding  in  the  manner 
described,  but  also  other  Hydras  like  themselves  by  bud- 
ding. All  these  intermediate  forms  are  transient  states 
of  the  Jelly-fish,  but  the  metamorphoses  cannot  be  said  to 
occur  in  the  same  individual.  While  a  Caterpillar  becomes 
a  Butterfly,  this  Hydra-like  individu&l  produces  a  number 
of  Medusae.  Alternate  generation  is,  then,  an  alternation 
of  asexual  and  sexual  methods  of  reproduction,  one  or 
more  generations  produced  from  buds  being  followed  by 
a  single  generation  produced  from  eggs.  Often,  as  in 
the  fresh-water  Hydra,  the  two  kinds  of  generations  are 
alike  in  appearance.  The  process  is  as  wide- spread  as 
asexual  reproduction,  being  found  mostly  in  Sponges, 
Coelenterates,  and  Worms.  It  is  also  found  in  certain 


214  COMPARATIVE  ZOOLOGY. 

Crustacea  and  Insects.    The  name  is  sometimes  limited  to 
cases  where  the  two  kinds  of  generations  differ  in  form. 

3.  Growth  and  Repair. 

Growth  is  increase  of  bulk,  as  Development  is  increase 
of  structure.  It  occurs  whenever  the  process  of  repair 
exceeds  that  of  waste,  or  when  new  material  is  added 
faster  than  the  tissues  are  destroyed.  There  is  a  specific 
limit  of  growth  for  all  animals,  although  many  of  the  low 
cold-blooded  forms,  as  the  Trout  and  Anaconda,  seem  to 
grow  as  long  as  they  live.  After  the  body  has  attained 
its  maturity,  i.  e.,  has  fully  developed,  the  tissues  cease  to 
grow ;  and  nutrition  is  concerned  solely  in  supplying  the 
constant  waste,  in  order  to  preserve  the  size  and  shape  of 
the  organs.  A  child  eats  to  grow  and  repair;  the  adult 
eats  only  to  repair.119  Birds  develop  rapidly,  and  so  spend 
most  of  their  life  full-fledged;  while  Insects  generally, 
Fishes,  Amphibians,  Reptiles,  and  Mammals  mature  at 
a  comparatively  greater  age.  The  perfect  Insect  rarely 
changes  its  size,  and  takes  but  little  food;  eating  and 
growing  are  almost  confined  to  larval  life.  The  crust  of 
the  Sea-urchin,  which  is  never  shed,  grows  by  the  addition 
of  matter  to  the  margins  of  the  plates.  The  shell  of  the 
Oyster  is  enlarged  by  the  deposition  of  new  laminae,  each 
extending  beyond  the  other.  At  every  enlargement,  the 
interior  is  lined  with  a  new  nacreous  layer;  so  that  the 
number  of  such  layers  in  the  oldest  part  of  the  shell  indi- 
cates the  number  of  enlargements.  When  the  shell  has 
reached  its  full  size,  new  layers  are  added  to  the  inner 
surface  only,  which  increases  the  thickness.  It  is  the 
margin  of  the  mantle  which  provides  for  the  increase  in 
length  and  breadth,  while  the  thickness  is  derived  from 
the  whole  surface.  The  edges  of  the  concentric  laminae 
are  the  "  lines  of  growth."  The  Oyster  is  full-grown  in 
about  five  years.  The  bones  of  Fishes  and  Reptiles  are 


DEVELOPMENT.  215 

continually  growing;  the  long  bones  of  higher,  animals 
increase  in  length  so  long  as  the  ends  (epiphyses)  are  sep- 
arate from  the  shaft.  The  limbs  of  Man,  after  birth, 
grow  more  rapidly  than  the  trunk. 

The  power  of  regenerating  lost  parts  is  greatest  where 
the  organization  is  lowest,  and  while  the  animal  is  in  the 
young  or  larval  state.  It  is  really  a  process  of  budding. 
The  upper  part  of  the  Hydra,  if  separated,  will  reproduce 
the  rest  of  the  body;  if  the  lower  part  is  cut  off,  it  will 
add  the  rest.  Certain  Worms  may  be  cut  into  several 
pieces,  and  each  part  will  regain  what  is  needed  to  com- 
plete the  mangled  organism.  The  Star-fish  can  reproduce 
its  arms ;  the  Holothurian,  its  stomach  ;  the  Snail,  its  ten- 
tacles ;  the  Lobster,  its  claws ;  the  Spider,  its  legs ;  the 
Fish,  its  fins ;  and  the  Lizard,  its  tail.  Nature  makes  no 
mistake  by  putting  on  a  leg  where  a  tail  belongs,  or  join- 
ing an  immature  limb  to  an  adult  animal.120  In  Birds  and 
Mammals,  the  power  is  limited  to  the  reproduction  of  cer- 
tain tissues,  as  shown  in  the  healing  of  wounds.  Very 
rarely  an  entire  human  bone,  removed  by  disease  or  sur- 
gery, has  been  restored.  The  nails  and  hair  continue  to 
grow  in  extreme  old  age. 

4.  Likeness  and  Variation. 

It  is  a  great  law  of  reproduction  that  all  animals  tend 
to  resemble  their  parents.  A  member  of  one  class  never 
produces  a  member  of  another  class.  The  likeness  is  very 
accurate  as  to  general  structure  and  form.  But  it  does 
not  descend  to  every  individual  feature  and  trait.  In 
other  words,  the  tendency  to  repetition  is  qualified  by  a 
tendency  to  variation.  Like  produces  like,  but  not  ex- 
actly. The  similarity  never  amounts  to  identity.  So  that 
we  have  two  opposing  tendencies  —  the  hereditary  ten- 
dency to  copy  the  original  stock,  and  a  distinct  tendency 
to  deviate  from  it. 


216  COMPARATIVE  ZOOLOGY. 

This  is  one  of  the  most  universal  facts  in  nature.  Ev- 
ery development  ends  in  diversity.  All  know  that  no 
two  individuals  of  a  family,  human  or  brute,  are  abso- 
lutely alike.  There  are  always  individual  differences  by 
which  they  can  be  distinguished.  Evidently  a  parent 
does  not  project  precisely  the  same  line  of  influences  upon 
each  of  its  offspring. 

This  variability  makes  possible  an  indefinite  modifica- 
tion of  the  forms  of  life.  For  the  variation  extends  to 
the  whole  being,  even  to  every  organ  and  mental  char- 
acteristic as  well  as  to  form  and  color.  It  is  very  slight 
from  generation  to  generation ;  but  it  can  be  accumulated 
Dy  choosing  from  a  large  number  of  individuals  those 
which  possess  any  given  variation  in  a  marked  degree, 
and  breeding  from  these.  Nature  does  this  by  the  very 

O  «/  «/ 

gradual  process  of  "  natural  selection ;"  Man  hastens  it,  so 
to  speak,  by  selecting  extreme  varieties.  Hence  we  have 
in  our  day  remarkable  specimens  of  Poultry,  Cattle,  and 
Dogs,  differing  widely  from  the  wild  races. 

Sometimes  we  notice  that  children  resemble,  not  then 
parents,  but  their  grandparents  or  remoter  ancestors.  This 
tendency  to  revert  to  an  ancestral  type  is  called  atavism. 
Occasionally,  stripes  appear  on  the  legs  and  shoulders  of 
the  Horse,  in  imitation  of  the  aboriginal  Horse,  which  was 
striped  like  the  Zebra.  Sheep  have  a  tendency  to  revert 
to  dark  colors. 

The  laws  governing  inheritance  are  unknown.  No  one 
can  say  why  one  peculiarity  is  transmitted  from  father  to 
son,  and  not  another;  or  why  it  appears  in  one  member 
of  the  family,  and  not  in  all.  Among  the  many  causes 
which  tend  to  modify  animals  after  birth  are  the  quality 
and  quantity  of  food,  amount  of  temperature  and  light, 
pressure  of  the  atmosphere,  nature  of  the  soil  or  water, 
habits  of  fellow-animals,  etc. 

Occasionally  animals  occur,  widely  different  in  struct- 


DEVELOPMENT.  217 

ure,  having  a  very  close  external  resemblance.  Barnacles 
were  long  mistaken  for  Mollusks,  Polyzoans  for  Polyps, 
and  Lamprey-eels  for  Worms.  Such  forms  are  termed 
homomorphic. 

Members  of  one  group  often  put  on  the  outward  ap- 
pearance of  allied  species  in  the  same  locality :  this  is 
called  mimicry.  "  They  appear  like  actors  or  masquerad- 
ers  dressed  up  and  painted  for  amusement,  or  like  swin- 
dlers endeavoring  to  pass  themselves  off  for  well-known 
and  respectable  members  of  society."  Thus,  certain  But- 
terflies on  the  Amazons  have  such  a  strong  odor  that  the 
Birds  let  them  alone ;  and  Butterflies  of  another  family 
in  the  same  region  have  assumed  for  protection  the  sam- 
form  and  color  of  wing.  So  we  have  bee -like  Moths, 
beetle-like  Crickets,  wasp-like  Flies,  and  ant-like  Spiders  : 
harmless  and  venomous  Snakes  copying  each  other,  ana 
Orioles  departing  from  their  usual  gay  coloring  to  imi 
tate  the  plumage,  flight,  and  voice  of  quite  another  style 
of  Birds.  The  species  which  are  imitated  are  much  more 
abundant  than  those  which  mimic  them.  There  is  also  •.: 
general  harmony  between  the  colors  of  an  animal  anu 
those  of  its  habitation.  We  have  the  white  Polar  Beai, 
the  sand-colored  Camel,  and  the  dusky  Twilight- moths.. 
There  are  Birds  and  Reptiles  so  tinted  and  mottled  as  ex 
actly  to  match  the  rock,  or  ground,  or  bark  of  a  tree  they 
frequent;  and  there  are  Insects  rightly  named  "Walking 
sticks"  and  "  Walking  -leaves."  These  coincidences  arc 
not  always  accidental,  but  often  intentional  on  the  part  o- 
nature,  for  the  benefit  of  the  imitating  species.  Gener- 
ally, they  wear  the  livery  of  those  they  live  on,  or  ape 
the  forms  more  favored  than  themselves. 

5.  Bomology,  Analogy,  and  Correlation. 
The  tendency  to  repetition  in  the  development  of  ani 
mals  leads  to  some  remarkable  affinities.    Parts  or  organs, 


218  COMPARATIVE  ZOOLOGY. 

having  a  like  origin  and  development,  and  therefore  the 
same  essential  structure,  whatever  their  form  or  function, 
are  said  to  be  homologous  y  while  parts  or  organs  corre- 
sponding in  use  are  called  analogous.  By  serial  homol- 
oyy  is  meant  the  homology  existing  between  successive 
parts  of  one  animal. 

The  following  are  examples  of  homology:  the  arms  of 
Man,  the  fore -legs  of  a  Horse,  the  paddles  of  a  Whale, 
the  wings  of  a  Bird,  the  front  flippers  of  a  Turtle,  and  the 
pectoral  fins  of  a  Fish;  the  proboscis  of  a  Moth,  and  the 
jaws  of  a  Beetle ;  the  shell  of  a  Snail,  and  both  valves  of 
a  Clam.  The  wings  of  the  Bird,  Flying  Squirrel,  and  Bat 
are  hardly  homologous,  since  the  wing  of  the  first  is  de- 
veloped from  the  fore-limb  only;  that  of  the  Squirrel  is 
an  extension  of  the  skin  between  the  fore  and  hind  limbs  ; 
while  in  the  Bat  the  skin  stretches  between  the  finders, 

O 

and  then  down  the  side  to  the  tail.  Examples  of  serial 
homology:  the  arms  and  legs  of  Man;  the  upper  and 
lower  set  of  teeth  :  the  parts  of  the  vertebral  column, 
however  modified;  the  scapular  and  pelvic  arches;  the 
humerus  and  femur;  carpus  and  tarsus;  the  right  and  left 
sides  of  most  Animals  ;  the  dorsal  and  anal  fins  of  Fishes. 
The  legs  of  a  Lobster  and  Lizard,  the  wings  of  a  Butter- 
fly and  Bird,  the  gills  of  a  Fish,  and  the  lungs  of  other 
Vertebrates,  are  analogous.  The  air-bladder  of  a  Fish  is 
homologous  with  a  lung,  and  analogous  to  the  air-cham- 
bers of  the  Nautilus. 

In  the  midst  of  the  great  variety  of  form  and  structure 
in  the  animal  world,  a  certain  harmony  reigns.  Not  only 
are  different  species  so  related  as  to  suggest  a  descent 
from  the  same  ancestor,  but  the  parts  of  any  one  organ- 
ism are  so  closely  connected  and  mutually  dependent  that 
the  character  of  one  must  receive  its  stamp  from  the  char- 
acter of  all  the  rest.  Thus,  from  a  single  tooth  it  may  be 
inferred  that  the  animal  had  a  skeleton  and  spinal  cord. 


DEVELOPMENT. 


219 


and  that  it  was  a  carnivorous,  hot-blooded  Mammal.  Cer- 
tain structures  always  co-exist.  Animals  with  two  occipi- 
tal condjles,  and  non  -  nucleated  blood  -  corpuscles,  suckle 


FIG.  181. 


FIG.  182. 


HOMOLOGIES   OF   LIMBS. 


FIG.  179.— Arm  and  Leg  of  Man,  as  they  are  when  he  gets  down  on  all-fonrs.  FIG. 
ISO.— Fore  and  Hind  Legs  of  Tapir.  FIG.  181.— Fore  Leg  of  Seal  and  Hind  Leg 
of  Alligator.  FIG.  182.— Wiug  of  the  Bat.  S,  scapula;  I,  ilium,  or  shin-bone  of 
pelvis ;  H,  hnmerus  ;  F,  femur  ;  O,  olecranon.  or  tip  of  the  elbow  ;  P,  patella ; 
U,  ulna;  T,  tibia;  R,  radius;  Fi,  Fibula;  Po,  pollex,  or  thumb;  Ha,  hallex,  or 
great  toe.  Compare  the  fore  and  hind  limbs  of  the  same  animal,  and  the  fore 
or  hind  limbs  of  different  animals.  Note  the  directions  of  the  homologous  seg- 
ments. 


220  COMPARATIVE  ZOOLOGY. 

their  young,  i.  e.,  they  are  Mammals.  All  Ruminant 
hoofed  beasts  have  horns  and  cloven -feet.  If  the  hoofs 
are  even,  the  horns  are  even,  as  in  the  Ox ;  if  odd,  as  in 
the  Rhinoceros,  the  horns  are  odd,  i.  e.,  single,  or  two 
placed  one  behind  the  other.  Recent  creatures  with  feath- 
ers always  have  beaks.  Pigeons  with  short  beaks  have 
small  feet;  and  those  with  long  beaks,  large  feet.  The 
long  limbs  of  the  Hound  are  associated  with  a  long  head. 
A  white  spot  in  the  forehead  of  a  Horse  generally  goes 
with  white  feet.  Hairless  Dogs  are  deficient  in  teeth. 
Long  wings  usually  accompany  long  tail-feathers.  White 
Cats  with  blue  eyes  are  usually  deaf.  A  Sheep  with  nu- 
merous horns  is  likely  to  have  long,  coarse  wool.  Homol- 
ogous parts  tend  to  vary  in  the  same  manner;  if  one  is 
diseased,  another  is  more  likely  to  sympathize  with  it  than 
cne  not  homologous.  This  association  of  parts  is  called 
correlation  of  growth. 

6.  Individuality. 

It  seems  at  first  sight  very  easy  to  define  an  individual 
animal.  A  single  Fish,  or  Cow,  or  Snail,  or  Lobster  is 
plainly  an  individual;  and  the  half  of  one  such  animal  is 
plainly  not  one.  But  when  we  consider  animals  in  colo- 
nies, like  Corals,  it  is  not  so  easy  to  say  whether  the  indi- 
vidual is  the  colony  or  the  single  Polyp.  Is  the  tree  the 
individual,  or  the  bud  'I  If  we  say  the  former — the  colony 
— what  shall  we  say  to  the  free  buds  of  a  Hydroid  colony, 
living  independent  lives,  and  scattered  over  square  miles 
of  ocean  ?  Are  they  parts  of  one  individual  ?  If  we 
choose  the  latter  as  our  standard,  we  are  in  equal  difficul- 
ty; for  we  must  then  call  an  individual  the  bud  of  the 
Portuguese  Man-of-war,  reduced  to  a  mere  bladder  or 
feeler,  and  incapable  of  leading  an  independent  life.  We 
thus  find  it  necessary  to  distinguish  at  least  two  kinds 
of  individuals — physiological  individuals,  applying  that 


DEVELOPMENT.  221 

name  to  any  animal  form  capable  of  leading  an  indepen- 
dent life ;  and  morphological  individuals,  one  of  which  is 
the  total  product  of  an  egg.  Such  an  individual  may  be 
a  single  physiological  individual,  as  the  Fish ;  or  many 
united,  as  the  Coral  stock;  or  many  separate  physiological 
individuals,  as  in  the  Hydroids  or  Plant-lice.  The  single 
members  of  such  a  compound  morphological  individual 
are  called  zooids,  or  persons,  and  are  found  wherever 
asexual  reproduction  takes  place. 

7.  Relations  of  Number,  Size,  Form,  and  Rank. 
The  Animal  Kingdom  has  been  likened  to  a  pyramid, 
the  species  diminishing  in  number  as  they  ascend  in  the 
scale  of  complexity.  This  is  not  strictly  true.  The  num- 
ber of  living  species  known  is  at  least  300,000,  of  which 
more  than  nine  tenths  are  Invertebrates.  A  late  enumer- 
ation gives  the  following  figures  for  the  number  of  de- 
scribed species : 


Protozoa 2,700 

Ccelenterata 1,560 

Vermes 5,580 


Echinodennata 800 

Mollusca 20,210 

Vertebrata 25,200 


Arthropoda 175,100 

These  figures  are  lower  than  those  usually  given.  Of 
Vertebrates,  Fishes  are  most  abundant ;  then  follow  Birds, 
Mammals,  Reptiles,  and  Amphibians.  There  are  usually 
said  to  be  about  200,000  species  of  Insects. 

The  largest  species  usually  belong  to  the  higher  classes. 
The  aquatic  members  of  a  group  are  generally  larger  than 
the  terrestrial,  the  marine  than  the  fresh-water,  and  the 
land  than  the  aerial.  The  extremes  of  size  are  an  Infu- 
sorium, Ts-Jinr  of  an  inch  in  diameter,  the  smallest  animal 
ever  measured,  and  the  Whale,  one  hundred  feet  long,  the 
largest  animal  ever  created.  The  female  is  sometimes 
larger  than  the  male,  as  of  the  Nautilus,  Spider,  and  Eagle. 
The  higher  the  class,  the  more  uniform  the  size.  Of  all 


222  COMPARATIVE  ZOOLOGY. 

groups  of  animals,  Insects  and  Birds  are  the  most  con- 
stant in  their  dimensions. 

Every  organism  has  its  own  special  law  of  growth:  a 
Fish  and  an  Oyster,  though  born  in  the  same  locality,  de- 
velop into  very  different  forms.  Yet  a  symmetry  of  plan 
underlies  tho  structure  of  all  animals.  In  the  embryo, 
this  symmetry  of  the  two  ends,  as  well  as  the  two  sides, 
is  nearly  perfect;  but  it  is  subsequently  interfered  with 
to  adapt  the  animal  to  its  special  conditions  of  life.  It  is 
a  law  that  an  animal  grows  equally  in  those  directions  in 
which  the  incident  forces  are  equal.  The  Polyp,  rooted 
to  the  rocks,  is  subjected  to  like  conditions  on  all  sides, 
and,  therefore,  it  has  no  right  arid  left,  or  fore  and  hind 
parts.  The  lower  forms,  generally,  are  more  or  less  geo- 
metrical figures:  spheroidal,  as  the  Sea-urchin;  radiate, 
as  the  Star -fish;  and  spiral,  as  many  Foramiriifers.  The 
higher  animals  are  subjected  to  a  greater  variety  of  con- 
ditions. Thus,  a  Fish,  always  going  through  the  water 
head  foremost,  must  show  considerable  difference  between 
the  head  and  the  hinder  end;  or  a  Turtle,  moving  over 
the  ground  with  the  same  surface  always  down,  must  have 
distinct  dorsal  and  ventral  sides. 

Nevertheless,  there  is  a  striking  likeness  between  the 
two  halves  or  any  two  organs  situated  on  opposite  sides 
of  an  axis.  And,  first,  a  bilateral  symmetry  is  most  com- 
mon. It  is  best  exhibited  by  the  Articulates  and  Verte- 
brates, but  nearly  all  animals  can  be  clearly  divided  into 
right  and  left  sides  —  in  other  words,  they  appear  to  be 
double.  A  vertical  plane  would  divide  into  two  equal 
parts  our  brain,  spinal  cord,  vertebral  column,  organs  of 
sight,  hearing,  and  smell;  our  teeth,  jaws,  limbs,  lungs, 
etc.  In  fact,  the  two  halves  of  every  egg  are  identical. 
There  are  many  exceptions:  the  heart  and  liver  of  the 
higher  Vertebrates  are  eccentric ;  the  nervous  system  of 
Mollusks  is  scattered;  the  hemispheres  of  the  human 


DEVELOPMENT.  223 

brain  are  sometimes  unequal ;  the  corresponding  bones  in 
the  right  and  left  arms  are  not  precisely  the  same  length 
and  weight;  the  Narwhal  has  an  immense  tusk  on  the  left 
side,  with  none  to  speak  of  on  the  other;  Rabbits  have 
been  born  with  one  ear,  and  Stags  with  one  horn;  the 
Rattlesnake  has  but  one  lung ;  both  eyes  of  the  Flounder 
and  Halibut  are  on  the  same  side;  the  claws  of  the  Lob- 
ster differ;  and  the  valves  of  the  Oyster  are  unequal. 
But  all  these  animals  and  their  organs  are  perfectly  sym- 
metrical in  the  embryo  state. 

Again,  animals  exhibit  a  certain  correspondence  be- 
tween the  fore  and  hind  parts.131  Thus,  the  two  ends  of 
the  Centipede  repeat  each  other.  Indeed,  in  some  Worms, 
the  eyes  are  developed  in  the  last  segment  as  well  as  the 
first.  So  a  Vertebrate  may  be  considered  not  only  as  two 
individuals  placed  side  by  side,  but  also  as  two  individu- 
als put  end  to  end — the  head  and  arms  representing  one, 
and  the  legs  the  other.  In  the  embryo  of  Quadrupeds, 
the  four  limbs  are  closely  alike.  But  in  the  adult,  the 
fore  and  hind  limbs  differ  more  than  the  right  and  left 
limbs,  because  the  functions  are  more  dissimilar.  An  ex- 
treme want  of  symmetry  is  seen  in  Birds  which  combine 
aerial  and  land  locomotion. 

There  is  also  a  tendency  to  a  vertical  symmetry,  of 
up-and-down  arrangement  —  the  part  above  a  horizontal 
plane  being  a  reversed  copy  of  the  part  below.  A  good 
example  is  the  posterior  half  of  a  Cod,  while  the  tail  of  a 
Shark  shows  the  want  of  it.  This  symmethy  decreases  as 
we  ascend  the  scale.  In  most  animals  there  is  consider- 
able  difference  between  the  dorsal  and  ventral  surfaces; 
and  in  all  the  nervous  system  is  more  symmetrically  dis- 
posed than  the  digestive. 

Every  animal  is  perfect  in  its  kind  and  in  its  place. 
Yet  we  recognize  a  gradation  of  life.  Some  animals  are 
manifestly  superior  to  some  others.  But  it  is  not  so  easy 


22-1  COMPARATIVE  ZOOLOGY. 

to  say  precisely  what  shall  guide  us  in  assorting  living 
forms  into  high  and  low.  Shall  we  make  structure  the 
criterion  of  rank?  Plainly  the  simple  Jelly-fish  is  be- 
neath complicated  Man.  An  ounce  of  muscle  is  worth  a 
pound  of  protoplasm,  and  a  grain  of  nervous  matter  is  of 
more  account  than  a  ton  of  flesh.  The  intricate  and  fin- 
ished build  of  the  Horse  elevates  him  immeasurably  above 
the  stupid  Snail.  The  repetition  of  similar  parts,  as  in  the 
Worm,  is  a  sign  of  low  life.  So  also  a  prolonged  posterior 
is  a  mark  of  inferiority,  as  the  Lobsters  are  lower  than  the 
Crabs,  Snakes  than  Lizards,  Monkeys  than  Apes.  The 
possession  of  a  head  distinct  from  the  region  behind 
it  is  a  sign  of  power.  And  in  proportion  as  the  fore- 
limbs  are  used  for  head  purposes,  the  animal  ascends 
the  scale :  compare  the  Whale,  Horse,  Cat,  Monkey,  and 
Man. 

But  shall  the  Fish,  never  rising  above  the  "  monotony 
of  its  daily  swim,"  be  allowed  to  outrank  the  skilful  Bee? 
Shall  the  brainless,  sightless,  almost  heartless  Amphioxus, 
a  Vertebrate,  be  allowed  to  stand  nearer  to  Man  than  the 
Ant?  What  is  the  possession  of  a  backbone  to  intelli- 
gence ?  No  good  reason  can  be  given  why  we  might  not 
be  just  as  intelligent  beings  if  we  carried,  like  the  Insect, 
our  hearts  in  our  backs  and  our  spinal  cords  in  our  breasts. 
So  far  as  its  activity  is  concerned,  the  brain  may  be  as  ef- 
fective if  spread  out  like  a  map  as  packed  into  its  present 
shape.  Even  animals  of  the  same  type,  as  Vertebrates, 
cannot  be  ranked  according  to  complexity.  For  while 
Mammals,  on  the  whole,  are  superior  to  Birds,  Birds  to 
Reptiles,  and  Reptiles  to  Fishes,  they  are  not  so  in  every 
respect.  Man  himself  is  not  altogether  at  the  head  of 
creation.  We  carry  about  in  our  bodies  embryonic  struct- 
ures. That  structural  affinity  and  vital  dignity  are  not 
always  parallel  may  be  seen  by  comparing  an  Australian 
and  an  English  man. iaa 


DEVELOPMENT.  225 

Function  is  the  test  of  worth.  Not  mere  work,  how- 
ever; for  we  must  consider  its  quality  and  scope.  An 
animal  may  be  said  to  be  more  perfect  in  proportion  as 
its  relations  to  the  external  world  are  more  varied,  pre- 
cise, and  fitting.  Complexity  of  organization,  variety, 
and  amount  of  power  are  secondary  to  the  degree  in 
which  the  whole  organism  is  adapted  to  the  circumstances 
which  surround  it,  and  to  the  work  which  it  has  to  do. 
Ascent  in  the  animal  scale  is  not  a  passage  from  animals 
with  simple  organs  to  animals  with  complex  organs,  but 
from  simple  individuals  with  organs  of  complex  function 
to  complex  individuals  with  organs  of  simple  function : 
the  addition  as  we  ascend  being  not  function,  but  of  parts 
to  discharge  those  functions ;  and  the  advantage  gained, 
not  another  thing  done,  but  the  same  thing  done  better. 
Advance  in  rank  is  exhibited,  not  by  the  possession  of 
more  life  (for  some  animalcules  are  ten  times  more  lively 
than  the  busiest  Man),  but  by  the  setting  apart  of  more 
organs  for  special  purposes.  The  higher  the  animal,  the 
greater  the  number  of  parts  combining  to  perform  each 
function.  The  power  is  increased  by  this  division  of  la- 
bor. The  most  important  feature  in  this  specialization  is 
the  tendency  to  concentrate  the  nervous  energy  towards 
the  head  (cephalizatioti).  It  increases  as  we  pass  from 
lower  to  higher  animals. 

As  a  rule,  fixed  species  are  inferior  to  the  free,  water 
species  to  land  species,  fresh-water  animals  to  marine,  arc- 
tic forms  to  tropical,  and  the  herbivorous  to  the  carniv- 
orous. Precocity  is  a  sign  of  inferiority:  compare  the 
chicks  of  the  Hen  and  the  Robin,  a  Colt  with  a  Kitten, 
the  comparatively  well  -  developed  Caterpillar  with  the 
footless  grub  of  the  Bee.  Among  Invertebrates,  the  male 
is  frequently  inferior,  not  only  in  size,  but  also  in  grade 
of  organization.  Animals  having  a  wide  range  as  to  cli- 

15 


226  COMPARATIVE  ZOOLOGY. 

mate,  altitude,  or  depth  are  commonly  inferior  to  those 
more  restricted:  Man  is  a  notable  exception. 

There  is  some  relation  between  the  duration  of  life  and 
the  size,  structure,  and  rank  of  animals.  Vertebrates  not 
only  grow  to  a  greater  size,  but  also  live  longer  than  In- 
vertebrates. Whales  and  Elephants  are  the  longest-lived; 
and  Falcons,  Eavens,  Parrots  and  Geese,  Alligators  and 
Turtles,  and  Sharks  and  Pikes,  are  said  to  live  a  century. 
The  life  of  Quadrupeds  generally  reaches  its  limit  when 
the  molar  teeth  are  worn  down:  those  of  the  Sheep  last 
about  15  years ;  of  the  Ox,  20 ;  of  the  Horse,  40 ;  of  the 
Elephant,  100.  Many  inferior  species  die  as  soon  as  they 
have  laid  their  eggs,  just  as  herbs  perish  as  soon  as  they 
have  flowered. 

8.  The  Struggle  for  Life. 

Every  species  of  animal  is  striving  to  increase  in  a  geo- 
metrical ratio.  But  each  lives,  if  at  all,  by  a  struggle  at 
some  period  of  its  life.  The  meekest  creatures  must  fight, 
or  die. 

"  There  is  no  exception  to  the  rule  that  every  organic 
being  naturally  increases  at  so  high  a  rate  that,  if  not  de- 
stroyed, the  earth  would  soon  be  covered  by  the  progeny 
of  a  single  pair."  If  the  increase  of  the  human  race  were 
not  checked,  there  would  not  be  standing-room  for  the 
descendants  of  Adam  and  Eve.  A  pair  of  Elephants,  the 
slowest  breeder  of  all  known  animals,  would  become  the 
progenitors,  in  seven  and  one  half  centuries,  of  19,000,000 
of  Elephants,  if  death  did  not  interfere.  Evidently  a  vast 
number  of  young  animals  must  perish  while  immature, 
and  a  far  greater  host  of  eggs  fail  to  mature.  A  single 
Cod,  laying  millions  of  eggs,  if  allowed  to  have  its  own 
way,  would  soon  pack  the  ocean. 

Yet,  so  nicely  balanced  are  the  forces  of  nature,  the 
average  number  of  each  kind  remains  about  the  same. 


DEVELOPMENT.  227 

The  total  extinction  of  any  one  species  is  exceedingly 
rare.  The  number  of  any  given  species  is  not  determined 
by  the  number  of  eggs  produced,  but  by  its  conditions.1" 
Aquatic  birds  outnumber  the  land  birds,  because  their 
food  never  fails,  not  because  they  are  more  prolific.  The 
Fulmar-petrel  lays  but  one  egg,  yet  it  is  believed  to  be 
the  most  numerous  bird  in  the  world. 

The  main  checks  to  the  high  rate  of  increase  are :  cli- 
mate (temperature  and  moisture),  acting  directly  or  indi- 
rectly by  reducing  food;  and  other  animals,  either  rivals 
requiring  the  same  food  and  locality,  or  enemies,  for  the 
vast  majority  of  animals  are  carnivorous.  Offspring  are 
continually  varying  from  their  parents,  for  better  or  worse. 
If  feebly  adapted  to  the  conditions  of  existence,  they  will 
finally  go  to  the  wall.  But  those  forms  having  the  slight- 
est advantage  over  others  inhabiting  the  same  region, 
being  hardier  or  stronger,  more  agile  or  sagacious,  will 
survive.  Should  this  advantageous  variation  become 
hereditary  and  intensified,  the  new  variety  will  gradually 
extirpate  or  replace  other  kinds.  This  is  what  Mr.  Dar- 
win means  by  Natural  Selection,  and  Herbert  Spencer  by 
the  Survival  of  ih#  Fittest. 


II. 

SYSTEMATIC    ZOOLOGY. 


Facts  are  stupid  things  until  brought  into  connection  with  some  general 
law. — AGASSIZ. 

No  man  becomes  a  proficient  in  any  science  who  does  not  transcend  sys- 
tem, and  gather  up  new  truth  for  himself  in  the  boundless  field  of  research. 
— DR.  A.  P.  PEABODY. 

Never  ask  a  question  if  you  can  help  it;  and  never  let  a  thing  go  un- 
known for  the  lack  of  asking  a  question  if  you  can't  help  it. — BEECHER. 

He  is  a  thoroughly  good  naturalist  who  knows  his  own  parish  thoroughly. 
—CHARLES  KINGSLEY. 


THE  CLASSIFICATION  OF  ANIMALS.  231 


CHAPTEE  XXI. 

THE   CLASSIFICATION   OF   ANIMALS. 

THE  Kingdom  of  Nature  is  a  literal  Kingdom.  Order 
and  beauty,  law  and  dependence,  are  seen  everywhere. 
Amidst  the  great  diversity  of  the  forms  of  life,  there  is 
unity;  and  this  suggests  that  there  is  one  general  plan, 
but  carried  out  in  a  variety  of  ways. 

Naturalists  have  ceased  to  believe  that  each  animal  or 
group  is  a  distinct,  circumscribed  idea.  "Every  animal 
lias  a  something  in  common  with  all  its  fellows :  much 
with  many  of  them;  more  with  a  few;  and,  usually,  so 
much  with  several,  that  it  differs  but  little  from  them." 
The  object  of  classification  is  to  bring  together  the  like, 
and  to  separate  the  unlike.  But  how  shall  this  be  done  ? 
To  arrange  a  library  in  alphabetical  order,  or  according  to 
size,  binding,  date,  or  language,  would  be  unsatisfactory. 
We  must  be  guided  by  some  internal  character.  We  must 
decide  whether  a  book  is  poetry  or  prose ;  if  poetry, 
whether  dramatic,  epic,  lyric,  or  satiric ;  if  prose,  whether 
history,  philosophy,  theology,  philology,  science,  fiction, 
or  essay.  The  more  we  subdivide  these  groups,  the  more 
difficult  the  analysis. 

A  classification  of  animals,  founded  on  external  resem- 
blances— as  size,  color,  or  adaptation  to  similar  habits  of 
life — would  be  worthless.  It  would  bring  together  Fish- 
es and  Whales,  Birds  and  Bats,  Worms  and  Eels.  Nor 
should  it  be  based  on  any  one  character,  as  the  quality 
of  the  blood,  structure  of  the  heart,  development  of  the 
brain,  embryo-life,  etc.;  for  no  character  is  of  equal  value 
in  every  tribe.  A  natural  classification  must  rest  on  those 


232  COMPARATIVE  ZOOLOGY. 

prevailing  characters  which  are  the  most  constant.™  And 
such  a  classification  cannot  be  linear.  It  is  impossible  to 
arrange  all  animal  forms  from  the  Sponge  to  Man  in.  a 
single  line,  like  the  steps  of  a  ladder,  according  to  rank. 
Nature  passes  in  so  many  ways  from  one  type  to  another, 
and  so  multiplied  are  the  relations  between  animals,  that 
one  series  is  out  of  the  question.  There  is  a  number  of 
series,  and  series  within  series,  sometimes  proceeding  in 
parallel  lines,  but  more  often  divergent.  The  animals  ar- 
range themselves  in  radiating  groups,  each  group  being 
connected,  not  with  two  groups  merely,  one  above  and  the 
other  below,  but  with  several.  Life  has  been  likened  to  a 
great  tree  with  countless  branches  spreading  widely  from 
a  common  trunk,  and  deriving  their  origin  from  a  com- 
mon root;  branches  bearing  all  manner  of  flowers,  every 
fashion  of  leaves,  and  all  kinds  of  fruit,  and  these  for 
every  use. 

The  groups  into  which  we  are  able  to  cast  the  various 
forms  of  animal  development  are  very  unequal  and  dis- 
similar. We  must  remember  that  a  genus,  order,  or  class 
is  not  of  equal  value  throughout  the  kingdom.  Moreover, 
each  division  is  allied  to  others  in  different  degrees — the 
distance  between  any  two  being  the  measure  of  that  affin- 
ity. The  lines  between  some  are  sharp  and  clear,  between 
others  indefinite.  Like  the  islands  of  an  archipelago,  some 
groups  merge  into  one  another  through  connecting  reefs, 
others  are  sharply  separated  by  unfathomable  seas,  yet  all 
have  one  common  basis.  Links  have  been  found  reveal- 
ing a  relationship,  near  or  distant,  even  between  animals 
whose  forms  are  very  unlike.  There  are  Fishes  (Dipnoi) 
with  some  Amphibian  characters,  and  fish-like  Amphibi- 
ans (Axolotl).  The  Ichthyosaurus  is  a  Lizard  with  fish- 
characteristics.  Birds  seem  isolated,  but  they  are  closely 
connected  with  Reptiles  by  fossil  forms.  Even  the  great 
gap  in  the  Animal  Kingdom — that  separating  Vertebrates 


THE  CLASSIFICATION  OF  ANIMALS.  233 

and  Invertebrates — is  partially  bridged  on  the  one  side 
by  Amphioxus,  and  on  the  other  by  the  Tunicates. 

We  have,  then,  groups  subordinate  to  groups,  and  inter- 
locking, but  not  representing  so  many  successive  degrees 
of  organization.  For,  as  already  intimated,  complication 
of  structure  does  not  rise  in  continuous  gradation  from 
one  group  to  another.  Every  type  starts  at  a  lower  point 
than  that  at  which  the  preceding  class  closes ;  so  that  the 
lines  overlap.  While  one  class,  as  a  whole,  is  higher  than 
another,  some  members  of  the  higher  class  may  be  infe- 
rior to  some  members  of  the  lower  one.  Thus,  certain 
Star-fishes  are  nobler  than  certain  Mollusks;  the  Nautilus 
is  above  the  Worm,  and  the  Bee  is  more  worthy  than  the 
lowest  Fish.  The  groups  coalesce  by  their  inferior  or  less 
specialized  members ;  e.  g.,  the  Fishes  do  not  graduate  into 
Amphibians  through  their  highest  forms,  but  the  two  come 
closest  together  low  down  in  the  scale.  Man  appears  to 
be  the  goal  of  creation ;  but  even  within  the  Vertebrate 
series,  every  step  of  development,  say  of  the  Fish,  is  away 
from  the  goal.  The  highest  Fish  is  the  one  farthest  from 
Man. 

A  number  of  animals  may,  therefore,  have  the  same 
grade  of  development,  but  conform  to  entirely  different 
types.  While  a  fundamental  unity  underlies  the  whole 
Animal  Kingdom,  suggesting  a  common  starting-point,  we 
recognize  several  distinct  plans  of  structure.1"  Animals 
like  the  Amoeba,  with  no  cellular  tissues  nor  true  eggs, 
form  the  subkingdom  Protozoa.  Animals  like  the  Sponge, 
with  independent  cells,  one  excurrent  and  many  incurrent 
openings,  form  the  subkingdom  Spongida.  Animals  like 
the  Coral,  unlike  all  others,  have  an  alimentary  canal  but 
no  body -cavity,  have  no  separate  nervous  and  vascular 
regions,  and  the  parts  of  the  body  radiate  from  a  centre. 
Such  form  a  subkingdom  called  Cmlenterata.  Animals 
like  the  Star-fish,  having  also  a  radiating  body,  but  a  closed 


234:  COMPARATIVE  ZOOLOGY. 

alimentary  canal,  and  a  distinct  symmetrical  nervous  sys- 
tem, constitute  the  subkingdom  Echinodermata.™  Ani- 
mals like  the  Angle- worm,  bilaterally  symmetrical,  one- 
jointed,  or  composed  of  joints  following  each  other  from 
front  to  rear,  with  no  jointed  limbs,  constitute  the  sub- 
kingdom  Vermes.  Animals  like  the  Snail,  with  a  soft, 
un jointed  body,  a  mantle,  a  foot,  a  two  or  three  cham- 
bered heart,  and  a  nervous  system  in  the  form  of  a  ring 
around  the  gullet,  constitute  the  subkingdom  Mollusca. 
Animals  like  the  Bee,  with  a  jointed  body  and  jointed 
limbs,  form  the  subkingdom  Arthropoda.  Animals  like 
the  Sea-squirts,  sack  or  barrel  shaped,  with  a  mantle  cav- 
ity penetrated  by  an  excurrent  and  an  incurrent  opening, 
with  heart  and  gills,  form  the  subkingdom  Tunicata.  An- 
imals like  the  Ox,  having  a  double  nervous  system,  one 
(the  sympathetic)  lying  on  the  upper  side  of  the  aliment- 
ary canal,  the  other  and  main  part  (spinal)  lying  along  the 
back,  and  completely  shut  off  from  the  other  organs  by  a 
partition  of  bone  or  gristle,  known  as  the  "  vertebral  col- 
umn," and  having  limbs,  never  more  than  four,  always  on 
the  side  opposite  the  great  nervous  cord,  constitute  the 
subkingdom  Vertebrata. 

Comparing  these  great  divisions,  we  see  that  the  Verte- 
brates differ  from  all  the  others  chiefly  in  having  a  double 
body-cavity  and  a  doable  nervous  system,  the  latter  lying 
above  the  alimentary  canal ;  while  Invertebrates  have  one 
cavity  and  one  nervous  system,  the  latter  being  placed 
either  below  or  around  the  alimentary  canal.  The  Vermes 
are  closely  related  to  all  the  following  subkingdoms  of 
Invertebrates,  most  nearly  to  Mollusks  and  Tunicates, 
while  the  latter  have  affinities  with  the  Vertebrates.  The 
Echinoderms  and  Coelenterates  are  built  on  the  common 
type  of  a  star;  but  they  differ  from  each  other  in  the 
presence  or  absence  of  distinct  alimentary,  circulatory, 
and  nervous  systems. 


THE  CLASSIFICATION  OF  ANIMALS.  235 

But  there  are  types  within  types.  Thus,  there  are  five 
modifications  of  the  Vertebrate  type  —  Fish,  Amphibian, 
Reptile,  Bird,  and  Mammal;  and  these  are  again  divided 
and  subdivided,  for  Mammals,  e.  g.,  differ  among  them- 
selves. So  that  in  the  end  we  have  a  constellation  of 
groups  within  groups,  founded  on  peculiar  characters  of 
less  and  less  importance,  as  we  descend  from  the  general 
to  the  special. 

Individuals  are  the  units  of  the  Animal  Creation.  An 
animal  existence,  complete  in  all  its  parts,  is  an  individual, 
whether  separate,  as  Man,  or  living  in  a  community,  as  the 
Coral.1" 

Species  is  the  smallest  group  of  individuals  which  can 
be  defined  by  distinct  characteristics,  and  which  is  sepa- 
rated by  a  gap  from  all  other  like  groups.  A  well-marked 
subdivision  of  a  species  is  called  a  variety.  Crosses  be- 
tween species  are  called  hybrids,  as  the  Mule. 

Genus  is  a  group  of  species  having  the  same  essential 
structure.  Thus,  the  closely  allied  species  Cat,  Tiger,  and 
Lion  belong  to  one  genus. 

Family,  or  Tribe,  is  a  group  of  genera  having  a  simi- 
lar form.  Thus,  the  Dogs  and  Foxes  belong  to  different 
genera,  but  betray  a  family  likeness. 

Order  is  a  group  of  families,  or  genera,  related  to  one 
another  by  a  common  structure.  Cats,  Dogs,  Hyenas,  and 
Bears  are  linked  together  by  important  anatomical  features; 
their  teeth,  stomachs,  and  claws  show  carnivorous  habits. 

Class  is  a  still  larger  group,  comprising  all  animals 
which  agree  simply  in  a  special  modification  of  the  type 
to  which  they  belong.  Thus,  Fishes,  Amphibians,  Rep- 
tiles, Birds,  and  Mammals  are  so  many  aspects  of  the  Ver- 
tebrate type. 

Subkingdom  is  a  primary  division  of  the  Animal  King- 
dom, which  includes  all  animals  formed  upon  one  of  the 
various  types  of  structure ;  as  Vertebrate. 


236  COMPARATIVE  ZOOLOGY. 

The  subkingdoms  are  grouped  into  two  great  Series, 
according  to  their  histological  structure  and  mode  of  de- 
velopment."8 

These  terms  were  invented  by  Linnaeus,  except  Family, 
Subkingdom,  and  Series.  To  Linnaeus  we  are  also  in- 
debted for  a  scientific  method  of  naming  animals.  Thus, 
a  Dog,  in  Zoology,  is  called  Canis  familiar  is,  which  is  the 
union  of  a  generic  and  a  specific  name,  corresponding  to 
the  surname  and  the  Christian  name  in  George  Washing- 
ton, only  the  specific  name  comes  last.  It  will  be  under- 
stood that  these  are  abstract  terms,  expressing  simply  the 
relations  of  resemblance:  there  is  no  such  thing  as  genus 
or  species. 

Classification  is  a  process  of  comparison.  He  is  the 
best  naturalist  who  most  readily  and  correctly  recognizes 
likeness  founded  on  structural  characters.  As  it  is  easier 
to  detect  differences  than  resemblances,  it  is  much  easier 
to  distinguish  the  class  to  which  an  animal  belongs  than 
the  genus,  and  the  genus  than  the  species.  In  passing 
from  species  to  classes,  the  characters  of  agreement  be- 
come fewer  and  fewer,  while  the  distinctions  are  more 
and  more  manifest;  so  that  animals  of  the  same  class  are 
more  like  than  unlike,  while  members  of  distinct  classes 
are  more  unlike  than  like. 

To  illustrate  the  method  of  zoological  analysis  by  search- 
ing for  affinities  and  differences,  we  will  take  an  example 
suggested  by  Professor  Agassiz.  Suppose  we  see  together 
a  Dog,  a  Cat,  a  Bear,  a  Horse,  a  Cow,  and  a  Deer.  The 
first  feature  which  strikes  us  as  common  to  any  two  of 
them  is  the  horn  in  the  Cow  and  the  Deer.  But  how 
shall  we  associate  either  of  the  others  with  these  ?  We 
examine  the  teeth,  and  find  those  of  the  Dog,  the  Cat,  and 
the  Bear  sharp  and  cutting ;  while  those  of  the  Cow,  the 
Deer,  and  the  Horse  have  flat  surfaces,  adapted  to  grind- 
ing and  chewing,  rather  than  to  cutting  and  tearing.  We 


THE  CLASSIFICATION  OF  ANIMALS.  237 

compare  these  features  of  their  structure  with  the  habits 
of  these  animals,  and  find  that  the  first  are  carnivorous — 
that  they  seize  and  tear  their  prey ;  while  the  others  are 
herbivorous,  or  grazing,  animals,  living  only  on  vegetable 
substances,  which  they  chew  and  grind.  We  compare, 
further,  the  Horse  and  Cow,  and  find  that  the  Horse  has 
front  teeth  both  in  the  upper  and  the  lower  jaw,  while 
the  Cow  has  them  only  in  the  lower;  and  going  still 
further,  and  comparing  the  internal  with  the  external 
features,  we  find  this  arrangement  of  the  teeth  in  direct 
relation  to  the  different  structure  of  the  stomach  in  the 
two  animals — the  Cow  having  a  stomach  with  four  pouch- 
es, while  the  Horse  has  a  simple  stomach.  Comparing 
the  Cow  and  Deer,  we  find  the  digestive  apparatus  the 
same  in  both;  but  though  both  have  horns,  those  of  the 
Cow  are  hollow,  and  last  through  life ;  while  those  of  the 
Deer  are  solid,  and  are  shed  every  year.  Looking  at  the 
feet,  we  see  that  the  herbivorous  animals  are  hoofed;  the 
carnivorous,  clawed.  The  Cow  and  Deer  have  cloven 
feet,  and  are  ruminants ;  the  Horse  has  a  single  hoof,  and 
does  not  chew  the  cud.  The  Dog  and  Cat  walk  on  the 
tips  of  their  fingers  and  toes  (digitigrade) ;  the  Bear  treads 
on  the  palms  and  soles  (plantigrade).  The  claws  of  the 
Cat  are  retractile;  those  of  the  Dog  and  Bear  are  fixed. 

In  this  way  we  determine  the  exact  place  of  each  ani- 
mal. The  Dog  belongs  to  the  kingdom  Animalia,  sub- 
kingdom  Vertebrata,  class  Mammalia,  order  Carnivora, 
family  Canidce,  genus  Canis,  species  Familiaris,  variety 
Hound  (it  may  be),  and  its  individual  name,  perhaps,  is 
"Rover."  The  Cat  differs  in  belonging  to  the  family 
Felidce,  genus  Felis.  species  Catus.  The  Bear  belongs  to 
the  family  Ursidce,  genus  Ursus,  and  species  Ferox,  if 
the  Grizzly  is  meant.  The  Horse,  Cow,  and  Deer  belong 
to  the  order  Ungulata  ;  but  the  Horse  is  of  the  family 
Equidce,  genus  Equus^  species  Caballus ;  the  Cow  is  of 


238  COMPARATIVE  ZOOLOGY. 

the  family  JBovidce,  genus  Bos,  species  Taurus  ;  the  Deer 
is  of  the  family  Cervidoe,  genus  Cervus,  species  Virgini- 
anus,  if  the  common  Deer  is  meant. 

The  diagram  on  the  opposite  page  roughly  represents 
(for  the  relations  of  animals  cannot  be  expressed  on  a 
plane  surface)  the  relative  positions  of  the  subkingdoms 
and  classes  according  to  affinity  and  rank.* 

SERIES  I.— PROTOZOA. 
Animals  without  cellular  tissues,  and  with  no  true  e^ers. 

J  OO 

The  body  which  corresponds  to  the  egg  does  not  develop 
a  blastoderm. 

Subkingdom. — PROTOZOA. 

This  division  was  proposed  by  Yon  Siebold  in  1845,  to 
contain  that  vast  cloud  of  microscopic  beings  on  the  verge 
of  the  Animal  Kingdom  which  could  not  be  received  into 
the  other  subkingdoms.  It  is  artificial  and  provisional. 
The  classes  composing  it  are  not  founded  on  a  common 
type,  but  are  distinguished  by  the  absence  rather  than  the 
presence  of  positive  characters.  Many  stand  parallel  to 
the  Protophyta  of  the  Vegetable  World,  and  no  definite 
line  can  be  drawn  between'  them. 

Protozoans  agree  in  being  minute,  aquatic,  and  exceed- 
ingly simple  in  structure,  their  bodies  consisting  mainly 
or  wholly  of  the  contractile,  gelatinous  matter  called  pro- 
toplasm, or  sarcode  —  the  first  homogeneous  substance 
which  has  the  power  of  controlling  chemical  and  physical 
forces.  They  have  no  cellular  organs  or  tissues,  yet  they 
take  and  assimilate  food,  grow,  and  multiply,  which  are 


*  The  student  should  master  the  distinctions  between  the  great  groups,  or 
classes,  before  proceeding  to  a  minuter  classification.  "The  essential  mat- 
ter, in  the  first  place,"  says  Huxley,  "is  to  be  quite  clear  about  the  different 
classes,  and  to  have  a  distinct  knowledge  of  all  the  sharply  definable  modifi- 
cations of  animal  structure  which  are  discernible  in  the  Animal  Kingdom." 


THE  CLASSIFICATION  OF  ANIMALS. 


239 


o  3   3   s: 


K 


K  8  > 

III 


S   ^    *    w 
g*  3*  ?    5 

p  S      g. 


240  COMPARATIVE  ZOOLOGY. 

the  essential  signs  of  life.     The  usual  methods  of  repro- 
duction are  self-division  and  budding. 

The  subkingdom  may  be  divided  into  four  classes :  Mo- 
nera,  Gregarinida,  Rhizopoda,  and  Infusoria. 

CLASS  I. — Monera. 

These  simplest  living  beings  are  organless 
bits   of   protoplasma,  with   no   distinction   of 
layers,  round   when    at   rest,  and  with  pseu- 
dopodia  when  active.     They  are  all  aquatic, 
Fio.i83.-Pro-  and  some  are  parasitic.     Such  is  Protamoeba, 

tamcebapri-    -.-,.       -.  Qo 
mitiva.  -big.  18d. 

CLASS  II. — Gregarinida. 

The  Gregarinse,  discovered  by  Dufour  in  1828,  are 
among  the  simplest  animal  forms  of  which  we  have  any 
knowledge.  They  closely  resemble  a  cell,  or  microscopic 
egg ;  the  only  organ  is  a  nucleus,  suspended  in  extremely 
mobile  granular  matter;  and  the  most  conspicuous  signs 


Fro.  ISl.—Gregarina  gigantea,  highly  magnified :  a,  nucleus. 

of  life  are  the  contraction  and  lengthening  of  the  worm- 
like  body.  They  feed  by  absorption,  and  are  all  parasites, 
living  in  the  alimentary  canal  of  higher  animals ;  as  in 
the  Cockroach,  Earth-worm,  and  Lobster.  The  name  is 
derived  from  the  fact  that  they  occur  in  large  numbers 
crowded  together. 

CLASS  III. — Rhizopoda. 

The  Ehizopods  are  characterized  by  the  power  of  throw- 
ing out  at  will  delicate  processes  of  their  bodies,  called 
pseudopodia,  or  false  feet,  for  prehension  or  locomotion. 


PROTOZOA. 


241 


They  possess  no  cilia.    The  representative  forms  are  Amce- 
bce,  Forartiinifera,  and  Polycystina. 

An  Amoeba  is  a  naked  fresh-water  Rhizopod;  an  in- 
definite bit  of  protoplasm,  as  structureless  as  a  speck  of 
jelly,  save  that  it  is  made  of 
two  distinct  layers,  and  has  a 
nucleus  and  a  contractile  cav- 
ity inside.  It  thus  differs 
from  the  Monera.  It  has  no 
particular  form,  as  it  changes 
continually.  It  moves  by  put- 
ting forth  short,  blunt  proc-  Fl«.Ar,>ceba ™eps,  x  150 ;  the 
esses,  and  eats  by  wrapping  Bame  auimal  iu  various  8hai)e8- 
its  body  around  the  particle  of  food.  The  size  ranges 
from  -fa  to  -sVoir  of  an  inch  in  diameter.  Specimens  can 
be  obtained  by  scraping  the  mucous  matter  from  the 
stems  and  leaves  in  stagnant  ponds, 

A  Foraminifer  differs  from  an  Amoaba  in  having  an 
apparently  simpler  body,  the  protoplasm  being  without 
layers  or  cavity ;  its  pseudopodia  are  long  and  thread-like, 
and  may  unite  where  they  touch  each  other.  It  has  the 
property  of  secreting  an  envelope,  usually  of  carbonate  of 


a 


FIG.  186. — Rhizopods :  a,  a  monothalamou*,  or  ^ngle-chambered,  Fornminifer  (Lo- 
gena  striata) ;  b,  a  polythalamous,  or  many-chambered,  Foraminifer  (Polystomella 
criApa),  with  pseudopodia  extended ;  c,  a  Radiolarian,  one  of  the  Polycystiues 
(Podocyrtis  Schomburgkii). 

16 


24:2  COMPARATIVE   ZOOLOGY. 

lime.  The  shell  thus  formed  is  sometimes  of  extraordi- 
nary complexity  and  singular  beauty.  It  is  generally  per- 
forated by  innumerable  minute  orifices  (foramina)  through 
which  the  animal  protrudes  its  myriad  of  glairy,  thread- 
like arms.  The  majority  are  compound,  resembling  cham- 
bered shells,  formed  by  a  process  of  budding,  the  new 
cells  being  added  so  as  to  make  a  straight  series,  a  spiral, 
or  a  flat  coil.  As  a  rule,  the  many -chambered  species 
have  calcareous,  perforated  shells  ;  and  the  one-chambered 
have  an  imperforated  membranous,  porcelaneous,  or  are- 
naceous envelope.  The  former  are  marine.  There  are 
few  parts  of  the  ocean  where  these  microscopic  shells  do 
not  occur,  and  in  astounding  numbers.  A  single  ounce 
of  sand  from  the  Antilles  was  calculated  to  contain  over 
three  millions.  The  bottom  of  the  ocean,  up  to  about  50° 
on  each  side  of  the  Equator,  and  at  depths  not  greater  than 
2400  fathoms,  is  covered  witli  the  skeletons  of  these  ani- 
mals,* which  are  constantly  falling  upon  it  (globigerina- 
ooze).  Their  remains  constitute  a  great  proportion  of  the 
so-called  sand-banks  which  block  up  many  harbors.  Yet 
they  are  the  descendants  of  an  ancestry  still  more  prolific ; 
for  the  Foraminifera  are  among  the  most  important  rock- 
building  animals.  The  chalk-cliffs  of  England,  the  build- 
ing-stone of  Paris,  and  the  blocks  in  the  Pyramids  of 
Egypt  are  largely  composed  of  extinct  Foraminifers.  Fo- 
raminifera are  both  marine  and  fresh-water,  chiefly  marine. 
A  Polycystine  differs  from  a  Foraminifer  in  secreting 
a  siliceous,  instead  of  a  calcareous,  shell,  studded  with 
spines;  and  the  central  part  of  the  body  is  made  np  of 
many  cells,  and  surrounded  by  a  strong  membrane.  They 
are  also  more  minute,  but  as  widely  diffused.  They  enter 
largely  into  the  formation  of  some  strata  of  the  earth's 
crust,  and  abound  especially  in  the  rocks  of  Barbadoes  and 
at  Richmond,  Ya.  The  living  forms  are  mostly  marine, 
but  some  are  fresh- water. 


PROTOZOA. 


243 


FIG.  1ST.— A   Compound  Monad 
(UoeUa),  X  1000. 


CLASS  IY. — Infusoria. 

This  unassorted  group  of  living  particles  derived  its 
name  from  the  fact  that  they  were  first  discovered  in  veg- 
etable infusions.  Every  drop  of 
a  stagnant  pool  is  crowded  with 
them.  They  are  all  single  and 
microscopic,  yet  of  various  sizes, 
the  difference  between  the  small- 
est and  largest  being  greater  than 
the  difference  between  a  Mouse 
and  an  Elephant.  Some  are  fixed 
(as  Vorticelld),  but  the  majority  are  free,  and  constantly 
in  motion,  propelled  by  countless  cilia,  as  a  galley  by  its 
oars.  The  delicate  body  consists  of  two 
layers  of  sarcode  (there  are  no  cellular 
tissues,  but  the  whole  body  represents  a 
single  cell),  covered  by  a  ihembrane,  or 
skin,  having  one  or  two  contractile  cavi- 
ties, and  a  nucleus.  Food-granules  can 
often  be  seen.  On  one  side  is  a  slight 
depression,  or  "  mouth,"  leading  to  a 
short,  funnel-shaped  throat.  A  mouth 
and  a  rudimentary  digestive  cavity  are 
among  the  distinctive  features  of  these 

FIG.    188.  —  Infusorium 

(Parameciumaurelia},    ProtOZOanS.     Some  have  a  pigmeilt-Speck 
X  300:   m,  mouth;  v,  .  .         .  . 

con  tractile  vesicles  ;  n,  — the  simplest  sense  organ — and  m  the 

stem  of  Yorticella  the  first  rudiments  of 

muscle  may  be  found.     They  multiply  so  rapidly  (chiefly 

by  self-division),  that  a  Paramecium,  the  most  common 

form,  may  become  the  parent  of  1,364,000  in  forty-two  days. 

There  are  two  main  groups:   Flagellata,  or  Monads, 

provided  with  one  or  two  flagella,  or  long,  bristle -like 

cilia;  and  Ciliata,  which  are  furnished  with  numerous 

vibratile  cilia. 


244  COMPARATIVE  ZOOLOGY. 

SERIES  II.— METAZOA. 

The  Metazoa  include  all  those  animals  which  reproduce 
by  true  eggs  and  spermatozoa,  whose  germ  develops  a 
blastoderm,  and  which  have  cellular  tissues.  There  are 
seven  subkingdoms. 

Subkingdom  I. — SPONGIDA. 

The  position  of  the  Sponges  has  been  much  disputed. 
At  first  they  were  thought  to  be  on  the  border-line  be- 
tween animals  and  plants,  and  were  assigned  by  some  to 
the  animals  and  by  others  to  the  vegetables.  Later,  and 
up  to  very  recent  years,  they  were  assigned  to  the  Proto- 
zoa. The  discovery  of  their  mode  of  reproduction  and 
development  has  determined  that  they  belong  to  the 
Metazoa. 

The  Sponges  are  formed  of  an  aggregate  of  membrane- 
less  amoeboid  or  ciliated  cells.  They  usually  have  a  skele- 
ton, which  may  be  calcareous,  horny,  or  siliceous.  They 
have  a  central  cavity,  with  numerous  incurrent  orifices 
and  one  excurrent  opening.  They  reproduce  by  true 
eggs,  as  well  as  by  budding  and  fission. 

The  cells  of  the  Sponge  are  relatively  independent, 
whence  they  have  been  regarded  as  colonies  of  amoeboid 
animals,  and  by  some  naturalists  are  still  so  considered. 

d 

h 


FIG.  189.— Hypothetical  Section  of  a  Sponge:  a,  superficial  layer;  b,  inhalant  pores  : 
c,  ciliated  chambers ;  d,  exhalaut  aperture,  or  osculutn ;  e,  deeper  substance  of 
the  Sponge. 


SPONGIDA.  245 

They  develop,  however,  regularly  from  the  egg,  and  the 
cells  acquire  their  independence  only  at  a  late  date  in  de- 
velopment. Some  of  the  cells  gain  cilia,  or  flagella,  and 
drive  the  water  through  numerous  channels  into  the  cen- 
tral cavity,  whence  it  is  discharged  by  one  opening.  Each 
cell  of  the  Sponge  feeds  itself  from  the  particles  con- 
tained in  the  water. 

The  Sponge-individual  consists  of  one  exhalant  orifice, 
with  the  channels  leading  into  it.     An  ordinary  bathing- 


Fia.  190.— Horny  Skeleton  of  a  Sponge. 

sponge  constitutes  a  colony  of  such  individuals,  which  are 
not  definitely  marked  off  from  each  other.  Other  Sponges 
have  only  one  osculum,  and  such  are  a  single  individual. 

Some  few  Sponges  have  no  skeleton.  Most  have  one 
of  horny  fibres,  strengthened  with  siliceous  spicules.  These 
last  are  absent  in  the  commercial  Sponges,  and  in  them 
the  horny  fibres  are  much  tougher  than  in  most  Sponges. 


210  COMPARATIVE  ZOOLOGY. 

A  few  Sponges,  as  the  Yenus's  Flower -basket  (Euplec- 
telld),  have  siliceous  and  others  have  calcareous  skeletons. 
Excepting  a  few  small  fresh -water  species  (as  Spon- 
gilla),  Sponges  are  marine.  In  the  former,  the  cellular 
part  is  greenish,  containing  chlorophyll;  in  the  latter,  it 
is  brown,  red,  or  purple.  In  preparing  the  Sponge  of 
commerce,  this  is  rotted  by  exposure,  and  washed  out. 
The  best  fishing-grounds  are  the  eastern  end  of  the  Medi- 
terranean and  around  the  Bahama  Islands. 

Subkingdom  II. — CCELENTERATA. 
These  radiate  animals  are  distinguished  by  having  a  dis- 
tinct cavity,  whose  walls  have,  at  least,  two  layers  of  cel- 
lular tissue,  an  outer  (ectoderm)  and  inner  (endoderm),  and 
usually  a  middle  layer  (mesoderm).  They  have  thread  cells, 
minute  sacs  containing  a  fluid,  and  connected  with  barbed 
filaments  capable  of  being  thrown  out  for  stinging  pur- 
poses. Most  are  provided  with  hollow  tentacles  around 
the  mouth.  All  are  aquatic,  and  nearly  all  are  marine. 
There  are  two  classes,  represented  by  the  Hydra  and  Sea- 
anemone.  Both  reproduce  by  budding  and  by  eggs. 

CLASS  I. — Hydrozoa. 

These  Coelenterates  have  no  separate  digestive  sac,  so 
that  the  body  is  a  simple  tube,  or  cavity,  into  which  the 
mouth  opens.  The  nervous  system  is  slightly  developed. 
Such  are  the  fresh-water  Hydra  and  the  oceanic  Jelly-fish 
(Acaleph  or  Medusa). 

The  body  of  the  Hydra  is  tubular,  soft,  and  sensitive, 
of  a  greenish  or  reddish  color,  and  seldom  over  half  an 
inch  long.  It  is  found  spontaneously  attached  by  one 
end  to  submerged  plants,  while  the  free  end  contains  the 
orifice,  or  mouth,  crowned  with  tentacles,  by  which  the 
creature  feeds  and  creeps.  The  body-wall  consists  of  two 
cellular  layers— ectoderm  and  endoderm.  These  surround 


CCELENTERATA. 


247 


a  central  cavity  with  one 

opening.     The   animal 

may  be  compared  to  a 

bag  with  a  two-layered 

wall,  and  tentacles  around 

the   opening.     It   buds, 

and  also  reproduces  by 

eggs.     The  buds,  when 

adult,  become  detached 

from  the  parent. 

In  most  of  the  other 

Hydroids  the  colony  is 

permanent,  and  support- 

ed by  a  horny  skeleton. 

There  are  two  kinds  of 

Polyps  in  each  colony,  Fia^_IIydra:  2)With  tontacleg  fully  extend. 

one  for  feeding  and  the  ed'  s.creepiug;  5,  budding. 

Sometimes  the  reproductive 
Potyps  are  separated 
from  the  stock  in  the 
form  of  little  Jelly- 
fishes.  The  larger 
Jelly  -  fishes  belong 
to  another  group 
—  the  AcalephcB  — 
and  are  produced  as 
told  on  page  212. 


other   for   reproduction. 


a  soft,  gelatinous, 
semi-transparent,bell- 
shaped  body,  with 
tubes  radiating  from 
the  central  cavity  to 
the  circumference, 

FIG.  192.-Hydroid  (Serfwfcma)  growing  on  a  Shell,     and  with  the  margin 


248 


COMPARATIVE  ZOOLOGY. 


FIG.  193.— Jelly-fish  (Pelagia  noctiluca).    Mediter- 
raueau. 


FIG.  194.— Portuguese  Man- 
of-war  (Physalia),  |  natu- 
ralsize.  Tropical  Atlantic. 


FIG.  195 — Jelly-fish  (Aurelia  aurita),  with  young  in  various  stages. 


CCELENTERATA. 


249 


radiating  and  marginal 

canals. 


fringed  with  tentacles,  furnished  with  stinging  thread- 

cells.      The   radiating  parts    are   in    multiples   of   four. 

Around  the  rim  are  minute  colored 

spots,   the    "  eye  -  specks."     In    fine 

weather,  these   "  sea  -  blubbers  "   are 

seen  floating  on  the  sea,  mouth  down- 

ward, moving  about  by  flapping  their 

sides,  like  the  opening  and  shutting 

of  an   umbrella,  with  great  regular- 

ity.    They   are   frequently  phospho- 

rescent when  disturbed.      Some  are 

quite    small,  resembling    little    glass 

bells;  the  common  Aurelia  is  over  a 

foot  in  diameter  when  full-grown;  Flo.196._A  MedU8a,  seeu  in 

while  the  Oyanea,  the  giant  among 

Jelly-fishes,  sometimes  measures  eight 

.         ,  .  T 

feet  in  diameter,  with  tentacles  one 

hundred  feet  long.     When  dried,  nothing  is  left  but  a 

film  of  membrane  weighing  only  a  few  grains. 

There  are  two  representative  types:   the  Lucernaria, 

the  Umbrella-acaleph,  having  a  short  pedicel  on  the  back 

for  attachment;  tentacles 
disposed  in  eight  groups 
around  the  margin,  the 
eight  points  alternating 
with  the  four  partitions 
of  the  body  -cavity  and 

FIG.  197.—  Lucernaria  auricula  attached  to  a    the    four    COl'IierS    of    the 
piece  of  sea-weed;  natural  size.    The  one  on  ,1  ,  , 

the  right  is  abnormal,  having  a  ninth  tuft  of    HI  OH  til  J      HOt     ICSS      tliail 

eight    radiating    canals, 

and  no  membranous  veil.  The  common  species  on  the 
Atlantic  shore,  generally  found  attached  to  eel-grass,  is  an 
inch  in  diameter,  of  a  green  color.  Discophora,  the  ordi- 
nary Jelly-fish,  is  free  and  oceanic.  It  differs  from  the 
Lucernaria  in  its  usually  larger  size  and  solid  disk,  four 


250  COMPARATIVE  ZOOLOGY. 

radiating  canals,  which  ramify  and  open  into  a  circular 
vessel,  and  a  "  veil,"  or  shelf,  always  running  around  the 
mouth  of  the  disk.129 

CLASS  II. — Anthozoa. 

These  marine  animals,  which  by  their  gay  tentacles  con- 
vert the  bed  of  the  ocean  into  a  flower-garden,  or  by  their 

secretions  build  up  coral-islands, 
have  a  body  like  a  cylindrical 
gelatinous  bag.  One  end,  the 
base,  is  usually  attached  ;  the 
other  has  the  month  in  the  cen- 
tre, surrounded  by  numerous 
hollow  tentacles,  which  are  cov- 
ered with  nettling  lasso -cells. 
This  upper  edge  is  turned  in  so 
as  to  form  a  sac  within  a  sac, 

FIG.  198. —Horizontal  Section  of  Ac- 
tinia through  the  stomach,  show-  like  the  neck  of  a  bottle  turned 

ing  septa  aud  compartments.  .        .          _ 

outsidem.    The  inner  sac,  which 

is  the  digestive  cavity,  does  not  reach  the  bottom,  but 
opens  into  the  general  body-cavity.130  The  space  between 
these  two  concentric 
tubes  is  divided  by  a 
series  of  vertical  parti- 
tions, some  of  which 
extend  from  the  body- 
wall  to  the  digestive 
sac,  but  others  fall 
short  of  it.  Instead, 
therefore,  of  the  radi- 
ating tubes  of  the  Aca- 
leph,  there  are  radiat- 
ing spaces.  No  mem- 
bers of  this  class  are 

Fid.  199. —Actinia  expanded,  seen  from  above, 
microscopic.       All    are  showing  mouth. 


CCELENTERATA. 


251 


long-lived  compared  with  the  Hydrozoa,  living  for  several 
years.  One  kept  in  aquaria  in  England  is  now  more  than 
sixty  years  old. 

1.  Soft -bodied  Polyps. — The  best -known  representa- 
tive of  this  group  is  the  Actinia,  or  Sea -anemone.     It 
leads  a  single  life,  and  is  capable  of  a  slow  locomotion. 
Muscular  fibres  run  around  the  body,  and  others  cross 
these  at  right  angles.     The  tentacles,  which  often  number 
over  two  hundred,  and  the  partitions,  which  are  in  reality 
double,  are  in  multiples  of  six.    At  night,  or  when  alarmed, 
the  tentacles  are  drawn  in,  and  the  aperture  firmly  closed, 
so  that  the  animal  looks  like  a  rounded  lump  of  fleshy 
substance  plastered  on  the  rock.     It  feeds  on  Crabs  and 
Mollusks.     It  abounds  on  every  shore,  especially  of  trop- 
ical seas.     The  size  varies  from  one  eighth  of  an  inch  to  a 
foot  in  diameter. 

2.  Coral  Polyps. — The  majority  of  Anthozoa  secrete 
a  calcareous  or  horny  framework  called  "coral."     With 
few    exceptions,    they    are   fixed 

and  composite,  living  in  colonies 
formed  by  a  continuous  process 
of  budding.  Their  structures  take 
a  variety  of  shapes:  often  dome- 
like, but  often  imitating  shrub- 
bery and  clusters  of  leaves.  The 
members  of  a  coral  community 
are  organically  connected;  each 
feeds  himself,  yet  is  not  indepen- 
dent of  the  rest.  We  can  speak 
of  the  individual  Corals,  a,  J,  <?, 
but  we  must  write  them  down 
abc.  The  compound  mass  is  "like  FIG.  200.— organ-pipe c 

i .     .  i  e          .         ,  pora  mnsica).    Indian     cean. 

a  living  sheet  of  animal  matter, 

fed  and  nourished  by  numerous  mouths  and  as  many 

stomachs."     Life    and  death    go    on    together,  the   old 


252  COMPARATIVE  ZOOLOGY. 

Polyps  dying  below  as  new  ones  are  developed  above.  The 
living  part  of  an  Astrcea  is  only  half  an  inch  thick.  The 
growth  of  the  branching  Madrepore  is  about  three  inches 
a  year.  The  prevailing  color  of  the  Coral  Polyps  is 
green ;  and  the  usual  size  varies  from  that  of  a  pin's  head 
to  half  an  inch,  but  the  Mushroom-coral  (which  is  a  single 
individual)  may  be  a  foot  in  diameter. 

Corals  are  of  two  kinds :  those  deposited  within  the  tis- 
sues of  the  animal  (sderodermic),  and  those  secreted  by 
the  outer  surface  at  the  foot  of  the  Polyp  (sclerobasic). 
The  Polyps  producing  the  former  are  Actinoid,  resem- 
bling the  Actinia  in  structure.131  The  skeleton  of  a  single 
Polyp  (called  corallite,  Fig.  95)  is  a  copy  of  the  animal, 
except  the  stomach  and  tentacles,  the  earthy  matter  being 
secreted  within  the  outer  wall  and  between  each  pair  of 
partitions.  So  that  a  corallite  is  a  short  tube  with  vertical 
septa  radiating  towards  the  centre.132  A  sclerobasic  Coral 
is  a  true  exoskeleton,  and  is  distinguished  by  being  smooth 
and  solid.  The  Polyps,  having  eight  fringed  tentacles,  are 
situated  on  the  outside  of  this  as  a  common  axis,  and  are  con- 
nected together  by  the  fleshy  ccenosarc  covering  the  Coral. 

(1)  Solerodermic  Corals. — Astrcea  is  a  hemispherical  mass 
covered  with  large  cells.  Meandrina,  or  "  Brain-coral," 
is  also  globular;  but  the  mouths  of  the  Polyps  open  into 
each  other,  forming  furrows.  Fungia,  or  "Mushroom- 
coral,"  is  disk-shaped,  and  differs  from  other  kinds  in  be- 
ing the  secretion  of  a  single  gigantic  Polyp,  and  in  not 
being  fixed.  Madrepora  is  neatly  branched,  with  pointed 
extremities,  each  ending  in  a  small  cell  about  a  line  in 
diameter.  Porites,  or  "Sponge-coral,"  is  also  branching, 
but  the  ends  are  blunt,  and  the  surface  comparatively 
smooth.  Tubipora,  or  "Organ -pipe  coral,"  consists  of 
smooth  red  tubes  connected  at  intervals  by  cross-plates. 
The  Astrcea,  Meandrina,  Madrepora,  and  Porites  are  the 
chief  reef-forming  Corals.  They  will  not  live  in  waters 


CCELENTERATA. 


253 


FIG.  201.—  Madrepora  aspera,  living  and  expanded ;  natural  size.    Pacific. 

whose  mean  temperature  in  the  coldest  month  is  below 
68°  Fahr.,  nor  at  greater  depth  than  twenty  fathoms.  The 
most  luxuriant  reefs  are  in  the  Central  and  Western  Pa- 
cific and  around  the  West  Indies. 


FIG.  202.— Ctenactis  echinata,  or  "  Mushroom-coral ;"  one  fourth  natural  size.    Pacific. 


254: 


COMPARATIVE  ZOOLOGY. 


FIG.  203.— Astrceapallida;  natural  size.    Fejee  Islands. 

A  coral-reef  is  formed  by  many  Corals  growing  togeth- 
er.    It  is  to  the  single  Coral-stock  as  a  forest  is  to  a  tree. 


FIG.  204. — Diploria  cerebriformis,  or  u  Brain-coral ;"  one  half  natural  size.   Bermttdn*. 


CCELENTEUATA. 


255 


FIG.  205.— Astrcea  rotulosa.     West  Iiidies. 


The  main  kinds  of  reefs  are  fringing,  where  the  reef  is 
close  to  the  shore ;  barrier,  where  there  is  a  channel  be- 


Fio.  206.— Cell  of  Madrepore  Coral, 
magnified.  The  cup-like  depres- 
sion at  the  top  of  a  coral  skeleton 
is  called  calicle. 


FIG.  20T Fragment  of  Red  Coral  (Coral- 
Hum  rubrum),  showing  living  cortex 
and  expanded  Polyps.  Mediterranean. 


256  COMPARATIVE  ZOOLOGY. 

tween  reef  and  shore ;  encircling,  where  there  is  a  small 
island  inside  of  a  large  reef;  and  coral  islands,  or  atolls, 
where  there  is  simply  a  reef  with  no  land  inside  of  it.  All 
reefs  begin  as  fringing- reefs,  and  are  gradually  changed 
into  the  other  forms  by  the  slow  sinking  of  the  bottom  of 
the  ocean.  This  sinking  must  be  slower  than  the  upward 
growth  of  the  reef,  else  it  will  be  drowned  out.  Probably 
the  reef  does  not  grow  more  than  five  feet  in  a  thousand 
years;  and,  as  reefs  are  often  more  than  two  thousand 
feet  thick,  they  must  be  very  old. 

(2)  Sclerobasic  Corals. — Corallium  rubrurn,  the  precious 
coral  of  commerce,  is  shrub -like,  about  a  foot  high,  solid 
throughout,  taking  a  high  polish,  finely  grooved  on  the 
surface,  and  of  a  crimson  or  rose-red  color.  In  the  living 


FIG.  203.— Sea-fan  (Gorgonia)  aud  Sea-peu  {t'enit 

state  the  branches  are  covered  with  a  red  coenosarc  stud- 
ded with  Polyps.  Gorgonia,  or  "Sea-fan,"  differs  from 
all  the  other  representative  forms  in  having  a  horny  axis 
covered  with  calcareous  spicules.  The  branches  arise  in 
the  same  vertical  plane,  and  unite  into  a  beautiful  net- 
work. 


ECHINODERMATA. 


257 


CLASS  III. — Ctenophora. 
The  Ctenophora  (as  the  Pleuro- 
Irachia,  Cesium,  and  Beroe)  secrete 
no  hard  deposit.  They  are  trans- 
parent and  gelatinous,  swimming  on 
the  ocean  by  means  of  eight  comb- 
like,  ciliated  bands,  which  work  like 
paddles.  The  body  is  not  contrac- 
tile, as  in  the  Jelly-fishes.  They  are 
considered  the  highest  of  Coelente- 
rates,  having  a  complex  nutritive  ap-FiG.209._ActenoPhore<p?e«- 

,     ,,     .  robrachia  pileus)  ;     natural 

paratus  and  a  dennite  nervous  sys-    size. 
tern. 

Subkingdom  III.— ECHINODEKMATA. 

The  Echinoderms,  as  Star -fishes  and  Sea-urchins,  are 
distinguished  by  the  possession  of  a  distinct  nervous  sys- 
tem (a  ring  around  the  mouth) ;  an  alimentary  canal,  com- 


Jl 


PIG.  210.— Forms  of  Echinoderms,  from  radiate  to  annnlose  type:   a,  Crinoids;   ft, 
Ophiurans;  c,  Star-fish;  d,  Echini;  e, llolothurians. 

pletely  shut  off  from  the  body-cavity,  and  having  both 
oral  and  anal  apertures ;  a  water-vascular  system  of  circu- 

17 


258  COMPARATIVE  ZOOLOGY. 

lar  and  radiating  canals,  connected  with  the  outside  water 
by  means  of  the  madreporic  tubercle,  and  a  symmetrical 
arrangement  of  all  the  parts  of  the  body  around  a  central 
axis  in  multiples  of  five.133  There  are  four  principal  class- 
es, all  exclusively  marine  and  solitary,  and  all  having  the 
power  of  secreting  more  or  less  calcareous  matter. 

CLASS  I. — Crinoidea. 

The  Crinoids,  or  "  Sea-lilies,"  are  fixed  to  the  sea-bottom 
by  means  »of  a  hollow,  jointed,  flexible  stem.  On  the  top 
of  the  stem  is  the  body  proper,  resembling  a  bud  or  ex- 
panded flower,  containing  the  digestive  apparatus,  witli 
the  surrounding  arms,  or  tentacles.  The  mouth  looks  up- 
ward. There  is  a  complete  skeleton  for  strength  and  sup- 
port, the  entire  animal — body,  arms,  and  stem — consisting 
of  thousands  of  stellate  pieces  connected  together  by -liv- 
ing matter.  Crinoids  were  very  abundant  in  the  old  geo- 
ologic  seas,  and  many  limestone  strata  were  formed  out  of 
their  remains.  They  are  now  nearly  extinct:  dredging 
in  the  deep  parts  of  the  oceans  has  brought  to  light  a  few 
living  representatives. 

CLASS  II. — Asteroidea. 

Ordinary  Star-fishes  consist  of  a  flat  central  disk,  with 
five  or  more  arms,  or  lobes,  radiating  from  it,  and  con- 
taining branches  of  the  viscera.  The  skeleton  is  leathery, 
hardened  by  small  calcareous  plates  (twelve  thousand  by 
calculation),  but  somewhat  flexible.  The  mouth  is  below  ; 
and  the  rays  are  furrowed  underneath,  and  pierced  with 
numerous  holes,  through  which  pass  the  sucker-like  tenta- 
cles— the  organs  of  locomotion  and  prehension.  The  red 
spots  at  the  ends  of  the  rays  are  eyes.  The  usual  color  of 
Star-fishes  is  yellow,  orange,  or  red.  They  abound  on  ev- 
ery shore,  and  are  often  seen  at  low  tide  half  buried  in 
the  sand,  or  slowly  gliding  over  the  rocks.  Cold  fresh 


ECHINODEKMATA. 


259 


Pia.  211. — A  living  Crinoid  (Pentacrinu*  asteria) ;  one  fourth  natural  siz6.    West 

Indian  Seas. 


260  COMPARATIVE  ZOOLOGY. 

water  is  instant  death  to  them.  They  have  the  power  of 
reproducing  lost  parts  to  a  high  degree.  They  are  very 
voracious,  and  are  the  worst  enemies  of  the  Oyster. 


FIG.  212. — Under  -  surface  of  Star-fish  (Goniaxtw  reticulatut*),  showing  ainbulacral 
grooves  and  protruded  suckers. 

About  one  hundred  and  fifty  species  are  known.  These 
may  be  divided  into  three  groups:  (1)  species  having  four 
rows  of  feet,  represented  by  the  common  five -fingered 
Asterias  ;  (2)  species  having  two  rows  of  feet,  as  the  many- 
rayed  Sofaeter,  or  "  Sun-star,"  and  the  pentagonal  Goni- 
aster;  (3)  species  having  long,  slender  arms,  which  are  not 
prolongations  of  the  body,  and  are  not  provided  with  suck- 
ers, as  the  Ophiura,  or  "  Brittle-star,"  and  Astrophyton,  or 
"  Basket-fish."  The  last  are  of  inferior  rank,  and  resemble 


ECHINODERMATA. 


261 


inverted,  stemless  Crinoids.    The  digestive  sac  is  confined 
to  the  disk,  and  the  inadreporic  tubercle  is  concealed. 


FIG.  213.  -  OpMocoma  Ritxsei,  an  Ophiuran ;  natural  size.    West  Indies. 


CLASS  III. — Echinoidea. 

The  Sea-urchin  is  encased  in  a  thin,  hollow  shell  cov- 
ered with  spines,  and  varying  in  shape  from  a  sphere  to  a 
disk.134  The  month  is  underneath,  and  contains  a  dental 
apparatus  more  complicated  than  that  of  any  other  creat- 
ure. It  leads  to  a  digestive  tube,  which  extends  spirally 
to  the  summit  of  the  body.  The  spines  are  for  burrow- 
ing and  locomotion,  and  are  moved  by  small  muscles,  each 
being  articulated  by  ball-and-socket  joint  to  a  distinct  tu- 
bercle. When  stripped  of  its  spines,  the  shell  (or  "test") 
is  seen  to  be  formed  of  a  multitude  of  pentagonal  plates, 
fitted  together  like  a  mosaic.185  Five  double  rows  of  plates, 


262 


COMPARATIVE  ZOOLOGY. 


passing  from  pole  to  pole,  like  the  ribs  of  a  melon,  alter- 
nate with  five  other  double  rows.     In  one  set,  called  the 

ambulacra,  the 
plates  are  perfo- 
rated for  the  pro- 
trusion of  tubular 
feet,  or  suckers,  as 
in  the  Star  -  fish. 
So  that  altogether 
there  are  twenty 
series  of  plates — 
ten  ambulacra!, 
and  ten  intern  in  bo- 
lacral.  The  shell 
is  not  cast,  but 
grows  by  the  en- 

PIQ.  214.—  Uncler-surface  of  a  Sea-urchin  (Echinus  escu-     • 

lentus),  showing  rows  of  suckers  among  the  spines.     largeiTient  of  each 
British  seas.  , .     .  ,       -,          -.    . 

individual     plate, 

and  the  addition  of  new  ones  around  the  mouth  and  the 
opposite  pole.  Every  part  of  an  Echinus,  even  sections 
of  the  spines,  show  the  principle  of  radiation.  If  the  up- 
per surface  of  a  Star-fish  should  shrink  so  as  to  bring 
the  points  of  the  arms  to  meet  above  the  month,  we 
should  have  a  close  imitation  of  a  Sea-urchin.  Echini  live 
near  the  shore,  in  rocky  holes  or  under  sea-weed.  They 
are  less  active  than  Star-fishes;  but,  like  them,  feed  on 
Mollusks  and  Crabs.  They  reproduce  by  minute  red  eggs. 
Regular  Echini,  as  the  common  Cidaris,  are  nearly 
globular,  and  the  oral  and  anal  openings  are  opposite. 
Irregular  Echini,  as  the  Clypeaster,  are  flat,  and  the  anal 
orifice  is  near  the  margin. 

CLASS  IV. — Holothuroidea. 

These  worm-like  "  Sea-slugs,"  as  they  are  called,  have  a 
soft,  elongated  body,  with  a  tough,  contractile  skin  contain- 


ECHINODERMATA.— VERMES.  263 

ing  calcareous  granules.  One  end,  the  head,  is  abruptly 
terminated,  and  has  a  simple  aperture  for  a  mouth,  en- 
circled with  feathery  tentacles.  There  are  usually  five 
longitudinal  rows  of  ambulacral  suckers,  but  only  three 
are  used  for  locomotion,  of  which  one  is  more  developed 
than  the  rest.  The  mouth  opens  into  a  pharynx  leading 
to  a  long  intestinal  canal.  Holothurians  have  the  singular 
power  of  ejecting  most  of  their  internal  organs,  surviving 


FIG.  215.— Sea-slugs  (llolothuria). 

for  some  time  the  loss  of  these  essential  parts,  and  after- 
wards reproducing  them.  They  occur  on  nearly  every 
coast,  especially  in  tropical  waters,  where  they  sometimes 
attain  the  length  of  three  or  four  feet.  As  found  on  the 
beach  after  a  storm,  or  when  the  tide  is  out,  they  are 
leathery  lumps,  of  a  reddish,  brownish,  or  yellowish  color. 
They  may  be  likened  to  a  Sea-urchin  devoid  of  a  shell, 
and  long  drawn  out,  with  the  axis  horizontal,  instead  of 
vertical. 

Subkingdom  IV. — VERMES. 

The  Vermes,138  or  Worms,  form  the  lowest  subkingdom 
of  the  bilaterally  symmetrical  animals.  The  group  in- 
cludes animals  very  different  in  form  and  rank,  and  the 
different  classes  are  widely  separated  from  each  other. 


264 


COMPARATIVE  ZOOLOGY. 


It  has  also  close  relations  with  the  other  subkingdoms  of 
the  bilaterally  symmetrical  animals.  Through  the  Poly- 
zoa  and  Brachiopoda,  it  approaches  the  Mollusca ;  through 
the  Annelides,  the  Arthropoda ;  and  through  other  forms, 
the  Tunicata,  and  so  the  Yertebrata.  The  subkingdorn 
thus  stands  in  the  centre  of  several  subkingdoms,  with 
affinities  towards  all.  Nor  are  indications  of  connection 
with  Coelenterata  and  Echinodermata  wanting. 

The  Yermes  are  bilaterally  symmetrical  animals,with  one 
or  many  segments,  no  jointed  legs.  They  usually  have  a  soft 
skin,  and  peculiar  excretory  organs — the  segmental  organs. 

Many  of  the  Worms  are  parasitic,  and  most  of  the  En- 
doparasites  belong  to  this  group. 

There  are  numerous  classes,  of  which  only  the  most  im- 
portant are  mentioned. 


CLASS  L- 


Platyhelminthes. 

The  Flat -worms 
include  some  free 
forms,  as  the  Plana- 
ria,  common  in  fresh 
water,  and  the  Tape- 
worms and  Flukes 
among  the  parasites. 

The  Tape  -  worm 
consists  of  the  so- 
called  head — the 
proper  worm  —  and 
the  body  segments, 


FIG.  216 — Tape-worm  (Tcenia  solium):  a,  head;  &,  c, 
d,  segments  of  the  body. 


FIG.  21T — Planarian 
worm. 


VERMES. 


265 


which  are  really  reproductive  joints.  It  develops  from 
the  egg  in  the  digestive  canal  of  the  Pig,  burrows  into 
the  cellular  tissue  of  the  animal,  and  there  becomes  en- 
cased. It  thus  causes  the  disease  "  measles."  If  the  pork 
be  eaten  by  man,  in  an  uncooked  condition,  this  case  is 
dissolved  by  the  gastric  juice,  and  the  embryo  develops 
into  the  Tape-worm,  attaching  itself  to  the  intestine  by 
its  "head,"  and  budding  off  the  reproductive  segments. 
As  these  become  ripe  and  filled  with  fertilized  eggs,  they 
are  detached,  and  pass  off  with  the  excrement. 

The  disease  called  "  rot,"  in  Sheep,  is  produced  by  the 
Fluke  (Distoma),  a  member  of  this  class. 

CLASS  II.  —  Nematelminthes. 

The  Round,  or  Thread,  Worms  include  free  forms,  as 
the  Yinegar-eel;  parasitic  forms,  as  the  Pin-worm  and 
Trichina  ;  and  forms 
free  when  adult,  and 
parasitic  when  young, 
as  the  Hair-worm  (Gor- 
dius). 

The  Trichina  is  usu- 
ally derived  by  Man 
from  the  flesh  of  the 
Pig.  It  exists  in  the 
muscles,  enclosed  in  mi- 
croscopic cases.  If  the 
meat  be  eaten  uncooked 
or  partially  cooked,  the 
cases  are  dissolved,  and 
the  Trichinae  become 
sexually  mature  in  the 
intestines.  The  young 

are    produced    and    bur-Fio.  MS.-  Trichina  spiraUs:  I.male;  a,  mouth; 

row  their  way  into  the 


ta  """' 


266  COMPARATIVE  ZOOLOGY. 

muscles,  where  they  become  encysted.    In  burrowing,  they 
cause  great  pain  and  fever,  and  sometimes  death.     The 

adult  "Worm  is  about  ^  inch  long. 

> 

CLASS  III.— Rotifera. 

The  Wheel-animalcules,  mostly  found  in  fresh  water, 
are  minute  Worms  of  few  segments,  having  on  the  ante- 
rior end  a  disk  ciliated  on  the  edge, 
whence  their  name.  They  are  from 
g-Jir  to  -3^  of  an  inch  long.  They  can 
bear  drying  and  revivifying,  like  seeds. 

CLASS  IV. — Polyzoa. 
These  minute  Worms  resemble  the 
Polyps  in  appearance,  living  in  clusters, 
each  individual  inhabiting  a  delicate 
cell,  or  tube,  and  having  a  simple  mouth 
surrounded  with  ciliated  tentacles.  The 
colony  often  takes  a  plant -like  form; 
sometimes  spreads,  like  fairy -chains  or 
lace-work,  over  other  bodies ;  or  covers 
rocks  and  sea -weeds  in  patches  with  a 
delicate  film.  The  majority  secrete  car- 
FIO.  219.  —  Rotifer,  or  bonate  of  lime.  A  Polyzoan  shows  its  su- 

"  Wheel-animalcule  "  ...  ,1       r~*        i        i  •    i     •>.   •      «j. 

(Hydatina),    highly  perionty  to  the  Coral,  which  it  imitates, 

in  possessing  a  distinct  alimentary  canal 

and  a  well-defined  nervous  system.     The  cells  of  a  group 

never  have  connection  with  a  common  tube,  as  in  Coelen- 

terates.     There  are  both  marine  and  fresh-water  species. 

This  group  and  the  next  following  are  related  to  the 

Mollusca. 

CLASS  Y. — Braohiopoda. 

These  Worms  have  a  bivalve  shell,  the  valves  being 
applied  to  the  dorsal  and  ventral  sides  of  the  body.  The 
valves  are  unequal,  the  ventral  being  usually  larger,  and 


VERMES. 


267 


Fro.  220. — Polyzrtans:  1.  ffornera  lichenoides,  natural  size.     2.  Branch  of  the  same, 
magnified.    3.  Discopora  Skenei,  greatly  enlarged. 

more  convex ;  but  they  are  symmetrical,  i.  e.,  a  vertical 
line  let  fall  from  the  hinge  divides  the  shell  into  two 
equal  parts.  The  ventral  valve  has,  in  the  great  major- 
ity, a  prominent  beak,  perforated  by  ^foramen,  or  hole, 
through  which  a  fleshy  foot  protrudes  to  attach  the  ani- 
mal to  submarine  rocks.  The  valves  are  opened  and  shut 
by  means  of  muscles,  and  in 
most  cases  they  are  hinged, 
having  teeth  and  sockets 


FIG.  221.. —  A  Bnichiopod  (Terebratulina 
septentrionalit).    Atlantic  coast. 

near  the  beak.  The  mouth 
faces  the  middle  of  the  mar- 
gin opposite  the  beak;  and 
on  either  side  of  it  is  a  long, 


FIG.  222.— Dorsal  Valve  of  a  Brachiopod 
(Terebratula),  showing,  in  descending 
order,  cardinal  process,  dental  sockets, 
hinge-plate,  septum,  and  loop  support- 
ing the  ciliated  arms. 


268 


COMPARATIVE  ZOOLOGY. 


fringed  "arm,"  generally  coiled  up,  and  supported  by  a 
calcareous  framework.  The  animal,  having  no  gills,  re- 
spires by  the  arms  and  the  mantle.  Brachiopods  were 
once  very  abundant,  over  two  thousand  extinct  species 
having  been  described ;  but  less  than  a  hundred  species 
are  now  living.137  They  are  all  marine,  and  fixed;  but  of 
all  Worms,  they  enjoy  the  greatest  range  of  climate  and 
depth. 


CLASS  VI. — Annelides. 


The  Annelides  include  the  highest  and  most  specialized 
Worms.  They  have  many  segments,  spines  or  suckers 
for  locomotion,  a  superoesophageal  brain,  a  ventral  chain 


Fio.  223.— Marine  Worm  (Cirratulus  grandis),  with  extended  cirri.    Atlantic. 

of  ganglia,  and  a  closed  blood-system.  There  are  three 
main  divisions :  the  flattened  Leeches,  without  definite 
segments  or  bristles,  and  with  suckers  for  locomotion  ;  the 


MOLLUSCA.  269 

Earth-worms  and  their  allies,  which  have  few  bristles  on 
each  segment  (OligochcBtce) ;  and  the  Sea-worms,  with  nu- 
merous bristles,  arranged  in  two  clusters  on  each  side  of 
each  segment  (Polychcetce). 

These  last  are  the  largest  of  the  Worms,  and  may  have 
a  distinct  head,  bearing  tentacles  and  eyes.  The  oesopha- 
gus is  often  turned  in,  so  as  to  form  a  proboscis,  which 
bears  horny  jaws,  and  can  be  protruded  at  the  will  of  the 
animal  (Fig.  17). 

Subkingdom  Y. — MOLLUSCA. 

A  Mollusk  is  a  soft -bodied  animal,  without  internal 
skeleton,  and  without  joints,  covered  with  a  moist,  sensi- 
tive, contractile  skin,  which,  like  a  mantle,  loosely  envel- 
ops the  creature.  In  some  cases  the  skin  is  naked,  but 
generally  it  is  protected  by  a  calcareous  covering  (shell). 
The  length  of  the  body  is  less  in  proportion  to  its  bulk 
than  in  other  animals.  The  lower  class  has  no  distinct 
head.  The  nervous  system  consists  of  three  well-devel- 
oped pairs  of  ganglia,  which  are  principally  concentrated 
around  the  entrance  to  the  alimentary  canal,  forming  a 
ring  around  the  throat.  The  other  ganglia  are,  in  most 
cases,  scattered  irregularly  through  the  body,  and  in  such 
the  body  is  unsymmetrical.  The  digestive  system  is 
greatly  developed,  especially  the  liver,  as  in  most  aquatic 
animals.  Except  in  the  Cephalopods,  the  muscles  are  at- 
tached to  the  skin,  or  shell.  There  is  a  heart  of  two 
chambers  (auricle  and  ventricle)  or  three  (two  auricles 
and  ventricle).  As  in  all  Invertebrates,  the  heart  is  arte- 
rial. In  Mollusks,  with  rare  exceptions,  we  find  no  repe- 
tition of  parts  along  the  antero-posterior  axis.  They  are 
best  regarded  as  Worms  of  few  segments,  which  are  fused 
together  and  much  developed.  The  total  number  of 
living  species  probably  exceeds  twenty  thousand.  The 
great  majority  are  water-breathers,  and  marine ;  some  are 


270  COMPARATIVE  ZOOLOGY. 

fluviatile  or  lacustrine,  and  a  few  are  terrestrial  air-breath- 
ers. All  bivalves,  and  nearly  all  univalves,  are  aquatic. 
Each  zone  of  depth  in  the  sea  has  its  particular  species. 

CLASS  I. — Lamellibranchiata. 
Lamellibranchs  are  all  ordinary  bivalves,  as  the  Oyster 

and  Clam.  The  shells  differ  from  those  of  Brachiopods 
in  being  placed  on  the  right  and  left 
sides  of  the  body,  so  that  the  hinge  is  on 
the  back  of  the  animal,  and  in  being 
unequilateral  and  eqnivalved.138  The 
umbo,  or  beak,  is  the  point  from  which 
the  growth  of  the  valve  commences. 

FLO.  224.— Pe»ri  Oyster  Both  Brachiopods   and   Lamellibranchs 

(Meleagrinamargariti-  ,         ,,  i      .    •      ,1        i    ,  •>  , 

fera)-,  one  fourth nat-  are  headless ;  but  in  the  latter  the  mouth 

uralsize.    Ceylon.         pOjntg  t}ie    game   way    ag    t]Je    umbo,  i.  6., 

towards  the  anterior  part.  The  length  of  the  shell  is 
measured  from  its  anterior  to  its  posterior  margin,  and  its 
breadth  from  the  dorsal  side,  where  the 
hinge  is,  to  the  opposite,  or  ventral,  edge. 
The  valves  are  united  to  the  animal  by 
one  muscle  (as  in  the  Oyster),  or  two  (as 
in  the  Clam),  and  to  each  other  by  a 
hinge.  In  some  species,  as  some  fresh- 
water Mussels,  the  hinge  is  simply  an 
elastic  ligament,  passing  on  the  outside 
from  one  valve  to  the  other  just  behind 
the  beak,  so  that  it  is  on  the  stretch  when 
the  valves  are  closed,  and  another  placed  FIG.  225.  — 

.  .  Mussel  (Mytihw  pel- 

between  the  edges  of  the  valves,  so  that  luddv*).  Atlantic 
it  is  squeezed  as  they  shut,  like  the  spring 
in  a  watch-case.  Such  bivalves  are  said  to  be  edentulous. 
But  in  the  majority,  as  the  Clam,  the  valves  also  articulate 
by  interlocking  parts  called  teeth.  The  valves  are,  there- 
fore, opened  by  the  ligaments,  and  closed  by  the  muscles. 


MOLLUSC  A.  271 

The  margin  of  the  shell  on  which  the  ligament  and  teeth 
are  situated  is  termed  the  hinge-line. 

Lamellibranchs  breathe  by  four  plate-like  gills  (whence 
the  name),  two  on  each  side  underneath  the  mantle  (Fig. 
78).  In  the  higher  forms,  the  mantle  is  rolled  up  into 
two  tubes,  or  siphons,  for  the  inhalation  and  exhalation  of 
water.  They  feed  on  infusorial  particles  filtered  from  the 
water.  A  few  are  fixed ;  the  Oyster,  e.  g.,  habitually  lying 


a- 

FIG.  226. — Lamellibranch  (Mactra):  a,  foot;  &,  c,  siphons. 

on  its  left  valve,  and  the  Salt-water  Mussel  hanging  to 
the  rocks  by  a  cord  of  threads  called  "  byssus ;"  but  most 
have  a  "foot,"  by  which  they  creep  about.  Unlike  the 
Oyster,  also,  the  majority  live  in  an  erect  position,  rest- 
ing on  the  edges  of  their  shells.  Over  four  thousand 
living  species  are  known.  These  are  fresh  -  water  and 
marine,  and  range  from  the  shore  to  a  depth  of  a  thou- 
sand feet. 

The  chief  characters  for  distinguishing  Lamellibranchs 
are  the  muscular  impressions,139  whether  one  or  two ;  the 
presence  of  a  pallial  sinus,  which  indicates  the  possession 
of  siphons ;  the  structure  of  the  hinge,  arid  the  symmetry 
of  the  valves. 

The  following  are  the  leading  types  of  structure,  as 
shown  by  the  shells : 

1.  Monomya:  with  one  adductor  muscle;  no  siphons; 
foot  wanting,  or  very  small;  shell  unequi  valve  and  eden- 


272 


COMPARATIVE  ZOOLOGY. 


tiilous — as  the  Oyster  (Ostrea\  Scallop  (Pecten\  and  Pearl 
Oyster  (Avicula). 

2.  Heteromya:  with  two  unequal  adductor  muscles  and 
no  siphons — as  the  Sea-mussel  (My- 
tilus). 

3.  Isomya :  with  two  equal  ad- 
ductor muscles.  There  are  two  sec- 
tions of  this  order:  a.  Those  with 
no  siphons,  and  hence  no  pallial 
sinus  —  as  the  Fresh -water  Mussel 
(  Unio),  Cockle  (Cardium),  and  "  the 
g^nt  of  the  bivalve  race"  (Tridae- 
size,  china  seas.  ne).  J.  Those  with  siphons  and  pal- 

lial sinus — as  the  common  Clam  (My a),  Quohog  (  Venus), 
and  Razor-shell  (Solen).140 

CLASS  II. — Gasteropoda. 

The  Snails  are,  with  rare  exceptions,  all   univalves.141 
The  body  is  coiled  up  in  a  conical  shell,  which  is  usually 


Fio.  228. — Whelk  (Buccinum),  showing  operculum,  o,  and  siphou,  «. 

spiral,  the  whorls  passing  obliquely  (and  generally  from 
right  to  left),148  around  a  central  axis,  or  "columella." 


MOLLUSCA.  273 

When  the  columella  is  hollow  (perforated),  the  end  is 
called  the  "  umbilicus."  When  the  whorls  are  coiled 
around  the  axis  in  the  same  plane,  we  have  a  discoidal 
shell,  as  the  Planorbis.  The  mouth,  or  "  aperture,"  of 
the  shell  is  "  entire  "  in  most  vegetable-feeding  Snails,  and 
notched  or  produced  into  a  canal  for  the  siphons  in  the 
carnivorous  species.  The  former  are  generally  land  and 
fresh-water  forms,  and  the  latter  all  marine.  In  some 
Gasteropods,  as  the  River -snails  and  most  Sea -snails,  a 
horny  or  calcareous  plate  (pperculuin)  is  secreted  on  the 
foot,  which  closes  the  aperture  when  the  animal  with- 
draws into  its  shell.  In  locomotion,  the  shell  is  carried 
with  the  apex  directed  backward. 

The  body  of  most  Gasteropods  is  unsymmetrical,  the 
organs  not  being  in  pairs,  but  single,  and  on  one  side, 
instead  of  central.  The  mantle  is  continuous  around  the 
body,  not  bilobed,  as  in  Lamellibranchs.  A  few,  as  the 
common  Garden-snail,  have  a  lung ;  but  the  vast  majority 
breathe  by  gills.  The  head  is  more  or  less  distinct,  and 
provided  with  two  tentacles,  with  auditory  sacs  at  their 
bases ;  two  eyes,  which  are  often  on  stalks ;  and  a  strap- 
like  tongue  covered  with  minute  teeth.  The  heart  is  sit- 
uated, in  the  majority,  on  the  right  side  of  the  back,  and 
has  two  cavities.  The  nervous  ganglia  are  united  into  an 
oesophageal  ring  or  collar.  All,  except  the  Pteropods, 
move  by  means  of  a  ventral  disk  or  foot. 

Gasteropods  are  now  the  reigning  Mollusks,  comprising 
three  fourths  of  all  the  living  species,  and  are  the  types 
of  the  subkingdorn.  They  have  an  extraordinary  range 
in  latitude,  altitude,  and  depth. 

Omitting  a  few  rare  and  aberrant  forms,  we  may  sepa- 
rate the  class  into  the  following  orders : 

1.  Pteropods. — These  are  small,  marine,  floating  Mol- 
lusks,  whose  main  organs  of  motion  resemble  a  pair  of 
wings  or  fins  corning  out  of  the  neck,  whence  the  com- 

18 


274 


COMPARATIVE  ZOOLOGY. 


inon  name,  "  Sea  -  butterflies."  Many  have  a  delicate, 
transparent  shell.  The  head  has  six  appendages,  armed 
with  several  hundred  thousand  micro- 
scopic suckers— a  prehensile  apparatus 
unequalled  in  complication.  Pteropods 
occur  in  every  latitude,  but  generally 
in  mid-ocean,  and  in  the  arctic  regions 
are  the  food  of  Whales  and  Sea-birds. 
2.  Opisthobranchs. — These  low.Gas- 
aiea  tridentata).  Atlantic,  teropods  are,  f or  the  most  part,  naked 
Sea-slugs,  a  few  only  having  a  small  shell.  The  feathery 
gills  are  behind  the  heart  (whence  the  name).  They  are 
found  in  all  seas,  from  the  arctic  to  the  torrid,  generally 
on  rocky  coasts.  When  disturbed, 
most  of  them  draw  themselves  up 
into  a  lump  of  jelly  or  tough  skin. 


FIG.  '229.— A  Pteropod  (Ht/- 


FIG.  230.— A  Tritonian  (Dendronolus  arboreacem). 
British  seas. 


FIG.  231.— Bullet  ampul- 
la, or  "Bubble-shell;" 
three  fourths  natural 
size.  Indian  Ocean 


Examples :  Sea-lemon  (Doris),  the  beautiful  Tritonia,  the 
painted  ^Eolis,  the  Sea-hare  (Aplysia),  which  discharges 
a  purple  fluid,  and  the  Bubble-shell  (Bulla). 

3.  Pulmonates. — These  air-breathing  Gasteropods,  rep- 
resented by  the  familiar  Snail,  have  the  simplest  form  of 
lung — a  cavity  lined  with  a  delicate  net-work  of  blood- 
vessels, which  opens  externally  on  the  right  side  of  the 
neck.  This  is  the  mantle-cavity.  The  entrance  is  closed 
by  a  valve,  to  shut  out  the  water  in  the  aquatic  tribes, 
and  the  hot,  dry  air  of  summer  days  in  the  land  species. 
They  are  all  fond  of  moisture,  and  are  more  or  less  slimy. 
Their  shells  are  lighter  (being  thinner,  and  containing  less 


MOLLUSCA. 


275 


earthy  matter)  than  those  of  marine  Mollusks,  having  to 
be  carried  on  the  back  without  the  support  of  the  water. 


Fio.  232—4,  Laiid-siiail  (Helix)  ;   B,   C,  D,  Slugs  (Limax)  ;   E,  F,  G,  Pond-snaiJs 
(Limncea,  Paludina,  and  Planorbis). 

Their  eggs  are  laid  singly,  while  the  eggs  of  other  orders 
are  laid  in  chains. 

They  are  found  in  all  zones,  but  are 
most  numerous  where  lime  and  moisture 
abound.  All  feed  on  vegetable  matter. 
A  few  are  naked,  as  the  Slug  ;  some  are 
terrestrial;  others  live  in  fresh  water. 
The  Land  -  snails,  represented  by  the 
common  Helix,  the  gigantic  Bulimus, 
and  the  Slug  (Limax),  are  distinguished 
by  their  four  "  horns,"  the  short  front 
pair  being  the  true  tentacles,  and  the 
long  hinder  pair  being  the  eye-stumps. 
They  have  a  saw  -like  upper  jaw  for 
biting  leaves,  and  a  short  tongue  covered  with  minute 
teeth.  The  Pond-snails,  as  Limncea  and  Planorbis^  differ 


8ize>   GuianJU 


276 


COMPARATIVE   ZOOLOGY. 


FIG.  234.— Cowry  (Cyprcea  capemift) ;  two 
thirds  natural  size.    South  Africa. 


FIG.  235.—Halioti8,  or  "  Pearly  Ear- 
shell."    Pacific  coasts. 


FIG.  236.  —  Spindle- 
shell  (Fusus  colus) ; 
one  half  natural 
size.  Ceylon. 


FIG.  237.  —  Cassis  rufa,  or 
"Helmet-shell;"  one  fourth 
natural  size.  Indian  Ocean. 


FIG.  233.— Auger-shell 
(Terebra  maculata) : 
one  half  natural 
size.  China  seas. 


FIG.  239.— Cone-shell  (Conus        F;o.  240.— Chiton  squa- 
marmoreus) ;    two   thirds  mosus;  one  half  nntu- 

nalural  size.    China  seas.  ral  size.    West  Indies. 


FIG.  241.— Volute  (Valuta 
musica) ;  one  half  nat- 
ural size.  West  Indies. 


MOLLUSCA. 


277 


FIG.  242.  —Top-shell  (Turbo  niarnio-         FIG.  243.— Strombms  gigas,  or  "Winged- 
ratus);    one  fourth  natural  size.  shell;"   one  fifth  natural  size.    West 

China  seas.  Indies. 


PIG.  244.  —Paludina,  a  Fresh-water         FIG.  245. -Key-hole  Limpet  (Fissurella 
Snail.  listert).    West  Indies. 


246.— Ear-shell  (U.  tuberculafa),  uud  Do^- 


278  COMPARATIVE  ZOOLOGY. 

in  having  no  eye-stalks,  the  eyes  being  at  the  base  of  the 
tentacles.  They  are  obliged  to  come  frequently  to  the 
surface  of  the  water  to  breathe. 

4.  Prosobranchs.  —  These  are  aquatic  Gasteropods, 
breathing  by  gills  situated  in  front  of  the  heart.  They 
are  the  most  highly  organized  and  the  most  abundant  of 
the  crawling  Mollusks.  Nearly  all  are  marine,  and  all 
have  a  shell. 

Among  the  lower  forms  are  the  singular  Chiton,  cov- 
ered with  eight  shelly  plates;  Limpet  (Patella),  well 
known  to  every  sea-side  visitor;  and  the  beautiful  Ear- 
shell  (Haliotis),  frequently  used  for  ornaments  and  inlaid- 
work. 

In  the  higher  Prosobranchs,  the  gills  are  comb-shaped 
and  the  sexes  are  distinct.  The  group  includes  all  the 
spiral  univalve  sea-shells,  and  a  few  fresh- water  shells. 
Many  have  the  aperture  entire,  which  is  closed  with  an 
operculum:  as  the  dull -colored  Paludina  and  Melania 
from  fresh  water,  and  the  pyramidal  Trochus,  pearly  Tur- 
bo, screw-like  Turritella,  common  Periwinkle  (Littorind), 
and  globular  Natica  from  the  sea.  Others,  the  highest 
of  the  race,  have  the  margin  of  the  aperture  notched  or 
produced  into  a  canal,  and  are  carnivorous  and  marine : 
such  are  nearly  all  the  sea -shells  remarkable  for  their 
beautiful  forms,  enamelled  surfaces,  and  brilliant  tints,  as 
the  Cowry  (Cyprcea),  Volute,  Olive,  Cone,  Harp,  Whelk 
(Buccinum),  Cameo-  shell  (Cassis),  Rock -shell  (Murex), 
Trumpet-shell  (Triton),  Spindle-shell  (Fusus),  and  Wing- 
shell  (Strombus). 

CLASS  III. — Cephalopoda. 

The  Cephalopods  stand  at  the  head  of  the  subkingdom. 
The  head  is  set  off  from  the  body  by  a  slight  constriction, 
and  furnished  with  a  pair  of  large,  staring  eyes,  a  mouth 
armed  with  a  rasping  tongue  and  a  parrot-like  beak,  and 


MOLLUSCA. 


279 


eight  or  more  tentacles  or  arms.  The  body  is  symmetri- 
cal, and  wrapped  in  a  muscular  mantle. 

The  nervous  system  is  more  concentrated  than  in  other 
Invertebrates;  the  cerebral  ganglia  are  partly  enclosed  in 
a  cartilaginous  cranium.  All  the  five  senses  are  present. 
The  class  is  entirely  marine  (breathing  by  plume-like  gills 
on  the  sides  of  the  body),  and  carnivorous.  The  naked 
species  are  found  in  every  sea.  Those  with  chambered 
shells  (as  Nautilus,  Ammonites,  and  Orthoceras)  were  once 
very  abundant:  more  than  two  thousand  fossil  species  are 
known,  but  only  one  living  representative  —  the  Pearly 
Nautilus. 

1.  Tetrabranohs.  —  This  order  is  characterized  by  the 
possession  of  four  gills,  forty  or  more  short  tentacles,  and 
an  external,  chambered  shell.  The  partitions,  or  septa,  of 
the  shell  are  united  by  a  tube  called  "  siphuncle,"  and  the 


PIG.  247— Pearly  Nautilus,  with  shell  bisected  ;  one  half  natural  size.    Indian  Ocean. 

animal  lives  in  the  last  and  largest  chamber.143  The  liv- 
ing Nautilus  has  a  smooth,  pearly  shell,  a  head  retractile 
within  the  mantle  or  "hood,"  and  calcareous  mandibles, 
well  fitted  for  masticating  Crabs,  on  which  it  feeds.  This 


280 


COMPARATIVE  ZOOLOGY. 


straggler  of  a  mighty  race  dwells  in  the  deep  parts  of  the 
Indian  Ocean,  crawling  on  the  bottom  ;  and,  while  the 
shell  is  well  known,  only  a  few  specimens  of  the  animal 
have  ever  been  obtained. 

2.  Dibranchs. — These  are  the  most  active  of  Mollusks, 
and  the  tyrants  of  the  lower  tribes.  Among  them  are 
the  largest  of  invertebrate  animals.  They  are  naked,  hav- 
ing no  external  shell  covering  the  body,  "but  usually  a 
horny  or  calcareous  part  within.  They  have  a  distinct 

head,  prominent  eyes,  horny 
mandibles,  eight  or  ten  arms 
furnished  with  suckers,  two 
gills,  a  complete  tubular  fun- 
nel, and  an  ink-bag  contain- 
ing a  peculiar  fluid  (sepia),  of 
intense  blackness,  with  which 
the  water  is  darkened  to  fa- 
cilitate escape.  They  have 
the  power  of  changing  color, 
like  the  Chameleon.  They 
crawl  with  their  arms  on 
the  bottom  of  the  sea,  head 
downward,  and  also  swim 
backward  or  forward,  usual- 
ly with  the  back  downward, 
by  means  of  fins,  or  squirt 
themselves  backward  by  forc- 
ing water  forward  through 
their  breathing  funnels. 

The  Paper  Nautilus  (Ar- 
gonauta)  and  the  Poulpe  (Octopus)  have  eight  arms.  The 
female  Argonaut  secretes  a  thin,  unchambered  shell  for 
carrying  its  eggs.  The  Squid  (Loligo)  and  Cuttle-fish 
(Sepia}  have  ten  arms,  the  additional  pair  being  much 
longer  than  the  others.  Their  eyes  are  movable,  while 


PIG.  248.— Cuttle-fish  (Sepia  officinalia) 
one  fifth  natural  size.    Atlantic  coasts. 


ARTHROPODA. 


281 


those  of  the  Argonaut  and  Poulpe  are  fixed.  The  Squid, 
so  much  used  for  bait  by  cod-fishermen,  has  an  internal 
horny  "pen,"  and  the  Cuttle  has  a  spongy,  calcareous 
"  bone."  The  extinct  Belemnlte  had  a  similar  structure. 


FIG.  249 — Paper  Nautilus  (Argonauta  argo):  1,  swimming  towards  a  by  ejecting  wa- 
ter from  funnel,  6;  2,  crawling  on  the  bottom;  3,  coiled  within  its  shell,  which  is 
one  fourth  natural  size.  Mediterranean. 

Squid  have  been  found  with  a  body  seven  feet  and  arms 
twenty-four  feet  long,  and  parts  of  others  still  larger — as 
much  as  fifty  feet  in  total  length. 

Subkingdom  VI. — ARTHROPODA. 

This  is  larger  than  all  the  other  subkingdoms  put  to- 
gether, as  it  includes  the  animals  with  jointed  legs,  such 
as  Crabs  and  Insects.  These  differ  widely  from  the  Mol- 
luscan  type  in  having  numerous  segments,  and  in  show- 
ing a  repetition  of  similar  parts;  and  from  the  Worms 
in  having  a  definite  number  of  segments  and  jointed 
legs. 

The  skeleton  is  outside,  and  consists  of  articulated  seg- 
ments or  rings.  The  limbs,  when  present,  are  likewise 
jointed  and  hollow.  The  jaws  move  from  side  to  side. 
The  nervous  system  consists  mainly  of  a  double  chain  of 


282  COMPARATIVE  ZOOLOGY. 

ganglia  running  along  the  ventral  surface  of  the  body 
under  the  alimentary  canal.  The  brain  is  in  the  form  of 
a  ring  encircling  the  gullet.  The  alimentary  canal  and 
the  circulatory  apparatus  are  nearly  straight  tubes  lying 
lengthwise — the  one  through  the  centre,  and  the  other 
along  the  back.  The  skeleton  is  composed  of  a  horny 
substance  (chitine),  or  of  this  substance  with  carbonate  of 
lime.  All  the  muscles  are  striated. 

There  are  four  classes,  of  which  th'e  first  is  water-breath- 
ing, and  the  others  air-breathing. 

CLASS  I. — Crustacea. 

The  Crustacea144  are  water-breathing  Arthropoda,  usu- 
ally with  two  pairs  of  antennae.145  Among  them  are  the 
largest,  strongest,  and  most  voracious  of  the  subkingdom, 
armed  with  powerful  claws  and  a  hard  cuirass  bristling 
with  spines.  Although  constructed  on  a  common  type, 
Crustaceans  exhibit  a  wonderful  diversity  of  external 
form :  contrast,  for  example,  a  Barnacle  and  a  Crab.  We 
will  select  the  Lobster  as  illustrative  of  the  entire  group. 

A  typical  Crustacean  consists  of  twenty-one  segments, 
of  which  seven  belong  to  the  head,  seven  to  the  thorax, 
and  seven  to  the  abdomen.146  In  the  Lobster,  however, 
as  in  all  the  higher  forms,  the  joints  of  the  head  and  tho- 
rax are  welded  together  into  a  single  crust,  called  the 
cephalo-thorax.  On  the  front  of  this  shield  is  a  pointed 
process,  or  rostrum;  and  attached  to  the  last  joint  of  the 
abdomen  (the  so-called  "tail")  is  the  sole  representative 
of  a  tail— the  telson.  This  skeleton  is  a  mixture  of  chitine 
and  calcareous  matter.147 

On  the  under-side  of  the  body  we  find  numerous  ap- 
pendages, feelers,  jaws,  claws,  and  legs  beneath  the  ceph- 
alo-thorax, and  flat  swimmerets  under  the  abdomen.  In 
fact,  as  a  rule,  every  segment  carries  a  pair  of  movable 
appendages.  The  seven  segments  of  the  head  are  com- 


ARTHROPOD  A. 


283 


pressed  into  a  very  small  space,  yet  have  the  following 
members:  the  eye-stalks;  the  short  and  the  long  anten- 
nae; the  mandibles,  or  jaws,  between  which  the  mouth 
opens;  the  two  pairs  of  maxillae;  and  a  pair  of  modified 
limbs,  called  "  foot-jaws."  The  thorax  carries  two  more 
pairs  of  foot-jaws  and  five  pairs  of  legs.  The  foremost 
legs,  "the  great  claws," 
are  extraordinarily  de- 
veloped, and  terminat- 
ed by  strong  pincers 
(chelae).  Of  the  four 
slender  pairs  succeed- 
ing, two  are  furnished 
with  claws,  and  two 
are  pointed.  The  last 
pair  of  swimmerets,  to- 
gether with  the  telson, 
form  the  caudal  fin— 
the  main  instrument  of 
locomotion ;  the  others 
(called  "false  feet") 
are  used  by  the  female 
for  carrying  her  eggs. 
The  eyes  are  raised  on 
stalks  so  as  to  be  mov- 
able (since  the  head  is  FlG'  25ft-— Uuder-side  of  the  Cray-fish,  or  Fresh- 
water Lobster  (AstacuK  flumatilix) :  a,  first  pair 

fixed     tO     the     thorax),        of  antennae;  b,  second  pair,  c,  eyes;  d,  open- 
ing of  kidney  ;  e,  foot-jaws  ;  /,  g,  first  and  fifth 

and    are    Compound,        pair  of  thoracic  legs;  ft,  abdominal  feet;    i, 
i  c      i  anus ;  k,  caudal  fin. 

made  up  of  about  two 

thousand  five  hundred  square  facets.  At  the  base  of  each 
small  antenna  is  a  minute  sac,  whose  mouth  is  guarded  by 
hairs :  this  is  the  organ  of  hearing.  The  gills,  twenty  on 
a  side,  are  situated  at  the  bases  of  the  legs  and  enclosed  in 
two  chambers,  into  which  water  is  freely  admitted,  in  fact, 
drawn,  by  means  of  a  curious  attachment  to  one  of  the 


284 


COMPARATIVE  ZOOLOGY. 


maxillae,  which  works  like  the  "screw"  of  a  propeller. 
The  heart  is  a  single  oval  cavity,  and  drives  arterial  blood 
— a  dusky  fluid  full  of  corpuscles.  The  alimentary  canal 
consists  of  a  short  gullet,  a  gizzard -like  stomach,  and  a 
straight  intestine. 

Crustaceans  pass  through  a  series  of  strange  metamor- 
phoses before  reaching  their  adult  form.  They  also  peri- 
odically cast  the  shell,  or  moult,  every  part  of  the  integu- 
ment being  renewed;  and  another  remarkable  endowment 
is  the  spontaneous  rejection  of  limbs  and  their  complete 
restoration.  Many  species  are 
found  in  fresh  water,  but  the  class 
is  essentially  marine  and  carnivo- 
rous. 

Of  the  numerous  orders  of  this 
great  class  we  will  mention  only 
four: 

1.  OirripedSj   distinguished    by 
being  fixed,  by   having  a   shelly 
covering,   and   by   their    feathery 
arms  (cirri).     Such  are  Barnacles 
(Lepas)  and  A  corn-shells  (Balanus), 
so  common  on  rocks  and  timbers 
a  Te-  by  the  sea-shore, 
tradecapod.   u.  s.  coast.  2.  Entomostracdns,  which  agree 

in  having  a  horny  shell  and  no  abdominal  limbs;  repre- 
sented by  the  little  Water-fleas  (Cyclops]  of  our  ponds,  and 


FHJ.  252. — Amphithoe  maculata;  a  Sand-flea. 

the  Brine-shrimps  (Artemia),  and  many  others.    The  King- 
crabs  (Limulus)  and  the  extinct  Trilobites  were  formerly 


FIG.  253.— Barnacles,  or  Pedunculate  Cirripedes  (Lepaa  anatifera). 

united  to  this  clas>,  but  now  are  known  to  be  widely  re- 
moved from  it.  The  former  is  by  some  authors  removed 
from  the  Crustacea. 

3.  Tetradecapods,  small,  fourteen-footed  species ;  as  the 


Fia.  264. — Acorn-shells  (Balanus)  on 
the  Shell  of  a  Whelk  (Buccinuin). 


FIG.  255.—  Water-fleas :  1,  Cyclops  comminu'x ; 
2.  Cypria  unifasdata;  3,  Daphnia  pulcx. 


286 


TIVE  Z 


COMPARATIVE  ZOOLOGY. 


Wood-louse,  or  Sow-bug  (Oniscus),  so  common  in  damp 
places, the  Slaters  (Idotea),M\&  the  Sand-fleas  (Gammarus), 
seen  by  the  sea-side. 

4.  Decapods,  having  ten  legs,  as  the  Shrimp  (Orangon\ 


f! 


FIG.  25(i.— Lobster  LH<m*o/tw  vulgaris). 


5^7.—  Swimming  Crab  (Platyonychus). 


ARTIIROPODA.  287 

Cray-fish  (Astacus),  Lobster  (Homarus),  and  Crab  (Can- 
cer). Crabs  differ  from  Lobsters  chiefly  in  being  formed 
for  creeping  at  the  bottom  of  the  sea  instead  of  swim- 
ming, and  in  the  reduction  of  the  abdomen  or  "  tail"  to  a 
rudiment,  which  folds  into  a  groove  under  the  enormous 
thorax.  They  are  the  highest  and  largest  of  living  Crus- 
tacea: they  have  been  found  at  Japan  measuring  fifteen 
feet  between  the  tips  of  the  claws. 

CLASS  II. — Arachnida. 

The  Arachnids  are  closely  related  to  the  Crustaceans, 
having  the  body  divided  into  a  cephalo-thorax  and  abdo- 
men.148 To  the  former  are  attached  eight  legs  of  seven 
joints  each ;  the  latter  has  no  locomotive  appendages. 
The  head  carries  two,  six,  or  eight  eyes,  smooth  and  ses- 
sile (i.  e.,  not  faceted  and  stalked,  as  in  the  Lobster),  and 
approaching  the  eye  of  the  Vertebrates  in  the  complete- 
ness and  perfection  of  their  apparatus.  The  antennae,  if 
present,  are  only  two,  and  these  are  not  "feelers,"  but 
modified  to  serve  for  the  prehension  of  food.149  They  are 
all  air-breathers,  having  spiracles  which  open  either  into 
air-sacs  or  tracheae.  The  young  of  the  higher  forms  un- 
dergo no  metamorphosis  after  leaving  the  egg. 

Arachnids  number  nearly  five  thousand  species.  The 
typical  forms  are  divided  into  three  groups : 

1.  Acarina,  represented  by  the  Mites  and  Ticks.    They 
have  an  oval  or  rounded  body,  without  any  marked  artic- 
ulations, the  head,  thorax,  and 
abdomen     being     apparently 
merged  into  one.     They  have 
no  brain;  only  a  single  gan-  FlG  m_A  Mite 

glion  lodged  in  the  abdomen.  rum),  one  of  the  lowest  Arachnids; 
%-,.-.  a  parasite  in  human  hair-sacs ;  X  125. 

They  breathe  by  tracheae.   The 

mouth  is  formed  for  suction,  and  they  are  generally  para- 
sitic. The  Mites  (Acarus)  are  among  the  lowest  of  Ar- 


288  COMPARATIVE  ZOOLOGY. 

ticulates.  The  body  is  soft  and  minute.  The  Ticks 
(Ixodes)  have  a  leathery  skin,  and  are  sometimes  half  an 
inch  long.  The  mouth  is  furnished  with  a  beak  for  pierc- 
ing the  animal  it  infests. 

O 

2.  Pedipalpi,  or  Scorpions,  characterized  by  very  large 
maxillary  palpi  ending  in  forceps,  and  a  prolonged,  joint- 
ed abdomen.  The  nervous  and  circulatory  systems  are 
more  highly  organized  than  those  of  Spiders;  but  the 
long,  tail-like  abdomen  and  the  abnormal  jaws  place  them 


PIG.  259— Scorpion  (under  surface)  and  Centipede. 

in  a  lower  rank.  The  abdomen  consists  of  twelve  seg- 
ments :  the  anterior  half  is  as  large  as  the  thorax,  with  no 
well-marked  division  between ;  the  other  part  is  compara- 
tively slender,  and  ends  in  a  hooked  sting,  which  is  perfo- 
rated by  a  tube  leading  to  a  poison-sac.  The  mandibles 
are  transformed  into  small,  nipping  claws,  and  the  eyes 
generally  number  six.  Respiration  is  carried  on  by  four 
pairs  of  pulmonary  sacs  which  open  on  the  under  surface 


ARTHROPODA. 


289 


of  the  abdomen.  The  heart  is  a  strong  artery,  extending 
along  the  middle  of  the  back,  and  divided  into  eight  separate 
chambers.  Scorpions  are  confined  to  the  warm-temperate 
and  tropical  regions,  usually  larking  in  dark,  damp  places. 

The  Harvest-men  (Phalangium),  frequently  seen  about 
our  houses,  belong  to  this  order.  They  have  a  short,  thick 
body  and  extremely  long  legs,  and  breathe  by  tracheae. 

3.  Araneina,  or  Spiders.  They  are  distinguished  by 
their  soft,  unjointed  abdomen,  separated  from  the  thorax 
by  a  narrow  constriction,  and  provided  at  the  posterior 
end  with  two  or  three  pairs  of  appendages,  called  "spin- 


FIQ.  260.— A,  female  Spider ;  B,  male  of  same  species ;  C,  arrangement  of  the  eyes. 

nerets,"  which  are  homologous  with  legs.  The  office  of 
the  spinnerets  is  to  reel  out  the  silk  from  the  silk-glands, 
the  tip  being  perforated  by  a  myriad  of  little  tubes, 
through  which  the  silk  escapes  in  excessively  fine  threads. 
An  ordinary  thread,  just  visible  to  the  naked  eye,  is  the 

10 


290  COMPARATIVE  ZOOLOGY. 

union  of  a  thousand  or  more  of  these  delicate  streams  of 
silk.160  These  primary  threads  are  drawn  out  and  united 
by  the  hind  legs. 

The  mandibles  are  vertical,  and  end  in  a  powerful  hook, 
in  the  end  of  which  opens  a  duct  from  a  poison-gland  in 
the  head.     The  maxillae,  or  "  palpi,"  which 
in  Scorpions  are  changed  to  formidable  claws, 
in  Spiders  resemble  the  thoracic  feet,  and  are 
often  mistaken  for  a  fifth  pair.     The  brain  is 
a      of  larger  size,  and  the  whole  nervous  system 
FIG.  2Gi.  —  spin-  more  concentrated  than  in  the  preceding  or- 
der,6^; a! pal"  der.     There  are  generally  eight  simple  eyes, 

piform  organs.      rarelv    gix>       y^    breatbe    b()tb    by    tracnege 

and  lung-like  sacs,  from  two  to  four  in  number,  situated 
under  the  abdomen.  All  the  species  are  carnivorous. 

The  instincts  of  Spiders  are  of  a  high  order.  They  are, 
perhaps,  the  most  wily  of  Articulates.  They  display  re- 
markable skill  and  industry  in  the  construction  of  their 
webs;  and  some  species  (called  " Mason  Spiders")  even 
excavate  a  subterranean  pit,  line  it  with  their  silken  tapes- 
try, and  close  the  entrance  with  a  lid  which  moves  upon  a 

hinge.'51 

CLASS  III. — Myriapoda. 

Myriapods  differ  from  Crustaceans  and  Spiders  in  hav- 
ing the  thorax  merged  in  the  abdomen,  while  the  head  is 
free.  In  other  words,  the  body  is  divided  into  similar 
segments,  so  that  thorax  and  abdomen  are  scarcely  distin- 
guishable. They  resemble  Worms  in  form  and  in  the 
simplicity  of  their  nervous  and  circulatory  systems ;  but 
the  skin  is  stiffened  with  chitine,  and  the  legs  (indefinite 
in  number)  are  articulated.  The  legs  resemble  those  of 
Insects,  and  the  head  appendages  follow  each  other  in  the 
same  order  as  in  Insects — eyes,  antennae,  mandibles,  max- 
illae, and  labium.  They  breathe  by  tracheae,  and  have  two 
antennae  and  a  variable  number  of  eyes. 


ARTHROPOD  A.  291 

There  are  two  orders : 

1.  Chilognatha,  having  a  cylindrical  body,  each  segment 
furnished  with  two  pairs  of  legs.     They  are  of  slow  loco- 
motion, harmless,  and  vegetarian.     The  Thousand-legged 
Worm  (Julus)  is  a  common  representative. 

2.  Chilopoda,  characterized  by  having  a  flattened  body 
composed  of  about  twenty  segments,  each  carrying  one 
pair  of  legs,  of  which  the  hindermost  is  converted  into 
spines.     They  have  longer  antennae  than  the  preceding, 
and  the  mouth  is  armed  with  two  formidable  fangs  con- 
nected with  poisonous  glands.     They  are  carnivorous  and 
active.     Such  is  the  Centipede  (Scolopendra,  Fig.  259). 

CLASS  IY. — Insecta. 

Insects  are  distinguished  by  having  head,  thorax,  and 
abdomen  distinct,  three  pairs  of  jointed  legs,  one  pair  of 
antennae,  and  generally  two  pairs  of  wings.  The  number 
of  segments  in  the  body  never  exceeds  twenty.  The  head, 
apparently  one,  is  formed  by  the  union  of  four  segments. 
The  thorax  consists  of  three  —  the  prothorax,  mesothorax, 
and  metathorax — each  bearing  a  pair  of  legs ;  the  wings, 
if  present,  are  carried  by  the  last  two  segments.  The  ab- 
domen is  normally  composed  of  ten  segments,  more  or  less 
movable  upon  one  another.  The  skin  is  hardened  with 
chitine,  and  to  it,  as  in  all  Arthropods,  the  muscles  are  at- 
tached. The  organs  of  sense  are  confined  to  the  cephalic 
division  of  the  body,  the  motor  organs  to  the  thoracic,  and 
the  vegetative  to  the  abdominal.  All  the  appendages  are 
hollow. 

The  antennae  are  inserted  between  or  in  front  of  the 
eyes.  There  is  a  great  variety  of  forms,  but  all  are  tubu- 
lar and  jointed.  They  are  supposed  to  be  organs  of  touch, 
and  also  seem  to  be  sensitive  to  sound.  The  eyes  are 
usually  compound,  composed  of  a  large  number  of  hexago- 
nal corneae,  or  facets  (from  fifty  in  the  Ant  to  many  thou- 


292 


COMPARATIVE  ZOOLOGY. 


sands  in  the  winged  Insects). 


They  are  never  placed  on 
movable  stalks,  as  the 
Lobster's.  Besides 
these,  there  are  three 
simple  eyes,  called 
.  ocelli.  The  mouth 
may  be  fitted  for  bit- 
ing (masticatory),  as 
in  Beetles,  or  for  suck- 
ing (suctorial),  as  in 
Butterflies.  The  mas- 
ticatory type,  which 
is  the  more  complete, 
and  of  which  the  other 
is  but  a  modification, 
consists  of  four  horny 
jaws  (mandibles  arid 
maxillce)  and  an  up- 
per and  an  under  lip 
(labrum  and  labium). 
Sensitive  palpi  (max- 
illary and  labial)  are 
developed  from  the 
lower  jaw  and  lower 
lip.  The  labium  is 
also  prolonged  into  a 
ligula,  or  tongue. 
The  legs  are  invari- 

nk]v  Q1'v  jn   4-V,p  adult 
'  r°V   S1X  1!  11U> 

palpus;  i,  mandible;  k,  buccal  opening;  I,  gula,  the  f Ore  -  legS  direct- 
ed forward  and  the 
hinder  pairs  back- 
ward. Each  consists 
of  a  hip,  thigh,  shank, 
Some  larvae  have  also  "false  legs,"  without 


FIG.  262.— Under  surface  of  a  Beetle  (Harpalus  cali- 
ginosus) :  o,  ligula;  b,  paraglossse;  c,  supports  of 
labial  palpi;  d,  labial  palpus;  e,  mentum ;  /,  in- 
ner lobe  of  maxilla ;  g,  outer  lobe ;  h,  maxillary 


or  throat:  m,  buccal  sutures;  n,  gular  suture;  o, 
prosternum  ;  p,  episteruum  of  prothorax  ;  p',  epi- 
meron ;  g,  5',  q",  coxae;  r,  r,  r,  trochanters;  #, 
*',  «",  femora,  or  thighs;  t,  t\  t",  tibse;  v,  veutral 
abdominal  segments ;  w,  episternaof  mesothorax  ; 
*,  mesosternum  ;  y,  episterna  of  metathorax;  y', 
epimeron ;  z,  metasteruum. 


and  foot.153 


ARTHROPODA.  293 

joints,  on  the  abdomen,  upon  which  they  chiefly  rely  in 
locomotion.  The  wings  are  expansions  of  the  crust, 
stretched  over  a  net-work  of  horny  tubes.  The  venation, 
or  arrangement  of  these  tubes  (called  veins  and  veinlets), 
particularly  in  the  fore-wings,  is  peculiar  in  each  genus. 
In  many  Insects,  the  abdomen  of  the  female  ends  in  a 
tube  which  is  the  sheath  of  a  sting,  as  in  the  Bee,  or  of  an 
ovipositor,  or  "borer,"  as  in  the  Ichneumon,  by  means  of 
which  the  eggs  are  deposited  in  suitable  places. 

Cephalization  is  carried  to  its  maximum  in  this  class, 
and  we  have  animals  of  the  highest  instincts  under  the 
articulate  type.  The  "brain"  is  formed  of  several  gan- 
glia massed  together,  and  lies  across  the  upper  side  of  the 
throat,  just  behind  the  mouth.  The  main  cord  lies  along 
the  ventral  side  of  the  bodjr,  with  a  swelling  for  each  seg- 
ment; besides  this,  there  is  a  visceral  nerve  representing, 
in  function,  the  sympathetic  system  of  Vertebrates.  The 
digestive  apparatus  consists  of  a  pharynx,  gullet  (to  which 
a  crop  is  added  in  the  Fly,  Butterfly,  and  Bee  tribes),  giz- 
zard, stomach,  and  intestine.  There  are  no  absorbent  ves- 
sels, the  chyme  simply  transuding  through  the  walls  of 
the  canal.  The  blood,  usually  a  colorless  liquid,  is  driven 
by  a  chain  of  hearts  along  the  back,  i.  e.,  by  a  pulsating 
tube  divided  into  valvular  sacs,  ordinarily  eight,  which 
allow  the  current  to  flow  only  towards  the  head.  As  it 
leaves  this  main  pipe,  it  escapes  into  the  cavities  of  the 
body,  and  thus  bathes  all  the  organs.  Although  the  blood 
does  not  circulate  in  a  closed  system  of  blood-vessels,  as  in 
Vertebrates,  yet  it  always  takes  one  set  of  channels  in  go- 
ing from  the  heart,  and  another  in  returning.  Respira- 
tion is  carried  on  by  tracheae,  a  system  of  tubes  opening 
at  the  surface  by  a  row  of  apertures  (spiracles),  generally 
nine  on  each  side  of  the  body. 

The  sexes  are  distinct,  and  the  larvae  are  hatched  from 
eggs.  As  a  rule,  an  Insect,  after  reaching  the  adult,  or 


COMPARATIVE  ZOOLOGY. 


imago,  state,  lives  from  a  few  hours  to  several  years,  and 
dies  after  the  process  of  reproduction.  Growth  takes 
place  only  during  larval  life,  and  all  metamorphoses  occur 
then.  Among  the  social  tribes,  as  Bees  and  Ants,  the 
majority  (called  "workers")  do  not  develop  either  sex. 

Insects  (the  six-footed  Arthropods)  comprise  nearly  one 
half  of  the  whole  Animal  Kingdom,  or  from  one  hundred 
arid  seventy  thousand  to  two  hundred  thousand  species. 
They  are  grouped  into  seven  orders:  -utArHd  CN1H 

Lower  series :  body  usually  flattened ;  prothorax  large  and 
squarish ;  mouth-parts  usually  adapted  for  biting ;  met- 
amorphosis often  incomplete ;  pupa  often  active ;  larva  Hemiptera, 


Neuroptera, 


Coleoptera. 
Diptera, 


flattened,  often  resembling  the  adult. 

Higher  series:  body  usually  cylindrical;   prothorax  small; 
mouth-parts  more  generally  formed  for  sucking ;  meta- 
morphosis complete ;  pupa  inactive ;  larva  usually  cylin- 
drical, very  unlike  the  adult. 
^ 

1.  Neuroptera  have  a  comparatively  long,  slender  body, 


Hymenoptera. 


FIG.  263.— Dragon-fly  (Libellula). 

and  four  large,  transparent  wings,  nearly  equal  in  size, 
membranous  and  lace-like.    Such  are  the  brilliant  Dragon- 


ARTHROPOD  A.  295 

flies,  or  Devil's  Darning-needles  (Libelluld),  well  known 
by  the  enormous  head  and  thorax,  large,  prominent  eyes 
(each  furnished  with  twenty -eight  thousand  polished 
lenses),  and  Scorpion -like  abdomen;  the  delicate  and 
short-lived  May-flies  (Ephemera) ;  Caddis-flies  (Phryya- 
nea),  whose  larvae  live  in  a  tubular  case  made  of  minute 
stones,  shells,  or  bits  of  wood ;  the  Horned  Corydalis 
(Corydalus),  of  which  the  male  has  formidable  mandibles 
twice  as  long  as  the  head ;  and  the  White  Ants  (Termes) 
of  the  tropics. 

2.  Orthoptera  have  four  wings:  the  front  pair  some- 
what thickened,  narrow,  and  overlapping  along  the  back ; 
the  hind  pair  broad,  net-veined,  and  folding  up  like  a  fan 


FIG.  264.— Metamorphosis  of  a  Cricket  (Gryllus). 

upon  the  abdomen.  The  hind  legs  are  usually  large,  and 
fitted  for  leaping,  all  the  species  being  terrestrial,  although 
some  fly  as  well  as  leap.  The  eyes  are  small,  the  mouth 
remarkably  developed  for  cutting  and  grinding.  The  lar- 


296 


COMPARATIVE  ZOOLOGY. 


FIG.  265.  — 


,  Water-boatruau  (NotonectcC). 


vae  and  pupsB  are  active,  and  resemble  the  imago.  They 
are  nearly  all  vegetarian.  Each  family  produces  charac- 
teristic sounds  (strid  illation).  The  representative  forms 


FIG.  266 — Seventeen-year  Cicada  (Cicada  sepf  ended  m):  a,  pupa;  b,  the  fame,  after 
the  imago,  c,  has  escaped  through  a  rent  in  the  back;  d,  holes  iu  a  twig,  where 
the  eggs,  e,  are  inserted. 


ARTHROPODA. 


297 


are  Crickets  (Gryllus\  Locusts  (Locusta),  Grasshoppers 
(Acrydium\  Walking-sticks  (Phasma\  and  Cockroaches 
(Blatta). 

3.  Hemiptera,  or  "  Bugs,"  are  chiefly  characterized  by 
a  suctorial  mouth,  which  is  produced  into  a  long,  hard, 
beak,  in  which  mandibles  and  maxillae  are  modified  into 
bristles  and  enclosed  by  the  labium.     The  four  wings  are 
irregularly  and  sparsely  veined,  sometimes  wanting.     The 
body  is  flat  above,  and  the  legs  slender.     The  larva  differs 
from  the  imago  in  wanting  wings.     In  some  species  the 
fore -wings  are  opaque  at  the  base  and  transparent  at 
the  apex,  whence  the  name  of  the  order.     Some  feed  on 
the  juices  of  animals,  others  on  plants.     Here  belong  the 
wingless  Bed-bug  (Cimex)  and  Louse   (Pediculus),  the 
Squash-bug  (Coreus),  Water-boatman  (Notonecta),  Seven- 
teen-year Locust  (Oicada),  Cochineal  (Coccus),  and  Plant- 
louse  (Aphis). 

4.  Coleoptera,  or  "  Beetles."     This  is  the  largest  of  the 
orders,  the   species   numbering   about   ninety  thousand. 
They  are  easily  recognized  by  the  elytra,  or  thickened. 


FIG.  267- 


i,  imago,  and  b,  larva,  of  the  Goldsmith  Beetle  (Cotalpa  lanigera) ;  c, 
pupa  of  J  une-bug  (Lachnosterna  fusca). 


horny  fore-wings,  which  are  not  used  for  flight,  but  serve 
to  cover  the  hind  pair.  When  in  repose,  these  elytra  are 
always  united  by  a  straight  edge  along  the  whole  length. 
The  'hind  wings,  when  not  in  use,  are  folded  transversely. 


298  COMPARATIVE  ZOOLOGY. 

The  mandibles  are  well  developed,  and  the  integument 
generally  is  hard.  The  legs  are  strong,  for  the  Beetles 
are  among  the  most  powerful  running  Insects.  The  lar- 
vae are  worm-like,  and  the  pupa  is  motionless.  The  high- 
est tribes  are  carnivorous.  The  most  prominent  forms 


Fie.  268.— Sexton  Beetles  (Necrophorus  vespillo),  with  larva  and  nymph.    They  are 
burying  a  mouse,  preparatory  to  laying  their  eggs  in  it. , 

are  the  savage  but  beautiful  Tiger  Beetles  (Cicindela); 
the  common  Ground  Beetles  (Carabux),  whose  hind  wings 
are  often  absent;  the  Diving  Beetles  (Dytiscus),  with 
boat-shaped  body,  and  hind  legs  changed  into  oars ;  the 
Carrion  Beetles  (Silpha\  distinguished  by  their  black,  flat 


ARTHROPODA. 


299 


bodies  and  club-shaped  antennae;  the  Goliath  Beetles 
(Scardbaius),  the  giants  of  the  order ;  the  Snapping-bugs 
(Elater) ;  the  Lightning-bugs  (Pyrophorus) ;  the  spotted 
Lady-birds  (Coccinella)  \  the  showy,  Long-horned  Beetles 


FIG.  269.— Metamorphosis  of  the  Mosquito  (Cuter  pipiens). 


300  COMPARATIVE  ZOOLOGY. 

(Ceranibycidce) ;   and  the  destructive  Weevils  (Curculio- 
nidce),  with  pointed  snouts. 

5.  Diptera,  or  "  Flies,"  are  characterized  by  the  rudi- 
mentary state  of  the  hinder  pair  of  wings.  Although 
having,  therefore,  but  one  available  pair,  they  are  gifted 
with  the  power  of  very  rapid  flight.  While  a  Bee  moves 
its  wings  one  hundred  and  ninety  times  a  second,  and  a 
Butterfly  nine  times,  the  House-fly  makes  three  hundred  and 
thirty  strokes.  A  few  species  are  wingless.  The  eyes  are 
large,  with  numerous  facets.  In  some  forms,  as  the  House- 
fly, all  the  mouth-parts,  except  the  labium,  are  rudimen- 
tary ;  and  the  labium  has  an  expanded  tip,  by  means  of 


FIG.  270.— Metamorphosis  of  the  Flesh-fly  (Sarcophaga  carnaria) :  a,  eggs;  b,  youug 
maggots  just  hatched;  c,  d,  full-grown  maggots ;  e,  pupa;  /,  imago. 

which  the  fly  licks  up  its  food.  In  other  forms,  as  the 
Mosquito,  the  other  mouth-parts  are  present  as  bristles  or 
lancets,  fitted  for  piercing ;  the  thorax  is  globular,  and  the 
legs  slender.  The  larvae  are  footless  grubs.  The  Diptera 
number  about  twenty-four  thousand.  Among  them  are 
the  Mosquitoes  (Culex)\  Hessian-fly  (Cecidomyia\  so  de- 
structive to  wheat;  Daddy-long-legs  (Tipula),  resembling 
a  gigantic  Mosquito ;  the  wingless  Flea  (Pulex) ;  besides 
the  immense  families  represented  by  the  House-fly  (Mus- 

ca)  and  Bot-fly  ((Estrus). 

6.  Lepidoptera,  or  "  But- 
terflies" and  "Moths,"  are 
known  chiefly  by  their  four 
large  wings,  which  are  thick- 
ly covered  on  both  sides  by 
minute,  overlapping  scales. 

FIG.  271.— Scales  from  the  Wiugs  of  vari-  r      & 

ous  Lepidoptera.  The  scales  are  of  different 


ARTHROPODA. 


301 


colors,  and  are  often  arranged  in  patterns  of  exquisite 
beauty.  They  are  in  reality  modi  tied  hairs,  and  every 
family  has  its  partic- 
ular form  of  scale. 
The  head  is  small, 
and  the  body  cylin- 
drical. The  legs  are 
not  used  for  locomo- 
tion. All  the  mouth 
parts  are  nearly  obso- 
lete except  the  maxil- 
lae, which  are  fash- 
ioned into  a  "  probos- 
cis "  for  PUinpinff  UP  Fio.272. -Part  of  the  Wing  of  a  Moth  (Saturnia), 
*  &  magnified  to  show  the  arrangement  of  scales. 

the  nectar  of  flowers. 

The  larvae,  called  "  caterpillars,"  have  a  worm-like  form, 
and  from  one  to  five  pairs  of  abdominal  legs,  in  addition 
to  the  three  on  the  thorax.  The  mouth  is  formed  for  mas- 
tication, and  (ex- 
cept in  the  larvae 
of  Butterflies)  the 
lip  has  a  spinneret 
connected  with  silk- 
glands. 

There  are  three 
groups  :  the  gay 
Butterflies,  having 
knobbed  or  hooked 

FIG.  273.— Vanessa  polycJdoros,  or  "Tortoise-shell  But-    antenn33  and  flvinff 
terfly."  *      & 

in    the    day   only ; 

the  dull-colored  Sphinges,  with  antennae  thickened  in  the 
middle,  and  flying  at  twilight ;  and  the  nocturnal  Moths, 
which  generally  prefer  the  night,  and  whose  antennae  are 
thread-like  and  often  feathery.  Generally,  when  at  rest, 
the  Butterflies  keep  their  wings  raised  vertically,  while 


302 


COMPARATIVE  ZOOLOGY. 


FIG.  274.— Moth  and  Larva  of  Attacus  pavonia-major. 


the  others  hold  theirs  horizontally.  The  pupa  of  the 
former  is  unprotected,  and  is  usually  suspended  by  a  bit 
of  silk  :"'  the  pupa  of  the  Moths  is  enclosed  in  a  cocoon. 


Fia.  275.— Fruit-moth  (Carpocapsa pomonella) :  b,  larva  ;  a,  chrysalis;  c,  imago. 


ARTHROPODA. 


303 


From  twenty-two  thousand  to  twenty-four  thousand 
Lepidopterous  species  have  been  identified.  Some  of  the 
most  common  Butterflies  are  the  swallow-tail  Papilio, 
the  white  Pieris,  the  sulphur- 
yellow  Colias;  the  Argynnis, 
with  silver  spots  on  the  under 
side  of  the  hind  wings ;  the 
Vanessa,  with  notched  wings. 
The  Sphinges  exhibit  little 
variety.  They  have  narrow, 
powerful  wings,  and  are  some- 
times mistaken  for  Humming- 
birds. The  "  potato  -worm" 
is  the  caterpillar  of  a  Sphinx. 
The  most  conspicuous  Moths 
are  the  large  and  beautiful 
Attacus,  distinguished  by  a 

FIG.  276. —  Head  of  a  Caterpillar,  from 
triangular,     transparent      Spot       beneath:  o,  antennae;  6,  horny  jaws; 

in  the  centre  of  the  wing ; 
the  white  Bombyx,  or  "silk- 
worm ;"  the  reddish-brown  Clisiocampa,  whose  larva,  "  the 
American  Tent-caterpillar,"  spreads  its  web  in  many  an 
apple  and  cherry  tree;  the  pale,  delicate  Geometrids ;  and 
the  small  but  destructive  Tineids,  represented  by  the 
Clothes-moth. 

7.  Hymenoptera,  comprising  at  least  twenty-five  thou- 
sand species,  include  the  highest,  most  social,  and,  we  may 
add  (if  we  except  the  Silk-worm),  the  most  useful,  of  In- 
sects. They  have  a  large  head,  with  compound  eyes  and 
three  ocelli,  mouth  fitted  both  for  biting  and  lapping, 
legs  formed  for  locomotion  as  well  as  support,  and  four 
wings  equally  transparent,  and  interlocking  by  small 
hooks  during  flight.  The  females  are  usually  provided 
with  a  sting,  or  borer.  The  larvae  are  footless,  helpless 
grubs,  and  generally  nurtured  in  cells,  or  nests.  Such  are 


c,  thread  of  silk  from  the  conical  fasu- 
las,  on  either  side  of  which  are  rudi- 
mentary palpi. 


304  COMPARATIVE  ZOOLOGY. 

the  Honey-bees  (Apis),  Humble-bees  (Sombus),  Wasps 
(Vespa),  Ants  (Formica),  Ichneumon-flies,  and  Gall-flies. 
Those  living  in  societies  exhibit  three  castes  :  females,  or 
"  queens  ;"  males,  or  "  drones  ;"  and  neuters,  or  sexless 
"  workers."  There  is  but  one  queen  in  a  hive,  and  she 
is  treated  with  the  greatest  distinction,  even  when  dead. 
She  dwells  in  a  large,  pear-shaped  cell,  opening  down- 
ward.. She  lays  three  kinds  of  eggs :  from  the  first 
come  forth  workers,  the  second  produces  males,  and  the 
last  females.  The  drones,  of  which  there  are  about  eight 
hundred  in  an  ordinary  hive,  are  marked  by  their  great 
size,  their  large  eyes  meeting  on  the  top  of  the  head,  and 


FIG.  27T. — Honey-bee  (Apis  vnelUfaa) :  a,  female ;  &,  worker ;  c,  male. 

by  being  stingless.  The  workers,  which  number  twenty 
to  one  drone,  are  small  and  active,  and  provided  with 
stings,  and  hollow  pits  in  the  thighs,  called  "  baskets," 
in  which  they  carry  pollen.  Their  honey  is  nectar  elabo- 
rated in  the  crop  by  an  unknown  process ;  while  the  wax 
is  secreted  from  the  sides  of  the  abdomen  and  mixed  with 
saliva.  There  is  a  subdivision  of  extra  labor:  thus  there 
are  wax-workers,  masons,  and  nurses.  Ants  (except  the 
Saiiba)  have  but  two  classes  of  workers.  While  Ants  live 
in  hollow  trees  or  subterranean  chambers  (called  formi- 
carium),  Honey-bees  and  Wasps  construct  hexagonal  cells. 
The  comb  of  the  Bee  is  hung  vertically,  that  of  the  Wasp 
is  horizontal. 


TUNICATA. 


305 


FIG.  278.— Au  Aseid'um. 


Subkingdom  VII. — TUNICATA. 

This  small  and  singular  group  of  animals  has  relations 
with  the  worms  on  the  one  hand  and  with  the  Vertebrates 
on  the  other.  The  most  common  forms  (the  solitary  As- 
cidians)  are  enclosed  in  a 
leathery,  elastic  bag,  one  end 
of  which  is  fastened  to  the 
rocks,  while  the  other  has 
two  orifices,  for  the  inlet 
and  exit  of  a  current  of 
water  for  nutrition  and  res- 
piration. They  are  without 
head,  feet,  arms,  or  shell.  In- 
deed, few  animals  seem  more 
helpless  and  apathetic  than  these  apparently  shapeless  be- 
ings. The  tubular  heart  exhibits  the  curious  phenomenon 
of  reversing  its  action  at  brief  intervals,  so  that  the  blood 
oscillates  backward  and  forward  in  the 
same  vessels.  Another  peculiarity  is  the 
presence  of  cellulose  in  the  skin.  The 
water  is  drawn  by  cilia  into  a  branchial 
sac,  an  enlargement  of  the  first  part  of 
the  intestine,  whence  it  escapes  through 
openings  in  the  sides,  to  the  excurrent  ori- 
fice, while  the  particles  of  food  drawn  in 
with  the  water  are  retained  and  passed 
into  the  intestine.  The  larva  is  active, 
swimming  by  means  of  a  long  tail.  It 
looks  like  a  tadpole,  and  has  a  notochord 
and  a  nervous  system  closely  resembling 
FiG.279.-Diagramorsim. those  of  a  Vertebrate.  Afterwards  it  at- 
pieAscidian:  s^bran-  taches  itself  by  the  head,  the  tail  is  ab- 

chial   sac  ;   n,  nervous  * 

ganglion  ;s,  stomach ;  r,  SOrbed,  and    the    nei'VOUS    System    is    re- 
intestine;   o,  reproduc-    -,          ,   ,  ,  ,,  ,. 

tive organ;  h, heart,      ouced  to  a  single  small  ganglion. 

20 


306 


COMPARATIVE  ZOOLOGY. 


Subkingdom  VIII. — VERTEBRATA. 
This  grand  division  includes  the  most  perfect  animals, 
or  such  as  have  the  most  varied  functions  and  the  most 
numerous  and  complex  organs.  Besides  the  unnumbered 
host  of  extinct  forms,  there  are  about  twenty-five  thousand 
living  species,  widely  differing  among  themselves  in  shape 
and  habits,  yet  closely  allied  in  the  grand  features  of  their 
organization,  the  general  type  being  endlessly  modified. 

The  fundamental  distinctive  character  of  Vertebrates 
is  the  separation  of  the  main  mass  of  the  nervous  system 

from  the  general  cav- 
ity of  the  body.  A 
transverse  section  of 
the  body  exhibits  two 
cavities,  or  tubes  —  the 
dorsal,  containing  the 
cerebro- spinal  nervous 
system  ;  the  ventral,  in- 
closing the  alimentary 
canal,  heart,  lungs,  and 
a  double  chain  of  gan- 
glia, or  sympathetic 
system.  This  ven- 
tral, or  hsemalj  cavity 
corresponds  to  the 

FIG.  280.— Ideal  Plans  of  the  Snbkingdoms.     F, 

transverse  section  of  vertebrate  type ;  v,  the    WllOle    body    OI    an    In- 
same,  inverted.    M,  transverse  section  of  mol-  ,  •  •,        ,  *  ••>        ,-1 

hiBcons  type ;  arm  Md,  of  moiiuscoid.  A  and  vertebrate  ;    while   the 

A d,  transverse  sections  of  articulate  type,  high  ^/-w^col        ^r      nmiral        ic 

and  low.     C,  longitudinal  section  of  coelente-  U       b<iJ>  <"> 

rate  type ;  a,  alimentary  canal ;  c,  body-cavity,  added. 

In  the  other  figures,  the  alimentary  canal  is 

shaded,  the  heart  is  black,  aud  the  nervous         Vertebrates    are    also 

cords  are  open  rings.  j .    , .  -131 

distinguished  by  an  in- 
ternal, jointed  skeleton,  endowed  with  vitality,  and  capa- 
ble of  growth  and  repair.  During  embryo-life  it  is  rep- 
resented by  the  notochord  ;  but  this  is  afterwards  replaced 


VERTEBRATA. 


307 


by  a  more  highly  developed 
vertebral  column  of  cartilage 
or  bone.  The  column  and 
cranium  are  never  absent  in 
the  craniota  ;  other  parts  may 
be  wanting,  as  the  ribs  in  Frogs, 
limbs  in  Snakes,  etc.154  The 
limbs  are  never  more  than 
four,  and  are  always  articu- 
lated to  the  haemal  side  of  the 
body,  while  the  legs  of  Inver- 
tebrates are  developed  from 
the  neural  side.  The  muscles 
moving  the  limbs  are  attached 
to  the  endoskeleton. 

The  circulation  of  the  blood 
is  complete,  the  arteries  being 
joined  to  the  veins  by  capil- 
laries, so  that  the  blood  never 
escapes  into  the  visceral  cav- 
ity as  in  the  Invertebrates. 
All  have  a  portal  vein,  carry- 
ing blood  through  the  liver; 
all  have  lacteals  and  lym- 
phatics. The  blood  is  red, 
and  contains  both  kinds  of 
corpuscles.155  The  teeth  are 
developed  from  the  dermis, 
never  from  the  cuticle,  as  in 
Mollusks  and  Articulates  ;  the 
jaws  move  vertically,  and  are 
never  modified  limbs.  The 

liver    and 


„ 

Fro.  2S1.  —  Diagram   of  Circulation    In 
are    always       the  higher  Vertebrates:   I,  heart;  '2, 


_,  . 

present.       JLlie   respiratory    OI*- 
•  •i  -ii  i 

gans  are  either  gills  or  lungs, 


lungs;  3,  head  and  upper  extremities; 
4,  spleen;  5,  intestine  ;  6,  kiduey;  T, 
lower  extremities;  8,  liver.  (From 

Daitou-e  -physiology.  S 


308  COMPARATIVE  ZOOLOGY. 

or  both.  Vertebrates  are  the  only  animals  which  breathe 
through  the  mouth. 

The  nervous  system  has  two  marked  divisions :  the 
cerebro-spinal,  presiding  over  the  functions  of  animal  life 
(sensation  and  locomotion) ;  and  the  sympathetic,  which 
partially  controls  the  organic  functions  (digestion,  respi- 
ration, and  circulation).  In  no  case  does  the  gullet  pass 
through  the  nervous  system,  as  in  Invertebrates,  and  the 
mouth  opens  on  the  side  opposite  to  the  brain.  Probably 
none  of  the  five  senses  are  ever  altogether  absent.  The 
form  of  the  brain  is  modified  by  the  relative  development 
of  the  various  lobes.  In  the  lower  Vertebrates,  the  cere- 
bral hemispheres  are  small  —  in  certain  Fishes  they  are 
actually  smaller  than  the  optic  lobes — in  the  higher,  they 
nearly  or  quite  overlap  both  olfactories  and  cerebellum. 
The  brain  may  be  smooth,  as  in  most  of  the  cold-blooded 
animals,  or  richly  convoluted,  as  in  Man. 

There  is  no  skull  in  Arnphioxus.  In  the  Marsipo- 
branchii  and  Elasmobranchii  it  is  cartilaginous.  In  other 
fishes  it  is  cartilage  overlaid  with  bone.  In  Amphibians 
and  Reptiles,  it  is  mingled  bone  and  cartilage.  In  Birds 
and  Mammals,  mainly  or  wholly  bony.  The  human  skull 
contains  fewer  bones  than  the  skull  of  most  animals,  ex- 
cepting Birds.  The  skull  of  all  Vertebrates  is  divisible 
into  two  regions :  the  cranium,  or  brain-case,  and  the  face. 
The  size  of  the  cranial  capacity,  compared  with  the  area 
of  the  face,  is  generally  the  ratio  of  intelligence.  In  the 
lower  orders,  the  facial  part  is  enormously  predominant, 
the  eye-orbits  are  directed  outward,  and  the  occipital  con- 
dyles  are  nearly  on  a  line  with  the  axis  of  the  body.  In 
the  higher  orders,  the  face  becomes  subordinate  to  the 
cranium,  the  sensual  to  the  mental,  the  eyes  look  forward, 
and  the  condyles  approach  the  base  of  the  cranium.  Com- 
pare the  "  snouty  "  skull  of  the4Crocodile  and  the  almost 
vertical  profile  of  civilized  Man.  A  straight  line  drawn 


VEKTEBBATA.  309 

from  the  middle  of  the  ear  to  the  base  of  the  nose,  and 
another  from  the  forehead  to  the  most  prominent  part  of 
the  upper  jaw,  will  include  what  is  called  the  facial  an- 
gle, which  roughly  gives  the  relation  between  the  two  re- 
gions, and  therefore  the  rank  of  the  animal.156  In  the 
cold-blooded  Vertebrates  the  brains  do  not  fill  the  cranium ; 
while  in  Birds  and  Mammals  a  cast  of  the  cranial  cavity 
well  exhibits  the  general  features  of  the  cerebral  surface.167 

All  Vertebrates  are  single  and  free.  Mammals  bring 
forth  their  young  alive,  having  directly  nourished  them 
from  the  mother  before  birth  (viviparous).  In  almost  all 
the  others  the  nourishment  is  laid  up  in  the  egg,  which  is 
laid  before  hatching  (oviparous),  or  is  retained  in  the 
mother  until  hatched  (ovoviviparous),  as  in  some  Reptiles 
and  Fishes. 

There  are  two  great  divisions  of  the  subkingdom, 
Acrania  and  Craniota,  or  Vertebrates  without  skulls  and 
those  with  skulls. 

The  Craniota  are  divided  into  five  great  classes :  Fishes, 
Amphibians,  Reptiles,  Birds,  and  Mammals.  The  first 
three  are  "cold-blooded,"  the  other  two  are  "warm- 
blooded." Fishes  and  Amphibians  have  gills  during  the 
whole  or  a  part  of  their  lives,  while  the  rest  never  have  gills. 
Fishes  and  Amphibians  in  embryo  have  neither  amnion 
nor  allantois,  while  the  other  three  are  provided  with  both. 

There  are  three  provinces  of  skull-bearing  Vertebrates. 

Fishes  and  Amphibians  agree  in  having  gills,  in  want- 
ing amnion  and  allantois,  and  in  possessing  nucleated  red 
blood-corpuscles  (Ichthyopsidd). 

Birds  and  Reptiles  agree  in  having  no  gills,  but  both 
amnion  and  allantois,  in  the  articulation  of  the  skull  with 
the  spine  by  a  single  condyle,  in  the  development  of  the 
skin  into  feathers  or  scales,  and  in  circulating  oval,  nucle- 
ated, red  corpuscles  (Sauropsida). 

Mammals  differ  from  Birds  and  Reptiles  in  having  two 


310 


COMPARATIVE  ZOOLOGY. 


occipital  condyles,  and  their  blood-corpuscles  are  not  nu- 
cleated 158  (Mammalia). 


DIVISION  I. — Acrania. 


Vertebrates  without  a  skull. 


II 


II 


fl.rf 

gla- 


SS,  8 

II! 
Ill 


it* 

ills 


CLASS. — Pharyngobranchii. 
The  Acrania  are  represented  by 
the  singular  animal  Amphioxus  or 
Lancelet.  It  is  about  two  inches  long, 
semi-transparent,  without  skull,  limbs, 
brain,  heart,  or  red  blood-corpuscles. 
It  has  for  a  skeleton  a  notochord  only. 
It  breathes  by  very  numerous  gill 
arches,  without  fringes,  and  the  water 
is  drawn  in  by  cilia,  which  line  the 
gill  slits.  The  embryo  develops  into 
a  gastrula  closely  resembling  that  of 
the  Invertebrates.  The  animal  lives 
in  the  sandy  bottom  of  shallow  parts 
of  the  ocean,  and  has  been  found  in 
the  Mediterranean  Sea,  in  the  Indian 
Ocean,  and  on  the  east  coast  of  North 
and  South  America. 

DIVISION  II. — Craniota. 
Vertebrates  with  a  distinct  skull. 

CLASS  I. — Pisces. 

Fishes  are  the  lowest  of  Verte- 
brates. They  fall  far  behind  the  rest 
in  strength,  intelligence,  and  sensi- 
bility. The  eyes,  though  large,  are 
almost  immovable,  bathed  by  no  tears, 
and  protected  by  no  lids.  Dwelling 
in  the  realm  of  silence,  ears  are  little 


VERTEBHATA. 


311 


needed,  and  such  as  they  have  are  without  external  parts, 
the  sound  being  obliged  to  pass  through  the  cranium. 
Taste  and  smell  are  blunted,  and  touch  is  nearly  confined 
to  the  lips. 

The  class  yields  to  no  other  in  the  number  and  variety 
of  its  forms.  It' includes  nearly  one  half  of  all  the  ver- 
tebrated  species.  So  great  is  the  range  of  variation,  it  is 
difficult  to  frame  a  definition  which  will  characterize  all  the 
finny  tribes.  It  may  be  said,  however,  that  Fishes  are  the 
only  backboned  animals  having  median  fins  (as  dorsal  and 
anal)  supported  by  fin-rays,  and  whose  limbs  (pectoral  and 
ventral  fins)  do  not  exhibit  that  threefold  division  (as  thigh, 
leg,  and  foot)  found  in  all  other  Vertebrates."9 

The  form  of  Fishes  is  admirably  adapted  to  the  element 
in  which  they  live  arid  move.  Indeed,  Nature  nowhere 
presents  in  one  class  such  elegance  of  proportions  with 
such  variety  of  form  and  beauty  of  color.  The  head  is 


ABC 

PIG.  283.— Scales  of  Fishes:  A,  cycloid  scale  (Salmon);  B,  ctenoid  scale  (Perch);  C, 
placoid  scale  (Ray) ;  D,  gauoid  scales  (Amblypteru^—a,  upper  surface  ;  b,  under 
surface,  showing  articulating  processes. 

disproportionately  large,  but  pointed  to  meet  the  resist- 
ance of  the  water.  The  neck  is  wanting,  the  head  be- 
ing a  prolongation  of  the  trunk.  The  viscera  are  closely 
packed  near  the  head,  and  the  long,  tapering  trunk  is  left 
free  for  the  development  of  muscles  which  are  to  move 
the  tail — the  instrument  of  locomotion.  The  biconcave 
vertebrae,  with  intervening  cavities  filled  with  elastic  gel- 
atine, are  designed  for  rapid  and  versatile  movements.  The 
body  is  either  naked,  as  in  the  Lamprey,  or  covered  with 


312  COMPARATIVE  ZOOLOGY. 

polished,  overlapping  scales,  as  in  the  Perch.  Rarely, 
as  in  the  Sturgeon,  it  is  defended  by  bony  plates,  ar  by 
minute,  hard  spines,  as  in  the  Shark.  Scales  with  smooth, 
circular  outline  are  called  cycloid ;  those  with  notched  or 
spiny  margins  are  ctenoid.  Enameled  scales  are  ganoid, 
and  those  with  a  sharp  spine,  like  those  of  the  Shark,  are 
placoid. 

The  vertical  fins  (dorsal,  anal,  and  caudal)  are  peculiar 
to  Fishes.  The  dorsal  vary  in  number,  from  one,  as  in 
the  Herring,  to  three,  as  in  the  Cod ;  and  the  first  dorsal 
may  be  soft,  as  in  the  Trout,  or  spiny,  as  in  the  Perch. 


FIG.  284.— Blue-fish  (Temnodon  saltator).    All  seas. 

If  the  dorsals  are  cut  off,  the  Fish  reels  to  and  fro.  The 
caudal  may  be  homocercal,  as  in  ordinary  species;  or  het- 
erocercal,  as  in  Sharks.  In  ancient  heterocercal  Fishes, 
the  tail  was  frequently  vertebrated.  The  pectoral  and 
ventral  fins  stand  for  the  fore  and  hind  limbs  of  other 
Vertebrates.  As  the  specific  gravity  of  the  body  is  greater 
than  that  of  the  water,  most  Fishes  are  provided  with 
an  air-bladder,  which  is  an  outgrowth  from  the  oesopha- 
gus. This  is  absent  in  such  as  grovel  at  the  bottom,  as 
the  Rays,  and  in  those,  like  the  Sharks,  endowed  with 
compensating  muscular  power. 

Fishes  have  no  prehensile  organ  besides  the  mouth. 
Both  jaws  are  movable.     The  teeth  are  numerous,  and 


VEKTEBUATA.  313 

may  be  recurved  spines,  as  in  the  Pike ;  flat  and  triangu- 
lar, witli  serrated  edges,  in  the  Shark ;  or  flat  and  tessel- 
lated in  the  Kay.  They  feed  principally  on  animal  mat- 
ter. The  digestive  tract  is  relatively  shorter  than  in  other 
Vertebrates.160  The  blood  is  red,  and  the  heart  has  rarely 
more  than  two  cavities,  an  auricle  and  a  ventricle,  both  on 
the  venous  side.  Ordinary  Fishes  have  four  gills,  which 
are  covered  by  the  operculum,  and  the  water  escapes  from 
an  opening  behind  this.  In  Sharks  there  is  no  operculum. 


FIG.  285.— Salmon  (Salmo  solar).    Both  hemispheres. 

and  each  gill  opens  separately.  The  brain  consists  of  sev- 
eral ganglia  placed  one  behind  the  other,  and  occupies  but 
a  small  part  of  the  cranial  cavity.  Its  average  weight  to 
the  rest  of  the  body  may  be  as  low  as  1  to  3000.  The 
eggs  of  bony  Fishes  are  naked  and  multitudinous,  some- 
times numbering  millions  in  a  single  spawn  ;  those  of  the 
Sharks  are  few,  and  protected  by  a  horny  shell. 

There  are  about  thirteen  thousand  species  of  Fishes,  of 
which  over  two  thirds  are  Teleostei.  There  are  two  sub- 
classes of  Pisces. 


314 


COMPARATIVE  ZOOLOGY. 


SUBCLASS  I. — Marsipobranchii. 

The  Lampreys  and  Hag-fish  have  a  persistent  noto- 

chord,  a  cartilaginous 
skull,  no  lower  jaw, 
a  round,  suctorial 
mouth,  horny  teeth, 
one  nasal -organ,  no 
scales,  limbs,  or  gill- 
.  286.—  Lamprey  (I'etromi/zon  Americanus).  At-  arcnes-  i-Q6  glJlS  ET8 

lantic-  pouch -like  (whence 

the  name  of  the  class),  and  open  separately.      They  are 
found  both  in  salt  and  fresh  water. 

SUBCLASS  II. — Pisces  Proper. 

The  true  Fishes  have  two  nasal  organs,  and  well-devel- 
oped jaws  and  gill-arches.  There  are  four  orders  : 

1.  Elasmobranchii,  having  a  cartilaginous  skeleton,  and 
a  skin  naked  or  with  placoid  scales.  The  gill-openings  are 
uncovered ;  and  the  mouth  is  generally  under  the  head. 
The  ventral  fins  are  placed  far  back;  the  pectorals  are 
large,  in  the  Kays  enormously  developed ;  and  the  tail  is 
heterocercal.  Such  are  the  Sharks,  Kays,  and  Chimaera, 


FIG.  2S7.— Shark  (Carcharias  vulgarin).    Atlantic. 


VERTEBRATA. 


315 


They  are  all  marine.    The  largest  Shark  found,  and  there- 
fore the  largest  Fish,  measured  forty  feet  in  length. 


FIG.  2SS.— Thorubuck  (Raia  clavata).    European  seas. 

2.  Ganoidei,  distinguished  by  their  enameled  scales  or 
bony  plates.     The  endoskeleton  is  usually  not  completely 
ossified;  the  ventral  fins  are  placed  far  back ;  and  the 
tail  is  generally  heterocercal.     The  gills  are  like  those  of 
the  bony  Fishes,  and  the  air-bladder  has  a  duct,  and  may 
aid  in  respiration.     This  was  one  of  the  largest  orders  in 
old  geological  history.     The  few  modern  representatives, 
as  the  Sturgeon,  Gar-pike,  Mud  (or  Dog)  Fish,  and  Polyp- 
terns^  are  essentially 

fresh-water. 

3.  Teleostei,     in- 
cluding all  the  com- 
mon Fishes   having 

a  boiiy  endoskeleton     FiG.289.-Gar-pike(£<^rfos'eu«o«ietts).  Lake  Ontario 


316 


COMPARATIVE  ZOOLOGY. 


FIG.  291.— Cat-fish,  or  Horned  Pout  (Pimelodus  catus) 
American  rivers. 


FIG.  290 — Sturgeon  (Acipenser  sturio).    Atlantic  coast. 

and  a  scaly  exoskeleton.     The  skull  is  extremely  com- 
plicated ;  the  upper  and  lower  jaws  are  complete,  and  the 

gills  are  comb -like 
or  tufted.  The  tail 
is  homocercal ;  the 
other  fins  are  varia- 
ble in  number  and 
position.  In  the 
soft  -  finned  Fishes, 
the  ventrals  are  ab- 
sent, as  in  the  Eels; 
or  attached  to  the 
abdomen,  as  in  the 
Salmons,  Herrings, 
Pikes,  and  Carps ;  or 
placed  under  the  throat,  as  in  the  Cod,  Haddock,  and 
Flounder.  In  the  spiny-finned  Fishes,  the  ventrals  are 
generally  under  or  in  front  of  the  pectorals,  and  the  scales 
ctenoid,  as  in  the  Perches,  Mullets,  and  Mackerels. 

4.  Dipnoi.  These  Fishes  connect  the  class  with  the 
Amphibia.  They  have  an  eel  -  like  body,  covered  with 
cycloid  scales;  an  embryonic  notochord  for  a  back-bone; 


FIG.  292. — Cod  (Morrhua  Americana).    Atlantic  coast. 


FIG.  293.— Protopterus  annectens;  one  fourth  natural  size.    African  rivers. 


VERTEBRATA,  317 

long,  ribbon-like  pectoral  and  ventral  fins,  set  far  apart ; 
two  auricles,  and  one  ventricle ;  and,  besides  gills,  a  cellu- 
lar air-bladder,  which  is  used  as  a  lung. 

The  representatives  are  Ceratodus  from  Australia,  Pro- 
topterus  from  Africa,  and  Lepidosiren  from  Brazil. 

CLASS  II.— Amphibia. 

These  cold-blooded  Vertebrates  are  distinguished  by 
having  gills  when  young,  and  true  lungs  when  adult. 
They  have  no  fin-rays,  and  the  limbs,  when  present,  have 
the  same  divisions  as  those  of  higher  animals.  The  skin 
is  soft,  and  generally  naked,  and  the  skeleton  is  ossified. 
The  skull  is  flat,  and  articulates  with  the  spinal  column 
by  two  condyles.  There  is  no  distinct  neck;  and  the  ribs 
are  usually  small  or  wanting.  The  heart  consists  of  two 
auricles  and  one  ventricle.  All  undergo  metamorphosis 
upon  leaving  the  egg,  passing  through  the  "  tadpole"  state. 
They  commence  as  water-breathing  larvae,  when  they  re- 
semble Fishes  in  their  respiration,  circulation,  and  locomo- 
tion. In  the  lowest  forms,  the  gills  are  retained  through 
life ;  but  all  others  have,  when  mature,  lungs  only,  the 
gills  disappearing.  The  cuticle  is  frequently  shed,  the 
mode  varying  with  the  habits  of  the  species.161  The  com- 
mon Frog,  the  type  of  this  class,  stands  intermediate  be- 
tween the  two  extremes  of  the  vertebrate  series ;  no  fun- 
damental part  is  excessively  developed. 

There  are  about  four 
hundred  and  fifty  liv- 
ing species,  grouped 
in  four  orders : 

1.  Urodela  have  a 
naked  skin,  a  tail,  and 
two  or  four  limbs. 
Some  retain  their  gills 

through     life,    as     the  ^-^- -Head and Gills^no&ranc/,,,, 


318 


COMPARATIVE  ZOOLOGY. 


Proteus  of  Austria,  MendbraricKua  of  the  eastern  United 
States,  and  the  two-legged  Mud-eel  (Siren)  of  South  Car- 
olina. Others  drop  their  gills,  and  always  have  four  limbs, 
as  the  aquatic  Newts  and  land  Salamanders.162  The  fore 
limbs  first  make  their  appearance  in  the  tadpole. 

2.  Labyrinthodontia^  now  extinct,  resembled  gigantic 
Salamanders,  except  in  their  complex  teeth  and  exoskele- 
ton  of  bony  plates. 

3.  CcBcilia  have  neither  tail  nor  limbs,  a  snake-like  form, 


They 


FIG.  295.  —  Proteus  anyuinits.    Europe. 

minute  scales  in  the  skin,  and  well-developed  ribs. 

are  confined  to  the  tropics. 

4.  BatracMa  include  all  the  well-known  tailless  Am- 

phibians, as  Frogs 
and  Toads.  They 
have  a  moist,  naked 
skin,  ten  vertebrae, 
and  no  ribs.  As  they 

FIG.  296.—  Red  Salamander  (Pseudotriton  ruber).         breathe  by  BWftlloW- 
United  States. 

ing  the  air,  they  can 
be  suffocated  by  holding  the  mouth  open.     They  have 


VERTEBRATA.  319 

four  limbs— the  hinder  the  longer,  and  the  first  developed. 
They  have  four  fingers  and  five  toes.  The  tongue  is  long, 
and,  fixed  by  its  an- 
terior end,  it  can  be 
rapidly  thrown  out  as 


laid  in  the  water  en- 
veloped in  a  glairy 
mass;  and  the  tadpoles 

resemble  the  Urodelans,  till  both  gills  and  tail  are  absorbed. 
Frogs  (Rana)  have  teeth  in  the  upper  jaw,  and  webbed 
feet ;  Toads  (Bufo)  are  higher  in  rank,  and  have  neither 
teeth  nor  fully  webbed  feet.  The  former  have  been 
known  to  live  sixteen  years,  and  the  latter  thirty-six. 

CLASS  III. — Reptilia. 

These  air-breathing,  cold-blooded  Vertebrates  are  dis- 
tinguished from  all  Fishes  and  Amphibians  by  never  hav- 
ing gills,  and  from  Birds  by  being  covered  with  horny 
scales  or  bony  plates.  The  skeleton  is  never  cartilaginous ; 
and  the  skull  has  one  occipital  condyle.  The  vertebras  are 
ordinarily  concave  in  front ;  and  the  ribs  are  well  devel- 
oped. With  few  exceptions,  all  are  carnivorous ;  and  teeth 
are  always  present,  except  in  the  Turtles,  where  a  horny 
sheath  covers  the  jaws.  The  teeth  are  never  fastened  in 
sockets,  except  in  Crocodiles.  The  jaws  are  usually  very 
wide.  The  heart  has  three  chambers,  save  in  Crocodiles, 
where  the  ventricle  is  partitioned.  But  in  all  cases  a 
mixture  of  arterial  and  venous  blood  is  circulated.  The 
lungs  are  large,  and  coarsely  cellular.  The  limbs,  when 
present,  are  provided  with  three  or  more  fingers  as  well 
as  toes. 

There  are  about  fifteen  hundred  species  and  four 
orders  of  living  Reptiles  :  the  first  two  have  horny 


320  COMPARATIVE  ZOOLOGY. 

scales,    the    others    have    bony    plates    combined    with 
scales. 

1.  Ophidia,)  or  Snakes,  are  characterized  by  the  absence 
of  visible  limbs;164  by  the  great  number  of  vertebrae, 
amounting  to  over  four  hundred  in  the  great  Serpents; 
by  a  corresponding  number  of  ribs,  but  no  sternum;  and 
no  true  eyelids,  the  eyes  being  covered  with  a  transparent 


FIG.  2<J8 — Adder,  or  Viper  (relicts  berlts).    England. 

skin.  The  tongue  differs  from  that  of  nearly  all  other 
Reptiles  in  being  bifid  and  extensile.  The  mouth  is  very 
dilatable.  The  skin  is  frequently  shed,  and  always  by  re- 
versing it.  Snakes  make  their  way  on  land  or  in  water 
with  equal  facility. 

As  a  rule,  the  venomous  Snakes,  as  Vipers  and  Rattle- 
snakes, are  distinguished  by  a  triangular  head  covered  with 
small  scales;  a  constriction  behind  the  head;  two  or  more 
fangs,  and  few  teeth;  small  eyes,  with  vertical  pupil;  and 
short,  thick  tail.  In  the  harmless  Snakes,  the  head  gradu- 
ally Mends  with  the  neck,  and  is  covered  with  plates ;  the 
teeth  are  comparatively  numerous  in  both  jaws ;  the  pu- 


VERTEBRATA. 


321 


FIG.  299 — a,  Head  of  a  Harmless  Suake  (upper  view) ;  &,  heads  of  various  Venomous 

Snakes. 

pil  is  round,  and  the  tail  tapering.     This  rule,  however, 
has  many  exceptions. 

2.  Lacertilia,  or  Lizards,  may  be  likened  to  Snakes  pro- 
vided with  four  limbs,  each  having  five  digits.185  The 
body  is  covered  with  horny  scales.  All  have  teeth,  which 
are  simple  in  structure;  and  the  halves  of  the  lower  jaw 
are  firmly  united  in  front,  while  those  of  Snakes  are 


Fio.  300.— Lizard  (Lacerta). 

21 


322 


COMPARATIVE  ZOOLOGY. 


loosely  tied  together  by  ligaments.  Nearly  all  have  a 
breast -bone,  and  the  eyes  (save  in  the  Gecko)  are  fur- 
nished with  movable  lids.  In  the  common  Lizards  and 
Chameleon,  the  tongue  is  extensile.  The  tail  is  usually 
long,  and  in  some  cases  each  caudal  vertebra  has  a  divis- 
ion in  the  middle,  so  that  the  tail,  when  grasped,  breaks 
off  at  one  of  these  divisions.  The  Chameleon  has  a  pre- 
hensile tail.  The  Iguana  is  distinguished  by  a  dewlap  on 
the  throat  and  a  crest  on  the  back.  Except  some  of  the 
Monitors  of  the  Old  World,  all  the  Lizards  are  terrestrial. 
3.  Chdonia,  or  Tortoises  and  Turtles,  are  of  anomalous 
structure.  The  skeleton  is  external,  so  as  to  include  not 
only  all  the  viscera,  but  also  the  whole  muscular  system, 
which  is  attached  internally;  and  even  the  limbs  are 


PIG.  301.— Hawk's-bill  Turtle  (Eretmochelys  imbncetta).    Tropical  Atlantic. 

inside,  instead  of  outside,  the  thorax.  The  exoskeleton 
unites  with  the  endoskeleton,  forming  the  carapace,  or 
case,  in  which  the  body  is  enclosed.  The  exoskeleton  con- 
sists of  horny  plates,  known  as  "tortoise-shell"  (in  the 
soft  Tortoises,  Trionyx,  this  is  wanting),  and  of  dermal 


VERTEBRATA.  323 

bones,  united  to  the  expanded  spines  of  the  vertebrae  and 
to  the  ribs,  making  the  walls  of  the  carapace.  The  ven- 
tral pieces  form  the 
plastron,  or  ster- 
num.1M  All  are 
toothless.  There 
are  always  four  stout 
legs;  and  the  order 
furnishes  the  only 

examples    Of    Vei'te-    FIQ.  302. —Box-tortoise  (Cistudo  Virginea).     United 

brates    lower    than  states. 

Birds  that  really  walk,  for  Lizards  and  Crocodiles  wrig- 
gle, and  drag  the  body  along.  There  are  no  teeth,  but  a 
horny  beak.  The  eggs  are  covered  with  a  calcareous 
shell. 

The  Sea -turtles,  as  the  edible  Green  Turtle  and  the 
Hawk's -bill  Turtle,  which  furnish  the  "tortoise-shell" 
of  commerce,  have  the  limbs  converted  into  paddles.  The 
fresh -water  forms,  represented  by  the  Snapping  Turtle 
(Chelydro),  are  amphibious,  and  have  palmated  feet.  Land 
Tortoises  (Testudo)  have  short,  clumsy  limbs,  fitted  for 
slow  motion  on  the  land ;  the  plastron  is  very  broad,  and 
the  carapace  is  arched  (while  it  is  flattened  in  the  aquatic 
species),  and  head,  legs,  and  tail  can  be  drawn  within  it. 
The  land  and  marine  species  are  vegetable-feeders ;  the 
others,  carnivorous. 

4.  Crocodilia,  the  highest  and  largest  of  Reptiles,  have 
also  two  exoskeletons — one  of  horny  scales  (epidermal),  and 
another  of  bony  plates  (dermal).  The  bones  of  the  skull 
are  firmly  united,  and  furnished  with  numerous  teeth,  im- 
planted in  distinct  sockets.  The  lower  jaw  extends  back 
of  the  cranium.  The  heart  has  four  cavities,  but  the  pul- 
monary artery  and  aorta  communicate  with  each  other,  so 
that  there  is  a  mixture  of  venous  and  arterial  blood. 
They  have  external  ear-openings,  closed  by  a  flap  of  the 


324 


COMPARATIVE  ZOOLOGY. 


skin,  and  eyes  with  movable  lids ;  a  muscular  gizzard ;  a 
long,  compressed  tail ;  and  four  legs,  with  feet  more  or 
less  webbed,  and  having  five  toes  in  front  and  four  be- 
hind. The  existing  species  are  confined  to  tropical  rivers, 
and  are  carnivorous.  The  eggs  are  covered  with  a  hard 
shell. 

There  are  three  representative  forms :  the  Gavial  of  the 
Ganges,  remarkable  for  its  long  snout  and  uniform  teeth ; 
the  Crocodiles,  mainly  of  the  Old  World,  whose  teeth  are 
unequal,  and  the  lower  canines  fit  into  a  notch  in  the  edge 
of  the  upper  jaw,  so  that  it  is  visible  when  the  mouth  is 


FIG.  303.— Alligator  (A.  Mississippiemis).    Southern  States. 

closed ;  and  the  Alligators  of  the  New  World,  whose  ca- 
nines, in  shutting  the  mouth,  are  concealed  in  a  pit  in*  the 
upper  jaw.  The  toes  of  the  Gavials  and  Crocodiles  are 
webbed  to  the  tip;  those  of  the  Alligators  are  not  more 
than  half-webbed. 

In  the  mediaeval  ages  of  geological  history,  the  class  of 
Reptiles  was  far  more  abundantly  represented  than  now. 
Among  the  many  forms  which  geologists  have  unearthed 
are  numerous  gigantic  Saurians,  which  cannot  be  classi- 
fied with  any  of  the  four  living  orders.  Such  are  the 
Ichthyosaurus,  Plesiosaurus,  Pterodactyle,  Megalosaurus, 
and  If/uanodon. 


VERTEBRATA.  325 

CLASS  IY. — Aves. 

Birds  form  the  most  clearly  defined  class  in  the  whole 
Animal  Kingdom.  The  Eagle  and  Hummer,  the  Ostrich 
and  Duck,  widely  as  they  seem  to  be  separated  by  size, 
form,  and  habits,  still  exhibit  one  common  type  of  struct- 
ure. On  the  whole,  Birds  are  more  closely  allied  to  Rep- 
tiles than  to  Mammals.  In  number,  they  approach  the 
Fishes,  ornithologists  having  determined  eight  thousand 
species,  or  more. 

A  Bird  is  an  air-breathing,  egg-laying,  warm-blooded, 
feathered  Vertebrate,  with  two  limbs  (legs)  for  perching, 
walking,  or  swimming,  and  two  limbs  (wings)  for  flying 
or  swimming.  Organized  for  flight,  it  is  gifted  with  a 
light  skeleton,  very  contractile  muscular  fibre,  and  a  res- 
piratory function  of  the  highest  development. 

The  skeleton  is  more  compact  than  those  of  Reptiles 
and  Mammals,  at  the  same  time  that  it  is  lighter,  and  the 
bones  are  harder  and  whiter.  It  contains  fewer  bones 
than  usual,  many  parts  being  anchylosed  together,  as  the 
skull-bones,  the  dorsal  vertebrae,  and  bones  of  the  tarsus 
and  metatarsus.  The  lumbar  vertebrae  are  united  to  the 
ilia.  The  neck  is  remarkably  long  (containing  from  nine 
to  twenty-four  vertebrae)  and  flexible,  enabling  the  head 
to  be  a  most  perfect  prehensile  organ.  The  ribs  are  gen- 
erally jointed  in  the  middle,  as  well  as  with  the  backbone 
and  sternum.  The  last,  where  the  muscles  of  flight  orig- 
inate, is  highly  developed.  The  skull  articulates  with 
the  spinal  column  by  a  single  condyle,  and  with  the  lower 
jaw,  not  directly,  as  in  Mammals,  but  through  the  inter- 
vention of  a  separate  bone,  as  in  Reptiles. 

All  Birds  always  have  four  limbs,  while  every  other 
vertebrate  class  shows  exceptions.  The  fore-limbs  are  fit- 
ted for  flight.  They  ordinarily  consist  of  nine  separate 
bones,  and  from  the  hand,  fore-arm,  and  hurnerus  are  de- 


326 


COMPARATIVE  ZOOLOGY. 


veloped  the  primary,  secondary,  and  tertiary  feathers  of 
the  wing.  The  hind-limbs  are  formed  for  progression  —  • 
walking,  hopping,  running,  paddling,  and  also  for  perch- 
ing and  grasping.  The  modifications  are  more  numerous 
and  important  than  those  of  the  bill,  wing,  or  tail.  There 
are  twenty  bones  ordinarily,  of  which  the  tibia  is  the  prin- 
cipal ;  but  the  most  characteristic  is  the  tarso-metatarsus, 

which  is  a  fusion  of 
the  lower  part  of  the 
tarsus  with  the  meta- 
tarsus. The  rest  of  the 
tarsus  is  fused  with 
the  tibia.  The  thigh 
is  so  short  that  the 
knee  is  never  seen  out- 
side of  the  plumage  ; 
the  first  joint  visible 
is  the  heel.167  Most 
Birds  have  four  toes 
f  e  d  c  b  a  (the  external  or  "  lit- 

FiG.304.—  Principal  Parts  of  a  Bird:  a,  primaries;            „  . 

&,  secondaries;  e,  spurious  wing;  d,  wing-coverts;  tie          t06  IS      always 

«,  tertiaries  ;  /,  throat,  or  jugulum  ;  g,  chin;   h,              ,  •       \  .  i 

bill;  the  meeting-Hue  between  the  two  mandi-  WaniingJ  ,  many  na\  6 


Or 


bles  is  the  commissure;  the  ridge  on  the  upper    foVQQ     the 

mandible  is  called  culmen  ;  that  of  the  lower, 

gonys  ;  the  space  between  the  base  of  the  upper    "big"    toe,   being   ab- 


mandible  and  the  eye  is  the  lore;  i,  forehead; 
crown  ;/,  scapular  feathers  ;  m,  back  ;  n,  meta- 
tarsus,  often  called  tarsus  or  tarso-metatarsus  ; 
o,  abdomen;  p,  rump;  q,  upper  tail-coverts  ;  r, 

lower  tan-coverts. 


SCllt  ;     Willie     the     Os- 

,    •    i     i          •> 

<™n  h^S   bllt  tWO,  an- 

swcriii     to  the  third 


and  fourth.  The  normal  number  of  phalanges,  reckoning 
from  the  hallnx,  is  2,  3,  4,  5.  The  toes  always  end  in 
claws. 

Birds  have  neither  lips  nor  teeth,  epiglottis  nor  dia- 
phragm. The  teeth  are  wanting,  because  a  heavy  masti- 
cating apparatus  in  the  head  would  be  unsuitable  for 
flight.  The  beak,  crop,  and  gizzard  vary  with  the  food. 
It  is  a  peculiarity  of  all  Birds,  though  not  confined  to 


VERTEBKATA.  327 

them,  that  the  generative  products  and  the  refuse  of  di- 
gestion are  all  discharged  through  one  common  outlet. 

The  sole  organs  of  prehension  are  the  beak  and  feet. 
The  circulation  is  double,  as  in  Mammals,  starting  from  a 
four -chambered  heart.  Respiration  is  more  complete 
than  in  other  Vertebrates.  The  lungs  are  fixed,  and  com- 
municate with  air-sacs  in  various  parts  of  the  body,  as 
along  the  vertebral  column,  and  also  with  the  interior  of 
many  bones,  as  the  humerus  and  femur,  which  are  usu- 
ally hollow  and  marrowless.168  Both  brain  and  cord  are 
much  larger  relatively  than  in  Reptiles;  the  cranium  is 
larger  in  proportion  to  the  face  ;  and  the  parts  of  the  brain 
are  not  situated  in  one  plane,  one  behind  the  other.  The 
cerebrum  is  round  and  smooth,  and  the  cerebellum  single- 
lobed.  The  ears  resemble  those  of  Crocodiles;  but  the 
eyes  are  well  developed,  and  protected  by  three  lids.  They 
are  placed  on  the  sides  of  the  head,  and  the  pupil  is  al- 
ways round.  The  sexes  generally  differ  greatly  in  plu- 
mage, in  some  cases  more  widely  than  two  distinct  species, 
but  the  coloration  of  either  sex  of  any  one  species  is  very 
constant. 

There  are  two  subclasses.1" 

SUBCLASS  I. — Ratitae  (Cur sores). 

This  small  and  singular  group  is  characterized  by  hav- 
ing no  keel  on  the  breastbone,  rudimentary  wings,  feath- 
ers with  disconnected  barbs,  and  stout  legs.  The  African 
Ostrich  has  two  toes,  the  Cassowary  three,  and  the  Apte- 
ryx  four. 

Its  representatives  are  the  Ostrich  (Struthio)  of  Africa 
and  Arabia,  South  American  Ostrich  (Rhea\  Cassowary 
(Oasuarius)  of  the  East  Indian  Archipelago  and  Austra- 
lia, Emu  (DromcGus)  of  Australia,  and  Apteryx,  or  Kiwi- 
kiwi,  of  New  Zealand.  Besides  these,  there  are  extinct 
gigantic  forms  from  Madagascar  (^pyornis)  and  from 


328 


COMPARATIVE  ZOOLOGY. 


New  Zealand  (Di- 
nornis,  or  Moa). 
This  singular  ge- 
ographical distri- 
bution, like  that 
of  the  Dipnoi  and 
Marsupials,  shows 
that  the  group  was 
once  widely  spread 
over  the  earth,  but 
is  now  greatly  re- 
stricted in  area. 

SUBCLASS  II. 
Carinatae. 

Birds  with  a 
keeled     sternum, 

FIG.  305.—  African  Ostrich  (Struthio  camelus).  an(J      with      devel- 

oped functional  wings. 

A.  AQUATIC  BIRDS. — Specially  organized  for  swimming; 
the  body  flattened,  and  cov- 
ered with  water-proof  cloth- 
ing— feathers  and  down  ;  the 
legs  short  (the  knees  being 
wholly  withdrawn  within  the 
skin  of  the  body),  and  set  far 
apart  and  far  back ;  the  feet 
webbed, and  hind-toe  elevated 
or  absent.  The  legs  are  al- 
ways feathered  to  the  heel  at 
least.  They  are  the  only  Birds 
whose  neck  is  sometimes 
longer  than  the  legs. 

1.  Pygopodes,  or  Divers.— 

mi  -I  e  L-\        t>      ±1  ^     Fl<^  306.—  Penguin  (Aptenndytes  Pe 

ihese  lowest  of  the  feathered  ta).  Faikiaud  islands. 


VERTEBRATA. 


329 


FIG.  307.  —  Loou  (Colymbus  torquatus).    North  America. 

tribe  have  very  short  wings  and  tail,  and  the  legs  are 
placed  so  far  back  that  they  are  obliged,  when  on  land,  to 
stand  nearly  bolt  upright.  They  are  better  fitted  for  div- 
ing than  for  flight,  or  even  swimming.  They  belong  to 
the  high  latitudes,  living  on  Fishes  mainly,  and  are  repre- 
sented by  the  Penguins,  Auks,  Loons,  and  Grebes. 

2.  Longipennes,  or  Gulls. — Distinguished  by  their  long. 


Pio.  308.— Tern  (Sterna). 


330 


COMPARATIVE  ZOOLOGY. 


FIG.  309.  — Cormorant  (Gracuhts). 

pointed  wings,  usually  long  tail,  and  by  great  powers  of 
flight.  They  are  all  carnivorous.  Such  are  the  Gulls  and 
Terns,  which  frequent  the  sea-coast,  lakes,  and  rivers ;  and 

the  Albatrosses  and  Pe- 
trels (the  largest  and 
smallest  of  web-footed 
Birds),  which  are  oce- 
anic. 

3.  Totipalmates,    or 
Corm  oran  ts. — Charac- 
terized by  a  long  bill, 
generally   hooked; 
\/fj   wings  rather  long;  and 
toes  long,  and  all  four 
joined  together   by 
broad    webs.      Throat 
generally    naked,  and 
furnished  with  a  sac.     The  majority  are  large  sea-birds, 


<j 


PIG.  310.-Wild  Goose  (Bernic 
United  States. 


Canadiensis). 


VERTEBRATA. 


331 


und  feed  on  Fishes,  Mollusks,  and  Insects.     Examples  are 
the  Cormorants,  Pelicans,  and  Gaimets. 

4.  Lamellirostres,  or  Ducks,  have  a  heavy  body,  moder- 
ate wings,  short  tail,  flattened  bill,  covered  by  a  soft  skin, 
X 


FIG.  311.  —Wild  Duck  (Anas  boschas).    North  America. 

with  ridges  along  the  edges.  Diet  more  commonly  vege- 
tarian than  animal.  The  majority  inhabit  fresh  water — 
as  the  Ducks,  Geese,  Swans,  and  Flamingoes. 

B.  TERRESTRIAL 
BtRDs—This  group 
exhibits  great  diver- 
sity of  structure ;  but 
all  agree  in  being  es- 
pecially terrestrial  in 
habit,  spending  most 
of  the  time  on  the 
ground,  not  on  trees  \ 
or  the  water,  al-  -^ 
though  many  of  them  "^j 

fly    and     Swim    Well.     FIQ.  312.—  Saudpiper  (Tringa  hypoleuca).   Euglnnd. 


332 


COMPARATIVE  ZOOLOGY. 


The  legs  are  long  or  strong,  and  the  knee  is  free  from  the 

body.  The  hind 
toe,  when  present, 
is  small  and  ele- 
vated. 

5.  Gr allator es,  or 
Waders. — These 
are  readily  distin- 
guished by  their 
long  and  bare  legs. 
Generally,  also,  the 
toes,  neck,  and  bill 
are  of  proportion- 
ate length,  and  the 
tail  short.  They 
feed  on  small  ani- 
mals, and,  with  a 
few  exception  s,  fre- 
quent the  banks  of  rivers.  In  flying,  their  legs  are 
stretched  out  behind,  while  in  most  other  Birds  they  are 
folded  under  the  body. 
Such  are  the  Rails, 
Cranes,  Herons,  Storks, 
Ibises,  Stilts,  Snipes, 
Sandpipers,  and  Plov- 
ers. 

6.  Rasores,m  Scratch- 
ers.  —  As  a  rule,  this 
order,  so  valuable  to  4% 
Man,  is  characterized 
by  a  short,  arched  bill ; 
short  and  concave 

Wings,  Unfitted  for  pro-    FIG.  314.-Rail,  or  Mars~h  Uen^llm  el 

tracted  flight;    stout  united  states. 

legs,  of  medium  length ;  and  four  toes,  the  three  in  front 


FIG.  313.— Heron  (Ardea). 


VERTEBRATA. 


333 


FIG.  315. — Prairie-chicken  (Cupidonia  cupido). 
Western  prairies. 


being  united  by  a  short  web,  and  terminating  in  blunt 

claws.     The  legs  are  usually  feathered  to  the  heel,  some- 
times (as  in  Grouse) 

to  the  toes.     The 

feathers  of  the  body 

are  large  and  coarse. 

The  males  generally 

have    gay    plumage, 

and  some  appendage 

to    the    head.      The 

nostrils   are   covered 

by  a  scale  or  valve. 

Their   main   food  is 

grain.     Such  are  the 

Grouse,  Partridges,  Turkeys,  Pheasants,  Poultry,  and  Cu- 

rassows.     To  these  may  be  added, 

7.  ColumbcB,  or  Pigeons  and  Doves,  although  they  stand 

intermediate  between  the 
terrestrial  and  perching 
Birds,  as  the  Flamingoes 
link  the  aquatic  and  terres- 
trial. They  differ  from  the 
typical  Rasores  in  having 
wings  for  prolonged  flight, 
and  slender  legs,  fitted  rath- 
er for  an  arboreal  life,  with 
toes  not  united,  and  the 
hind  toe  on  a  level  with 
the  rest. 

C.  AERIAL  BIRDS. — This 

FIG.  SIB. -Ring-dove  (Coi^iba  paiumbus).    highest  and  largest  group 
El'sland-  includes    all    those    Birds 

whose  toes  are  fitted  for  grasping  or  perching,  the  hind 

toe  being  on  a  level  with  the  rest.     The  knee  is  free  from 

the  body,  and  the  leg  is  generally  feathered  to  the  heel. 


334 


COMPARATIVP:  ZOOLOGY. 


The  wings  are  adapted  for  rapid  or  long  flight ;  and  they 
hop,  rather  than  walk,  on  the  ground.170  They  always 
live  in  pairs ;  and  the  young  are  hatched  helpless. 

8.  Raptores,  or  Birds  of  Prey,  differ  from  all  other 
Birds,  except  Parrots,  in  having  a 
strongly  hooked  bill  and  a  waxy 
membrane  (cere)  at  the  base  of  the 
upper  mandible ;  and  from  Parrots, 


FIG.  317 — Barn-owl  (Strix  flam- 
mea).    Both  hemispheres. 


FIG.  318.  —  Fish  -  hawk    ( Pandion 
United  States. 


in  having  three  toes  in  front  and  one  behind.  The  toes 
are  armed  with  long,  strong,  crooked  talons ;  the  legs  are 
robust;  and  the  wings  are  of  considerable  size,  adapted 


FIG.  319. — Golden  Eagle  (Aquila  chrysaetos).    North  America  and  Europe. 


VERTEBRATA.  335 

for  rapid  and  powerful  flight.  The  bill  is  stout  and  sharp, 
and  usually  toothed.  All  are  carnivorous.  The  female  is 
larger  than  the  male,  except  the  Condor.  There  are  two 


FIG.  320.— Foot  of  Parrot  and  Woodpecker. 

sections :  the  Diurnal,  whose  eyes  are  on  the  sides  of  the 
head,  wings  pointed,  and  metatarsus  and  toes  covered  over 
with  scales,  as  the  Vultures,  Kites,  Hawks,  Falcons,  and 
Eagles ;  the  Nocturnal,  whose  large  eyes  are  directed  for- 
ward, and  surrounded  by  radiating  feathers,  metatarsus 
feathered,  and  plumage  soft,  as  the  Owls. 

9.  Picarice. — This  polymorphic  group  has  hardly  any 
peculiarities  in  common.171  The  toes  are  usually  paired, 
two  in  front  and  two  behind. 

There  are  three  divisions  of  the  order:  Cypseli,  or 
Swifts,  Goat -suckers,  and  Humming-birds;  Cuculi,  or 
Cuckoos,  Kingfishers,  Trogons,  Toucans,  Hornbills,  and 
Hoopoes  ;  and  Pici,  or  Woodpeckers.  These  Birds  are  not 
musical,  and  only  ordinary  fliers.  They  feed  on  Insects 
or  fruit.  The  majority  make  nests  in  the  hollows  of  old 
trees ;  but  the  Cuckoos  lay  in  the  nests  of  other  Birds.  In 
climbing,  the  Woodpeckers  are  assisted  by  their  stiff  tail. 


336 


COMPARATIVE  ZOOLOGY. 


FIG.  321.— Trogon  elegans.    Central  America. 


VERTEBRATA. 


337 


10.  Psittaci,  or  Parrots. — These  birds  have  a  strong, 
arched  upper  bill,  ivith  a  cere  at  the  base,  a  fleshy,  thick, 


FIG.  322.— Head  of  a  Fly-catcher  (Tyrannux). 

and  movable  tongue,  and  paired  toes.     They  have,  usual- 
ly, brilliant  plumage.     They  live  in  trees  and  feed  on 
fruits.     Such  are  the  Parrots,  Paroquets,  and  Cockatoos. 
11.  Insessores,  or  Perchers. — This  order  is  the  most  nu- 


FIG.  323.—  Goat-sucker  (Caprimulgug). 


338 


COMPARATIVE  ZOOLOGY. 


Fi«.  324.— White- throa red  Sparrow  (Zonotrichia 
albicollis).    United  States. 


merous  and  varied  in  the  whole  class.    It  comprehends  all 
those  tribes  which  live  habitually  among  trees,  excepting 

the  Rapacious  and 
Climbing  Birds,  and 
whose  toes  —  three 
in  front,  and  one  be- 
hind —  are  eminently 
fitted  for  perching 
only.  The  legs  are 
slender,  and  seldom 
used  for  locomo- 
tion. 

They  are  divisible 
into    two    sections  : 

a.  Glamatores,  witli 
nothing  in  common 
but  a  harsh  voice.  In 
most,  the   tarsus   is 
enveloped  in  a  row 
of  plates,  which  meet 
behind  in  a  groove, 
and  the  bill  broad, 
and  bent  down   ab- 
ruptly   at    the    tip. 
The    typical    repre- 
sentatives    are    the 
Tyrant  Fly-catchers. 

b.  Oscines,  or  Song- 
sters, all   of    whom 
have  a  vocal  appara- 
tus,  though    all    do 

not     Sing.       The     ail- 
,.       . 

tenor  race  ot  the 
tarsus  is  one  continuous  plate,  or  divided  transversely 
into  large  scales  ;  and  the  plates  on  the  sides  meet  be- 


Fio.  325.—  Redstart  (Setophaga  rttiicilla). 
States. 


United 


FIG.  326.—  White-eyfd  Vireo  (Vireo  Noveboracensis). 
United  States. 


VERTEBRATA. 


339 


hind  in  a  ridge.     The  toes,  always  three  in  front   and 
one  behind,  are  on  the  same  level.     The  eggs  are  usu- 


Fio.  327 Kingfisher  (Ceryle). 

ally  colored.    Here  belong  the  Eavens,  Crows,  Jays,  Birds- 
of  -  Paradise,  Blackbirds,  Orioles,  Larks,  Sparrows,  Tan- 


FIG.  328.— Swallow  (Hirundo). 


340'  COMPARATIVE  ZOOLOGY. 

agers,  Wax-wings,  Swallows,  Wrens,  Warblers,  Thrushes, 

etc. 

CLASS  Y. — Mammalia. 

Mammals  are  distinguished  from  all  other  Vertebrates 

O 

by  any  one  of  the  following  characters:  they  suckle  their 
young ;  the  thorax  and  abdomen  are  separated  by  a  per- 
fect diaphragm ;  the  red  corpuscles  of  the  blood  have  no 
nucleus,  and  are  therefore  double-concave;  and  either  a 
part  or  the  whole  of  the  body  is  hairy  at  some  time  in 
the  life  of  the  animal.172 

They  are  all  warm-blooded  Vertebrates,  breathing  only 
by  lungs,  which  are  suspended  freely  in  the  thoracic  cav- 
ity ;  the  heart  is  four-chambered,  and  the  circulation  is 
double,  as  in  Birds ;  the  aorta  is  single,  and  bends  over 
the  left  bronchial  tube  ;  the  large  veins  are  furnished  with 
valves  ;  the  red  corpuscles  differ  from  those  of  all  other 
Vertebrates  in  having  no  nucleus  and  in  being  circular 
(except  in  the  Camel) ;  the  entrance  to  the  windpipe  is 
always  guarded  by  an  epiglottis ;  the  cerebrum  is  more 
highly  developed  than  in  any  other  class,  containing  a 
greater  amount  of  gray  matter  and  (in  the  higher  orders) 
more  convolutions;  the  cerebellum  has  lateral  lobes,  a 
mammalian  peculiarity,  and  there  is  a  corpus  callosum 
and  a  pans  varolii^  the  cranial  bones  are  united  by 
sutures,  and  they  are  fewer  than  in  cold-blooded  Verte- 
brates ;  the  skull  has  two  occipital  condyles,  a  feature 
shared  by  the  Amphibians  ;  the  lower  jaw  consists  of 
two  pieces  only  (often  united),  and  articulates  directly 
with  the  cranium;  with  four  exceptions  there  are  always 
seven  cervical  vertebrae  ;173  the  dorsal  vertebrae,  and  there- 
fore the  ribs,  vary  from  ten  to  twenty-four  ;  the  lumbar 
vertebrae  number  from  two  to  nine ;  the  sacral  from  three 
to  nine,  and  the  caudal  from  two  to  forty-six  ;  the  articu- 
lating surfaces  of  the  vertebrae  are  generally  flat ;  the 
fore-limbs  are  never  wanting,  and  the  hind-limbs  only  in 


VERTEBKATA. 


341 


a  few  aquatic  forms ;  excepting  the  Whales,  each  digit  car- 
ries a  nail,  claw,  or  hoof;  the  teeth  (always  present,  save 
in  certain  low  tribes)  are  planted  in 
sockets ;  the  mouth  is  closed  by  flexi- 
ble lips ;  an  external  ear  is  rarely  ab- 
sent ;m  the  eyes  are  always  present, 
though  rudimentary  in  some  burrow- 
ing animals  ;  they  are  viviparous  ; 
and,  finally,  and  perhaps  above  all, 
while  in  all  other  animals  the  embryo 
is  developed  from  the  nourishment 
laid  up  in  the  egg  itself,  in  Mammals 
it  draws  its  support,  almost  from 
the  beginning,  directly  from  the 
parent,  and,  after  birth,  it  is  sus- 
tained for  a  time  by  the  milk  se- 
creted by  the  mammary  glands. 
From  the  first,  therefore,  till  it  can 
care  for  itself,  the  young  Mam- 
mal is  in  vital  connection  with  the 
parent. 


Fio.  329.— Longitudinal  Section 
of  Human  Body  (theoretical) : 
a,  cerebro-ppinal  nervous  sys- 
tem ;  b,  cavity  of  nose ;  c,  cav- 
ity of  month  ;  d,  alimentary 
canal ;  e,  chain  of  sympathet- 
ic ganglia;  /,  heart;  g,  dia- 
phragm. 


FIG.  330. —Transverse  Section  of  Human  Body 
(theoretical):  a,  cerebro- spinal  nervous  axis 
contained  in  neural  tube ;  e,  chain  of  sympa- 
thetic ganglia  ;  d,  alimentary  canal ;  /,  heart ; 
ft,  haemal  tube. 


SUBCLASS  I. — Ornithodelphia. 

These  Mammals  have  but  one  outlet  for  the  intestine, 
urinary  and  reproductive  organs,  as  in  Birds.  They  are 
implacental.  There  is  but  one  order. 


342  COMPARATIVE  ZOOLOGY. 

1.  Monotrernata.  —  This   order   includes   two   singular 

O 

forms,  the  Duck-mole  (Ornithorhynchus}  and  Spiny  Ant- 
eater  (Echidna),  both  confined  to  the  Australian  conti- 
nent and  New  Guinea.  The  former  has  a  covering  of 
fur,  a  bill  like  that  of  a  Duck,  and  webbed  feet.  The  lat- 
ter is  covered  with  spines,  has  a  long,  toothless  snout,  like 
the  Ant-eater's,  and  the  feet  are  not  webbed.  Both  bur- 


Fio.  331.— Ornithorhyuchus. 

row,  and  feed  upon  Insects.  The  brain  is  smooth  in  the 
Ornithorhynchus,  and  folded  in  the  Echidna.  In  both, 
the  cerebral  hemispheres  are  loosely  united  by  transverse 
fibres,  and  do  not  cover  the  cerebellum  and  olfactory 

lobes.176 

SUBCLASS  II. — Didelphia. 

In  these  implacental  Mammals  the  uterus  is  divided 
into  two  parts. 

2.  Marsupialia  are  distinguished  by  the  fact  that  the 
young,  always  born  premature,  are  transferred  by  the 
mother  to  a  pouch  on  the  abdomen,  where  they  are  at- 
tached to  the  nipples,  and  the  milk  is  forced  into  their 
mouths  by  special  muscles.178  They  have  "  marsupial 


VERTEBRATA.  343 

bones"  projecting  from  the  pelvis,  which  may  serve  to 
support  the  pouch  ;  but  as  the  Monotremes  have  the  same 
bones,  but  no  pouch,  they  doubtless  have  some  other  func- 
tion. These  bones  are  peculiar  to  animals  having  no  pla- 
centa, namely,  to  Monotremes  and  Marsupials.  The  brains 
of  Marsupials  resemble  those  of  the  Monotremes,  except 
that  the  cerebrum  of  the  Kangaroo  covers  the  olfactory 
lobes.  All  have  the  four  kinds  of  teeth,  and  all  are  cov- 
ered with  fur,  never  with  spines  or  scales.  Except  the 
Opossums  of  America,  all  are  restricted  to  Australia  and 


FIG.  332. — Virginian  Opossum  (Didelphys  Virginiana), 

adjacent  islands.  The  Marsupials  are  almost  the  only 
Mammals  of  Australia,  a  few  species  of  Rodents  and  Bats 
being  the  only  placental  Mammals.  The  Marsupials  have 
here  developed  into  forms  corresponding  in  their  habits 
to  the  orders  of  placental  Mammals  in  the  rest  of  the 
world.  The  Kangaroos  take  the  place  of  the  large  her- 
bivores—  the  Ungulates.  The  Thylacinus  and  Dasyurus 
are  the  marsupial  carnivora.  Other  forms  are  squirrel- 
like  in  shape  and  habits,  and  still  others  are  insectivorous. 


COMPARATIVE  ZOOLOGY. 


SUBCLASS  III. — Monodelphia  or  Placental  Mammals. 
In  these  Mammals  the  young  are  connected  with  the 
mother  by  means  of  a  vascular  structure,  the  placenta,  by 
which  they  are  nourished.    They  are  born  in  a  relatively 
perfect  condition. 

3.  Edentata. — This  strange  order  contains  very  diverse 
forms,  as  the  leaf -eating  Sloths  and  the  insectivorous  Ant- 
eaters  and  Armadillos  of  South  America,  and  the  Pango- 
lin and  Orycteropus  of  the  Old  World.  The  gigantic  fos- 
sils, Megatherium  and 
Glyptodon,  belong  to 
this  group.  The  Sloths 

Fie.  333.-Sknll  of  the  Great  Ant-eater  Wyrme-  and  Ant-eaters  are  COV- 
cophaga  jubata) :  15,  uasal ;  11,  frontal ;  7,  pa-  6red  With  COarSC  hair; 
rietal;  3,  snperoccipital ;  2,  occipital  condyles; 

28,  tympanic ;  73,  lachrymal ;  32,  lower  mandi-   the  Armadillos  and  Pan- 
ble.    Teeth  wanting.  , . 

golins,  with  an  armor  of 

plates  or  scales.  The  Ant-eaters  and  Pangolins  are  strict- 
ly edentate,  or  toothless ;  the  rest  have  molars,  wanting, 
however,  enamel  and  roots.  In  general,  it  may  be  said 
that  the  order  includes  all  quadrupeds  having  separate, 
clawed  toes  and  no  incisors.  The  Sloths  are  arboreal ;  the 


FIG.  334.— Armadillo  (Dasj/pu»). 


VERTEBRATA. 


345 


others  burrow.  The  brain  is  generally  smooth ;  but  that 
of  the  Ant-eater  is  convoluted,  and  has  a  large  corpus  cal- 
losum;  but  in  all  the  cerebellum  and  part  of  the  olfac- 
tory lobes  are  exposed. 

4.  Rodentia,  or  Gnawers,  are  characterized  by  two  long, 
curved  incisors  in  each  jaw,  enameled  in  front,  and  per- 
petually growing ;  they  are  specially  formed  for  nibbling. 


Fio.  335.— Skull  of  a  Rodent  (Capybara) :  22,  premaxlllary  ;  21,  maxillary ;  20,  mo- 
lar ;  27,  sqnaniosal ;  73,  lachrymal ;  15,  nasal ;  11,  frontal ;  4,  occipital  processes, 
unusually  developed  ;  i,  incisors ;  a,  angle  of  lower  jaw. 

Separated  from  them  by  a  wide  space  (for  canines  are 
wanting),  are  the  flat  molars,  admirably  fitted  for  grind- 
ing. The  lower  jaw  has  longitudinal  condyles,  which 
work  freely  backward  and  forward  in  longitudinal  fur- 
rows. Nearly  all  have  clavicles ;  and  the  toes  are  clawed. 
The  cerebrum  is  nearly  or  quite  smooth,  and  covers  but  a 
small  part  of  the  cerebellum.  All  are  vegetarian. 


"W 

FIG.  336.— Incisor  Teeth  of  the  Hare. 


346 


COMPARATIVE  ZOOLOGY. 


More  than  one  half  of  all  known  Mammals  are  .Rodents. 
They  range  from  the  equator  to  the  poles,  over  every  con- 
tinent, over  mountains  and  plains,  deserts  and  woods.  The 


Pio.  337.—  Beaver  (Castor  Canadensix).    North  America. 

more  important  representatives  are  the  Porcupines,  Capy- 
baras,  Guinea-pigs,  Hares,  Mice,  Rats,  Squirrels,  and  Bea- 
vers. The  Capybara  and  Beaver  are  the  giants  of  the 
race. 

5.  Jnsectivora  are   diminutive,  insect -eating   animals, 
some,  as   the   Shrew,  being   the    smallest   of   Mammals. 

They  have  small,  smooth  brains, 
which,  as  in  the  preceding  orders, 
leave  uncovered  the  cerebellum 
and  olfactory  lobes.  The  molar 
teeth  bristle  with  sharp,  pointed 
cusps,  and  are  associated  with  ca- 

FIG.  338. — Shrew  Mous-e  (Sorex).        •  j     •       •  mi  i 

nines  and  incisors.     They  have  a 

long  muzzle,  short  legs,  and  clavicles.  The  feet  are  formed 
for  walking  or  grasping,  and  are  plantigrade,  five-toed,  and 
clawed.  The  Shrew,  Hedgehog,  and  Mole  are  examples. 

6.  Cheiroptera,  or  Bats,  repeat  the  chief  characters  of 
the  Insectivores;  but  some  (as  the  Flying-fox)  are  fruit- 
eaters,  and  have  corresponding  modifications  of  the  teeth. 
They  are  distinguished  by  their  very  long  fore -limbs, 


VEUTEBRATA. 


847 


which  are  adapted  for  flight,  the  fingers  being  immense- 
ly lengthened,  and  united  by  a  membranous  web.  The 
toes,  and  one  or  two  of  the  fingers,  are  armed  with  hooked 


FIG.  339.— Bat  ( Vtupcrtilio}. 

nails.  The  clavicles  are  remarkably  long,  and  the  ster- 
num is  of  great  strength  ;  but  the  whole  skeleton  is  ex- 
tremely light,  though  not  filled  with  air,  as  in  Birds.  The 
eyes  are  small,  the  ears  large,  and  the  sense  of  touch  is 
very  acute.  The  favorite  attitude  of  a  Bat  when  at  rest 
is  that  of  suspension  by  the  claws,  with  head  downward. 
Thev  are  all  nocturnal. 


Fift.  34fl.  —Skeleton  of  a  Bat. 


348  COMPARATIVE  ZOOLOGY. 

7.  Cetacea,  or  Whales,  have  the  form  and  life  of  Fishes, 
yet  they  possess  a  higher  organization  than  the  preceding 
orders.  They  have  a  broad  brain,  with  many  and  deep 
foldings;  the  foramen  magnum  of  the  skull  is  entirely 
posterior ;  the  whole  head  is  disproportionately  large,  and 
the  jaws  greatly  prolonged.  The  body  is  covered  with  a 
thick,  smooth  skin,  with  a  layer  of  fat  ("  blubber")  under- 


Pio.  341.—  Outline  of  the  Sperm-whale  (Physeter) :  a,  blow-hole  ;  &,  the  case  contain- 
ing spermaceti ;  c,  junk  ;  d,  bunch  of  the  neck— between  it  and  the  corner  of  the 
month  is  the  eye ;  ft,  hump ;  i,  ridge  ;  k,  the  small ;  /,  tail,  or  flukes.  Between 
the  dotted  lines  are  the  spiral  strips  of  blubber.  Maximum  length,  sixty  feet. 
South  Atlantic, 

neath ;  there  are  no  clavicles ;  the  hind-limbs  are  want- 
ing, and  the  front  pair  changed  to  paddles;  the  tail  ex- 
pands into  a  powerful,  horizontal  fin ;  neck  and  external 
ears  are  wanting ;  the  eyes  small,  with  only  two  lids ;  the 
nostrils  ("blow-holes") — double  in  the  Whale,  single  in 
the  Porpoise — are  on  the  top  of  the  head.  All  are  carniv- 
orous, and  essentially  marine,  a  few  Dolphins  only  be- 
ing found  in  the  great  rivers.  In  the  Whalebone  Whales, 
the  teeth  are  absorbed,  and  disappear  before  birth,  and 
their  place  is  supplied  by  horny  "  baleen"  plates.  "The 
Whale  feeds  by  putting  this  gigantic  strainer  into  opera- 
tion, as  it  swims  through  the  shoals  of  minute  Mollusks, 
Crustaceans,  and  Fishes,  w.hich  are  constantly  found  at  the 
surface  of  the  sea.  Opening  its  capacious  mouth,  and  al- 
lowing the  sea-water,  with  its  multitudinous  tenants,  to  fill 
the  oral  cavity,  the  Whale  shuts  the  lower  jaw  upon  the 
baleen  plates,  and,  straining  out  the  water  through  them, 
swallows  the  prey  stranded  upon  its  vast  tongue."  In  the 


VERTEBRATA. 


349 


FIG.  342.— Greenland  Whale  (Balcena  mysticetm).    North  Atlantic. 

other  Cetaceans  teeth  are  developed,  especially  in  Dol- 
phins and  Porpoises  ;  but  the  Sperm  Whale  has  them  only 
in  the  lower  jaw,  and  the  Narwhal  can  show  but  a  single 
tusk.  The  Dolphins  are  the  only  Mammals  having  no 
organ  of  smell. 

8.  Sirenia  resemble  the  Cetaceans  in  shape,  but  are  close- 
ly allied  to  the  hoofed  animals  in  organization.  They 
have  the  limbs  of  the  Whales,  and  are  aquatic ;  but  they 
are  herbivorous,  and  frequent  great  rivers  and  estuaries. 
They  have  two  sets  of  teeth,  the  Cetaceans  having  but 


350 


COMPARATIVE  ZOOLOGY. 


PIG.  343.— Troop  of  Dolphins,  with  Manatee  in  the  distance. 

one.  They  have  a  narrow  brain  ;  bristles  scantily  cover- 
ing the  body  ;  and  nostrils  placed  on  the  snout,  which  is 
large  and  fleshy.  The  living  representatives  are  the  Ma- 
natee, of  both  sides  of  the  tropical  Atlantic  Ocean,  and  the 
Dugong,  of  the  East  Indies. 

9.  Proboscidia.  —  This  race  of  giants,  now  nearly  ex- 
tinct, is  characterized  by  two  upper  incisors  in  the  form  of 
tusks,  mainly  composed  of  dentine  (ivory).  In  the  extinct 
Dinotherium  the  tusks  projected  from  the  lower  jaw;  and 
in  the  Mastodon,  from  both  jaws.  Canines  are  wanting. 
The  molars  are  few  and  large,  with  transverse  ridges  (Ele- 
phant) or  tubercles  (Mastodon).  The  cerebrum  is  large 
and  convoluted,  but  does  not  cover  the  cerebellum.  The 
skull  is  enormous,  the  size  arising  in  great  measure  from 
the  development  of  air -cavities  between  the  inner  and 
outer  plates.  The  nose  is  prolonged  into  a  flexible  trunk, 
which  is  a  strong  and  delicate  organ  of  prehension.  There 
are  four  massive  limbs,  each  with  five  toes  incased  in 


VERTEBRATA.  351 

broad,  shallow  hoofs,  and  also  with  a  thick,  tegnmentary 
pad.  The  knee  is  below  and  free  from  the  body,  as  in 
Monkeys  and  Men.  Clavicles  are  wanting.  The  body  of 
the  Elephant  is  nearly  naked  ;  but  the  Mammoth,  an  ex- 
tinct species,  had  a  covering  of  long  woolly  hair.  Ele- 
phants live  in  large  herds,  and  subsist  on  foliage  and  grass. 
There  are  but  two  living  species  :  the  Asiatic,  with  long 
head,  concave  forehead,  small  ears,  and  short  tusks  ;  and 
the  African,  with  round  head,  convex  forehead,  large  ears, 
and  long  tusks.177 

10.  Ungulata,  or  Hoofed  Quadrupeds.  —  This  large  or- 
der, comprehending  many  animals  most  useful  to  Man,  is 
distinguished  by  four  well-developed  limbs,  each  furnished 
with  not  more  than  four  complete  toes,  and  each  toe  in- 
cased in  a  hoof.  The  leg,  therefore,  has  no  prehensile 
power  ;  it  is  only  for  support  and  locomotion.  Clavicles 
are  wanting  ;  and  the  radius  and  ulna  are  so  united  as  to 
prevent  rotation.  There  are  always  two  sets  of  teeth,  i.  e.9 
milk-teeth  are  succeeded  by  a  permanent  set.  The  grind- 
ers have  broad  crowns.  As  a  rule,  all  are  herbivorous. 
The  brain  is  always  convoluted,  but  the  cerebellum  is 
largely  uncovered. 

Ungulates  are  divided  into  the  odd  and  even  toed.  a. 
The  Odd-toed,  as  the  three-toed  Rhinoceros  and  Tapir,178 
and  the  one-toed  Horse.179  The  first  is  distinguished  by 
its  very  thick  skin,  the  absence  of  canines,  and  one  or  two 
horns  on  the  nose.  The  Tapir  has  the  four  kinds  of  teeth, 
and  a  short  proboscis.  The  dental  formula  of  the  Horse 
is  — 


m    i     m  3_n    -  40 

3  —  3         1  —  l  3  —  3'          3  —  3  ~ 

The  canines  are  often  wanting  in  the  mare.  The  Horse 
walks  on  the  third  finger  and  toe.  The  metacarpals  and 
metatarsals  are  greatly  elongated,  so  that  the  wrist  and 
heel  are  raised  to  the  middle  of  the  leg.  b.  The  Even-toed 


352 


COMPARATIVE  ZOOLOGY. 


Ungulates— Hog,  Hippopotamus,  and  "Ruminants  —  have 
two  or  four  toes.     The  Hog  and  Hippopotamus  have  the 


FIG.  344. — Indian  Rhinoceros  (R.  unicornis). 

four  kinds  of  teeth,  and,  in  the  wild  state,  are  vegetarian. 
The  Ruminants  have  two  toes  on  each  foot,  enveloped  in 
hoofs  which  face  each  other  by  a  flat  side,  so  that  they  ap- 
pear to  be  a  single  hoof  split  or  "cloven."  Usually  there 
are  also  two  supplementary  hoofs  behind,  but  they  do  not 
ordinarily  touch  the  ground.  All  chew  the  cud,  and  have 
a  complicated  stomach.  They  have  incisors  in  the  lower 
jaw  only,  and  these  are  apparently  eight ;  but  the  two 
outer  ones  are  canines.180  The  molars  are  flat,  typical 
grinders.  The  dental  formula  of  the  Ox  is — 


With  few  exceptions,  as  the  Camel,  all  Ruminants  have 
horns,  which  are  always  in  pairs.  Those  of  the  Deer  are 
solid,  bony,  and  deciduous ;  those  of  the  Giraffe  and  An- 


VERTEBRATA. 


353 


JmRyr    a  In*          ^^a«ui 


FIG.  346.— Stag,  or  Red  Deer  (Cervus  daphus).    Europe. 

telope   are   solid,  horny,  and    permanent;    in    the   Goat, 
Sheep,  and  Ox  they  are  hollow,  horny,  and  permanent. 

II.  Carnivora,  or  Beasts  of  Prey,  may  be  recognized  by 
their  four  long,  curved,  acute,  canine  teeth,  the  gap  be- 
tween the  incisors  and  canines  in  the  upper  jaw  for  the 
reception  of  the  low- 
er canine,  and  molars 
graduating  from  a  tu- 
bercnlate  to  a  trench- 
ant form,  in  propor- 
tion as  the  diet  de- 
viates from  a  miscel- 
laneous kind  to  one 
strictlv  of  flesh.  The 
incisors,  except  in  the 

r   FIG.  346.—  Raccoon  (Procyon  lotor).    United  States. 

23 


354 


COMPARATIVE  ZOOLOGY. 


FIG.  347 Wolf  (Lupus  occidental™).    United  States. 


six   in    each   jaw.     There   are   always    two   sets.      The 
skull  is   comparatively  small,  the  jaws  are  shorter  and 

deeper  than  in  Un- 
gulates, and  there 
arenumerousbony 
ridges  on  the  in- 
side and  outside 
of  the  cranium — 
the  high  occipital 
crest  being  special- 
ly characteristic. 
The  cerebral  hem- 
ispheres are  joined 
by  a  large  corpus 
callosum,  but  the 
cerebellum  is  nev- 
er completely  cov- 
ered. Both  pairs 
of  limbs  are  well 
developed,  the 
front  being  pre- 
hensile; but  the 
clavicles  are  rudi- 
mentary. The  bu- 
rn erus  and  femur 
are  mainly  en- 
closed in  the  body. 
The  digits,  never 
less  than  four,  al- 
ways have  sharp 
and  pointed 

FIG.  349.—  Hed  Fox  (Vulpes  fulvus) .    United  States.        claWS  I81    The  bodv 

is  covered  with  abundant  hair. 

Carnivores  are  divided  according  to  the  modifications 
of  the  limbs:  a.  Pinnigrades,  having  short  feet  expanded 


FIG.  348. — Ermine- weasel   (Putorius  Noveboracen&is). 
United  States. 


VERTEBRATA.  355 

into  webbed  paddles  for  swimming,  the  hinder  ones  being 
bound  in  with  the  skin  of  the  tail.  Such  are  the  Seals, 
Walrus,  and  Eared  Seals,  or  Sea-lions,  b.  Plantigrades,  in 
which  the  whole,  or  nearly  the  whole,  of  the  hind-foot 
forms  a  sole,  and  rests  on  the  ground.  The  claws  are  not 
retractile ;  the  ears  are  small,  and  tail  short.  Bears,  Bad- 
gers, and  Raccoons  are  well-known  examples,  c.  Digiti- 
grades  keep  the  heel  raised  above  the  ground,  walking  on 
the  toes.  The  majority  have  long  tails.  Such  are  the 
Weasels,  Otters,  Civets,  Hyenas,  Foxes,  Jackals,  Wolves, 
Dogs,  Cats,  Panthers,  Leopards,  Tigexs,  and  Lions.  The 


FIG.  350.— Southeru  Sea-lion  (Otaria  jubata).    Antarctic  Ocean. 

last  five  differ  from  all  others  in  having  retractile  claws, 
and  the  radius  rotating  freely  on  the  ulna.  The  Cats 
have  thirty  teeth;  the  Dogs,  forty-two,  or  twelve  more 
molars.  In  the  former,  the  tongue  is  prickly;  in  the 
latter,  smooth. 

12.  Prosimii  or  Lemurs.  These  singular  mammals, 
sometimes  included  in  the  next  order,  have  affinities  with 
Kodents,  Insect! vora,  and  Primates.  They  are  covered 
with  soft  fur,  have  usually  a  long  tail,  pointed  ears,  fox- 
like  muzzle,  and  curved  nostrils.  They  walk  on  all  fours, 
and  the  thumb  and  great  toe  are  generally  opposable  to 
the  digits.  The  second  toe  has  a  long,  pointed  claw  in- 


356 


COMPARATIVE  ZOOLOGY. 


stead  of  a  nail.  The  cerebrum  is  relatively  small,  and 
flattened,  and  does  not  cover  the  cerebellum  and  olfactory 

lobes.182    They  are  found 
mainly  in  Madagascar. 

13.  Primates,  the  head 
of  the  kingdom,  are  char- 
acterized by  the  posses- 
sion of  two  hands  and 
two  feet.  The  thigh  is 
free  from  the  body,  and 
all  the  digits  are  fur- 
nished with  nails, the  first 

PIG.  351.— Lemur  (L.ruber).    Madagascar.         Oil  the  foot  enlarged  to  a 

"great  toe."  Throughout  the  order,  the  hand  is  eminently 
or  wholly  prehensile,  and  the  foot,  however  prehensile  it 
may  be,  is  always  locomotive.193  The  clavicles  are  perfect. 
The  eyes  are  situated  in  a  complete  bony  cavity,  and 
look  forward.  There  are  two  sets  of  teeth,  all  enamelled  ; 
and  the  incisors  number  four  in  each  jaw.  They  are 
divided  into  Monkeys  and  Apes,  and  Man. 

The  Monkeys  of  tropical  America  have,  generally,  a 
long,  prehensile  tail ;  the  nostrils  are  placed  far  apart, 
so  that  the  nose  is  wide  and  flat :  the  thumbs  and  great 
toes  are  fitted  for  grasping,  but  are  not  opposable  to  the 
other  digits ;  and  they  have  four  molars  more  than  the 
Apes  or  Man  —  that  is,  thirty -six  teeth  in  all.,  In  the 
Apes  of  the  Old  World  the  tail  is  never  prehensile:  and 
is  sometimes  wanting;  the  nostrils  are  close  together; 
both  thumbs  and  great  toes  are  opposable ;  and  the  teeth, 
though  numbering  the  same  as  Man's,  are  uneven  (the 
incisors  being  prominent,  and  the  canines  large),  and  the 
series  is  interrupted  by  a  gap  on  one  side  or  other  of 
the  canines.  Their  average  size  is  much  greater  than 
that  of  the  Monkeys,  and  they  are  not  so  strictly  arboreal. 
In  both  Monkeys  and  Apes,  the  cerebrum  covers  tho  cere- 


VERTEBKATA. 


357 


FIG.  352.— White-throated  Sapajou  (Cebus  hyjwlencus).    Central  America. 

bellu in.184  While  in  the  Monkeys  the  skull  is  rounded 
and  smooth,  that  of  the  Apes,  especially  those  coming 
nearest  to  Man — the  anthropoid,  or  long-armed,  Apes,  as 
Gorilla,  Chimpanzee,  Orang,  and  Gibbon — is  characterized 
by  strong  crests.  Monkeys  take  a  horizontal  position ; 

but  the  Apes  assume  a  semi- 
erect  attitude,  the  legs  being 
shorter  than  the  arms.  In 


FIG.  353.— Skull  of  Orang-utau  (Simia 
satyrus). 


FIG.  354.— Skull  of  Chimpanzee  (Troglo- 
dytes Niger). 


COMPARATIVE  ZOOLOGY. 

all  the  Primates  but  Man,  the  body  is  clothed  with  hair, 
which  is  generally  longest  on  the  back.  Several  Mon- 
keys and  Apes  have  a  beard,  as  the  Howler  and  Orang. 


PIG.  355.— Female  Orang-utan  (from  photograph).    Borneo. 

The  Orang  is  the  least  human  of  all  the  anthropoid 


FIG.  356. — Skeletons  of  Mail,  Chimpanzee,  aud  Oraug. 


VERTEBRATA. 


359 


Apes  as  regards  the  skeleton,  but  comes  nearest  to  Man 
in  the  form  of  the  brain.  The  Chimpanzee  approaches 
Man  more  closely  in  the  character  of  its  cranium  and 
teeth,  and  the  proportional  size  of  the  arms.  The  Gorilla 
is  most  Man-like  in  bulk  (sometimes  reaching  the  height 
of  live  feet  six  inches),  in  the  proportions  of  the  leg  to 
the  body  and  of  the  foot  to  the  hand,  in  the  size  of  the 
heel,  the  form  of  the  pelvis  and  shoulder-blade,  and  vol- 
ume of  brain. K* 

Man  differs  from  the  Apes  in  being  an  erect  biped. 
In  him,  the  vertebrate  type,  which  began  in  the  horizon- 
tal Fish,  finally  became  vertical.  No  other  animal  habit- 
ually stands  erect;  in  no  other  are  the  fore-limbs  used 
exclusively  for  head  -  purposes,  and  the  hind  pair  solely 
for  locomotion. 

His  limbs  are  naturally  parallel  to  the  axis  of  his  body, 
not  perpendicular.  They  have  a  near  equality  of  length, 
but  the  arms  are  always  somewhat  shorter  than  the  legs. 
In  all  the  great  Apes  the  arms  reach  below  the  knee,  and 
the  legs  of  the  Chimpanzee  and  Gorilla  are  relatively 
shorter  than  Man's. 

Man  only  has  a  finished  hand,  most  perfect  as  an  organ 
of  touch,  and  most  versatile.  Both  hand  and  foot  are 
relatively  shorter  than  in  the  Apes.  The  foot  is  planti- 


a  b 

Fio.  357.— Foot  (a)  and  Hand  (6)  of  the  Gorilla. 


360  COMPARATIVE  ZOOLOGY. 

grade;  the  leg  bears  vertically  upon  it;  the  heel  and 
great  toe  are  longer  than  in  other  Primates;  and  the 
great  toe  is  not  opposable,  but  is  used  only  as  a  fulcrum 
in  locomotion.  The  Gorilla  has  both  an  inferior  hand 
and  inferior  foot.  The  hand  is  clumsier,  and  with  a 
shorter  thumb  than  Man's;  and  the  foot  is  prehensile, 
and  is  not  applied  flat  to  the  ground.186 

The  scapular  and  pelvic  bones  are  extremely  broad, 
and  the  neck  of  the  femur  remarkably  long.  Man  is 
also  singular  in  the  double  carve  of  the  spine :  the  Ba- 
boon comes  nearest  to  Man  in  this  respect. 

The  human  skull  has  a  smooth,  rounded  outline,  ele- 
vated in  front,  and  devoid  of  crests.  The  cranium  great- 
ly predominates  over  the  face,  being  four  to  one;187  and 
no  other  animal  (except  the  Siamang  Gibbon)  has  a  chin. 

Man  stands  alone  in  the  peculiarity  of  his  dentition  : 
his  teeth  are  vertical,  of  nearly  uniform  height,  and  close 
together.  In  every  other  animal  the  incisors  and  canines 
are  more  or  less  inclined,  the  canines  project,  and  there 
are  vacant  spaces.188 

Man  has  a  longer  lobule  to  his  ear  than  any  Ape,  and 
no  muzzle.  The  bridge  of  his  nose  is  decidedly  convex; 
in  the  Apes  generally  it  is  flat. 

Man  has  been  called  the  only  naked  terrestrial  Mam- 
mal. His  hair  is  most  abundant  on  the  scalp;  never  on 
the  back,  as  in  the  Apes. 

Man  has  a  more  pliable  constitution  than  the  Apes,  as 
shown  by  his  world-wide  distribution.  The  animals  near- 
est him  soon  perish  when  removed  from  their  native  places. 

Though  Man  is  excelled  by  some  animals  in  the  acute- 
ness  of  some  senses,  there  is  no  other  animal  in  which  all 
the  senses  are  capable  of  equal  development.  He  only 
has  the  power  of  expressing  his  thoughts  by  articulate 
speech,  and  the  power  of  forming  abstract  ideas. 

Man  differs  from  the  Apes  in  the   absolute   size   of 


VERTEBRATA. 


361 


PIG.  358.— Australian  Savage. 

brain,  and  in  the  greater  complexity  and  less  symmetrical 
disposition  of  its  convolutions.  The  cerebrum  is  larger 
in  proportion  to  the  cerebellum  (being  as  8J  to  1),  and 
the  former  not  only  covers  the  latter,  but  projects  beyond 
it.  The  brain  of  the  Gorilla  scarcely  amounts  to  one 
third  in  volume  or  one  half  in  weight  of  that  of  Man. 


FIG.  359.— Skull  of  European.  FIG.  360.— Skull  of  Negro. 

Yet,  so  far  as  cerebral  structure  goes,  Man  differs  less 
from  the  Apes  than  they  do  from  the  Monkeys  and  Le- 
murs. The  great  gulf  between  Man  and  the  brute  is  not 
physical,  but  psychical.189 


362 


COMPARATIVE  ZOOLOGY. 


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ARRANGEMENT  OF   REPRESENTATIVE   FORMS.      363 


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COMPARATIVE  ZOOLOGY. 


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ARHANGEMENT  OF  REPRESENTATIVE  FOltMS.       367 


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Reptilia.  —  Having  lungs 
and  allantois. 

.  OPUIIUA.—  Body  elongated, 
and  ribs;  no  eyelids;  I 

.  LAOICRTILIA  —  Scaly;  lower 

.  CHKT.ONIA  —  Horny  and  bon 

CBOCOBILIA.  —  Covered  witt 
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ARRANGEMENT  OF  REPRESENTATIVE  FORMS.       369 


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r;    o.         ~ 


370 


COMPARATIVE  ZOOLOGY. 


THE  DISTRIBUTION  OF  ANIMALS.  371 


CHAPTER  XXIII. 

THE   DISTRIBUTION   OF   ANIMALS. 

LIFE  is  everywhere.  In  the  air  above,  the  earth  be- 
neath, and  the  waters  under  the  earth,  we  are  surrounded 
with  life.  Nature  lives :  every  pore  is  bursting  with  life ; 
every  death  is  only  a  new  birth,  every  grave  a  cradle. 
The  air  swarms  with  Birds,  Insects,  and  invisible1  animal- 
cules. The  waters  are  peopled  with  innumerable  forms, 
from  the  Protozoan,  millions  of  which  would  not  weigh  a 
grain,  to  the  Whale,  so  large  that  it  seems  an  island  as  it 
sleeps  upon  the  waves.  The  bed  of  the  sea  is  alive  with 
Crabs,  Shells,  Polyps,  Star-fishes,  and  Foraminifera.  Life 
everywhere — on  the  earth,  in  the  earth,  crawling,  creep- 
ing, burrowing,  boring,  leaping,  running. 

Nor  does  the  vast  procession  end  here.  The  earth  we 
tread  is  largely  formed  of  the  debris  of  life.  The  quarry 
of  limestone,  the  flints  which  struck  the  fire  of  the  old 
Revolutionary  muskets,  are  the  remains  of  countless  skele- 
tons. The  major  part  of  the  Alps,  the  Rocky  Mountains, 
and  the  chalk  cliffs  of  England  are  the  monumental  rel- 
ics of  by-gone  generations.  From  the  ruins  of  this  living 
architecture  we  build  our  Parthenons  and  Pyramids,  our 
St.  Peters  and  Louvres.  So  generation  follows  generation. 
But  we  have  not  yet  exhausted  the  survey.  Life  cradles 
within  life.  The  bodies  of  animals  are  little  worlds  hav- 
ing their  own  fauna  and  flora.  In  the  fluids  and  tissues, 
in  the  eye,  liver,  stomach,  brain,  and  muscles,  parasites  are 
found ;  and  these  parasites  often  have  their  parasites  liv- 
ing on  them. 


372  COMPARATIVE  ZOOLOGY. 

"Great  fleas  have  little  fleas  and  smaller  fleas  to  bite  'em ; 
And  these  again  have  other  fleas,  and  so  ad  infinitum." 

Thus  the  ocean  of  life  is  inexhaustible.  It  spreads  in 
every  direction,  into  time  past  and  present,  flowing  every- 
where, eagerly  surging  into  every  nook  and  corner  of  cre- 
ation. On  the  mountain-top,  in  the  abysses  of  the  Atlan- 
tic, in  the  deepest  crevice  of  the  earth's  crust,  we  find 
traces  of  animal  life.  Nature  is  prodigal  of  space,  but 
economical  in  filling  it.190 

Animals  are  distributed  over  the  globe  according  to 
definite  laws,  and  with  remarkable  regularity. 

Each  of  the  three  great  provinces,  Earth,  Air,  and  Wa- 
ter, as  also  every  continent,  contains  representatives  of  all 
the  classes;  but  the  various  classes  are  unequally  repre- 
sented. Every  great  climatal  region  contains  some  species 
not  found  elsewhere,  to  the  exclusion  of  some  other  forms. 
Every  grand  division  of  the  globe,  whether  of  land  or 
sea,  each  zone  of  climate  and  altitude,  has  its  own  fauna. 
And,  in  spite  of  the  many  causes  tending  to  disperse  ani- 
mals beyond  their  natural  limits,  each  country  preserves 
its  peculiar  zoological  physiognomy. 

The  space  occupied  by  the  different  groups  of  animals 
is  often  inversely  as  the  size  of  the  individuals.  Compare 
the  Coral  and  Elephant. 

The  fauna  now  occupying  a  separate  area  is  closely  al- 
lied to  the  fauna  which  existed  in  former  geologic  times. 
Thus,  Australia  has  always  been  the  home  of  Marsupials, 
and  South  America  of  Edentates. 

It  is  a  general  rule  that  groups  of  distinct  species  are 
circumscribed  within  definite,  and  often  narrow,  limits. 
Man  is  the  only  cosmopolitan ;  yet  even  he  comprises  sev* 
eral  marked  races,  whose  distribution  corresponds  with  the 
great  zoological  regions.  The  natives  of  Australia  are  as 
grotesque  as  the  animals.  Certain  brutes  likewise  have  a 
great  range :  thus,  the  Puma  ranges  from  Canada  to  Pata- 


THE  DISTRIBUTION  OF  ANIMALS.  373 

gonia;  the  Musk  -  rat,  from  the  Arctic  Ocean  to  Florida; 
the  Ermine,  from  Behring's  Straits  to  the  Himalayas ;  and 
the  Hippopotamus,  from  the  Nile  and  Niger  to  the  Orange 
Eiver.191 

Frequently,  species  of  the  same  genus,  living  side  by 
side,  are  widely  different,  while  there  is  a  close  resem- 
blance between  forms  which  are  antipodes.  The  Mud-eel 
of  South  Carolina  and  Menobranchus  of  the  Northern 
States  have  their  relatives  in  Japan  and  Austria.  The 
American  Tapir  has  its  mate  in  Sumatra ;  the  Llama  is 
related  to  the  Camel,  and  the  Opossum  to  the  Kangaroo. 

The  chief  causes  modifying  distribution  are  tempera- 
ture, topography,  ocean  and  wind  currents,  humidity  and 
light.  To  these  may  be  added  the  fact  that  animals  are 
ever  intruding  on  each  other's  spheres  of  existence.  High 
mountain -ranges,  wide  deserts,  and  cold  currents  in  the 
ocean  are  impassable  barriers  to  the  migration  of  most 
species.  Thus,  river- fish  on  opposite  sides  of  the  Andes 
differ  widely,  and  the  cold  Peruvian  current  prevents  the 
growth  of  coral  at  the  Galapagos  Islands.  So  a  broad 
river,  like  the  Amazons,  or  a  deep,  narrow  channel  in  the 
sea,  is  an  effectual  barrier  to  some  tribes.  Thus,  Borneo 
belongs  to  the  Indian  region,  while  Celebes,  though  but  a 
few  miles  distant,  is  Australian  in  its  life.  The  faunae  of 
North  America,  on  the  east  coast,  west  coast,  and  the  open 
plains  between,  are  very  different. 

Animals  dwelling  at  high  elevations  resemble  those  of 
colder  latitudes.  The  same  species  of  Insects  are  found 
on  Mount  Washington,  and  in  Labrador  and  Greenland. 

The  range  does  not  depend  upon  the  powers  of  loco- 
motion. The  Oyster  extends  from  Halifax  to  Charles- 
ton, and  the  Snapping  -  turtle  from  Canada  to  the  equa- 
tor ;  while  many  Quadrupeds  and  Birds  have  narrow  hab- 
itats. 

The  distribution  of  any  group  is  qualified  by  the  nature 


374  COMPARATIVE  ZOOLOGY. 

of  the  food.  Carnivores  have  a  wider  range  than  herbi- 
vores. 

Life  diminishes  as  we  depart  from  the  equator  north 
or  south,  and  likewise  as  we  descend  or  ascend  from  the 
level  of  the  sea. 

The  zones  of  geography  have  been  divided  by  zoolo- 
gists into  narrower  provinces.  Five  vertical  regions  in 
the  sea  have  been  recognized:  the  Littoral,  extending  be- 
tween tide -marks;  the  Laminarian,  from  low  water  to 
fifteen  fathoms;  the  Coralline,  from  fifteen  to  twenty 
fathoms ;  the  deep-sea  Coral,  from  fifty  to  one  hundred 
fathoms ;  and  the  Bathybian,  from  one  hundred  fathoms 
down ;  but  since  life  has  been  found  to  extend  to  great 
depths  in  the  ocean — as  great  as  three  thousand  fathoms 
— these  divisions  are  of  little  importance.  Every  marine 
species  has  its  own  limits  of  depth.  It  would  be  quite  as 
difficult,  said  Agassiz,  for  a  Fish  or  a  Mollusk  to  cross 
from  the  coast  of  Europe  to  the  coast  of  America  as  for  a 
Reindeer  to  pass  from  the  arctic  to  the  antarctic  regions 
across  the  torrid  zone.  Marine  animals  congregate  mainly 
along  the  coasts  of  continents  and  on  soundings.  The 
meeting -place  of  two  maritime  currents  of  different  tem- 
peratures, as  on  the  Banks  of  Newfoundland,  favors  the 
development  of  a  great  diversity  of  Fishes. 

Every  great  province  of  the  ocean  contains  some  repre- 
sentatives of  all  the  subkingdoms.  Deep-sea  life  is  diver- 
sified, though  comparatively  sparse.  Examples  of  all  the 
five  invertebrate  divisions  were  found  in  the  Bay  of  Bis- 
cay, at  the  depth  of  two  thousand  four  hundred  and  thir- 
ty-five fathoms.192 

Distribution  in  the  sea  is  influenced  by  the  temperature 
and  composition  of  the  water  and  the  character  of  the 
bottom.  The  depth  acts  indirectly  by  modifying  the 
temperature.  Northern  animals  approach  nearer  to  the 
equator  in  the  sea  than  on  the  land,  on  account  of  cold 


THE  DISTRIBUTION  OF  ANIMALS.  375 

currents.  The  heavy  aquatic  Mammals,  as  Whales,  Wal- 
ruses, Seals,  and  Porpoises,  are  mainly  polar. 

The  land  consists  of  the  following  somewhat  distinct 
areas :  the  Neotropic,  comprising  South  America,  the  West 
Indies,  and  most  of  Mexico ;  the  Nearctic,  including  the 
rest  of  America ;  the  Pulaearctic,  composed  of  the  eastern 
continent  north  of  the  Tropic  of  Cancer,  and  the  Hima- 
layas ;  the  Ethiopian,  or  Africa  south  of  the  Tropic  of 
Cancer;  the  Oriental,  or  India,  the  southern  part  of  Chi- 
na, the  Malay  Peninsula,  and  the  islands  as  far  east  as 
Java,  Borneo,  and  the  Philippine  Islands ;  and  the  Aus- 
tralian, or  the  eastern  half  of  the  Malay  Islands  and  Aus- 
tralia. These  are  Mr.  Wallace's  regions.  Other  writers 
unite  the  northern  parts  of  both  hemispheres  into  one 
region,  and  the  Oriental  with  the  Ethiopian  regions. 

Life  in  the  polar  regions  is  characterized  by  great  uni- 
formity, the  species  being  few  in  number,  though  the 
number  of  individuals  is  immense.  The  same  animals  in- 
habit the  arctic  portions  of  the  three  continents ;  while  the 
antarctic  ends  of  the  continents,  Australia,  Cape  of  Good 
Hope,  and  Cape  Horn,  exhibit  strong  contrasts.  Those 
three  continental  peninsulas  are,  zoologically,  separate 
worlds.  In  fact,  the  whole  southern  hemisphere  is  pecul- 
iar. Its  fauna  is  antique.  Australia  possesses  a  strange 
mixture  of  the  old  and  new.  South  America,  with  newer 
Mammals,  has  older  Reptiles;  while  Africa  has  a  rich 
vertebrate  life,  with  a  striking  uniformity  in  its  distribu- 
tion. Groups,  old  geologically  and  now  nearly  extinct, 
are  apt  to  have  a  peculiar  distribution  ;  as  the  Edentata  in 
South  America,  Africa,  and  India  ;  the  Marsupials  in  Aus- 
tralia and  America;  the  Ratitae  in  South  America,  Africa, 
Australia,  and  New  Zealand. 

In  the  tropics,  diversity  is  the  law.  Life  is  more  varied 
and  crowded  than  elsewhere,  and  attains  its  highest  devel- 
opment. 


376  COMPARATIVE  ZOOLOGY. 

The  New-world  fauna  is  old-fashioned,  and  inferior  in 
rank  and  size,  compared  with  that  of  the  eastern  con- 
tinents. 

As  a  rule,  the  more  isolated  a  region  the  greater  the 
variety.  Oceanic  islands  have  comparatively  few  species, 
but  a  large  proportion  of  endemic  or  peculiar  forms.  Ba- 
trachiaiis  are  absent,  and  there  are  no  indigenous  terrestrial 
Mammals.  The  productions  are  related  to  those  of  the 
nearest  continent.  When  an  island,  as  Britain,  is  sepa- 
rated from  the  mainland  by  a  shallow  channel,  the  mam- 
malian life  is  the  same  on  both  sides. 

Protozoans,  Coelenterates,  and  Echinoderms  are  limited 
to  the  waters,  and  nearly  all  are  marine.  Sponges  are 
mostly  obtained  from  the  Grecian  Archipelago  and  Baha- 
mas, but  species  not  commercially  valuable  abound  in  all 
seas.  Coral-reefs  abound  throughout  the  Indian  Ocean 
and  Polynesia,  east  coast  of  Africa,  Eed  Sea,  and  Persian 
Gulf,  West  Indies,  and  around  Florida ;  and  Corals  which 
do  not  form  reefs  are  much  more  widely  distributed,  be- 
ing found  as  far  north  as  Long  Island  Sound  and  Eng- 
land. Crinoids  have  been  found,  usually  in  deep  sea,  in 
very  widely  separated  parts  of  the  world — off  the  coast  of 
Norway,  Scotland,  and  Portugal,  and  near  the  East  and 
West  Indies.  The  other  Echinoderms  abound  in  almost 
every  sea :  the  Star-fishes  chiefly  along  the  shore,  the  Sea- 
urchins  in  the  Laminarian  zone,  and  the  Sea-slugs  around 
coral-reefs.  Worms  are  found  in  all  parts  of  the  world, 
in  sea,  fresh  water,  and  earth.  They  are  most  plentiful 
in  the  muddy  or  sandy  bottoms  of  shallow  seas.  Living 
Brachiopods,  though  few  in  number,  occur  in  tropical, 
temperate,  and  arctic  seas,  and  from  the  shore  to  great 
depths.  Polyzoa  have  both  salt  and  fresh  water  forms, 
and  Annelids  include  land  forms,  as  the  Earth-worm  and 
some  Leeches. 

Mollusks  have  a  world -wide  distribution  over  land  and 


THE  DISTRIBUTION  OF  ANIMALS.  377 

sea.  The  land  forms  are  restricted  by  climate  and  food, 
the  marine  by  shallows  or  depths,  by  cold  currents,  by 
a  sandy,  gravelly,  or  mud  bottom.  The  Bivalves  are  also 
found  on  every  coast  and  in  every  climate,  as  well  as  in 
rivers  and  lakes,  but  do  not  flourish  at  the  depth  of  much 
more  than  two  hundred  fathoms.  The  fresh-water  Mus- 
sels are  more  numerous  in  the  United  States  than  in 
Europe,  and  west  of  the  Alleghanies  than  east.  The  sea- 
shells  along  the  Pacific  coast  of  America  are  unlike  those 
of  the  Atlantic,  and  are  arranged  in  five  distinct  groups : 
Aleutian,  Californian,  Panamic,  Peruvian,  and  Magel- 
lanic.  On  the  Atlantic  coast,  Cape  Cod  and  Cape  Hatte- 
ras  separate  distinct  provinces.  Of  land  Snails,  Helix  has 
an  almost  universal  range,  but  is  characteristic  of  North 
America,  as  Bulimus  is  of  South  America,  and  Achatina 
of  Africa.  The  Old  World  and  America  have  no  species 
in  common,  except  a  few  in  the  extreme  north. 

The  limits  of  Insects  are  determined  by  temperature 
and  vegetation,  by  oceans  and  mountains.  There  is  an 
insect -fauna  for  each  continent,  and  zone,  and  altitude. 
The  Insects  near  the  snow-line  on  the  sides  of  mountains 
in  the  temperate  region  are  similar  to  those  in  polar  lands. 
The  Insects  on  our  Pacific  slope  resemble  those  of  Europe, 
while  those  near  the  Atlantic  coast  are  more  like  those  of 
Asia.  Not  half  a  dozen  Insects  live  in  the  sea. 

The  distribution  of  Fishes  is  bounded  by  narrower  lim- 
its than  that  of  other  animals.  A  few  tribes  may  be  called 
cosmopolitan,  as  the  Sharks  and  Herrings ;  but  the  species 
are  local.  Size  does  not  appear  to  bear  any  relation  to 
latitude.  The  marine  forms  are  three  times  as  numerous 
as  the  fresh-water.  The  migratory  Fishes  of  the  northern 
hemisphere  pass  to  a  more  southern  region  in  the  spring, 
while  Birds  migrate  in  the  autumn. 

Living  Reptiles  form  but  a  fragment  of  the  immense 
number  which  prevailed  in  the  Middle  Ages  of  Geology. 


378 


COMPARATIVE  ZOOLOGY. 


Being  less  under  the  influence  of  Man,  they  have  not  been 
forced  from  their  original  habitats.  None  are  arctic. 
America  is  the  most  favored  spot  for  Frogs  and  Salaman- 
ders, and  India  for  Snakes.  Australia  has  no  Batrachians, 
and  two  thirds  of  its  Snakes  are  venomous.  In  the  United 


FIG.  361.— Zoues  of  Animal  Life. 

States,  only  twenty-two  out  of  one  hundred  and  seventy- 
six  are  venomous.  Frogs,  Snakes,  and  Lizards  occur  at 
elevations  of  over  fifteen  thousand  feet.  Crocodiles,  and 
most  Lizards  and  Turtles,  are  tropical. 

Swimming  Birds,  which  constitute  about  one  fourteenth 
of  the  entire  class,  form  one  half  of  the  whole  number  in 


THE  DISTRIBUTION  OF  ANIMALS.  379 

Greenland.  As  we  approach  the  tropics,  the  variety  and 
number  of  land  Birds  increase.  Those  of  the  torrid  zone 
are  noted  for  their  brilliant  plumage,  and  the  temperate 
forms  for  their  more  sober  hues,  but  sweeter  voices.  In- 
dia and  South  America  are  the  richest  regions.  Hum- 
mers, Tanagers,  Orioles,  and  Toucans  are  restricted  to  the 
New  World.  Parrots  are  found  in  every  continent  ex- 
cept Europe ;  and  Woodpeckers  occur  everywhere,  save  in 
Australia. 

The  vast  majority  of  Mammals  are  terrestrial;  but  Ce- 
taceans and  Seals  belong  to  the  sea,  Otters  and  Beavers  de- 
light in  lakes  and  rivers,  and  Moles  are  subterranean.  As 
of  Birds,  the  aquatic  species  abound  in  the  polar  regions. 
Marsupials  inhabit  two  widely  separated  areas  —  America 
and  Australia.  In  the  latter  continent  they  constitute 
two  thirds  of  the  fauna,  while  all  placental  Mammals,  ex- 
cept Bats  and  a  few  Kats  and  Squirrels,  are  wanting. 
Excepting  a  few  species  in  South  Africa  and  South  Asia, 
Edentates  are  confined  to  tropical  South  America.  The 
equine  family  is  indigenous  to  South  and  East  Africa  and 
Southern  Asia.  In  North  America,  Rodents  form  about 
one  half  the  number  of  Mammals;  there  are  but  three 
species  in  Madagascar.  Ruminants  are  sparingly  repre- 
sented in  America.  Carnivores  flourish  in  every  zone 
and  continent.  The  prehensile-tailed  Monkeys  are  strict- 
ly South  American ;  while  the  anthropoid  Apes  belong 
to  the  west  coast  of  Africa,  and  to  Borneo  and  Sumatra. 
Both  Monkeys  and  Apes  are  most  abundant  near  the  equa- 
tor ;  in  fact,  their  range  is  limited  by  the  distribution  of 
palms. 


NOTES. 


1  The  complete  and  elaborate  natural  history  of  a  single  species  or  limited 
group  is  called  a  Monograph,  as  Darwin's  "Monograph  of  the  Cirripedia." 
A  Memoir  is  not  so  formal  or  exhaustive,  giving  mainly  original  investiga- 
tions of  a  special  subject,  as  Owen's  "  Memoir  on  the  Gorilla." 

2  Before  the  time  of  Linna3us,  the  Lady-bug,  e.  g.,  was  called  "the  Cocci- 
nella  with  red  coleopters  having  seven  black  spots."     He  called  it  Coccinella 
septem-punctata. 

3  Mandino  (1315)  and  Berenger  (1518),  of  Bologna,  and  Vesalius,  of  Brus- 
sels (1550),  were  the  first  anatomists.     Circulation  of  the  blood  discovered 
by  Harvey,  1616.     The  lacteals  discovered  by  Asellius,  1622,  and  the  lym- 
phatics by  Rudbek,  1650.    Willis  made  the  first  minute  anatomy  of  the  brain 
and  nerves,  1664.     The  red  blood-corpuscles  were  discovered  by  Leeuwen- 
hoek  and  Malpighi,  1675.     Infusoria  first  observed  by  Leeuwenhoek,  1675; 
the  name  given  by  Miiller,  1786.     Svvammerdam  was  the  founder  of  Ento- 
mology, 1675.     Comparative  anatomy  was  first  cultivated  by  Perrault,  Pec- 
quet,  Duverney,  and  Mery,  of  the  Academy  ot  Paris,  the  latter  part  of  the 
seventeenth  century.     Malpighi,  the  founder  of  structural  anatomy,  was  the 
first  to  demonstrate  the  structure  of  the  lungs  and  skin,  1 690.     About  the 
same  time,  Kay  and  Willoughby  first  classified  Fishes  on  structural  grounds. 
Foraminifers  were  seen  by  Beccarius  one  hundred  and  fifty  years  ago;  but 
their  true  structure  was  not  demonstrated  till  1835,  by  Dujardin.     Peyssonel 
published  the  first  elaborate  treatise  on  Corals,  1727.    Haller  was  the  first  to 
distinguish  between  contractility  and  sensibility,  1757.     White  blood-corpus- 
cles discovered  by  Hewson  in  1775.    Spallanzani  was  the  first  to  demonstrate 
the  true  nature  of  the  digestive  process,  1780.    Cuvier  and  Geoffroy,  in  1797, 
proposed  the  first  natural  classification  of  animals.     Before  that,  all  Inverte- 
brates were  divided  into  Insects  and  Worms.    Lamarck  was  the  first  to  study 
Mollusks,  1800;  before  him,  attention  was  confined  to  the  shell.     He  sepa- 
rated Spiders  from  Insects  in  1812.     The  law  of  correlation  enunciated  by 
Cuvier,  1826.     Von  Baer  was  the  founder  of  Embryology,  establishing  the 
doctrine  omnia  ex  ovo,  1827 ;  but  the  first  researches  in  Reproduction  were 
made  by  Fabricius  about  1600.  and  by  Harvey  in  1651.     Wolff,  in  the  last 
century,  was  the  pioneer  in  observing  the  phenomena  of  Development,     Sars 
first  observed  alternate  generation,  !833.     Dumerii  is  considered  the  father 
of  Herpetolngy,  and  Owen  of  Odontology.      Schleiden  and  Schwann  pub- 
lished their  celebrated  researches  in  cell-structure,  1841;  but  Bichat,  who 
died  1802,  was  the  founder  of  Histology.     Protoplasm  was  discovered  bjf 
Dujardin  in  1 835,  and  called  Sarcode. 


382  NOTES. 

*  This  twofold  division  is  arbitrary.  No  essential  distinction,  founded  on 
the  nature  of  the  elements  concerned,  or  the  laws  of  their  combination,  can 
be  made;  and  so  many  so-called  organic  substances,  as  urea,  ammonia,  alco- 
hol, tartaric  and  oxalic  acids,  alizarine,  and  glucose,  have  been  prepared  by 
inorganic  methods,  that  the  boundary-line  is  daily  becoming  fainter,  and  may 
in  time  vanish  altogether.  We  would  here  utter  our  protest  against  the  in- 
'troduction  of  any  more  terms  like  inorganic,  invertebrate,  acephalous,  etc., 
which  express  no  qualities. 

6  Even  the  works  of  nearly  all  animals  proceed  in  curves. 

6  London  Quarterly  Review,  January,  1869,  p.  142.    It  is  true  of  any  great 
primary  group  of  animals,  as  of  a  tree,  that  it  is  much  more  easy  to  define 
the  summit  than  the  base. 

7  De  Bary  on  "  Myxomycetse  ;"  Darwin  on  "  Carnivorous  Plants." 

8  "There  are  certain  phenomena,  even  among  the  higher  plants,  connected 
with  the  habits  of  climbing  plants  and  with  the  functions  of  fertilization, 
which  it  is  very  difficult  to  explain  without  admitting  some  low  form  of  a 
general  harmonizing  and  regulating  function,  comparable  to  such  an  obscure 
manifestation  of  reflex  nervous  action  as  we  have  in  Sponges  and  in  other 
animals  in  which  a  distinct  nervous  system  is  absent." — Prof.  WYVILLE 
THOMSON'S  Introductory  Lecture  at  Edinburgh, 

9  "  If  nature  had  endowed  us  with  microscopic  powers  of  vision,  and  the 
integuments  of  plants  had  been  rendered  perfectly  transparent  to  our  eyes, 
the  vegetable  world  would  present  a  very  different  aspect  from  the  apparent 
immobility  and  repose  in  which  it  is  now  manifested  to  our  senses." — HUM- 
BOLDT'S  Cosmos,  i.,  341. 

10  See  Gray's  "Structural  Botany,"  p.  350 ;  Rolleston's  "Forms  of  Ani- 
mal Life,"  p.  143. 

11  "Life  has  been  called  the  vital  force,  and  it  has  been  suggested  that  it 
may  be  found  to  belong  to  the  same  category  as  the  convertible  forces,  heat 
and  light.     Life  seems,  however,  to  be  more  a  property  of  matter  in  a  certain 
state  of  combination  than  a  force.     It  does  no  work,  in  the  ordinary  sense." 
— Prof.  WYVILLE  THOMSON. 

12  There  was  a  time  in  our  history  when  a  single  membrane  discharged 
all  the  functions  of  life  —  digesting,  respiring,  secreting.      The  separation 
of  a  heart,  lung,  stomach,  liver,  etc.,  for  special  duty  was  an  after-considera- 
tion. 

13  The  vegetable  cell  has  usually  two  concentric  coverings:   cell-wall  and 
primordial  utricle.      In  animal  cells  the  former  is  wanting,  the  membrane 
representing  the  utricle.     As  a  general  fact,  animal  cells  are  smaller  than 
vegetable  cells. 

14  Cells  are  not  the  sources  of  life,  as  once  thought,  but  are  the  products 
of  protoplasm.     "  They  are  no  more  the  producers  of  vital  phenomena  than 
the  shells  scattered  in  orderly  lines  along  the  sea-beach  are  the  instruments 
by  which  the  gravitation  -  force  of  the  moon  acts  upon  the  ocean.      Like 
these,  the  cells  mark  only  where  the  vital  tides  have  been  and  how  they 
have  acted." — Prof.  HUXLEY. 

15  Many  of  the  bones  of  the  skull  are  preceded  by  membrane — hence  called 
membrane-bones. 


NOTES.  383 

16  In  the  heart,  the  muscular  fibres  are  striated,  yet  involuntary;  but  the 
sarcolemma  is  wanting. 

17  Other  names  are  medullary  sheath  and  white  substance  of  Schwann. 

18  We  may,  however,  infer  that  the  animal  functions  are  not  absolutely 
essential  to  the  vegetative,  from  the  facts  that  plants  digest  without  mus- 
cles or  nerves,  and  that  nutrition  takes  place  in  the  embryo  long  before  the 
nerves  have  been  developed. 

19  This  is  not  strictly  true,  for  the  Elm  and  Oak,  the  Trout  and  Alligator, 
do  reach  a  maximum  size. 

20  Scorpions  and  Spiders  properly  feed  upon  the  juices  of  their  victims 
after  lacerating  them  with  their  jaws,  but  fragments  of  Insects  have  been 
found  in  their  stomachs. 

21  The  real  tongue  forms  the  floor  of  the  mouth,  and  is  found  as  a  distinct 
part  in  a  few  Insects,  as  the  Crickets. 

22  In  the  Marsipobranchii,  it  is  circular  or  oval. 

23  The  mouth  of  the  Whale  is  exceptional,  the  walls  not  being  dilatable. 
The  act  of  sucking  is  characteristic  of  all  young  Mammals,  hence  the  need 
of  lips. 

24  The  Ant-eater  has  two  callous  ridges  in  the  mouth,  against  which  the 
insects  are  crushed  by  the  action  of  the  tongue. 

35  The  baleen  plates  do  not  represent  teeth ;  for  in  the  embryo  of  the 
Whale  we  find  minute  calcareous  teeth  in  both  jaws,  which  never  cut  the 
gum.  The  whalebone  is  a  peculiar  development  of  hair  in  the  palate,  and 
under  the  microscope  it  is  seen  to  be  made  up  of  fibres  which  are  hollow 
tubes. 

26  The  "  tusks"  of  the  Elephant  are  prolonged  incisors  ;  those  of  the  Wal- 
rus, Wild  Boar,  and  Narwhal  are  canines. 

37  "I  was  one  day  talking  with  Prof.  Owen  in  the  Ilunterian  Museum, 
when  a  gentleman  approached,  with  a  request  to  be  informed  respecting  the 
nature  of  a  curious  fossil  which  had  been  dug  up  by  one  of  his  workmen. 
As  he  drew  the  fossil  from  a  small  bag,  and  was  about  to  hand  it  for  exam- 
ination, Owen  quietly  remarked,  'That  is  the  third  molar  of  the  under- 
jaw  of  an  extinct  species  of  rhinoceros.'"  —  LEWES'S  Studies  in  Animal 
Life. 

3S  This  gap  or  interspace,  so  characteristic  of  the  inferior  Mammals,  is 
called  diastema.  It  is  wanting  in  the  extinct  Anoplotherium,  is  hardly  per- 
ceptible in  one  of  the  Lemurs,  and  is  not  found  in  Man. 

29  In  the  Spermaceti-whale,  the  teeth  are  fixed  to  the  gum. 

:0  The  Iguana  among  Reptiles,  and  Fishes  with  pavement-teeth,  approach 
the  Mammals  in  this  respect. 

31  This  movement  is  called  peristaltic  or  vermicular,  and  characterizes  all 
the  successive  movements  of  the  alimentary  canal. 

-3  Fishes  and  Amphibians  have  no  saliva,  but  a  short  gullet.  Birds  are 
aided  by  a  sudden  upward  jerk  of  the  head. 

31  Fishes  and  Reptiles  have  no  pharynx  proper,  the  nostrils  and  glottis 
opening  into  the  mouth. 

34  This  movement  of  the  pharynx  and  oesophagus  is  wholly  involuntary. 
Liquids  are  swallowed  in  exactly  the  same  way  as  solids. 


384  NOTES. 

36  The  few  animals  in  which  the  digestive  cavity  is  wanting  are  calleA 
agattric,  and  agree  in  having  a  very  simple  structure.  Such  are  some  Ento- 
zoa  (as  Tape- worm)  and  unicellular  Protozoa  (as  Gregarina).  They  absorb 
the  juices,  already  prepared,  by  the  physical  process  of  endosmose.  There 
are  other  minute  organisms  which  seem  to  be  able  to  extract  the  necessary 
elements,  C  H  O  N,  from  the  medium  in  which  they  live. 

36  The  cavity  of  a  Sponge  is  perhaps  homologous  with  the  digestive  cavity, 
but  ia  not  functionally  such.  Each  cell  lining  it  does  its  own  digestion,  tak- 
ing the  food  from  the  water  circulating  in  the  cavity. 

"Nothing  is  more  curious  and  entertaining  than  to  watch  the  neatness 
and  accuracy  with  which  this  process  is  performed.  One  may  see  the  rejected 
bits  of  food  passing  rapidly  along  the  lines  upon  which  these  pedicellariae 
occur  in  greatest  number,  as  if  they  were  so  many  little  roads  for  the  con- 
veying away  of  the  refuse  matters ;  nor  do  the  forks  cease  from  their  labor 
till  the  surface  of  the  animal  is  completely  clean  and  free  from  any  foreign 
substance." — AGASSIZ'S  Sea-side  Studies. 

88  In  the  larva  of  the  Bee,  the  anal  orifice  is  wanting. 

39  The  length  of  the  canal  in  Insects  is  not  so  indicative  of  the  habits  as  in 
Mammals.     Thus,  it  is  nearly  as  long  and  more  complicated  in  the  carnivo- 
rous Beetles  than  in  the  honey-sipping  Butterflies. 

40  The  object  of  this  is  unknown.     It  does  not  occur  in  the  Oyster. 

41  In  the  Nautilus,  this  is  preceded  by  a  capacious  crop. 

42  In  the  Shark,  this  is  impossible,  owing  to  a  great  number  of  fringes  in 
the  gullet  hanging  down  towards  the  stomach. 

43  At  the  beginning  of  the  large  intestine  in  the  Lizards  (and  in  many  Ver- 
tebrates above  them,  especially  the  vegetarian  orders),  there  is  a  blind  sue, 
called  caecum. 

44  The  Crocod'ile  is  said  to  swallow  stones  sometimes,  like  Birds,  to  aid 
the  gastric  mill. 

*5  In  the  crop  of  the  common  Fowl,  vegetable  food  is  detained  sixteen 
hours,  or  twice  as  long  as  animal  food.  The  Dormouse,  among  Mammals, 
has  an  approach  to  a  crop. 

46  In  Invertebrates,  the  gizzard,  when  present,  is  situated  between  the  crop 
and  the  true  stomach  ;  in  Birds,  it  comes  after  the  stomach. 

47  The  Tape-worm  has  no  digestive  apparatus,  but  absorbs  the  already  di- 
gested food  of  its  host.     This  is  no  exception  to  the  rule.     The  chemical 
preparation  of  the  food  has  preceded  its  absorption. 

48  We  find  the  most  abundant  saliva  in  those  Mammals  that  feed  on  herbs 
and  grain,  but  its  action  on  starch  is  extremely  feeble. 

49  It  is  probable  that  the  digestive  part  of  the  alimentary  canal  in  all 
animals  manifests   a  similar  mechanical  movement.      It  is  most  remark- 
able in  the  gizzard  of  a  fowl,  which  corresponds  to  the  pyloric  end  of 
the  human  stomach.     This  muscular  organ,  supplying  the  want  of  a  mas- 
ticatory apparatus  in  the  head,  is  powerful  enough  to  pulverize  not  only 
grain,  but  even  pieces  of  glass  and   metal.      This  is  done   by  two  hard 
muscles  moving  obliquely  upon  each  other,  aided  by  gravel  purposely  swal- 
lowed by  the  bird.     The  grinding  may  be  heard  by  means  of  the  stetho- 
scope. 


NOTES.  385 

53  Chyle  is  opnque  in  carnivores ;  more  or  less  transparent  in  all  other  Ver- 
tebrates, as  in  Birds,  since  the  food  does  not  contain  fatty  matter. 

Si  In  Fishes,  the  villi  are  few  or  wanting.  Jn  Man,  they  number  about 
10,000  to  the  square  inch. 

°a  Except,  perhaps,  the  tendons,  ligaments,  epidermis,  etc. 

53  The  phenomenon  produced  by  these  properties  conjointly,  capillary  at- 
traction and  diffusion,  is  called  endosmosis. 

6*  The  blood  is  colorless  also  in  the  muscular  part  of  Fishes.  That  of 
Birds  is  of  the  deepest  red.  The  coloring  matter  of  the  red  blood  in  worms 
is  not  in  the  corpuscles,  but  in  the  plasma. 

55  Coagulation  may  be  artificially  arrested  by  common  salt.     Arterial  blood 
coagulates  more  rapidly  than  venous.     The  disposition  of  the  red  corpuscles 
in  chains,  or  rouleaux,  does  not  occur  within  the  blood-vessels.     The  cause 
has  not  been  discovered. 

56  The   corpuscles   of  Invertebrates  are  usually  colorless,  even  when  the 
Mood  is  tinged. 

57  Except  during  the  foetal  life.     The  corpuscles  of  the  Camel  are  non- 
nucleated,  as  in  other  Mammals.     If  the  transparent  fluid  from  a  boil  be 
examined  with  a  microscope,  it  will  be  seen  to  be  almost  composed  of  col- 
orless corpuscles,  showing  their  use  in  repairing  injuries. 

58  There  are  no  valves  in  the  veins  of  Fishes,  Reptiles,  and  Whales,  and 
few  in  Birds. 

59  Capillaries  are  wanting  in  the  epidermis,  nails,  hair,  teeth,  and  cartilages. 
Hence,  the  epidermis,  for  example,  when  worn  out  by  use,  is  not  removed  by 
the  blood,  like  other  tissues,  but  is  shed. 

60  A  part  of  the  blood,  however,  in  going  from  the  capillaries  to  the  heart, 
is  turned  aside  and  made  to  pass  through  the  liver  and  kidneys  for  purifica- 
tion.    This  is  called  the  portal  circulation,  and  exists  in  all  Vertebrates,  ex- 
cept that  in  Birds  and  M;tmm:ils  it  is  confined  to  the  liver. 

61  Two  in  the  higher  Mammals,  three  in  the  lower  Mammals,  Birds,  and 
Keptiles.     They  are  called  vence  catve. 

62  Tricuspid  in  Mammals,  triangular  in  Birds. 

63  The  pulse  of  a  Hen  is  140;  of  a  Cat,  110  to  120;  of  a  Dog,  90  to  100; 
and  of  an  Ox,  25  to  42. 

64  The  bivalve  Brachiopods  breathe  by  delicate  arms  about  the  mouth,  and 
by  the  "  mantle." 

65  The  air-bladder,  found  in  most  Fishes,  is  another  rudiment  of  a  lung, 
although  it  is  used,  not  for  respiration,  but  for  altering  the  specific  gravity 
of  the  Fish.     In  the  Gar-pike  of  our  Northern  lakes,  it  very  closely  resem- 
bles a  lung,  having  a  cellular  structure,  a  tracheal  tube,  and  a  glottis.     It  is 
here  functional.     The  gills  represent  lungs  only  in  function;  they  are  totally- 
distinct  parts  of  the  organism. 

66  In  the  human  lungs  they  number  600,000,000,  each  about  TJ7  of  an 
inch  in  diameter,  with  an  aggregate  area  of  132  square  feet.     The  thickness 
of  the  membrane  between  the  blood  and  the  air  is  33^  of  an  inch.     The 
lungs  of  Carnivores  are  more  highly  developed  than  those  of  Herbivores.     In 
the  Manatee,  they  are  not  confined  to  the  thorax,  but  extend  down  nearly  to 
the  tail. 

25 


386  NOTES. 

67  Crocodiles  are  the* only  Reptiles  whose  nostrils  open  in  the  throat  behind 
the  palate,  instead  of  directly  into  the  mouth-cavity.     This  enables  the  Croc- 
odile to  drown  its  victim  without  drowning  itself;  for,  by  keeping  its  snout 
above  water,  it  can  breathe  while  its  mouth  is  wide  open. 

68  A  rudimentary  diaphragm  is  seen  in  the  Crocodile  and  Ostrich. 

69  The  poison-glands  of  venomous  Serpents  and  the  silk-vessels  of  Cater- 
pillars are  considered  to  be  modified  salivary  glands.     Birds,  Snakes,  and 
Cnrtilaginous  Fishes  have  no  urinary  bladder. 

70  Since  the  weight  of  a  full-grown  animal  remains  nearly  uniform,  it  must 
lose  as  much  as  it  receives;   that  is,  the  excretions,  including  the  solid  resid- 
uum ejected  from  the  intestinal  canal,  equal  the  food  and  drink. 

71  Other  names  for  derm  are,  cutis,  corium,  enderon,  and  true  skin;  and 
for  epidermis,  cuticle,  ecderon,  and  scarf-skin.     The  derm  is  often  so  inti- 
mately blended  with  the  muscles  that  its  existence  as  a  distinct  layer  is  not 
easily  made  out.     Even  in  Infusoria,  we  find  the  tunic  double,  an  outside 
cuticula  lined  by  a  soft  cortical  layer ;  and  in  Jelly-fishes,  naturalists  distin- 
guish an  ectoderm,  endoderm,  and  mesoderm. 

72  See  Fig.  148.    Papilla?  are  scarcely  visible  in  the  skin  of  Reptiles  and  Birds. 

73  The  animal  basis  of  this  structure  is  chitine,  a  peculiar  horn-like  substance 
found  in  the  hard  parts  of  all  the  articulated  animals. 

74  The  shell  is  always  an  epidermal  structure,  even  when  apparently  internal. 
The  horny  "  pen"  of  the  squid,  the  "  bone"  of  the  Cuttle-fish,  and  the  cal- 
careous spot  on  the  back  of  the  Slug  are  only  concealed  under  a  fold  of  the 
mantle.      So  the  shell  of  the  common  Unio,  or  fresh-water  clam,  is  covered 
with  a  brownish  or  greenish  membrane,  which  is  the  outer  layer  of  the  epider- 
mis.    Where  the  mantle  covers  the  lips  of  a  shell,  as  in  most  of  the  large  sea- 
snails,  or  where  its  folds  cover  the  whole  exterior,  as  in  the  polished  Cowry, 
the  epidermis  is  wanting,  or  covered  up  by  an  additional  layer. 

75  The  pearls  of  commerce,  found  in  the  mantle  of  some  Mollusks,  are  simi- 
lar in  structure  to  the  shell ;  but  what  is  the  innermost  layer  in  the  shell  is 
placed  on  the  outside  in  the  pearl,  and  is  much  finer  and  more  compact.     The 
pearl  is  formed  around  some  nucleus,  as  an  organic  particle,  or  grain  of  sand. 

76  When  the  centrum  is  concave  on  both  sides,  as  in  Fishes,  it  is  said  to  be 
amphiccelous ;  when  concave  in  front  and  convex  behind,  as  in  Crocodiles, 
it  is  called  procwlous ;  when  concave  behind  and  convex  in  front,  as  in  the 
neck-vertebra?  of  the  Ox,  it  is  opisthoccelous.     In  the  last  two  cases,  the  ver- 
tebrae unite  by  ball-and-socket  joints. 

77  Whether  the  skull  represents  any  definite  number  of  vertebra?  is  still 
under  discussion.      We  cannot  speak  of  "cranial  vertebra?"  in  the  same 
sense  as  "cervical  vertebra?."     The  most  that  can  be  said  is  that  in  a  general 
way  the  skull  is  homologous  to  part  of  the  vertebral  column  (B). 

78  A  few  have  but  one  pair,  the  Whale  and  Siren  wanting  the  hind  pair ; 
while  some  have  none  at  all,  as  the  Snakes  arid  lowest  Fishes.     In  land  ani- 
mals, the  posterior  limbs  are  generally  most  developed  :  in  aquatic  animals, 
the  anterior.     Dr.  Wyman  contends  that  the  limbs  are  tegumentary  organs, 
and  attached  to  the  vertebral  column  in  the  same  sense  that  the  teeth  are 
attached  to  the  jaws.     Other  theories  are  that  they  originate  from  gill-arches 
(Gegenbaur)  or  that  they  are  remains  of  a  once  continuous  lateral  fin  (Thacher). 


NOTES.  387 

79  The  first  trace  of  muscular  tissue  is  found  in  the  stem  of  Vorticella — an 
Itifusorian.     In  Hydra  we  find  neuro-muscular  cells,  and  the  Jelly-fishes 
have  muscular  tissue. 

80  The  muscles  of  some  Invertebrates,  as  Spiders,  are  yellow. 

81  The  muscles  of  the  heart  and  gullet  are  striped.     In  the  lower  animals 
these  distinctions  of  voluntary  and  involuntary,  striated  and  smooth,  solid 
and  hollow,  muscles  can  seldom  be  made. 

82  The  skeleton  of  the  Carrion-crow,  for  example,  weighs,  when  dry,  only 
twenty-three  grains. 

b3  The  Dragon-fly  can  outstrip  the  Swallow ;  nay,  it  can  do  in  the  air  more 
than  any  bird — it  can  fly  backward  and  sidelong,  to  right  or  left,  as  well  as 
forward,  and  alter  its  course  on  the  instant  without  turning.  It  makes  twen- 
ty-eight beats  per  second  with  its  wings ;  while  the  Bee  makes  one  hundred 
and  ninety,  and  the  House-fly  three  hundred  and  thirty.  The  swiftest  Race- 
horse can  double  the  rate  of  the  Salmon.  So  that  Insect,  Bird,  Quadruped, 
and  Fish  would  be  the  order  according  to  velocity  of  movement. 

84  The  theory  that  Flies  adhere  by  atmospheric  pressure  is  now  abandoned. 

85  More  precisely,  the  term  brain,  or  brains,  applies  only  to  the  cerebrum, 
while  the  total  contents  of  the  cranium  are  called  encephalon. 

b6  The  exact  functions  of  the  cerebrum  are  not  yet  clearly  understood. 
If  we  remove  it  from  Fishes,  or  even  Birds,  their  voluntary  movements  are 
little  affected;  while  the  Amphioxus,  the  lowest  of  Fishes,  has  no  brain  at 
all,  but  its  life  is  regulated  by  the  spinal  cord.  Such  mutilated  animals, 
however,  make  no  intelligent  efforts.  The  substance  of  the  cerebrum,  as 
also  the  cerebellum,  is  insensible,  and  may  be  cut  away  without  pain  to  the 
animal;  and  when  both  are  thus  removed,  the  animal  still  retains  sensation, 
but  not  consciousness. 

87  It  is  very  difficult  to  define  sensation,  or  sensibility.     The  power  is  pos- 
sessed by  animals  which  have   neither   nervous  system  nor  consciousness. 
These  low  manifestations  of  sensibility  are  called  irritability — the  power  by 
which  an  animal  is  capable  of  definitely  responding  to  a  stimulus  from  with- 
out.    The  response  is  not  called  out  by  the  direct  action  of  the  stimulus,  but 
is  determined  mainly  by  the  internal  structure  and  condition  of  the  animal. 

88  Parts  destitute  of  blood-vessels,  as  hair,  teeth,  nails,  cartilage,  etc.,  are 
not  sensitive.     The  impressibility  of  the  nerves  is  proportioned  to  the  activ- 
ity of  circulation.     According  to  the  recent  investigations  of  Dr.  Bowditch, 
the  channels  of  motor  and  sensitive  impressions  lie  in  the  lateral,  and  not  in 
the  anterior  and  posterior,  columns  of  the  spinal  cord. 

89  "Tentacles"  and  "horns"  are  more  or  less  retractile,  while  antennae 
are  not,  but  all  are  hollow.     Antenna}  alone  are  jointed. 

90  In  Man,  the  soft  palate  and  tonsils  also  have  the  power  of  tasting. 

91  No  organ  of  hearing  has  been  discovered  with  certainty  in  the  Radiates 
and  Spiders.     The  "ear"  of  many  lower  animals  is  probably  an  organ  for 
perceiving  the  animal's  position  rather  than  sound — an  "equilibrium  organ." 

98  It  is  wanting  in  the  aquatic  Mammals.  Crocodiles  have  the  first  repre- 
sentative of  an  outside  ear  in  the  form  of  two  folds  of  skin. 

93  This,  like  the  definition  of  smell  and  hearing,  is  loose  language.  There 
is  no  such  thing  as  sound  till  the  vibrations  strike  the  tympanum,  nor  even 


388  NOTES. 

then,  for  it  is  the  work  of  the  brain,  not  of  the  auditory  nerve.  Sound  is 
the  sensation  produced  by  the  wave-movement  of  the  air.  If  thus  defined 
in  terms  of  sensation,  light  is  nothing;  without  eyes  the  world  would  be 
wrapped  in  darkness.  Some  Protozoa  have  a  pigment  spot  as  an  eye. 

94  In  Invertebrates  and  aquatic  Vertebrates,  the  crystalline  lens  is  globu- 
lar; or,  in  other  words,  it  is  round  in  short-sighted  animals,  and  flattish  in 
the  long-sighted.     The  lens  of  the  Invertebrate  is  not  exactly  the  same  as 
the  lens  of  the  Vertebrate  eye,  though  it  performs  the  same  function ;  it  ie 
really  a  part  of  the  cornea. 

95  The  Ant  has  fifty  in  each  eye,  the  House-fly  four  thousand,  the  Dragon- 
fly twenty-eight  thousand. 

'6  The  pigment,  therefore,  while  apparently  in  front  of  the  retina,  is  really 
behind  it,  as  in  Vertebrates.  The  layer  beneath  the  cornea,  serving  as  an 
"iris,"  is  wanting  in  nocturnal  Insects,  since  they  need  every  ray  of  light. 
The  optic  nerve  alone  is  insensible  to  the  strongest  light. 

97  It  should  be  noticed  that  this  corresponds  with  another  peculiar  fact 
already  mentioned,  that  either  hemisphere  of  the  brain  controls  the  muscles 
on  the  opposite  side  of  the  body.     In  Invertebrates,  the  motor  apparatus  is 
governed  on  its  own  side. 

98  Sharks  have  eyelids,  while  Snakes  have  none.     The  third  eyelid  (called 
nictitating  membrane')  is  rudimentary  in  many  Mammals. 

99  An  infant  would  doubtless  learn  to  walk  if  brought  up  by  a  wild  beast, 
since  it  was  made  to  walk.     Just  as  an  Infusorium  moves  its  cilia,  not  be- 
cause it  has  any  object,  but  because  it  can  move  them.     New-born  puppies, 
deprived  of  brains,  have  suckled ;  and  decapitated  Centipedes  run  rapidly. 
Such  physical  instincts  exist  without  mind,  and  may  be  termed  "blind  im- 
pulses." 

100  We  say  "apparently,"  because  it  may  be  a  fixed  habit,  first  learned  by 
experience,  transmitted  from  generation  to  generation.     A  duckling  may  go 
to  the  water,  and  a  hound  may  follow  game  in  some  sense,  as  Sir  John  Her 
schel  takes  to  astronomy,  inheriting  a  taste  from  his  father.     Breeders  take 
advantage  of  this  power  of  inheritance. 

101  We  may  divide  the  apparently  voluntary  actions  of  animals  into  three 
classes.     First,  organic,  in  which  consciousness  plays  no  part,  and  which  are 
due  wholly  to  the  animal  machine.     Second,  instinctive,  in  which  conscious- 
ness may  be  present,  but  which  are  not  controlled  by  intelligence.     Third, 
associative,  in  which  the  animals  act  under  conscious  combination  of  distinct, 
single  ideas,  or  past  impressions.     To  these  we  may  add  rational  acts,  in 
which  the  mental  process  takes  place  under  the  laws  of  thought. 

102  "Thus,  while  the  human  organism  may  be  likened  to  a  keyed  instru- 
ment, from  which  any  music  it  is  capable  of  producing  can  be  called  forth  at 
the  will  of  the  performer,  we  may  compare  a  Bee,  or  any  other  Insect,  to  a 
barrel-organ,  which  plays  with  the  greatest  exactness  a  certain  number  of 
tunes  that  are  set  upon  it,  but  can  do  nothing  else." — CARPENTER'S  Mental 
Physiology,  p.  61.     This  constancy  may  be  largely  due  to  the  uniformity  of 
conditions  under  which  Insects  live. 

108  We  may  say,  as  a  rule,  that  the  proportion  of  instinct  and  intelligence 
in  an  animal  corresponds  to  the  relative  development  of  the  spinal  cord  and 


NOTES.  389 

cerebrum.  As  a  rule,  also,  the  addition  of  the  power  to  reason  comes  in 
with  the  addition  of  a  cerebrum,  and  is  proportioned  to  its  development. 
Between  the  lowest  Vertebrate  and  Man,  therefore,  we  observe  successive 
types  of  intelligence.  Intelligence,  however,  is  not  according  to  the  size  of 
the  brain  (else  Whales  and  Elephants  would  be  wisest),  but  rather  to  the 
amount  of  gray  matter  in  it.  A  honey-comb  and  an  Oriole's  nest  are  con- 
structed with  more  care  and^art  than  the  hut  of  the  savage.  It  is  true,  this 
is  no  test  of  the  capability  of  the  animal  in  any  other  direction ;  but  when 
they  are  fashioned  to  suit  circumstances,  there  is  proof  of  intelligence  in  one 
direction. 

104  An  exception  to  the  general  rule  that  the  smaller  animals  have  mere 
acute  voices. 

105  It  is  wanting  in  a  few,  as  the  Storks. 

106  The  Nightingale  and  Crow  have  vocal  organs  similarly  constructed,  yet 
one  sings  and  the  other  croaks. 

107  These  cells  are  detached  portions  of  the  parental  organisms.     Gener- 
ally, these  two  kinds  of  cells  are  produced  by  separate  sexes;  but  in  some 
cases,  as  the  Snail,  they  originate  in  the  same  individual.     Such  an  animal, 
in  which  the  two  sexes  are  combined,  is  called  an  hermaphrodite. 

108  The  eggs  of  Mammals  are  of  nearly  uniform   size ;    those  of  Birds, 
Insects,  and  most  other  animals  are  proportioned  to  the  size  and  habits  of 
the  adult.     Thus,  the  egg  of  the  ^Epyornis,  the  great  extinct  bird  of  Mada- 
gascar, has  the  capacity  of  fifty  thousand  Humming-birds'  eggs. 

109  As  a  general  rule,  when  both  sexes  are  of  gay  and  conspicuous  colors, 
the  nest  is  such  as  to  conceal  the  sitting  Bird ;  while,  whenever  there  is  a 
striking  contrast  of  colors,  the  male  being  gay  and  the  female  dull,  the  nest 
is  open.     Such  as  form  no  nest  are  many  of  the  Waders,  Swimmers,  Scratch- 
ers,  and  Goatsuckers. 

110  This  lies  at  first  transversely  to  the  long  axis  of  the  egg.     As  the  chick 
develops,  it  turns  upon  its  side. 

111  The  blood  appears  before  the  true  blood-vessels,  in  intercellular  spaces. 
It  is  at  first  colorless,  or  yellowish. 

112  Exactly  as  the  blood  in  the  capillaries  of  the  lungs  is  aerated  by  the 
external  air. 

113  Thus,  the  hollow  wing-bone  was  at  first  solid,  then  a  marrow-bone,  and 
finally  a  thin-walled  pneumatic  bone.     The  solid  bones  of  Penguins  are  ex- 
amples of  arrested  development. 

114  The  thigh-bone  ossifies  from  five  centres.     The  bone  eventually  unites 
to  one  piece. 

115  Muscle  is  mainly  fibrine  and  myosin,  while  nerve  is  neurin. 

116  For  this  reason,  Mammals  are  called  viviparous ;  but,  strictly  speaking, 
they  are  as  oviparous  as  Birds.     The  process  of  reproduction  is  the  same, 
whether  the  egg  is  hatched  within  the  parent  or  without.     The  eggs  of 
Birds  contain  whatever  is  wanted  for  the  development  of  the  embryo,  except 
hear,  which  must  come  from  without.     Mammals,  having  no  food-yolk,  obtain 
their  nutrition  from  the  blood  of  the  parent,  and  after  birth  from  milk. 

117  The  larvae  of  Butterflies  and  Moths  are  called  caterpillars;  those  of 
Beetles,  grubs;  those  of  Flies,  maggots;  those  of  Mosquitoes,  wigglers.    The 


390  NOTES. 

terras  larva,  pupa,  and  imago  are  relative  only ;  for,  while  the  grub  and  cat- 
erpillar are  quire  different  from  the  pupa,  the  hee-stare  is  reached  by  a  very 
gradual  change  of  form,  so  that  it  is  difficult  to  say  where  the  pupa  ends 
and  the  imngo  begins.  In  fact,  a  large  number  of  Insects  reach  maturity 
through  an  indefinite  number  of  slight  changes.  The  Humble-bee  moults  at 
least  ten  times  before  arriving  at  the  winged  state. 

18  Every  tissue  of  the  larva  disappears  before  the  development  of  the  new 
tissues  of  the  imago  is  commenced.  The  organs  do  not  change  from  one 
into  the  other,  but  the  new  set  is  developed  out  of  formless  matter.  The 
pupa  of  the  Moth  is  protected  by  a  silken  cocoon,  the  spinning  of  which  was 
the  last  act  of  the  larva ;  that  of  the  Butterfly  is  simply  enclosed  in  the  dried 
skin  of  the  larva,  which  is  called  chrysalis  because  of  its  golden  spots.  The 
pupa  of  the  Honey-bee  is  called  nymph ;  it  is  kept  in  a  wax-cell  lined  with 
silk,  spun  by  the  nursing-bee,  not  by  the  larva.  The  time  required  to  pass 
from  the  egg  to  the  imago  varies  greatly  :  the  Bee  consumes  less  than  twenty 
days,  while  the  Cicada  requires  seventeen  years. 

119  Compare  the  amount  of  food  required  in  proportion  to  the  bulk  of  the 
body,  and  also  with  the  amount  of  work  done,  in  youth,  manhood,  and  old  age. 

120  Excepting,  perhaps,  that  the  new  tail  of  a  Lizard  is  cartilaginous. 

181  The  patella,  or  knee-pan,  has  no  representative  in  the  fore-limb,  and. 
strictly,  it  belongs  to  the  muscular  system,  rather  than  to  the  skeleton.  Some 
anatomists  contend  that  the  great  toe  is  homologous  with  the  little  finger,  in- 
stead of  the  thumb. 

122  "The  structure  of  the  highest  plants  is  more  complex  than  is  that  of 
the  lowest  animals ;  but,  for  all  that,  powers  are  possessed  by  Jelly-fishes  of 
which  oaks  and  cedars  are  devoid." — MIVART. 

121  It  is,  however,  true  that  the  number  of  eggs  laid  is  proportioned  to  the 
risk  in  development. 

124  According  to  Mr.  Darwin,  the  characters  which  naturalists  consider  as 
showing  true  affinity  between  two  or  more  species  are  those  which  have  been 
inherited  from  a  common  parent;  and,  in  so  far,  all  true  classification  is  gene- 
alogical ;  i.  e.,  it  is  not  a  mere  grouping  of  like  with  like,  but  it  includes  like 
descent,  the  cause  of  similarity.     In  the  existing  state  of  science,  a  perfect 
classification  is  impossible,  for  it  involves  a  perfect  knowledge  of  all  animal 
structure  and  life's  history.     As  it  is,  it  is  only  a  provisional  attempt  to  ex- 
press the  real  order  of  nature,  and  it  comes  as  near  to  it  as  our  laws  do  in 
explaining  phenomena.     It  simply  states  what  we  now  know  about  compar- 
ative anatomy  and  physiology.     As  science  grows,  its  language  will  become 
more  precise  and  its  classification  more  natural. 

125  The  term  type  is  also  used  to  signify  that  form  which  presents  all  the 
characters  of  the  group  most  completely.     Each  genus  has  its  typical  species, 
each  order  its  typical  genus,  etc.     The  word  is  also  applied  to  the  specimen 
on  which  a  new  species  is  founded.     A  persistent  type  is  one  which  has  con- 
tinued with  very  little  change  through  a  great  range  of  time.     The  family  of 
Oysters  has  existed  through  many  geological  ages. 

126  The  Ccelenterata  and  Echinodermata  together  make  up  the  hadiata, 
the  old  subkingdom  of  Cuvier.     Echinoderrna  is  probablv  more  correct  than 
fichinodermata,  but  we  retain  the  old  orthography. 


NOTES. 


391 


127  Strictly  speaking,  no  individual  is  independent.     Such  is  the  division 
of  labor  in  a  hive,  that  a  single  Bee,  removed  from  the  community,  will  soon 
die,  for  its  life  is  hound  up  with  the  whole.     An  individual  repeats  the  type  of 
its  kingdom,  subkingdom,  class,  order,  family,  genus,  and  species,  through  its 
whole  line  of  descent. 

128  These  definitions  of  the  various  groups  are  mainly  taken  from  Agassiz. 
They  are  not  practically  very  useful,  as  they  are  not  used  by  working  natu- 
rsdists.     The  kind  and  degree  of  difference  entitling  a  group  to  a  particular 
rank  varies  greatly  with  the  naturalist,  and  the  part  of  the  Animal  Kingdom 
where  the  group  is  found.     Some  families  of  Insects  are  separated  by  g;ips 
less  than  those  which  divide  genera  of  Mammals. 

129  The  Millepore  coral,  so  abundant  in  the  West  Indian  Sea,  is  the  work 
of  Hydroids.     The  surface  is  nearly  smooth,  with  minute  punctures.     Ge- 
genhauer,  Haeckel,  and  others  hold  that  the  Acalephs  have  no  body-cavity 
at  all,  the  internal  system  of  canals  being  homologous  with  the  intestinal 
cavity  of  other  animals. 

130  This  digestive  cavity  is  really  homologous  to  the  proboscis  of  the  Jelly- 
fish, turned  in.     It  is  lined  with  ectoderm.     The  "body-cavity"  is  not  really 
such,  but  homologous  to  the  digestive  sac  of  the  Hydra. 

131  Among  the  exceptions  are  Tubipora,  which  have  eight  tentacles  and  no 
septa,  and  the  extinct  Cyathophylla,  whose  septa  are  eight  or  more. 

la2  The  longer  septa  (called  primary)  are  the  older;  the  shorter,  secondary 
ones,  are  developed  afterwards.  As  a  rule,  sclerodermic  corals  are  calcare- 
ous, and  a  section  is  star-like ;  the  sclerobasic  are  horny  and  solid.  The 
latter  are  higher  in  rank. 

133  Some  Star-fishes  (Solaster)  have  twelve  rays.  In  all  Echinoderms, 
probably,  sea-water  is  freely  admitted  into  the  body-cavity  around  the  viscera. 
34  The  shell  is  not  strictly  external,  like  the  crust  of  a  Lobster,  but  is 
coated  with  the  soft  substance  of  the  animal. 

135  Six  hundred  pieces  have  been  counted  in  the  shell  alone,  and  twelve 
hundred  spines.  The  feet  number  about  eighteen  hundred.  They  can  be 
protruded  beyond  the  longest  spines. 

*36  The  classification  of  this  edition  maybe  compared  with  that  of  the  for- 
mer by  the  following  table,  in  which  the  order  of  the  groups  is  altered  to  show 
the  relation  more  easilv. 


III. 
MOLLUSCA. 


Former  Edition. 

Class. 

4.  Lnmellibranchiata. 

5.  Gasteropoda. 

0.  Cephalopoda. 
3.  Tunicata 

2.  Brachiopoda. 

1.  Polzoa. 


Class. 
Do. 
Do. 
Do. 


1.  Annelida  — 

IV. 

ARTICULATA. 

2.  Crustacea. 
3.  Arachnida. 
4.  Myriapoda. 
w  5.  Insecta. 

Present  Edition. 

Subkingilom. 

1.  1  V.' 

2.  )>    MOLLUSCA. 

3.  J  VII. 

TUNICATA. 

Do.  4.  "I 

Do.  5.   | 

1.  Platyhelminthes.   !  IV. 

2.  Nematelminthes.   [       VERMES. 

3.  Rotifera. 
6.  Annelides. 

Do.  1. 

Do.  2.   I  VI. 

Do.  3.  [  ARTHUUPODA, 

Do.  4. 


392  NOTES. 

The  two  subkingdoms  of  the  earlier  edition  are  thus  divided  into  four.  The 
Classes  remain  the  same,  except  the  Annelida. 

137  The  most  important  genera  are  Terebratula,  R/iynchonella,  Discina, 
Lingula,  Orthis,  Spirifer,  and  Productus.  The  first  four  have  representa- 
tives in  existing  seas.  Most  naturalists  now  admit  their  affinity  to  tlie 
worms,  although  some  still  keep  them  in  the  subkingdom  Mollusca. 

13B  There  are  some  exceptions :  the  Oyster  is  unequivalved,  and  the  Pecten 
equilateral. 

139  The  chief  impressions  left  on  the  shell  are  those  made  by  the  muscles — 
the  dark  spots  called  "eyes"  by  oyster-men;  the  pallial  line  made  by  the 
margin  of  the  mantle ;  and  the  bend  in  the  pallial  line,  called  pallial  sinus, 
which  exists  in  those  shells  having  retractile  siphons,  as  the  Clam. 

140  The  Clam  is  the  highest  of  Lamellibranchs,  and  the  Oyster  one  of  the 
lowest.     The  Mya  arenaria,  or  "Soft  Clam,"  has  its  shell  always  open  a 
little;  while  Venus  mercenaria,  or  "Hard  Clam,"  keeps  its  shell  closed. 

141  The  Slug  has  no  shell  to  speak  of,  and  the  Chiton  is  covered  with  eight 
pieces.     It  may  be  remembered,  as  a  rule,  that  all  univalve  shells  in  and 
around  the  United  Stales  are  Gasteropods,  and  that  all  bivalves  in  our  rivers 
and  lakes,  and  along  our  sea-coasts  (save  a  few  Brachiopods),  are  Lamelli- 
branchs. 

142  Hold  the  shell  with  the  apex  up  and  the  mouth  towards  the  observer. 
]f  the  mouth  is  on  his  right,  the  shell  is  right-handed  or  dextral,  if  on  his 
left,  sinistral.     In  other  word*,  a  right-handed  shell  is  like  a  right-handed 
screw. 

143  Instead  of  a  strong  breathing-tube  with  a  valve,  answering  for  a  force- 
pump  and  propeller,  as  in  the  Cuttle-fish,  it  has  only  an  open  gutter  made  by 
a  fold  in  the  mantle,  like  the  siphons  of  the  Gasteropods.     The  back  cham- 
bers are  filled  with  nitrogen  gas. 

The  common  Poulpe  has  two  thousand  suckers,  each  a  wonderful  little  air- 
pump,  under  the  control  of  the  animal's  will. 

144  The  order  of  the  classes  is  one  of  relation  rather  than  of  rank.     They 
cannot  be  arranged  serially.     The  Myriapods  have  a  worm-like  multiplica- 
tion of  parts,  degrading  them,  and  their  nervous  system  is  simpler  than  that 
of  Caterpillars ;  yet  their  heads  show  a  close  relationship  to  Insects.     The 
Arachnids  include  some  lower  forms  than  Myriapods ;  on  the  other  hand, 
for  their  wonderful  instincts,  Owen  places  them  above  the  Insects.     They  are 
closely  allied  to  Crustaceans,  and  stand  more  nearly  between  Crustaceans  and 
Insects  than  between  Myriapods  and  Insects. 

145  Certain  Crabs  live  on  dry  land,  but  they  manage  to  keep  their  gills 
wet. 

146  The  student  should  remember  that  this  threefold  division  is  not  equiva- 
lent to  the  like  division  of  a  vertebrate  body. 

147  Each  ring  (called  somite)  is  divisible  in  two  arcs,  a  dorsal  and  ventral, 
and  each  arc  consists  of  four  pieces. 

148  The  four  pairs  of  legs  in  Arachnids  answer  to  the  third  pair  of  maxilla? 
and  the  three  pairs  of  maxillipedes  in  the  Lobster.     The  great  claws  of 
Scorpions   are  the  first  maxilla  of  the  Lobster,  as  are  the  pedipalpi   of 
Spiders. 


NOTES.  393 

149  The  antennae  are  more  probably  altogether  undeveloped,  and  the  jaws 
of  the  Spider  correspond  to  the  mandibles  of  the  Lobster. 

150  Compare  the  single  thread  of  the  Silk-worm  and  other  caterpillars. 

161  The  common  Spider,  Epeira,  which  constructs  with  almost  geometri- 
cal precision  its  net  of  spirals  and  radiating  threads,  will  finish  one  in  forty 
minutes,  and  just  as  regularly  if  confined  in  a  perfectly  dark  place. 

152  These  parts  do  not  correspond  to  the  parts  so  named  in  human  anatomy. 
See  also  p.  162. 

153  The  pupa-case  is  often  ornamented  with  golden  spots  in  Butterflies ; 
hence  the  common  name  chrysalis. 

154  In  aquatic  animals  the  posterior  limbs  are  the  ones  aborted  or  reduced, 
if  any ;  in  land  animals  the  fore-limbs  are  usually  sacrificed. 

155  The  smallest  corpuscles  are  found  in  Ruminants;  the  largest  in  Am- 
phibians with  permanent  gills.     The  average  size  in  Birds  is  double  that  in 
Man,  and  about  equal  to  that  in  the  Elephant.     Those  of  Monkeys  are  a 
trifle  smaller  than  the  human.     In  the  embryo  they  are  larger  than  in  the 
adult.     Camels  only  among  Mammals  have  oval  disks. 

156  The  facial  angle  becomes  of  less  and  less  importance  as  we  go  away 
from  man,  and  for  two  reasons.     Where  the  brains  do  not  fill  the  brain-case 
the  angle  is  obviously  of  little  value,  arid  if  the  jaws  are  largely  developed  the 
angle  is  reduced,  although  intelligence  may  not  be  altered. 

157  Oblong  human  skulls,  whose  diameter  from  the  frontal  to  the  occipital 
greatly  exceeds  the  transverse  diameter,  are  called  dolichocephalic ;  and  such 
are  usually  prognathous,  i.  e.,  have  projecting  jaws,  as  the  negro's.     Round 
.skulls,  whose  extreme  length  does  not  exceed  the  extreme  breadth  by  a 
greater  proportion  than  100  to  80,  are  brachycephalic ;  and  such  are  gener- 
ally orthognathous,  or  straight-jawed. 

158  The  classes  are  variously  grouped   into  the   Hwmatocrya,  or  Cold- 
blooded, and  the  Hcematotherma,  or  Warm-blooded  ;    into  the  Branchiate 
and  Abranchiata  ;  into  the  Allantoidea  and  Anallantoidea. 

139  It  would  be  safe  to  say  that  any  living  Vertebrate  with  side  fins  sup- 
ported by  fin-rays  is  a  Fish ;  but  the  extinct  Reptile  Ichthyosaurus  also  ha/d 
them. 

leo  «  rp^e  Capac5ty  for  growing  as  long  as  life  lasts,  which  some  Fishes  are 
said  to  possess,  may  be  explained  by  the  facts  that  their  bodies  are,  firstly,  of 
very  nearly  the  same  specific  gravity  as  the  water  in  which  they  live,  and, 
secondly,  of  a  temperature  which  is  but  a  very  little  higher  than  that  which 
they  are  there  exposed  to.  Thus  the  force  which  in  other  animals  is  ex- 
pended in  the  way  of  opposition  to  that  of  gravity  and  in  the  way  of  pro- 
ducing heat  is  available  for  sustaining  continuous  growth." — ROLLESTON. 

61  Amphibians  with  a  moist  skin  are  also  remarkable  for  their  cutaneous 
respiration.  They  will  live  many  days  after  the  lungs  are  removed.  Their 
vertebrae  vary  in  form  :  in  the  lowest  they  are  biconcave,  like  those  of  Fishes  ; 
in  Salamanders  they  are  opisthocalous :  ?n  the  Frogs  and  Toads  they  are 
usually  procoelous. 

163  Salamanders  are  often  taken  for  Lizards,  but  differ  in  having  gills  in 
early  life  and  a  naked  skin.  The  Proteus  and  Siren  resemble  a  tadpole  ar- 
rested in  its  development. 


394:  NOTES. 

163  The  Surinam  Toad  has  no  tongue. 

54  The  posterior  pair  of  limbs  is  sometimes  represented  by  a  pair  of  small 
bones ;  and  the  Boas  and  Pythons  show  traces  of  external  hind-limbs. 

65  There  are  some  notable  exceptions.  The  Slow-worm  is  legless,  and 
the  Chameleon  has  a  soft  skin,  with  minute  scales. 

166  According  to  Owen  ;  but  Huxley  insists  that  the  plastron  belongs  to 
the  exoskeleton. 

167  Knees  always  bend  forward,  and  heels  always  bend  backward. 

168  We  cannot  claim  that  this  airy  skeleton  is  necessary  for  flight.     The 
bones  of  the  Bat  are  free  from  air,  yet  it  is  able  to  keep  longer  on  the  wing 
than  the  Sparrow.     The  common  Fowl  has  a  hollow  humerus;  while  some 
Birds  of  long  flight,  as  the  Snipe  and  Curlew,  have  airless  bones. 

69  The  fossil  Archteopteryx,  a  lizard-like  Bird,  is  placed  in  a  separate  di- 
vision, Saururce.  Birds  have  also  been  divided  according  to  their  degree  of 
development  at  birth  into  ( 1 )  Hesthoyenous,  as  Fowls,  Ostriches,  Plovers, 
Snipes,  Rails,  Divers,  and  Ducks,  whose  chick  is  hatched  completely  clothed, 
has  perfect  senses,  runs  about,  and  feeds  itself.  When  full  grown,  it  uses  its 
feet  rather  than  wings,  flying  with  a  rapid,  labored  stroke,  and  taking  the 
first  opportunity  to  settle  on  land  or  water,  not  on  trees ;  the  male  is  po- 
lygamous and  pugnacious;  the  female  makes  little  or  no  nest;  and  neither 
sex  sings.  This  group  is  of  the  best  use  to  man,  and  approaches  more  near- 
ly to  Mammals,  the  habitual  use  of  the  legs  and  preference  for  land  or  water 
degrading  it  as  a  Bird  and  raising  it  in  the  list  of  animals ;  (2)  Gymnogenous, 
as  Gulls,  Pelicans,  Birds  of  Prey,  Herons,  Sparrows,  Woodpeckers,  and 
Pigeons,  whose  chick  comes  helpless,  blind,  and  naked;  it  can  neither  walk 
nor  feed  itself,  but  gapes  for  food ;  the  adult  is  monogamous,  and  builds 
elaborate  nests  in  trees  and  perches  ;  many  sing ;  all  are  habitual  fliers. 
These  are  birds  par  excellence,  gifted  with  higher  intelligence  than  the 
others,  and  are  never  domesticated  for  food. 

170  Hopping  is  characteristic  of  and  confined  to  the  Perchers ;  but  many 
of  them,  as  the  Meadow-lark,  Blackbird,  and  Crow,  walk. 

171  This  order  is  artificial.     But  it  is  better  to  retain  it  until  ornithologists 
agree  upon  some  natural  arrangement.     The  classification  of  birds  is  taken 
from  Coues's  "Key  to  North  American  Birds,"  as  being  the  work  on  orni- 
thology in  most  general  use. 

172  rJ»he  Whales  are  hairy  during  fetal  life  only! 

173  The  Manati  has  6 ;  Hoffmann's  Sloth  6 ;  and  two  species  of  three-toed 
Sloth  have  respectively  8  and  9. 

174  As  in  the  Whale,  Porpoise,  Seal,  and  Mole.     Teeth  are  wanting  in  the 
Whalebone  Whales,  Ant-eaters,  Manis,  and  Echidna. 

75  The  Monotremes  resemble  Marsupials  in  having  marsupial  bones,  but 
have  no  pouch.  They  differ  from  all  other  Mammals  in  having  no  distinct 
nipples. 

176  The  pouch  is  wanting  in  some  Opossums  and  the  Dasyurus. 

177  For  the  best  account  of  the  Elephant,  see  Tennant's   "Ceylon"  or 
Brehm's  "Thierleben." 

178  The  fore-feet  of  the  Tapir  have  four  toes,  but  one  does  not  touch  the 
ground. 


NOTES.  395 


179  The  extinct  Horse  (Hippariori)  had  three  toes,  two  small  hoofs  dangling 
behind.     The  foot  of  the  Horse  is  of  wonderful  structure.     The  bones  are 
constructed  and  placed  with  a  view  to  speed,  lightness,  and  strength,  and 
bound  together  by  ligaments  of  marvellous  tenacity.     There  are  elastic  pads 
and  cartilages  to  prevent  jarring ;   and  all  the  parts  are  covered  by  a  living 
membrane  which  is  exquisitely  sensitive,  and  endows  the  foot  with  the  sense 
of  touch,  without  which  the  animal  could  not  be  sure-footed.     The  hoof 
itself  is  a  world  of  wonders,  being  made  of  parallel  fibres,  each  a  tube  com- 
posed of  thousands  of  minute  cells,  the  tubular  form  giving  strength.     There 
are  three  parts,  "wall,"  "  sole,"  and  "frog" — the  triangular,  elastic  piece 
in  the   middle,  which  acts  as   a   cushion   to  prevent  concussion  and  also 
slipping. 

180  The  Cr.mel  and  Llama  are  exceptional,  having  two  upper  incisors  and 
canines,  are  not  strictly  cloven-footed,  having  pads  rather  than  hoofs,  and 
are  hornless. 

181  The  Hyena  alone  of  the 'Carnivores  has  only  four  toes  on  all  the  limbs, 
and  the  Dog  has  four  hind-toes.     The  Lion  is  the  king  of  beasts  in  majesty, 
but  not  in  strength.     Five  men  can  easily  hold  down  a  Lion,  while  it  re- 
quires nine  to  control  a  Tiger. 

188  The  eye-orbits  of  the  Lemurs  are  open  behind.  The  Flying  Lemur 
(Galeo/rithectis)  is  considered  an  Insectivore. 

183  The  old  term  Quadrumana  is  rejected  because  it  misleads,  for  Apes,  as 
well  as  Men,  have  two  feet  and  two  hands.     There  is  as  much  anatomical 
difference  between  the  feet  and  hands  of  an  Ape  as  between  the  feet  and 
hands  (>f  Man.    Owen,  however,  with  Cuvier,  considers  the  Apes  truly  "  four- 
bunded." 

184  It  fails  to  cover  in  the  Howling  Monkey  and  Siamang  Gibbon ;  but  in 
the  Squirrel  Monkey  it  more  than  covers,  overlapping  more  than  in  Man. 
As  to  the  convolutions,  there  is  every  grade,  from  the  almost  smooth  brain 
of  the  Marmoset  to  that  of  the  Chimpanzee  or  Orang,  which  falls  but  little 
below  Man's. 

183  The  tailed  Apes  of  the  Old  World  have  longer  legs  than  arms,  and 
generally  have  "cheek-pouches,"  which  serve  as  pockets  for  the  temporary 
stowage  of  food. 

186  In  the  human  infant,  the  sole  naturally  turns  inward;  and  the  arms 
of  the  embryo  are  longer  than  the  legs. 

187  The  Aye-aye,  the  lowest  of  the  Lemurs,  is  remarkable  for  the  large 
proportion  of  the  cranium  to  the  face. 

8  This  feature  was  shared  by  the  extinct  Anoplotherium,  and  now  to 
some  extent  by  one  of  the  Lemurs  (Tarsius}. 

19  We  have  treated  Man  zoologically  only.  His  place  in  Nature  is  a 
\\ider  question  than  his  position  in  Zoology;  but  it  involves  metaphysical 
and  psychological  considerations  which  do  not  belong  here. 

90  See  Lewes's  charming  "Studies  in  Animal  Life."  Doubtless  an  ex- 
amination of  all  the  strata  of  the  earth's  crust  would  disclose  forms  im- 
mensely outnumbering  all  those  at  present  known-  And  even  had  we  every 
fossil,  we  would  have  but  a  fraction  of  the  whole,  for  many  deposits  have 
been  so  altered  by  heat  that  all  traces  have  been  wiped  out.  Animal  life  is 


396  NOTES. 

much  more  diversified  now  than  it  was  in  the  old  geologic  ages ;  for  several 
new  types  have  come  into  existence,  and  few  have  dropped  out. 

191  Among  the  types  characteristic  of  America  are  the  Gar-pike,  Snnpping- 
turtle,  Hummers,  Sloths,  and  Musk-rat.  Many  of  our  most  common  animals 
are  importations  from  the  Old  World,  and  therefore  are  not  reckoned  witli 
tiie  American  fauna ;  such  as  the  Horse,  Ox,  Dog  and  Sheep,  Rats  and 
Mice,  Honey-bee,  House-fly,  Weevil,  Currant- worm,  Meal-worm,  Cheese- 
maggot,  Cockroach,  Croton-bug,  Carpet-moth  and  Fur- moth.  Distribution 
is  complicated  by  the  voluntary  migration  of  some  animals,  as  well  as  by 
Man's  intervention.  Besides  Birds,  the  Bison  and  Seals,  some  Rats,  certain 
Fishes,  as  Salmon  and  Herring,  and  Locusts  and  Dragon -flies  among  In- 
sects, are  migratory. 

193  When  the  cable  between  France  and  Algiers  was  taken  up  from  a  depth 
of  eighteen  hundred  fathoms,  there  came  with  it  an  Oyster,  Cockle-shells, 
Annelid  tubes,  Polyzoa,  and  Sea-fans.  Ooze  brought  up  from  the  Atlantic 
plateau  (two  thousand  fathoms)  consisted  of  ninety-seven  per  cent,  of  Fora- 
nainirers. 


THE  NATURALIST'S  LIBRARY. 


THU  following  works  of  reference,  accessible  to  the  American  student, 
arc  recommended : 


General  Works  and  Text-books. 

AoAsaiz,  Methods  of  Study  in  Natural 
History. 

AGASSIS  and  GOULD,  Principles  of  Zool- 
ogy- 

KOLLESTON,  Forms  of  Auimal  Life. 

LKWKS,  Studies  of  Animal  Life. 

JONKS,  General  Outline  of  the  Organiza- 
tion of  the  Animal  Kingdom. 

HUXLEY  and  MARTIN,  Elementary  Biol- 
ogy- 

OWKN,  Comparative  Anatomy  of  Inverte- 
brates and  Vertebrates. 

VAN  DKR  HOEVEN,  Handbook  of  Zoology. 

WOOD,  Illustrated  Natural  History. 

NICHOLSON,  Manual  of  Zoology. 

TKNNKY,  Elements  of  Zoology. 

MORSE,  First  Book  of  Zoology. 

JONES,  Animal  Creation. 

PACKARD,  Zoology. 

GKOENBAUR,  Comparative  Anatomy. 

Invertebrates. 

HCXLEY,  Anatomy  of  Invertebrated  Ani- 
mals*. 

MAOALLISTKR,  Introduction  to  Animal 
Morphology. 

I.ROOKS,  Handbook  of  Invertebrate  Zool- 
ogy- 

SIKIIOLD,  Anatomy  of  Invertebrates. 

Vertebrates. 

HUXLEY,  Anatomy  of  Vertebrated  Ani- 
mala. 

M  AOALLISTER,  Morphology  of  Vertebrates. 

HUXLEY  and  HAWKINS,  Atlas  of  Compar- 
ative Osteology. 

FLOW  KB,  Osteology  of  Mammalia. 

CJIAUVKAU,  Comparative  Anatomy  of  Do- 
mesticated Animals. 

MIVART,  Lessons  in  Elementary  Anatomy. 


MIVART,  The  Cat. 

GRAY,  Anatomy,  Descriptive  and  Surgical. 
STRIOKER,  Handbook  of  Human  and  Com- 
parative Histology. 

Embryology. 

BAZFOUR,  Comparative  Embryology. 
FOSTER  and  BALFOUR,  Elements  of  Embry- 
ology. 
PACKARD,  Life  Histories  of  Animals. 

Physiology. 

CARPENTER,  Comparative  Physiology. 
HUXLEY,  Lessons  in  Elementary  Physiol- 
ogy- 

FOSTER,  Text-book  of  Physiology. 
MARTIN,  The  Human  Body. 
FLINT,  Physiology. 

Geographical  Distribution. 
WALLACE,  Geographical  Distribution  of 

Animals. 
MUBBAY,  Geographical  Distribution    of 

Mammals. 

Microscopy. 

CARPENTER,  The  Microscope  and  its  Rev- 
elations. 

GRIFFITHS  and  HENFREY,  The  Micrograph- 
ic  Dictionary. 

Darwinism. 

SCHMIDT,  Descent  and  Darwinism. 
HAEOKEL,  History  of  Creation. 
DARWIN,  Origin  of  Species. 
HUXLF.Y,  Lay  Sermons,  etc. 
MIVART,  Lessons  from  Nature. 

Special  Works. 
CLARK,  Mind  in  Nature. 
AOASSIZ,  Sea-side  Studies  in  Natural  His- 
tory. 


398 


THE  NATURALIST'S  LIBRARY. 


TAYI.OE,  Half-hours  at  the  Sea-side. 

GKEENE,  Manuals  of  Sponges  and  Ccelen- 
terata. 

DANA,  Corals  and  Coral  Islands. 

VEHEII.T.  and  SMITH,  Invertebrates  of  Vine- 
yard Sound. 

Gocr.D  and  BINNEY,  Invertebrata  of  Mas- 
sachusetts. 

WOODWARD,  Manual  of  Mollusca. 

PACKARD,  Guide  to  the  Study  of  Insects. 

DUNCAN,  Transformations  of  Insects. 

STOEICR,  Fishes  and  Reptiles  of  Massachu- 
setts. 


COUES,  Key  to  North  American  Birds. 

JORDAN,  Popular  Key  to  the  Birds,  etc., 
of  Northern  United  States. 

BAIBD,  BREWER,  and  K  ice  WAY,  Birds  of 
North  America. 

BAIRD,  Mammals  of  North  America. 

AI,T,EN,  Mammalia  of  Massachusetts. 

SOAMMON,  Marine  Mammals  of  North  Pa- 
cific. 

PKBOUEI,,  The  Races  of  Man. 

MAUBH,  Man  and  Nature. 

TVI.OR,  Primitive  Culture. 

NICHOLSON,  Palaeontology. 


Of  serial  publications,  the  student  should  have  access  to  the  American 
Naturalist,  American  Journal  of  Science,  Popular  Science  Monthly,  Sinith- 
sonian  Contributions  and  Miscellaneous  Collections,  Bulletins  and  Proceed- 
ings of  the  various  societies,  Annals  and  Magazine  of  Natural  History,  and 
Nature. 

The  following  German  works  are  recommended  as  having  no  English 
equivalents: 


CLAFS,  Grundzuge  der  Zoologie. 
PAYENSTECIIKR,  All<remeine  Zoologie. 
BBONN,  Classen  und  Orduuugeu  des  Thier- 

Also  the  periodicals — 

Zoologiscfter  Anzeiyer. 


reichs  (unfinished  and  expensive,  but 
indispensable  to  the  working  zoolo- 
gist). 


Biologisches  Centralblatt. 


INDEX. 


In  the  Index  the  numbers  in  Roman  type  (21)  refer  to  pages;  those  in  "bold-faced 
type  (40)  refer  to  cuts.  No  attempt  is  made  to  analyze  the  statements  made  for 
each  group  in  Part  II.  Reference  is  made  for  each  class  or  prominent  order  to  those 
cuts  in  Part  I.  which  illustrate  the  group. 


ABSORPTION,  Invertebrates,  94. 

"          Vertebrates,  94,  60,  61. 
Acalepha?,  247. 

"     .     see  Jelly-flsh. 
A  car!  nn,  237,  258. 
Acarns,  287. 
Acetabulum,  147. 
Acipenser,  315,  290. 
Acorn-shell,  284,  254. 

"  see  Barnacle. 

Acrania,  309,  310,  282. 
Actinaria,  251,  199,  201-206. 
Actiuoid  Polyp,  251,  199. 

"        anatomy  of,  38,  95,  198. 
"         blood  of,  97. 

development  of,  205,  208. 
liver-cells  of,  124. 
mouth  of,  55,  199. 
nettle-cells  of,  51. 
prehension  of,  51. 
reproduction  of,  192. 
respiration  of,  112. 
skeleton  of,  130,  96. 
skin  of,  127. 
Adder,  320,  298. 
Adipose  Tissue,  3S,  10. 
JEolis,  274. 
Air-bladder,  117. 
Albatross,  330. 
Albumen,  19. 

Alcyonaria,  256,  200,  207,  208. 
Alcyonium,  256,  208. 
Alimentary  Canal,  74. 

"  "      Coelenternta,  75. 

"  "      Crustacea,  76. 

"  "      development  of,  203. 

"  "      duodenum,  90. 

"  "      Echinoderms,  76. 

««  "      Fishes,  80. 

"  "     Insects,  78. 


Alimentary  Canal,  Mammals,  R5. 

"  "      microscopic    anatomy 

of,  57,  58. 

"  "       Mollusks,  80. 

"  "      Protozoa,  74. 

"  "      Spiders,  79. 

"  "      stomach,  87. 

"  "      structure  of,  89. 

"  "      see   Intestine,   Month, 

Stomach,  Teeth. 
Allantoidea,  393. 
Allautois,  117,  203,  169-171. 
Alligator,  324,  303. 
"          nest,  196. 
Alternate  generation,  212. 
Ambulacra,  131. 
Ammonite,  279. 
Ainnion,  202,  170,171. 
Amoeba,  241, 185. 

"       conjugation  of,  196. 
"        ectosarc  of,  75. 
"       feeding  of,  55. 
"        locomotion  of,  154, 157. 
Amphibia,  317,  63,  65,  76,  85,  87,  294- 
296. 

"          blood  of,  9l>,  63-65. 

"          brain  of,  172,  140. 

"          circulation  of,  108,  76.- 

"          lungs  of,  118. 

"          mouth  of,  Cl. 

"          see  Frog. 
Amphicoelous,  386. 
Amphioxus,  310,  282. 

*'  feeding  of,  50. 

"  skeleton  Of,  139. 

AmphithoC,  284,  252. 
Analogy,  218. 
Anchylosis,  143. 
Animal,  defined,  22. 
Animalcule,  see  Protozoa. 


400 


INDEX. 


Annelides,  2u8, 17,  223. 

Auodon,  78 ;  see  Clam. 

Anoura,  318. 

A  lit,  304. 

Aiit-eater,  344,  333. 

Antennae,  ITT,  117. 

Authozoa,  250,  38,  95,  198,  208. 

Ape,  35T,  120,  353-357. 

Apis,  304,  277. 

Aplysia,  2T4. 

Apteryx,  32T. 

Arachnida,  2ST. 

"         sf-e  Ceutipede,  Scorpion,  Spi- 
der. 
Araueiua,  289,  18,  25,  260,  261. 

"         see  Spider. 
Arden,  332,  313. 
Arenicola,  113,  77. 
Areolar  Tissue,  35,  3. 
Argonauta,  280,  249. 
Armadillo,  135,  344,  101,  334. 
Artery,  104. 
Arthropoda,  281. 

blood  of,  99. 

development  of,  205. 

number  of,  221. 

skin  of,  12T. 

see  Crab,  Insect,  Lobster,  My- 

rinpodn,  Spider. 
Ascidian,  305,  278,  279. 

"         circulation  of,  10T. 
li         mouth  of,  60. 
"         skinof,12T. 
Astacus,  283,  250. 
Aster  las,  260. 

"        see  Starfish. 

Asteroidea,  258,  126,  133,  212,  213. 
Astraea,  252,  203. 
Astrophyton,  260. 
Atavism,  216. 
Attacns,  302,  274. 
Auger-shell,  2TO,  288. 
Auk,  329. 
Aurelia,  248,  195. 

"        nee  Jelly-fish. 

Aves,  325,  60,  65,  76,  105,  116,  125,  162, 
170. 

BAWIRUSA,  69,  34. 
Baboon,  869. 

Balaena,  see  Whale. 
Balanus,  284,  254. 
Barnacle,  284,  253,  254. 

"         metamorphosis  of,  210. 

"         mouth  of,  5T. 

"         see  Cirripedia. 
Basket-fish,  260. 
Batrachia,  318,  63,  65,  76,  85,  87,  296, 297. 

"  see  Frog. 
Bats,  346,  339,  840. 
Beaver.  346,  337. 


Bed-bug,  29T. 
Bee,  303,  277. 

alimentary  canal  of,  42. 
eggs  of,  195. 
eye  of,  155. 
instincts  of,  185. 
mode  of  feeding  of,  50. 
mouth  of,  59,  22. 
section  of,  81. 
temperature  of,  121. 
see  Hymenoptera,  Insecta. 
Beetle,  29T,  267,  268. 

"       alimentary  canal  of,  41. 
development  of,  29T,  267. 
eye  of,  182,  156. 
mouth  of,  5T. 
skeleton  of,  292,  262. 
see  Coleoptera,  Insecta. 
Belemnite,  281. 
TBernicla,  310. 
Beroe,  25T. 
Bile,  93. 

Bird-of-Paradise,  339. 
Birds,  325,  304-328. 

"     alimentary  canal  of,  84,  5©. 
41     anatomy  of,  50,  304. 
"     beak  of,  54. 

"      blood  corpuscles  of,  99,  65. 
"     brain  of,  141. 
"     breathing  of,  119. 
"     circulation  of,  10T,  76. 
"      distribution  of,  3TS. 
"     drinking  of,  50. 
egg  of,  193,  162. 
embryo  of,  170. 
eye  of,  184. 

feather  of,  13T,  204.  106. 
flight  of,  160.  125. 
gizzard  of,  84,  384,  50. 
heart  of,  109. 
locomotion  of,  166. 
lungs  of,  118,  50. 
mouth  of,  62. 
skeleton  of,  143, 116. 
smell  of,  118. 
temperature  of,  121. 
"     voice  of,  189. 
"     wings  of,  160,  304. 
Bivalve,    see    Clam,    Lamellibranchiata, 

Oyster. 

Blackbird,  339. 
Blastema,  33. 
Blastula,  198,  165. 
Blood,  9T. 

"      circulation  of,  103. 

"      corpuscles,  98, 99,  62-65. 

"      development  of,  200. 

"      functions  of,  9T 

"      of  Invertebrates,  9T. 

"      rate  of  motion  of,  111. 

"      temperature  of,  100. 


INDEX. 


401 


Blood  of  Vertebrates,  98. 

"     vessels,  104. 
Blubber,  348. 
Bluefish,  312,  284. 
Boa,  skull  of,  72,  37. 
Bone,  composition  of,  147. 

"     development  of,  203. 

"     structure  of,  36,  7,  8. 
Bos,  see  Ox. 

Brachiopoda,  260,  221,  222. 
Brachycephalic,  393. 
Bradypus,  344. 
Brain,  170. 

"     case  of,  see  Skull. 

"     development  of,  204. 

"     functions  of,  173. 

"     parts  of,  170. 

"     weight  of,  170. 
Brain-coral,  232,  204. 
Bronchus,  119,  86. 
Bryozoa,  see  Polyzoa. 
Bubble-shell,  274,  281. 
Buccinum,  272,  228. 
Budding,  192. 
B»fo,318. 

"     see  Toad. 
Bugs,  mouth  of,  59. 

"     nee  Hemiptera. 
Btilitnui?,  275,  238. 
Bulla,  272,  281. 
Butterfly,  273. 

anatomy  of,  43. 
metamorphosis  of,  208, 172. 
"        mimicry  of,  217. 
"         mouth  of,  59,  23. 
scales  of,  271,  272. 

CA.DTHB-FLY,  295. 
Csecilia,  318. 
Caecum,  51. 
Calcispongia,  246. 
Camel,  352. 
Cameo-shell,  278,  237. 
Canaliculi,  37,  8. 
Canine  teeth,  69,  34,  85. 
Capillaries,  104,  66,  68. 
Caprimulgus,  338,  828. 
Capybara,  346. 
Carapace,  323, 115. 
Cardium,  227. 
Carinatse,  328. 

Carnivora,  353,  90,  92,  106,  108-110,  128, 
142,  346,  350. 

"         brain  of,  142. 

11         teeth  of,  70. 
Cartilage,  36,  5. 
Cassis,  278,  237. 
Cassowary,  327. 
Castor,  346,  837. 
Cat,  355. 
"   brain  of,  142. 


Cat,  teeth  of,  70. 
Caterpillar,  301. 

"         anatomy  of,  78,  40. 

"          circulation  in,  105,  69. 

"         false  legs  of,  172. 
head  of,  303,  276. 

"          heart  of,  105,  69. 
jaws  of,  53,  276. 

"          locomotion  of,  162. 

"          muscles  of,  156. 

"         nervous  system  of,  169,  130. 

"          see   Butterfly,  Insecta,  Lepi- 

doptera. 
Catfish,  316,  291. 
Cebus,  357,  852. 
Cell,  31,1. 
Cement,  66,  31. 
Centipede,  291,  259. 
Cephalizatiou,  225. 
Cephalopoda,  278,  16,  47,  151,  247-240. 

see  Cuttlefish,  Squid. 
Cephalo-thorax,  282. 
Cerebellum,  171. 
Cerebrum,  170. 
Ceryle,  338,  327. 
Cetacea,  348,  30,  341,  342. 

"       see  Whale. 
Chalaza,  193, 162. 
Chameleon,  322. 

"  tongue  of,  81. 
Cheiroptera,  346,  839,  340. 
Chelonia,  322, 115,  301,  802. 

"         see  Turtle. 
Chelydra,  323. 
Chilognatha,  291. 
Chilopoda,  291,  269. 
Chimaera,  314. 
Chimpanzee,  357,  354,  356. 

"  skeleton  of,  120. 

teeth  of,  36. 
Chitine,132. 
Chiton,  276,  240. 
Chlorophyl,  23. 
Choroid,  183. 
Chrysaora,  213, 178. 
Chrysalis,  20S,  390, 172. 
Chyle,  93,  59. 
Chyme,  92. 
Cicada,  297,  266. 
Cicatricula,  194. 
Cidaris,  262,  96,  97. 
Cilia,  154,  2. 
Ciliata,  248, 188. 
Circulation  in  Arthropoda,  106. 

"          in  Ascidiaus,  107. 

"          in  Birds,  109. 

k'          development  of,  200. 

"          in  Echinodermata,  105. 

"          in  Insects,  105. 

"          in  Mammalia,  109. 

"          in  Mollusca,  106. 


402 


INDEX 


Circulation  in  Vermes,  105. 

"          iu  Vertebrata,  10T,  281. 
"          see  Heart 
Cirripedia,  284,  253,  254. 

"         see  Barnacle. 
Clam,  272. 

4     adductors  of,  46. 
'     alimentary  canal  of,  80,  44, 46- 
' '   anatomy  of,  46. 
;     circulation  in,  106. 
'     ear  of,  ITS,  150. 
'     foot  of,  161,  46. 
'     gills  of,  113,  78. 
'     heart  of,  106,  46. 
'     hinge  of,  270. 
'     locomotion  of,  161. 
'     mouth  of,  56. 
4     nervous  system  of,  168,  135. 
4     prehension  of,  50. 
'     shell  of,  133,  99. 
'     siphons  of,  46. 
4     see  Lamellibranchiata,  Oyster. 
Clamatores,  338,  322. 
Class,  235. 
Classification,  231. 

"  Table,  239. 

14  synopsis  of,  362. 

Claws,  136, 
Cloaca,  85. 
Clypeaster,  262. 
Coagulation,  98. 
Cochineal,  297. 
Cockle,  272,  227. 
Cockroach,  297. 
Cod,  316,  292. 

44    eggs  of,  195 
Cceleuterata,  246. 

"          number  of,  221. 

44          see  Actinoid  Polyp,  Hydra, 

Jelly-fish. 
Coleoptera,  297,  41, 156,  267,  268. 

44          see  Beetle. 
Columbae,  323,  316. 
Condor,  335. 
Cone-shell,  276,  239. 
Conjugation,  196. 
Connective  Tissue,  34,  3,  4. 
Coral,  130,  251,  95,  201-208. 

"     see  Actinoid  Polyp. 
Corallium,  256,  207. 
Coral  reef,  254. 
Cormorant,  330,  309. 
Cornea,  183. 
Corpuscles,  see  Blood. 
Correlation,  218. 
Cowry,  276,  234. 
Corydalns,  295. 
Crab,  287,  257. 

44     locomotion  of,  162. 
"     vocal  organs  of,  188. 
"     see  Lobster. 


Crane,  332. 
Craniota,  309. 
Cranium,  141. 
Cray-fish,  282,  250. 
Cricket,  295,  264. 
Crinoidea,  258,  211. 
Crocodilia,  323,  303. 

exoskeleton  of,  135. 
heart  of,  108. 
locomotion  of,  163. 
mouth  of,  61,  26. 
skeleton  of,  149,  118. 
stomach  of,  82,  49. 
see  Reptilia. 
Crow,  339. 
Crustacea,  282. 

44         uauplius  of,  211,  171. 
44        see  Crab,  Lobster. 
Cteuactis,  253,  202. 
Ctenophora,  257,  209. 
Cuckoo,  335. 
Cuculi,  335,  321. 
Curassow,  333. 
Cursores,  327,  305. 
Cuticle,  128. 
Cutis,  128. 
Cuttlefish,  280,  248. 

44         anatomy  of,  47. 

44         alimentary  canal  of,  80,  47. 

beak  of,  52,  47. 
44         brain  of,  168, 151. 
44         circulation  in,  107. 
44        ear  of,  151. 

eye  of,  181,  151. 
44        heart  of,  107. 

ink-bag  of,  47. 
44         mouth  of,  57. 
44        pancreas  of,  123. 
44         prehension  of,  52. 
44         skeleton  of,  134. 
'4         suckers  of,  16. 
44        see  Cephalopoda,  Squid. 
Cyclops,  284,  255. 
Cyprsea,  276,  234. 
Cypris,  284,  255. 
Cypseli,  335,  320. 

DADDY-LONG-LKOS,  289, 300. 

Daphuia,  284,  255. 

Dasypus,  344,  334. 

Dasyurns,  343. 

Decapoda  (Crustacea),  286,  70,  248, 

256,  257. 

"         (Dibrauchiata),  280. 
Decussation,  184. 
Deglutition,  72. 
Delphinus,  349,  34& 
Demodex,  287,  258. 
Dental  Formulae,  70. 

44      Tissue,  38,  31. 
Dentine,  38,  66,  31. 


INDEX. 


403 


Dermis,  l«a 
Development,  197. 

"  by  alternate  generation,  211. 

of  Bird,  199. 
ofblastula,  198,  165. 
"  of  embryonic  forms,  207. 

"  of  gastrula,  193,  166. 

"  of  Invertebrates,  204. 

"  by  metamorphosis,  207. 

"  by  metamorphosis,  retro- 

grade, 210. 

•'  oviparous,  309. 

"  ovoviviparous,  309. 

segmentation  of  egg,  197. 
"  of  Vertebrates,  205. 

"  viviparous,  309. 

see  Metamorphosis,  Repro- 
duction. 

Diaphragm,  86,  88. 
Diastema,  70,  383. 

Dibranchiata,  2SO,  16,  47, 151,  248,  249. 
Differentiation,  31. 
Digestion,  chemical,  92. 

"         of  Invertebrate,  92. 
"         of  Man,  93. 
"         object  of,  91. 
"         of  Vertebrate,  92. 
Digitigrade,  355,  128. 
Diploria,  254,  204. 
Dipnoi,  316,  293. 
Diptera,  300,  24, 127, 173,  269,  270. 

"       see  Fly,  Mosquito. 
Discophora,  220. 
Distribution,  371-379. 
Divers,  328. 
Dog,  354. 
"    brain  of,  171. 
"    skull  of,  143. 
"    teeth  of,  68. 
Dolichocephalic,  393. 
Dolphin,  349,  343. 

teeth  of,  68. 
Doris,  274. 
Dove,  333,  316. 
Dragon-fly,  294,  263. 

flight  of,  387. 
Duck,  331,  811. 
Duck-mole,  342,  331. 
Dugoug,  350. 

•«       heart  of,  73. 
Duodenum,  90. 

EAGLE,  334,  319. 
Ear,  179,  387,  152. 
Ear-shell,  278,  235,  246. 
Earth-worm,  269. 

alimentary  canal  of,  77. 

"  circulation  in,  105. 

"  locomotion  of,  162. 

"  nervous  system  of,  168. 

"  prehension  of,  52. 


Ecderon,  127. 
Echidna,  342. 
Echinodermata,  257. 

"  number  of  species  of,  221 

Echinoidea,  261,  28, 39,  96,  97,  214. 
Echinus,  262,  214. 

"       see  Sea-urchin. 
Edentata,  344,  101,  333,  334. 
Egg,  fertilization  of,  197. 
"    form  of,  195. 
"    number  of,  195. 
"    segmentation  of,  197, 165. 
"    structure  of,  192,  161, 163. 
Elasmobranchii,  314,  287,  288. 

"  see  Ray,  Shark. 

Elephant,  350. 

"         brain  of,  170. 
foot  of,  129. 
"         skeleton  of,  119. 
"         teeth  of,  69,  86. 
"         trunk  of,  66. 

tusks  of,  71,  66, 119. 
"         voice  of,  189. 
Elytra,  297. 
Embryology,  197. 
Emu,  327. 
Enamel,  66,  31. 
Encephalon,170. 
Enderon,  127. 
Endoskeleton,  127. 
Entomostraca,  284,  255. 
Epiblast,  199. 
Epidermis,  34. 
Epiglottis,  119,  159. 
Epithelium,  33,  2. 
Equus,  see  Horse. 
Euplectella,  246. 
Excretion,  121, 125. 
Exoskeleton,  127. 
Eye,  of  Invertebrates,  180. 
"    of  Vertebrates,  181. 
"    development  of,  204. 

FACIAL  ANGLE,  309. 
Falcon,  335. 
Family,  235. 
Fat,  38,  10. 
Feathers,  137, 105. 

"        development  of,  204. 
Felis,  355. 

Fertilization  of  Egg,  197, 
Fibrine,  98. 
Fishes,  310. 

air-bladder  of,  117,  48. 

alimentary  canal  of,  80,  48. 

blood  of,  99, 100,  65. 

brain  of,  172,  189. 

circulation  in,  107,  51,  76. 

eye  of,  184. 

fins  of,  158, 123. 
"      gills  of,  114,  48. 


4-04: 


INDEX. 


Pishes,  heart  of,  108, 48. 

locomotion  of,  159,  124. 
mouth  of,  61. 
muscles  of,  157,  48. 
number  of  species  of,  313. 
ovary  of,  48. 
pancreas  of,  123. 
prehension  of,  54. 
scales  of,  135,  102,  283. 
skeleton  of,  112. 
skull  of,  138,  112. 
teeth  of,  61,  67,  32. 
Fish-hawk,  335,  318. 
Fission,  191,  160. 
Flagella,  154,  187. 
Flagellata,  243, 182. 
Flamingo,  331. 
Flea,  300. 

Flight  of  Bats,  161. 
"     of  Birds,  160. 
"      of  Insects,  159. 
Fluke,  265. 
Flustra,  267,  220. 
Fly,  300. 

"    buzzing  of,  188. 
"    foot  of,  127. 
"   metamorphosis  of,  270* 
"    mode  of  feeding  of,  50. 
"    mouth  of,  59,  24. 
"   see  Diptera,  Mosquito. 
Fly-catcher,  338,  322. 
Flying  Fox,  346. 
Follicle,  123,  90. 
Food,  47-49. 
Foramen  magnum,  172. 
Foraminifera,  51,  241,  15, 186. 
Forms  of  animals,  222. 
Fox,  355,  349. 
Frog,  318,  297. 

alimentary  canal  of,  82. 
blood-corpuscles  of,  99,  63,  65. 
breathing  of,  119. 
circulation  in,  108,  76. 
food  of,  49. 
heart  of,  108. 
lungs  of,  118,  85. 
lymph-heart  of,  96. 
metamorphosis  of,  209. 
respiration  in,  117-119. 
skeleton  of,  119, 140, 145,  87. 
tongue  of,  61. 
vertebrae  of,  140,  87. 
Fruit-moth,  303,  275. 
Function,  41. 
Fuugia,  252,  202. 

GALL-BLADDER,  124,  92. 
Gall-fly,  303. 
Ganglion,  166,  14,  146. 
Gannet,  331. 
Ganoidei,  315,  289,  290,. 


Gar-pike,  315,  289. 

Gasteropoda,  20,  29, 45,100, 154, 176,  272. 

"  see  Snail. 

Gastric  glands,  123,  90. 

"      juice,  93. 
Gastrula,  198,  166. 
Gavial,  324. 
Gecko,  322. 
Gelatine,  36. 
Genus,  235. 
Germinal  vesicle,  192. 
Gibbon,  357. 
Gills,  114, 125,  48. 
Giraffe,  353. 
Gizzard  of  Invertebrates,  7\ 

"       of  Vertebrates,  84. 
Gland,  121,  89. 

"      gastric,  123,  90. 

"      liver,  123,  92. 

"      pancreas,  123,  91. 

"      salivary,  122. 

"      sweat,  126,  94. 
Globigeriua,  242. 
Glottis,  119. 
Glycogen,  23. 
Goatsucker,  338,  323. 
Goniaster,  260,  212. 
Goose,  331,  310. 
Gorgonia,  256,  208. 
Gorilla,  357,  357. 
Grallatores,  332,  318. 


Grassh 


>pper,  297. 


development  of,  20& 
gizzard  of,  79. 
mouth-parts  of,  58,  21 
stridulation,  188. 

Grebe,  329. 

Gregariuida,  240, 184. 

Grouse,  333,  315. 

Growth,  214. 

Grubs,  389. 

Gryllus,  295,  264. 

Guinea  pig,  345. 

Gulls,  329. 

HjiMATOORYA,  393. 

Hsematotherma,  393, 
Haemocyanin,  102. 
Haemoglobin,  102. 
Hag-fish,  54,  314. 
Hair,  136,  94, 104. 
Hair-worm,  262. 
Haliotis,  278,  235,  246. 
Hand,  359. 
Hare,  346,  336. 
Harvest-man,  289. 
Haversian  Canals,  37,  7. 
Hawk,  335,  818. 
Hearing  of  Invertebrates,  178, 

"      of  Vertebrates,  179. 
Heart,  Arthropoda,  105, 69,  70l 


INDEX. 


405 


Heart,  development  of,  200, 168. 
"     ofMollusks,  106. 
"     of  Tunicates,  107,  279. 
"     of  Vertebrates,  107-109,  71-74. 
Heat,  121. 
Hedgehog,  346. 
Helix,  275,  232. 
Hemiptera,  297,  265,  266. 
"          mouth  of,  59. 
Heron,  332,  813. 
Heterocercal,  159,  123. 
Heteromya,  272. 
Hippopotamus,  352. 

foot  of,  129. 
Histology,  12. 
Hog,  352. 

"    teeth  of,  67. 
Holothuroidea,  262,  215. 
Homarus,  see  Lobster. 
Homo,  see  Man. 
Homocercal,  159,  287. 
Homology,  217. 

"         serial,  218. 
Homomorphism,  217. 
Hoofs,  136,  103. 
Hornera,  267,  220. 
Horns,  136. 
Horse,  brain  of,  171, 138. 

hoof  of,  136,  164,  103,  129. 
skeleton  of,  151, 117. 
skull  of,  144,  111. 
splint-bones  of,  207. 
stomach  of,  88,  53. 
Horse-fly,  mouth  of,  60,  24. 
Horseshoe-crab,  284. 

44  "     jaws  of,  53. 

44  "      skeleton  of,  131. 

Hummer,  335. 
Hyalea,  274,  229. 
Hydra,  246,  191. 

44      budding  of,  192. 
44      digestive  cavity  of,  75. 
44      nerve-cells  of,  168. 
44      repair  of,  215. 
Hydroid,  see  Hydrozoa. 
Hydrozoa,  246, 178, 191-196. 
14         development  of,  205. 
44         metamorphosis  of,  212. 
44        see  Jelly-fish. 
Hyena,  355. 
Hymenoptera,  303,  22,  42,  81,  277. 


Ilypoblast,  199. 

Ibis,  332. 
Ichneumon,  304. 
Ichthyopsida,  309. 
Ichthyosaurus,  324. 
Idotia,  286,  251. 
Iguana,  322. 
Incisors,  68. 


Individual,  220. 
Infusoria  described,  243,  160. 
44        digestive  cavity  of,  75. 

fission,  191, 160. 
44        mode  of  feeding  of,  50. 
14        motion  of,  154. 
44        mouth  of,  55. 
44        respiration  of,  112. 
41        skin  of,  127. 
Inheritance,  21T. 
Insectivora,  346. 
Insecta,  291. 

44       absorption  of,  94. 

44       alimentary  canal  of,  79,  41-43. 

44        anatomy  of,  43,  81. 

44       antennae  of,  147. 

44       chrysalis  of,  172. 

circulation  in,  105,  292. 

development  ofi  205. 

ear  of,  179. 

eye  of,  181,  155,  156. 

feet  and  legs  of,  162,  127,  181. 

flight  of,  159. 

gizzard  of,  79. 

heart  of,  105,  69. 

kidney  of,  126,  41,  42. 

liver  of,  124. 

locomotion  of,  159, 162. 

metamorphosis  of,  207,  172,  178, 

264-267. 

44        mouth  of,  57. 
"        mouth-parts  of,  53,  21-24. 
41       muscles  of,  156,  131. 
"       nervous  system  of,  169,  48. 

respiration  in,  114,  291. 
44       salivary  glands  of,  122. 
14       silk  glands  of,  40. 
44       skeleton  of,  132,  292,  98,  262. 
14        smell  of,  178. 

spiracle  of,  114,  79. 
44       touch  of,  177,  147. 

tracheae  of,  114,  40,  80,  81. 
"       wings  of,  159. 
Insessores,  337,  322-328. 
Inspiration,  modes  of,  115, 119, 120. 
Instinct,  184. 
Intelligence,  187. 
Intestine  of  Amphibian,  82. 
of  Bird,  84. 
of  Fish,  81. 
44        of  Mammal,  85. 
44       of  Keptile,  82. 
44       see  Alimentary  Canal. 
Isomya,  272. 
Ivory,  66. 

JAWS,  51-71. 
Jay,  339. 

Jelly-fish,  247, 193-197. 
44         blood  of,  97. 

development  of,  212,  178,  196. 


406 


INDEX. 


Jelly-fish,  eye  of,  180. 

"         mode  of  feeding  of,  51. 

"         mouth  of,  55. 

"         nerves  of,  168. 

"         nettle-cells  of,  51. 

"        reproduction  of,  212. 
Joints,  147. 
Julus,  291. 

KANGABOO,  88,  343. 
Kidney,  126,  41, 93. 
King-crab,  see  Horseshoe-crab. 
Kingfisher,  335,  327. 
Kite,  335. 


LABIUM  and  LABRTJM,  58,  21. 
Labyrinthodontia,  318. 
Lacerta,  321,    tM). 
Lacertilia,  32. 
Lachuosterna,  297,  267. 
Lacteals,  94,  60. 
Lacunae,  37,  8. 

Laraellibranchiata,  270,   44,   46,   78,  99, 
135,  150,  224-227 
eye  of,  181,  153. 
"  see  Clam. 

Lamellirostres,  331,  311. 
Lamprey,  286. 
Lamp-shell,  266,  221. 
Lancelet,  310,  282. 
Land-snail,  275,  232. 
Lark,  340. 
Larynx,  189,  169. 
Lasso-cells,  51. 
Leech,  268. 

"     alimentary  canal  of,  77. 

"     jaws  of,  64. 

"      locomotion  of,  161. 

"     mode  of  feeding  of,  50. 
Lemur,  355,  351. 
Lepas,  284,  253. 
Lepidoptera,  300,  43,  172. 
"  see  Butterfly. 

Lepidosiren,  317 ' 
Lepidosteus,  315,  289. 
Libellula,  294,  263. 
Life,  distribution  of,  372. 
"    duration  of,  226. 
"    nature  of,  28. 
"    straggle  for,  227. 
Lightning-bug,  299. 
Ligula,  58,  21. 
Likeness,  215. 
Limax,  275,  232. 
Limbs,  development  of,  204. 

"      skeleton  of,  146. 
Limnaea,  275,  232. 
Limpet,  278,  245. 
Limulus,  284. 

"        see  Horseshoe-crab. 


Lion,  355. 
"     foot  of,  128 
"     skeleton  of,  106. 
"     stomach  of,  88,  65. 
Liver,  123,  92. 
Lizard,  see  Lacertilia. 
Lobster,  106,  70,  256. 

"       alimentary  canal  of,  78. 
"        anatomy  of,  282. 

circulation  in,  106,  70. 
ear  of,  179. 
eggs  of,  196. 
gills  of,  114. 
gizzard  of,  64. 
locomotion  of,  158. 
moulting  of,  132. 
mouth  of,  57. 
prehension  of,  53,  57. 
respiration  in,  114. 
skeleton  of,  131. 
Lob-worm,  77. 

Locomotion  of  Arthropoda,  162. 
of  Birds,  16C 
of  Fishes,  158. 
of  Insects,  159. 
ofMollu*ks,161. 
of  Starfish,  AC1. 
of  Vertebrates,  103. 
of  Worms,  161. 
Locust,  297. 
Loligo,  see  Squid. 
Longipennes,  329,  308. 
Loon,  328,  307. 
Louse,  297,  60. 
Lucernaria,  197. 
Lumbricus,  see  Earth-worm 
Lnngs,  function  of,  125. 
"       of  Snail,  116. 
"      surface  of,  3S5. 
"       of  Vertebrates,  117. 
Lymph,  102. 
Lymphatics,  94,  6L 
Lymph-heart,  96. 

MAOTRA,271,  46,  226. 
Madrepore,  252,  201,  206. 
Madreporic  plate,  258,  39. 
Maggots,  389. 
Mammalia,  309. 

"          alimentary  canal  of,  85. 
"  anatomy  of,  87,  52. 

"  blood-corpuscles  of,  90,  66. 

brain  of,  171, 138, 142-145. 
"  circulation  in,  109,  76,  281. 

digestion  of,  92,  51. 
drinking  of,  50, 
"          ear  of,  179, 152. 
egg  of,  198, 165. 
embryo  of,  202, 171. 
eye  of,  183,  157. 
hair  of,  136, 104. 


INDEX. 


407 


Mammalia,  heart  of,  109,  73,  74. 
"          locomotion  of,  163. 

lungs  of,  118,  86. 
"          mouth  of,  62. 

palate  of,  86,  27,  51. 
"          placenta  of,  19G,  203, 171. 
"          respiration  in,  120. 
"          skeleton  of,  139. 

smell  of,  178, 149. 
"          teeth  of,  68. 
"          touch  of,  1T7. 
"          voice  of,  189, 159. 
Man,  359. 

"     blood-corpuscles  of,  99,  62. 
"     brain  of,  170, 171, 187, 144, 145. 
"     digestive  tract  of,  51. 
"     ear  of,  179, 152. 
"     eye  of,  198, 157. 
"     mouth  of,  86,  27. 
"     muscles  of  leg  of,  165, 130. 
"     nose  of,  178, 149. 
Manatee,  350,  343. 
Mandibles,  58,  21. 
Mantis,  53. 
Mantle,  127,  46. 
Marsipobranchii,  314,  286. 
Marsupialia,  342,  332. 
Mastodon,  350. 
May-fly,  295. 
Meandrina,  252. 
Medulla  oblongata,  172. 
Medusa,  see  Jelly-fish. 
Megatherium,  344. 
Melania,  278. 
Menobranchus,  317,  294. 
Mesentery,  S3. 
Mesoblast,  199. 
Metamorphosis,  207. 

of  Crab,  209. 
"  of  Frog,  209. 

"  of  Insect,  208. 

of  Grasshopper,  208. 
of  Starfish,  208. 
Metazoa,  244. 

Millepede,  see  Myriapoda. 
Millepore,  391. 
Mimicry,  217. 

Minerals  and  Organisms,  19. 
Mite,  287,  258. 
Molar  Teeth,  69. 
Mole,  346. 
Mollusca,  269. 

"         absorption  of,  94. 
"        anatomy  of,  45,  46,  47,  78. 
"         circulation  in,  106. 
"        development  of,  205. 
"        digestion  of,  92. 
"        distribution  of,  377. 
"         growth  of,  214. 
"         kidney  of,  126,  78. 
liver  of,  124. 


Mollnsca,  locomotion  of,  161. 
"         metamorphosis  of,  269. 
"         mode  of  feeding  of,  52. 
"         mouth  of,  56. 
"        nervous  system  of,  16S,  134. 135, 

151, 157. 
"        number  of  species  of,  221. 

respiration  In,  113,  46,  47,  78. 
"        salivary  glands  of,  122. 

shell  of,  133,  385,  99,  100. 
"         skin  of,  127. 
"         see    Clam,   Cuttle-fish,    Snail, 

Squid, 

Monad,  243, 187. 
Monera,  240, 183. 
Monkey,  356, 19,  352. 
see  Primates. 
Monomya,  271. 
Monotremata,  342,  331. 

"  mouth  of,  62. 

Mosquito,  300, 173,  269. 

"         metamorphosis  of,  208. 
"        mode  of  feeding  of,  50. 
Moth,  302,  274-276. 
"      anatomy  of,  79,  43. 
"      metamorphosis  of,  274. 
11     see  Butterfly,  Lepidoptera, 
Motor  Nerves,  167. 
Moulting,  128,  209. 
Mouse,  346. 
Month,  55. 

"      of  Arthropoda,  57. 
11       of  Ascidia,  60. 
"       of  Birds,  02. 
"      of  Coelenterata,  55. 
"      of  Echinodermata,  56. 
"      of  Fishes,  61. 
"      of  Infusoria,  55. 
"       of  Mammals,  62. 
"       of  Mollusks,  56. 
"      of  Parasites,  55. 
"      of  Reptilia,  61. 
"      ofVermes,  57. 
"      ofVertebrata,  60. 
Mucous  Membrane,  89. 
Mud-fish,  315. 
Mures,  278. 
Mus,  346. 

Musca,  see  Diptera,  Fly. 
Muscle,  39, 12, 122. 

"       development  of,  204 
"       of  In  vertebrates,  156. 
"       kinds  of,  155. 
"       of  Verteb  rates,  1RG. 
Mushroom-coral,  252,  202. 
Mussel,  270,  225. 
Myriapoda,  290,  259. 

"          alimentary  canal  of,  T£ 
"  mouth  of,  57. 

"          respiration  in,  lid. 
"          see  Centipede. 


408 


INDEX. 


Myrmecophaga,  344,  333. 
Mytilus,  270,  225. 


Narwhal,  223,  68. 
Natatores,  328. 
Natica,  278. 
Natural  Selection,  227. 
Nauplius,  211, 177. 
Nautilus,  279,  247. 
Nematelmiuthes,  265,  218. 
Nereis,  268,  17. 
Nerve-cells,  40, 182. 
"      fibres,  40,  13. 
"      kinds  of,  167. 
"      velocity  of  impulse  of,  167. 
Nervous  System,  168. 

"       of  Arthropoda,  169. 
"       Brain,  170. 

development  of,  199,  67. 

ofMollusks,  168. 

Spinal  Cord,  175. 

of  Starfish,  168. 

Sympathetic,  175, 146. 

of  Vertebrates,  169. 

of  Worms,  16S. 
Netiroptera,  294,  263. 

"          see  Dragon-fly. 
Neuroskeleton,  141. 
Newt,  318,  296. 

Nomenclature,  Zoological,  236. 
Notochord,  200,  167. 
Nucleolns,  31, 1. 
Nucleus,  31, 1. 
Nummulite,  242. 
Nutrition,  45. 
Nymph,  377. 

OOEI/LI,  181. 
Octopus,  280. 
(Esophagus,  86. 
Olfactory  Lobes,  172. 

"         Nerves,  178. 
Olive-shell,  278. 
Oniscns,  286. 

Operculum,  114, 134,  228. 
Ophidia,  320. 

"       see  Snake. 
Ophiura,  260. 

Opisthobranchs,  274,  352,  230,  231. 
Opisthocoelous,  383. 
Opossum,  342,  332. 
Optic  Lobes,  172. 
Orang-utan,  357,  853,  355. 
Order,  235. 
Organ,  41. 
Organization,  30. 
Organ-pipe  Coral,  251,  200. 
Oriole,  339. 

Ornithorhynchus,  342,  881. 
Orthoceras,  287. 


Orthoptera,  217, 295,  21,  284. 
"          see  Grasshopper. 
Orycteropus,  344. 
Oscines,  338. 

Osseous  Tissue,  see  Bone. 
Ossification,  37,  203. 
Ostrea,  272. 

"      see  Oyster. 
Ostrich,  327,  305. 
Otoliths,  178, 156. 
Ovipositor,  293. 
Owls,  335,  317. 
Ox,  alimentary  canal  of,  90. 
"    foot  of,  352, 129. 
"    teeth  of,  352. 
"    see  Ungulata. 
Oyster,  anatomy  of,  80,  44. 

"      development  of,  205. 

"      eggs  of,  195. 

"      heart  of,  106,  44. 

"       mouth  of,  56. 

"      prehension  of,  50. 

"       respiration  in,  113. 

"      see  Clam,  Lamell:branch,ata. 

PALATE,  61. 

Pallial  Sinus,  271,  99. 

Palpi,  58,  21. 

Paludina,  278,  244. 

Pancreas,  123,  91. 

Pancreatic  Juice,  93. 

Pangolin,  344. 

Paper  Nautilus,  2SO,  249. 

Papilio,  303. 

Papillae,  128,  148. 

Paramecium,  243, 188. 

see  Infusoria. 
Parrot,  337,  320. 

"       tongue  of,  62. 
Partridge,  333. 
Patella,  278. 
Pavement-teeth,  67,  82. 
Pearl-oyster,  224. 
Pectoral  Arch,  146. 
Pedicelliirife,  77,  97. 
Pedipalpi,  288. 

"         see  Scorpion. 
Pelias,  320,  298. 
Pelican,  331. 
Penguin,  329,  306. 
Penuatula,  256,  208. 
PentacrimiP,  258,  211. 
Pepsin,  93. 
Peptone,  93. 
Perch,  skeleton  of,  112. 
Perchers,  337. 
Periosteum,  138. 
Peristaltic  Movement,  89. 
Periwinkle,  278. 
Petrel,  330. 
Petromyzon,  314,  286. 


INDEX. 


409 


Pharyngcbranchii,  310,  282. 
Pharynx,  85. 
Pheasant,  333. 
Phoca,  354. 
Physalia,  246,  194. 
Physeter,  348,  841. 

see  Whale. 
Picarite,  33P 
Pici,  335,  820. 
Pigeon,  333,  316- 
Piunigrade,  354, 128. 
Pisces,  310,  48,  51,  65,  75,  102,  112,  123, 

124,  189,  283-293 
"      see  Fish. 
Placenta,  196, 171. 
Planm-ia, '264,  217. 
Plant,  22. 

"      food  of,  25. 
"      functions  of,  24. 
Plantigrade,  355, 128. 
Plant-louse,  297. 
Plasma  of  blood,  98. 
Plastron,  323. 
Platyhelminthes,  264,  216,  217. 

"  see  Tape-worm. 

Platyonychus,  28T,  257. 
Pleurobrachia,  'J57,  209. 
Plover,  332'. 
Poison -fangs,  68,  83. 
Polycistina,  242, 186. 
Polyp,  250. 

"      see  Actinia. 
Polyzoa,  266,  220. 
Pond-snail,  275,  232. 
Porcupine,  346. 
Porites,  252. 
Porpoise,  88,  349,  54. 
Portal  circulation,  307,  385,  281 
Portuguese  Man-of-war,  246, 194. 
Potato-worm,  303. 
Poulpe,  280. 

Prairie  Chicken,  333,  815. 
Primates,  356,  35, 120, 143-145.  352-358. 

brain  of,  143-145. 

skeleton  of  Chimpanzee,  120. 

teeth  of  Chimpanzee,  35. 

see  Ape,  Man,  Monkey. 
Prob  >scidea,  350,  36, 119, 129. 


Prob 


>scis  of  Butterfly,  59,  23. 


of  Elephant,  62,  119. 
Procoelous,  3S3. 
Prognathous,  393. 
Prosobranchs,  278,  234-246. 
Proteus,  318,  295. 

*'       blood-corpuscle  of,  99,  65. 
Protista,  21. 
Protoplasm,  31. 
Protopterus,  316,  293. 
Protozoa,  238. 

"         number  of  species  of,  221. 

"        see  Amoeba,  Infusoria. 


Psendopodia.S!,  15. 
Pseudotritou,  318,  296. 
Psittaci,337,  820. 
Pteropoda,  274,  229. 

mouth  of.  56. 

Palmonates,  274,  232,  28& 
Pulse,  385. 
Pupil,  183, 158. 
Pygopodes,  328,  306,  807. 

QtJAimUMANA,  356. 

RACCOON,  355,  846. 
Radiates,  233. 
Radiolaria,  241,  186. 
Rail,  332,  814. 
Rana,  see  Frog. 
Range  of  Animals,  373. 
Rank  of  Animals,  2-24. 
Raptores,  334,  116,  317-319. 
Rasores,  332,  316. 
Rat,  346. 
Ratitse,  327,  305. 
Rattlesnake,  68,  33. 
Raven,  339. 
Rny,  314,  288. 

"    teeth  of,  C7.  32. 
Razor-shell,  272. 
Redstart,  338,  325. 
Repair,  215. 
Reproduction,  191. 

asexual,  191. 
by  budding,  192. 
checks  on,  227. 
by  division,  191. 
rapidity  of,  226. 
sexual,  192. 
Reptilia,  319. 

'         alimentary  canal  of,  82. 
brain  of,  172,141. 
circulation  in,  108,  76- 
'         corpuscles  of,  99,  65 
distribution  of,  378. 
lungs  of,  118,  84. 
'        mouth  of,  61. 
'         prehension  of,  61. 
'         scales  of,  135. 
'         teeth  of,  67. 
voice  of,  189. 
see    Crocodile,    Lizard,    Snake 

Turtle. 
Respiration,  111. 

in  Crustacea,  114. 
in  Echinoderms,  112. 
in  Fishes,  114. 
"  in  Insects,  114. 

in  Mollusks,  113. 
rate  of,  120. 
in  Vertebrates,  11T. 
in  Worms,  113. 
Hele  mucosum,  128. 


410 


INDEX. 


Itetina,  183, 158. 
Kheti,  327. 

Ithiiiuceros,  351,  814. 
Rhizopoda,  240,  15,  185, 186. 

"          skeleton  of,  129. 
Rodentia,  345,  835,  386,  337. 

"         teeth  of,  71,  335. 
Rotifera,  26C,  219. 

"       jaws  of,  64. 
Rudimentary  Organs,  207. 
Ruminantia,  351. 

"          stomach  of,  SS,  56. 

"          see  Ox,  Uuguiaia. 

SALAMANDER,  318,  296. 

metamorphosis  of,  174. 
Saliva,  function  of,  93. 
Salivary  Glands,  122. 
Salmon,  31C,  285. 
Sand-flea,  284,  252. 
Sandpiper,  332,  312. 
Sarcolemma,  39,  204. 
Sauropsida,  309. 
Saururse,  394 
Scales  of  Butterflies,  301,  272. 

"     of  Fishes  and  Reptiles.135,102,283. 
Scallop,  eye  of,  181,  153. 

shell  of,  272. 
Scapular  Arch,  146. 
Scarabseus,  299. 
Scarf-skin,  12& 
Sclerobase,  129. 
Scleroderm,  129. 
Sclerotic,  183. 
Scolopendra,  291,  259. 
Scorpion,  288,  269. 
"         mouth  of,  60. 
"         respiration  in,  116. 
Sea-anemone,  see  Polyp. 
Sea-blubber,  247. 
Sea-butterfly,  273,  229. 
Sea-fan,  256,  208. 
Sea-hare,  274. 
Seal,  355,  128. 
Sea-lemon,  274. 
Sea-lily,  258,  211. 
Sea-lion,  355,  360. 
Sea-sing,  274. 
Sea-nrchin,  262,  214. 

absorption  by,  94. 

alimentary  canal  of,  76,  39. 

anatomy  of,  39. 

circulation  in,  105. 

digestion  in,  92. 

growth  of,  214. 

mode  of  feeding,  62. 

mouth  of,  56. 

respiration  in,  112. 

shell  of,  28. 

skeleton  of,  130,  96. 

spines  of,  130,  97. 


Sea-urchin,  teeth  of,  C.4,  28. 
Sea-worm,  268,  17,  223. 
Secretion,  121. 

"         see  Gland. 
Segmentation  of  egg,  11)7,  16b. 
Self-division,  191,  160. 
Sensation,  176. 
Sense  of  hearing,  178. 
"     of  sight,  180. 
"     of  smell,  177. 
"     of  taste,  177. 
"     of  touch,  176. 
Sense-organs,  see  Sense. 

"  development  of,  204 

Sensibility,  176. 
Sepia,  280,  248. 
Serpent,  see  Snake. 
Sertularia,  247,  192. 
Serum,  98. 
Setse,  269. 

Setophaga,  340,  825. 
Seventeen-year  locust,  297,  26£. 
Shark,  314,  287. 

"      eggs  of,  194,  164 
"      gills  of,  114,  287 
"       skeleton  of,  137,  145. 
Shells  of  Crustacea,  131. 
"     of  Echinoderms,  130. 
"     ofMollnsks,  133. 
Shoulder-girdle,  146. 
Shrew,  63,  346,  338. 
Shrimp,  286. 

Sight,  of  Arthropods,  181. 
"     of  Coelenterate.s  ISO. 
"     ofMollusks,  181. 
"     of  Vertebrate*,  182. 
Silk-gland,  40. 
Silk-worm,  303. 
Simia,  358,  353,  355. 
Sinuses,  138. 
Siphonophora,  248,  194. 
Siphuncle,  279,  247. 
Siren,  318. 

Sirenia,  349,  73,  348- 
"       see  Dugong. 
Size  of  Animals,  221. 
Skeleton,  of  Arthropoda,  13L. 
of  Birds,  116,  144. 
of  Ccelenterates,  130. 
of  Echinoderms,  130. 
of  Fish,  138,  144,  112. 
of  limbs,  146. 
Lion,  139,  116. 
Mammals,  189,  106,  114,  117- 

120. 

Mollnsks,  133. 
Reptiles,  113,  115. 
of  skull,  141,  108,  111. 
of  Vertebrates,  134 
of  Whale,  114. 
see  Exoskeletou. 


INDEX. 


Skin  of  Invertebrates,  12T. 

"     of  Verte 'unites,  128. 
Skull,  141. 
Slater,  284,  251. 
Slug,  274,  232. 
Smell,  17T. 
Snail,  272. 

"      alimentary  canal  of,  SO,  45. 
"      anatomy  of,  46. 
"      circulation  in,  106,  46. 
"     eye  of,  181, 164. 
gills  of,  113. 
gizzard  of,  64. 
heart  of,  46. 
jaw  of,  56,  20V 
larva  of,  176. 
locomotion  of,  161. 
lung  of,  116,  274,  46. 
mode  of  feeding,  52. 
mouth  of,  56. 

nervous  system  of,  168, 184, 154. 
operculnm  of,  114,  134,  228. 
respiration  in,  116,  45,  228. 
shell  of,  133,  100,  228,  233-246. 
siphon  of,  228. 
smell  of,  178. 
teeth  of,  65,  29. 
tentacles  of,  176, 154,  228. 
"      see  Gasteropoda. 
Snake,  320,  298,  299. 
"      deglutition  of,  73. 
"      locomotion  of,  162. 
"      lungs  of,  119,  84. 
"•      poison  apparatus  of,  68,  83. 
"     scales  of,  135. 
"      skull  of,  37. 

stomach  of,  82. 
''      tongue  of,  61. 
"      Vertebrae  of,  140. 
"      voice  of,  189. 
"      see  Boa,  Ophidia,  Reptilia. 
Snapping-bug,  299. 
Snipe,  332. 
Solaster,  260. 
Somite,  392. 
Songsters,  338. 
Sorex,  346,  888. 
Sow-bug,  285. 
Sparrow,  339. 
Species,  defined,  235. 

"       number  of,  221. 
Sperm-whale,  see  Whale, 
sphinx-moth,  303,  48. 
Spider,  classification  of,  289,  260. 
"       alimentary  canal  of,  79. 
appendages  of,  25. 
circulation  in,  106. 
fangs  of,  53, 18,  25. 
mouth  of,  60,  25. 
respiration  in,  116. 
spinnerets  of,  28i),  25,  261. 


Spider,  web  of,  2S9,  260. 
Spinal  column,  140. 

"      cord, 175. 
Spinneret  of  Spider,  289,  261. 

"         of  Caterpillar,  301,  276. 
Spiracle,  114,  79. 
Spnngidu,  244,  189,  190. 

alimentary  canal  of,  76. 
anatomy  of,  189. 
egg  of,  194,  163. 
feeding  of,  50, 189. 
"         respiration  in,  112. 
"         skeleton  of,  129, 190. 
Squash-bug,  297. 
Squid,  280. 

"      locomotion  of,  158. 
"      see  Cuttlefish. 
Squirrel,  346. 
Stag,  352,  845. 

Star-fish,  alimentary  canal  of,  76, 126. 
"         anatomy  of,  126. 
"         circulation  in,  105, 126. 
"         classification  of,  258. 
"         development  of,  208. 
kl         digestion  in,  92. 

locomotion  of,  101,  126. 
metamorphosis  of,  207. 
mode  of  feeding  of,  51. 
mouth  of,  56. 

nervous  system  of,  168, 183. 
respiration  in,  112. 
"         see  Echiuodermata. 
Stilt,  332. 
Stomach,  82-89. 

"        digestion  in,  93. 
Stork, 332. 
Stridulation,  188. 
Strombus,  278,  248. 
Struggle  for  Life,  226. 
Struthio,  327,  305. 
Sturgeon,  315,  290. 
Subkingdom,  233. 
Sun-fish,  247. 
Sun-star,  260. 
Survival  of  Fittest,  226. 
Suture,  147. 
Swallow,  340,  328. 
Swan,  331. 
Swift,  335. 
Swimmeret,  282. 
Symmetry,  222. 

Sympathetic  nervous  system,  175,  144 
Synovia,  147. 

T^ENIA,  see  Tape-worm. 
Tanager,  339. 
Tapetum,  184. 
Tape-worm,  264,  216. 

"  feeding  of,  49. 

Tapir,  63,  351. 
Taste,  177. 


412 


INDEX. 


Teeth,  of  Amphibia,  6T. 
"      of  Fishes,  61,  66,  67. 
"      of  Iiiveriebrates,  63. 
"  ,    of  Mammals,  68,  70. 

of  Reptiles,  67. 

"      structure  of,  3S,  66,  9,  31. 
Teleostei,  315,  284,  290-202. 
Telson,  282. 

Temperature  of  Animals,  121. 
Tendon,  36. 
Tentac.e,  51. 
Tent-caterpillar,  303. 
Tenr.es,  295. 
Terebra,  278,  238. 
Terebratula,  267,  222. 
Terebratulina,  '267,  221. 
Termite,  295. 
Tern,  329,  308. 
Testndo,  see  Turtle. 
Tetrabranchs,  279,  247. 
Tetradecapods,  285,  251,  252. 
Thoracic  duct,  95,  61. 
Thorax,  119,  88. 
Thornback,  315,  288. 
Thousand-legged  Worm,  see  Jnlua. 
Thrush,  340. 
Tnylacinus,  343. 
Thyroid  Cartilage,  189, 159. 
Ticks,  288. 
Tissue,  33. 
Toad,  318. 

Tongue,  of  Batrachiaus,  61. 
of  Birds,  62. 
of  Fishes,  61. 
of  Insects,  50,58. 
of  Mammals,  63. 
ofMollusks,52. 
of  Spiders,  60. 
Top-shell,  278,  242. 
Tortoise,  323,  302. 

"        see  Turtle. 
Totipalmates,  330,  309. 
Toucan,  335. 
Touch,  176. 
Trachea,  119. 

Tracheae,  114,  40.  79,  80,  81. 
Trichina,  265,  218. 
Tridacne,  272. 
Trilobite,  284. 
Trionyx,  322. 
Triton,  318,  296. 
Tritonian,  274,  230. 
Trochosphere,  211, 175. 
Trochus,  278. 

"        embryo  of,  211, 176. 
Trogon,  335,  821. 
Tubipora,  252,  200. 
Tuuicata,  305,  278,  279. 
"         nee.  Ascidians. 
Turbo,  278,  242. 
Turkey,  333. 


Tnrritella,  278. 
Turtle,  322,  301,  302. 

'       alimentary  canal  of,  82. 

'       breathing  of,  11S>. 

'       mouth  of,  61. 

'      shell  of,  135. 

'      skeleton  of,  116. 

"      see  Chelonia. 
Tnsk3,  383. 
Types,  233. 

UNGULATA,  351,  53, 56,  103,  111,  117,  118, 

129, 138,  344,  345. 
feet  of,  129. 
Unio,  272. 

"     eggs  of,  196. 
Univalve,  see  Snail. 
Urodela,  317,  294-296. 

VARIATION,  216. 
Variety,  235. 
Veins,  104,  67. 
Veliger,  211,  176. 
Vena  cava,  104. 
Venus,  272. 
Venus'-basket,  246. 
Vermes,  263,  17,77,175. 

"        see  Earth-worm,  Worms. 
Vertebrae,  development  ot,  203. 
"         kinds  of,  140,  106,  107. 
"         number  of,  140. 
Vertebrata,  306. 

"          absorption  in,  94. 

"          alimentary  canal  of,  80. 

blood  of,  9S. 
"          brain  of,  170. 
"          circulation  in,10.,  281. 
"          development  of,  205. 
"          digestion  in,  92. 
"          ear  of,  179. 

exoskeleton  of,  134. 
eye  of,  183. 

gastric  glands  of,  123. 
heart  of,  107. 
kidney  of,  126. 
liver  of,  124. 
lungs  of,  117. 
mode  of  feeding  of,  54. 
mouth  of,  60. 
muscles  of,  156. 
nervous  system  of,  169. 
number  of  species  of,  221- 
pancreas  of,  123. 
salivary  glands  of,  122. 
skeleton  of,  137. 
skin  of,  128. 
stomach  of,  SO. 
teeth  of,  66. 
tongue  of,  60. 

see     Bird,    Crocodile,    Fish, 
Frog,  Mammal,  Reptile. 


INDEX. 


413 


Villi,  00,  58. 

Vinegar-eel,  265. 

Vireo,  340,  826. 

Vitelline  MembraLe,  193. 

Viviparous,  309. 

Vocal  Cords,  18J). 

Voice,  of  Invertebrates,  188. 

"     of  Vertebrates,  189. 
Volnte,  278,  241. 
Vorticella,  243,  160. 
Vulture,  335,  116. 

WALKING-STICK,  29T. 
Walrus,  355,383. 
Warbler,  340. 
Wasp,  304. 

Water-boatman,  29T,  265. 
Water-fleas,  284,  255. 
Wax-wing,  340. 
Weasel,  355,  348. 
Weevil,  300. 
Whale,  348,  341,  342. 

baleeu  of,  65,  30. 

"      brain  of,  170. 

"      fat  of,  39. 

"      mode  of  feeding  of,  50. 

"      month  of,  62. 

"      swimming  of,  159, 

"      teeth  of,  383. 
Whelk,  278,  228. 

"       see  Snail. 
White  Ant,  295. 


Windpipe,  119,  86. 
Wings,  of  Bats,  161,  339,  340. 
"      of  Birds,  160,  304. 
"      of  Insects,  159,  266. 
Wolf,  355,  347. 
Wombat,  343. 
Woodpecker,  335,  320. 
Worms,  263. 

"        absorption  in,  94. 
"        alimentary  canal  of,  7T. 
blood  of,  98. 
eye  of,  17. 
head  of,  17. 
jaws  of,  17. 
larva  of,  175. 
locomotion  of,  161. 
mouth  of,  57. 
number  of  speries  of,  22 
proboscis  of,  IV. 
"        reproduction  in,  192. 
"        respiration  of,  113,  77. 

skin  of,  127. 
"        see  Earth-worm. 
Wren,  340. 

YOLK,  192. 

ZOOLOGICAL  analysis,  236. 

"  barriers,  375. 

"  hibtory,  18. 

"          provinces,  376, 
Zoology,  19. 


THE    END. 


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