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BERKELEY^ 

LIBRARY    U 

UNIVERSITY  OP    j  I 
CALIFORNIA     Al 

— 

!3£AfT 


THE  ELEMENTS 

OF 

ANIMAL  BIOLOGY 


HOLMES 


THE  ELEMENTS 

OF 

ANIMAL  BIOLOGY 


BY 


S.  J.  HOLMES,  PH.  D. 

PROFESSOR   OF  ZOOLOGY,    UNIVERSITY   OF   CALIFORNIA 


WITH  249  ILLUSTRATIONS 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO. 

1012  WALNUT  STREET 


NIVERSITY  OF  CALIFORNIA 
SEUM  OF  VERTEBRATE  ZOOLOGY 


COPYRIGHT,  1919,  BY  P.  BLAKISTON'S  SON  &  Co. 


- ?^- 

.' 


THE  MAPLE  PRESS  YORK  PA 


Hr 


PREFACE  - 

This  volume  is  intended  as  an  introduction  to  the 
elements  of  animal  biology  for  the  use  of  students  in  the 
high  school.  The  cut-and-dried  method  of  exposition 
which  is  so  commonly  found  in  text-books  and  which  so 
frequently  deprives  them  of  all  traces  of  stimulating 
quality  has  been  avoided  so  far  as  was  deemed  compatible 
with  the  presentation  of  such  subject  matter  as  a  text-book 
should  contain.  Although  the  book  would  best  fulfil  its 
purpose  if  read  in  connection  with  laboratory  work,  I 
have  not  included  directions  for  such  work,  partly  be- 
cause it  would  add  considerably  to  the  bulk  of  the  volume, 
but  chiefly  because  so  many  teachers  nowadays  prefer  to 
make  laboratory  outlines  of  their  own. 

The  order  in  which  the  main  topics  are  treated  is  essen- 
tially like  that  which  is  followed  in  several  of  the  best 
recent  text-books.  The  general  experience  of  teachers 
of  biology  has  shown  it  to  be  eminently  desirable  that  the 
student  should  possess  a  general  knowledge  of  the  animal 
kingdom  as  a  preparation  for  the  study  of  physiology. 
The  section  on  the  elements  of  physiology  has  therefore 
been  placed  after  the  part  devoted  to  a  survey  of  the 
principal  groups  of  animals.  Rather  more  than  the 
usual  amount  of  attention  is  given  to  the  role  of  bacteria 
in  causing  disease,  and  to  the  way  in  which  diseases  are 
spread  and  how  they  may  be  avoided. 

The  third  part  of  the  book  dealing  with  general  topics 
such  as  evolution,  heredity  and  eugenics  begins  with  a 


335 


VI  PREFACE 

brief  survey  of  the  phenomena  of  sex  and  reproduction 
in  the  chapter  on  the  Perpetuation  of  Life.  No  reference 
is  made  in  the  text  to  the  much  discussed  problems  of  sex 
hygiene.  It  was  thought  desirable  to  leave  this  topic  to  the 
discretion  of  the  teacher  to  be  handled  in  whatever  way 
he  or  she  considers  to  be  most  effective.  An  attempt, 
however,  has  been  made  to  supply  the  students  with  a 
general  basis  of  knowledge  of  the  facts  of  reproduction 
and  development  so  that  a  little  added  instruction  of  the 
right  sort  will  aid  them  in  avoiding  the  dangers  and  pit- 
falls into  which  ignorance  is  continually  leading  so  many 
of  our  youth.  Sex  hygiene  should  be  associated  not  merely 
with  considerations  of  personal  welfare,  but  with  the  wel- 
fare of  future  generations.  It  is  highly  important  that  the 
youth  of  to-day  who  are  to  be  the  parents  of  to-morrow 
should  be  imbued  with  a  sense  of  their  obligations  as 
fathers  and  mothers  of  children.  They  need  to  be  made 
aware  that  it  is  a  matter  of  great  moment  what  kind  of 
people  are  supplying  the  larger  part  of  our  future  popula- 
tion. And  an  effort  has  accordingly  been  made  in  the 
discussion  of  heredity  and  eugenics  to  prepare  them  for  an 
appreciation  of  the  importance  of  a  knowledge  of  the  forces 
that  are  working  toward  the  improvement  or  the  deteriora- 
tion of  the  inborn  qualities  of  the  race. 

In  the  preparation  of  this  book  I  have  profited  by  the 
criticism  of  several  of  my  colleagues.  I  am  indebted  to 
Dr.  W.  W.  Cort  for  reading  the  entire  manuscript,  to  Dr. 
J.  Grinnell  for  reading  the  chapters  on  birds  and  mammals, 
to  Mr.  Tracy  Storer  for  reading  the  chapters  on  reptiles 
and  amphibians,  to  Dr.  J.  F.  Daniel  for  reading  the  chap- 
ter on  fishes,  and  to  Dr.  E.  C.  Van  Dyke  for  reading  the 


PREFACE  Vll 

chapters  on  insects.  Dr.  L.  J.  Cole  of  the  University  of 
Wisconsin  has  had  the  exceptional  patience  to  read  several 
of  the  chapters  in  the  almost  illegible  script  in  which  they 
were  originally  written.  I  wish  to  thank  Prof.  J.  S. 
Kingsley  and  Henry  Holt  and  Co.  for  permission  to  use 
figures  from  Kingsley's  translations  of  Hertwig's  Zoology. 
Dr.  Paul  Carus  has  very  kindly  permitted  me  to  use 
several  cuts  from  Romanes'  Darwin  and  After  Darwin 
issued  by  the  Open  Court  Publishing  Company.  To 
Dr.  B.  W.  Evermann  I  am  indebted  for  photographs  of 
several  groups  of  mammals  and  birds  in  the  museum  of 
the  California  Academy  of  Sciences.  Most  of  all  I  am 
indebted  to  my  wife  for  help  in  many  ways  during  the 
preparation  of  this  work. 

S.  J.  H. 
BERKELEY,  CALIF. 


CONTENTS 


PART  I. — THE  ANIMAL  KINGDOM. 

CHAPTER.  PAGE 

I.  The  Grasshopper  and  other  Orthoptera i 

II.  How  Animals  are  Classified 17 

III.  The  Lepidoptera  or  Butterflies  and  Moths 20 

IV.  The  Hemiptera,  or  the  Bugs  and  their  Allies 31 

V.  The  Diptera  or  Flies ; . .  40 

VI.  The  Coleoptera  or  Beetles 51 

VII.  The  Hymenoptera  or  Bees,  Ants,  Wasps  and  their  Allies. .  56 

VIII.  The  Dragon  Flies,  Damsel  Flies,  May  Flies,  Stone  Flies 
and  Caddis  Flies »,._ 70 

IX.  The  Myriapods  and  Arachnids 75 

X.  The  Crayfish  and  Other  Crustacea 84 

XI.  The  Mollusca 98 

XII.  The  Echinoderms 108 

XIII.  The  Ringed  Worms  or  Annelids 114 

XIV.  The  Round  Worms  and  Flat  Worms 122 

XV.  The  Coelenterates  and  Sponges 130 

XVI.  The  Protozoa  or  the  Simplest  Animals 141 

XVII.  The  Lowest  Vertebrates  and  their  Nearest  Allies 153 

XVIII.  The  Fishes 158 

XIX.  The  Amphibia  (Frogs,  Toads,  Newts  and  Salamanders)..  169 

XX.  The  Reptiles 176 

XXI.  The  Birds 183 

XXII.  The  Mammals 209 

PART  II. — THE  ELEMENTS  OF  PHYSIOLOGY. 

XXIII.  The  Chemical  Basis  of  Life 232 

XXIV.  Cells  and  Tissues 240 

XXV.  Digestion 245 

XXVI.  Foods  and  Their  Uses 252 

ix 


X  CONTENTS 

CHAPTER.  PAGE 

XXVII.  The  Blood  and  Circulation 259 

XXVIII.  Respiration 269 

XXIX.  Excretion . 277 

XXX.  Internal  Secretions  and  the  Ductless  Glands 280 

XXXI.  The  Skin ' 283 

XXXII.  The  Skeleton  and  the  Muscles 287 

XXXIII.  The  Nervous  System 294 

XXXIV.  The  Organs  of  Sense 304 

XXXV.  Alcohol  and  Tobacco 311 

XXXVI.  Bacteria  and  Disease 317 

PART  III.— GENERAL  FEATURES  AND  ADAPTATIONS. 

XXXVII.  The  Perpetuation  of  Life 331 

XXXVIII.  The  Evolution  of  Life 341 

XXXIX.  Divergence  and  Adaptation 362 

XL.  Heredity  and  Human  Improvement 370 


PART  I 
THE  ANIMAL  KINGDOM 


ANIMAL  BIOLOGY 

CHAPTER  I 
THE  GRASSHOPPER  AND  OTHER  ORTHOPTERA 

Among  the  most  common  things  with  which  we  come 
into  contact  in  this  world  are  living  beings,  and  it  is  there- 
fore highly  desirable  that  we  know  a  good  deal  about  them. 
The  science  which  deals  with  the  living  world  is  called 
Biology,  and  it  falls  into  two  subdivisions,  one,  Botany, 
which  is  concerned  with  plants,  and  the  other,  Zoology, 
which  treats  of  animals.  No  one,  be  he  ever  so  dull,  can 
escape  picking  up  some  information  on  the  subject  matter 
of  these  branches  of  science,  yet  comparatively  few  realize 
the  great  importance  and  interest  which  attaches  to  the 
study  of  the  world  of  life.  Most  of  us  are  blind  to  count- 
less wonderful  and  beautiful  things  which  a  little  well-di- 
rected observation  would  disclose  to  our  view.  And  we 
often  shrink  from  many  forms  with  a  feeling  of  repug- 
nance which  a  closer  acquaintance  would  change  to  one 
of  interest  and  admiration  for  the  remarkable  adaptations 
of  their  structure  and  activities. 

To  begin  our  study  of  animal  life,  we  shall  select  a  com- 
mon and  familiar  form,  the  grasshopper.  All  living 
creatures  have  much  in  common,  and  what  we  learn  about 
one  kind  will  help  us  very  materially  in  learning  about 
others.  The  grasshopper  is  a  member  of  the  great 
class  of  insects  which  is  the  largest  group  in  the  animal 
kingdom.  It  is  a  creature  of  complex  structure,  but 
formed  upon  a  pattern  very  different  from  that  of  our 


2  ANIMAL  BIOLOGY 

own  body.  Like  ourselves,  however,  it  can  walk,  jump, 
eat,  breathe,  see,  hear,  smell,  make  sounds  and  perform  a 
great  number  of  other  activities  which  show  that  it  is  not 
so  different  from  a  human  being  as  we  might  at  first  be 
disposed  to  believe. 

In  order  to  understand  how  these  activities  are  carried 
on  it  is  necessary  to  study  briefly  the  grasshopper's  struc- 
ture. The  skeleton  of  the  grasshopper's  body  is  on  the 
outside,  instead  of  on  the  inside  as  in  ourselves,  and  it  is 
composed  of  a  substance  called  chitin,  which  is  thickened 
in  some  regions  where  it  has  acquired  a  certain  rigidity. 
Externally  the  body  shows  a  division  into  rings  marking 


Prosteritdl  6 fin 

FIG.  i. — Side  view  of  a  typical  grasshopper.     (After  Woodworth.) 

the  individual  segments  of  which  the  body  is  built  up. 
Some  of  the  segments  can  move  one  upon  the  other. 
In  these  cases  the  chitin  between  the  segments  is  thinner 
than  elsewhere  so  as  to  become  flexible,  thus  allowing 
freedom  of  movement.  In  other  cases  the  segments  are 
so  closely  united  that  there  is  no  motion  between  them. 
The  body  of  the  grasshopper  shows  a  division  into  three 
parts,  the  head,  thorax  and  abdomen.  Look  with  a  hand 
lens  at  the  large  eyes  at  the  sides  of  the  head  and  you  may 
see  that  they  present  a  finely  checkered  appearance  due 
to  their  being  composed  of  smaller  elements.  The  grass- 
hopper's eye  is  compound,  and  when  we  look  at  the  trans- 


THE    GRASSHOPPER   AND    OTHER   ORTHOPTERA 


parent  outer  covering,  or  cornea,  of  the  eyes  with  a  micro- 
scope it  will  be  seen  to  be  divided  into  a  number  of  six- 
sided  areas.  Each  of  these  areas  lies  over  a  sort  of  simple 
eye;  in  fact  the  compound  eye  may  be  regarded  as 
composed  of  a  large  number  of  simple  eyes  lying  side 
by  side,  the  whole  forming  a  very  efficient  organ  of  sight 
as  you  may  easily  convince  yourself  by  trying  to  catch 
grasshoppers  in  the  field.  Besides  the  compound  eyes 
there  are  three  simple  ones  or 
ocelli  at  the  top  of  the  head, 
but  little  is  known  concerning 
their  precise  use. 

The  long  feelers  or  antenna 
on  the  front  of  the  head  are 
composed  of  many  movable 
segments.  By  watching  a  live 
grasshopper  you  may  discover 
indications  that  the  antennae 
are  used  as  organs  of  touch. 
They  are  also,  curiously 
enough,  organs  of  the  sense  of 
smell.  The  microscope  shows 
that  they  contain  numerous 
pits,  the  olfactory  pitSj  which 
are  probably  organs  for  detect- 
ing odorous  substances.  On 
the  mouth  parts  of  the  grass- 
hopper there  are  certain  organs-  resembling  short  feelers, 
called  the  palps,  which  the  grasshopper  uses  considerably 
when  feeding.  These  palps  have  been  thought  to  contain 
organs  of  taste,  but  it  is  probable  that  taste  organs  occur 
further  within  the  mouth  also. 

The  grasshopper  is  furnished  with  three  pairs  of  mouth 
parts:  (i)  a  pair  of  strong  jaws  or  mandibles;  (2)  a  pair  of 


PIG.  2. — Face  of  grasshopper. 
ANT,  antennae;  C,  clypeus;  L, 
upper  lip;  O,  ocellus;  P,  palpi. 


4  ANIMAL  BIOLOGY 

smaller  accessory  jaws,  the  first  maxilla  and  (3)  the  la- 
bium  or  lower  lip,  which  is  composed  of  the  second  max- 
illa more  or  less  fused  together.     The  peculiar  working  of 
these  organs  may  be  readily  seen  in  a  living  specimen. 
The  thorax,  or  the  part  of  the  body  immediately  behind 
the  head,  consists  of  three  segments  called  the  prothorax, 
mesothorax  and  metathorax  in  order  from  be- 
fore backward.     Like  nearly  all  insects  the 
grasshopper  has  six  legs,  a  single  pair  being 
attached    to    each   segment    of  the  thorax. 
The  first  two  pairs  which  are  fitted  for  walk- 
ing or  climbing  are  quite  different  from  the 
last  pair  which  is  mainly  used  for  jumping. 
It  may  readily  be  seen  that  the  parts  of  the 
legs  are  united  by  flexible  membranes  at  the 
joints  so  as  to  permit  of  free  movement. 
Each  leg  consists  of  two  short  segments  near 
the  base,  a  relatively  large  part,  the  femur, 
followed  by  the  tibia,  and  finally  the  foot, 
or  tarsus.     The  latter  ends  in  a  pair  of  claws 
and  is  furnished  wih  pads  below  the  segments. 
The  hind  legs  are  especially  noticeable  on 
Mouth 'parts~of  account  of  their  large  size  and  the  double 
grasshopper.  row  of  sharp  spines  on  the  posterior  side  of 

m,       mandible; 

max,  maxilla;  /.  the  tibia.     The  function  of  these  spines  may 
^abmm;  p,  pal-  rea(^jjy  be  discovered  by  observing  live  grass- 
hoppers. 

The  first  pair  of  wings  which  are  situated  on  the  meso- 
thorax are  often  called  the  wing  covers  as  they  lie  over  the 
large  second  pair  of  wings  which  are  the  chief  organs  of 
flight.  The  first  wings  are  narrow,  relatively  thick  and 
usually  of  a  dull  color.  The  second  pair  are  broad, 
thin  of  texture  and  frequently  brightly  colored.  Ordina- 
rily the  latter  are  not  seen  except  during  flight  as  they  lie 


THE    GRASSHOPPER   AND    OTHER    ORTHOPTERA  5 

folded  up  under  the  first  pair.  Both  pairs  of  wings  may 
be  regarded  as  folds  of  the  general  chitinous  covering  of 
the  body.  Consequently  they  consist  of  a  double  chiti- 
nous membrane.  In  certain  places  the  chitin  is  thickened 
to  form  the  so-called  veins  which  serve  to  give  the  wings 
the  degree  of  rigidity  necessary  for  flight. 

The  abdomen  is  composed  of  segments  most  of  which  are 
similar  in  structure  and  freely  movable  upon  one  another. 
The  upper  and  lower  parts  of  the  segments  are  united 
by  a  flexible  membrane  so  as  to  permit  a  certain  amount 
of  vertical  movement  between  these  parts.  At  the  pos- 
terior end  of  the  abdomen  is  the  opening  of  the  intestine 
and  certain  appendages  used  in  reproduc- 
tion. The  end  of  the  abdomen  differs  in 
the  two  sexes  and  affords  an  easy  means 
of  distinguishing  the  male  from  the  female. 
In  the  female  the  tip  of  the  abdomen  is  fur- 
nished with  two  pairs  of  acute  processes 
forming  an  organ  called  the  ovipositor  which  FlG-  4-— Part 

ofatrachealtube 

is  used  in  laying  the  eggs  in  the  ground,  with  coating  of 

In   the  male   the  end   of  the  abdomen  is  c 

blunt  and  swollen  and  is  entirely  devoid  of  an  ovipositor. 

One  of  the  most  peculiar  features  of  the  grasshopper's 
life  is  its  mode  of  breathing.  Watch  the  extension 
and  contraction  of  the  abdomen  and  the  changes  in  shape 
of  the  segments.  We  might  easily  conjecture  that  these 
movements  had  to  do  with  breathing,  but  it  is  not  so 
apparent  where  air  is  taken  into  and  expelled  from  the 
body.  With  a  hand  lens,  however,  one  may  see  a  number 
of  small  apertures  called  the  spiracles  along  the  sides  of 
the  abdomen,  and  two  larger  pairs  on  the  thorax.  These 
lead  to  the  breathing  tubes  or  tracheae  which  ramify  through- 
out the  body  and  carry  air  to  all  the  internal  organs. 

The  grasshopper  also  differs  greatly  from  most  animals 


6  ANIMAL  BIOLOGY 

in  the  location  of  its  organ  of  hearing.  Look  on  the  side 
of  the  first  segment  of  the  abdomen  and  you  will  find  an 
oval  aperture  covered  with  membrane;  this  is  furnished 
with  a  delicate  apparatus  which  is  stimulated  by  the  vi- 
brations of  the  air  and  thus  makes  its  possessor  aware  of 
the  presence  of  sound.  As  animals  which  hear  usually 
have  some  means  of  making  a  noise  themselves,  we  find 
that  grasshoppers  are  frequently  furnished  with  an  instru- 
ment for  the  production  of  song,  although  it  is  present 
only  in  the  male  sex.  This  instrument  consists  in  most 
cases  of  a  series  of  fine  teeth  on  the  inner  side  of  the  femur. 
As  this  apparatus  is  rubbed  over  one  of  the  veins  of 
the  wing  cases  it  produces  a  shrill  note.  If  one  carefully 
approaches  a  singing  grasshopper  he  may  see  the  femur 
drawn  across  the  wing  cover,  producing  a  sound  much  as 
the  violinist  does  by  drawing  his  bow  over  a  string. 
The  musical  sound  probably  serves,  like  the  songs  of 
birds,  as  a  means  of  bringing  the  sexes  together. 

After  this  study  of  the  external  parts  of  the  grasshopper 
let  us  consider  briefly  some  of  the  features  of  its  internal 
structure.  The  part  of  the  body  concerned  with  the 
digestion  of  food  is  the  alimentary  canal  which  is  a  tube 
leading  from  the  mouth  to  the  posterior  end  of  the  body. 
Different  parts  of  this  tube  differ  in  structure  and  in 
function.  Leading  from  the  mouth  is  a  short  and  narrow 
division  called  the  esophagus.  Connected  with  a  promi- 
nence at  the  anterior  end  of  the  esophagus  are  the  salivary 
glands  whose  function  is  to  secrete  and  pour  into  the 
alimentary  canal  a  fluid  which  aids  in  digestion.  Pos- 
teriorly the  esophagus  leads  to  a  crop  lined  internally  with 
rows  of  chitinous  teeth  which  probably  serve  to  grind 
up  the  food.  Behind  the  crop  is  a  large,  thin-walled 
stomach  at  the  anterior  end  of  which  open  a  number  of 
tubes  called  gastric  caeca.  The  stomach  passes  into  the 


THE   GRASSHOPPER  AND   OTHER   ORTHOPTERA  7 

intestine  which  is  narrow  and  more  or  less  coiled.  The 
latter  leads  to  the  terminal  portion  of  the  alimentary 
canal,  the  rectum,  which  opens  through  the  last  segment 
of  the  body.  The  food  as  it  passes  down  the  alimentary 
canal  is  acted  on  by  the  saliva,  the  secretion  of  the  gastric 
cceca,  and  other  fluids  formed  by  the  walls  of  the  stomach 
whereby  it  undergoes  a  process  of  digestion  after  which 
the  soluble  materials  are  absorbed  through  the  walls  of 
the  alimentary  canal,  especially  the  stomach  and  intestine, 
and  carried  to  various  parts  of  the  body.  The  undigested 
residue  is  expelled  through  the  rectum. 


FIG.  5. — Diagram  of  the  internal  organs  of  a  grasshopper,  c,  crop; 
gc,  gastric  coeca;  vn,  ventriculus,  il,  ileum  or  anterior  part  of  the  intestine; 
co,  colon,  r,  rectum;  e,  eye;  g,  g,  ganglia;  nc,  nerve  cord;  sg,  salivary  glands; 
mt,  Malpighian  tubules;  ov,  ovary;  od,  oviduct;  op,  ovipositor.  (Modified 
from  Brooks.) 

The  absorbed  food  materials  are  carried  to  different 
organs  by  means  of  the  blood  which  is  not  red  as  in  our- 
selves, but  nearly  colorless.  The  organ  for  propelling  the 
blood  is  the  heart,  an  organ  very  different  in  appearance 
and  position  from  our  own  heart,  as  it  consists  of  a  long 
tube  lying  along  the  upper  part  of  the  abdomen.  It  is 
closed  behind  but  open  in  front,  and  is  perforated  by 
several  pairs  of  openings  along  the  sides.  Blood  enters 
through  these  lateral  openings  and  is  prevented  from 
flowing  back  by  valves.  The  heart  beats  or  contracts  from 
behind  forward  so  that  the  blood  which  is  drawn  in  through 


8 


ANIMAL  BIOLOGY 


the  sides  is  expelled  at  the  front  of  the  heart  through  short 
blood  vessels.  There  are  almost  no  well-defined  blood 
vessels  in  the  grasshopper,  and  the  blood,  after  being  forced 
out  of  the  short  vessels  at  the  front  of  the  heart,  passes  into 
irregular  spaces  between  the  tissues  and  organs  of  the  body 
until  it  finds  its  way  back  to  the  heart  again,  when  it  is 
taken  in  through  the  lateral  openings  and  sent  out  on  a 
new  journey.  In  many  insects,  es- 
pecially the  transparent  young  or 
larval  stages  of  aquatic  species,  it 
is  possible  to  see  the  beating  of  the 
heart  and  the  flow  of  blood  in  the 
living  organism. 

The  organs  in  the  grasshopper 
which  correspond  in  function  to  the 
human  kidneys  and  which  therefore 
serve  as  a  means  of  getting  rid  of 
certain  waste  products  in  the  blood 
consist  of  a  series  of  fine  thread-like 
tubules,  called  Malpighian  or  urinary 
tubules,  which  empty  into  the  intes- 
tine close  to  where  it  joins  the 
stomach.  The  waste  matter  col- 
lected by  these  tubules  therefore 
passes  out  of  the  body  with  the  undigested  portions  of 
the  food.  Other  waste  products,  especially  carbon  dioxide, 
are  removed  by  the  tracheal  tubes. 

The  brain  of  the  grasshopper  is  situated  in  the  upper 
part  of  the  head  above  the  esophagus.  From  the  brain 
nerves  go  to  the  eyes,  ocelli  and  antennae,  and  from  the 
lower  side  a  nerve  cord  passes  on  either  side  of  the  esopha- 
gus to  a  nerve  mass  called  the  subesophageal  ganglion 
which  supplies  nerves  to  the  mouth  parts.  This  ganglion 
is  the  first  of  a  series  of  paired  ganglia  extending  along  the 


--so 


FIG.  6.— -Brain  of 
grasshopper  from  in 
front.  C,  commissures 
around  the  esophagus; 
E,  nervous  supply  of  eye; 
O,  nerves  to  ocelli;  SO, 
subesophageal  ganglion. 


THE  GRASSHOPPER  AND  OTHER  ORTHOPTERA      9 

ventral  side  of  the  body.  These  ganglia  are  connected 
by  a  double  nerve  cord,  the  two  parts  of  which  lie  very 
close  together  and  appear  in  the  abdomen  as  a  single  strand. 
There  is  a  paired  ganglion  in  each  of  the  three  segments 
of  the  thorax  and  five  ganglia  in  the  abdomen.  From 
these  ganglia  nerves  are  given  off  to  the  muscles  and  sense 
organs  of  neighboring  parts. 

Movements  of  parts  of  the  body  are  effected  by  means 
of  muscles.  The  thorax  contains  muscles  of  unusually 
large  size  which  are  used  for  moving  the  wings.  Muscles 
'act  by  contracting  and  thereby  producing  movement  in 
the  parts  upon  which  they  are  inserted.  The  impulses 
causing  the  contraction  are  conveyed  by  nerves  which 
pass  to  the  muscles  from  the  ganglia. 

The  ovaries,  or  organs  for  producing  the  eggs,  are  situa- 
ted in  the  abdomen  of  the  female.  They  present  the 
appearance  of  paired  masses  of  eggs  in  various  stages  of 
growth  from  an  exceedingly  minute  size  to  the  lull  grown 
egg.  When  the  eggs  have  attained  their  full  size  they  are 
discharged  from  the  ovary  into  a  tube,  the  oviduct.  A 
short  distance  from  the  posterior  end  of  the  body  the  two 
oviducts  unite  to  form  a  median  duct  which  opens  between 
the  bases  of  the  valves  of  the  ovipositors  previously  de- 
scribed. During  their  passage  down  the  oviduct  the 
eggs  become  surrounded  by  a  sticky  substance  secreted  by 
certain  glands  which  open  near  the  junction  of  the  two 
oviducts.  It  is  this  sticky  substance  which  causes  the 
eggs  to  adhere  in  masses  after  they  are  laid  and  which 
subsequently  protects  them  'from  the  injurious  effects  of 
moisture. 

The  male  organs  corresponding  to  the  ovaries  are  called 
the  spermaries  or  testes.  They  lie  in  the  abdomen  above 
the  intestine  and  are  so  closely  united  that  they  appear 
as  a  single  organ.  They  give  rise  to  slender  ducts  which 


10  ANIMAL  BIOLOGY 

open  at  the  posterior  end  of  the  body.  The  spermaries 
produce  minute  bodies  called  spermatozoa  whose  function 
it  is  to  unite  with  or  fertilize  the  eggs  and  thereby  render 
them  capable  of  development. 

The  eggs  are  fertilized  before  they  are  laid.  In  the  late 
summer  or  fall  the  female  bores  with  her  abdomen  a 
shallow  hole  in  the  earth  and  deposits  her  mass  of  eggs 
which  lie  there  over  winter  and  hatch  out  in  the  following 
summer.  The  young  grasshopper  at  its  first  appearance 


FIG.  7. — Grasshoppers  laying  eggs,  a,  a,  a,  female  in  different  posi- 
tions, b,  egg  pod,  c,  separate  eggs,  d,  e,  earth  removed  to  expose  the  pods. 
(After  Riley.). 

upon  the  stage  of  life  is  conspicuously  different  from  the 
adult  in  several  respects;  it  is  small  in  size,  soft  bodied, 
entirely  devoid  of  wings,  and  provided  with  a  head  which 
seems  all  out  of  proportion  to  its  diminutive  body.  It 
starts  at  once  on  the  main  business  of  its  early  life  which  is 
eating,  eagerly  devouring  all  sorts  of  plant  life  and  con- 
sequently growing  rapidly.  As  a  result  of  its  growth  the 
chitinous  skin  or  exoskeleton  which  is  made  of  compara- 
tively inelastic  and  unyielding  material  becomes  too  small. 
Then  comes  the  process  of  molting  or  shedding  the  skin. 


THE   GRASSHOPPER  AND   OTHER   ORTHOPTERA  II 

The  skin  splits  down  the  middle  of  the  back,  the  abdomen 
is  drawn  forward  out  of  its  old  case,  the  legs  are  pulled 
out  of  their  coverings  and  the  grasshopper  slowly  pulls 
itself  out  of  all  of  its  old  clothes  and  appears  in  a  new  but 
thin  external  covering  which  had  been  forming  preparatory 
to  casting  off  the  older  one.  The  recently  molted  grass- 


FIG.  8. — Three  stages  in  the  metamorphosis  of  a  grasshopper.     (After 

Herrns.) 

hopper  appears  quite  suddenly  larger  than  before.  The 
new  skin  hardens,  the  grasshopper  eats  and  grows,  and 
before  long  it  has  to  undergo  a  new  molt.  The  skin  is 
shed  four  or  five  times  before  the  grasshopper  reaches 
maturity.  During  this  series  of  molts  gradual  changes 
of  form,  which  are  spoken  of  as  metamorphosis,  take  place. 
One  of  the  most  salient  features  of  this  process  is  the 


12  ANIMAL  BIOLOGY 

development  of  the  wings  which  first  appear  as  small  folds 
on  the  posterior  margins  of  the  second  and  third  segments 
of  the  thorax.  The  wings  become  larger  with  successive 
molts  and  acquire  a  joint,  or  articulation,  at  the  base 
which  renders  them  freely  moveable.  Forms  such  as  the 
grasshopper  and  its  allies  in  which  the  newly  hatched 
young  resembles  the  adult  and  passes  into  the  latter  by 
gradual  stages  are  said  to  undergo  an  incomplete  meta- 
morphosis. Insects  with  a  complete  metamorphosis  pass 
through  stages  marked  by  abrupt  and  extensive  changes. 
In  these  forms  the  larva  passes  into  a  usually  quiescent 
pupa  from  which  finally  emerges  the  imago  or  aduh 
insect. 

The  description  of  a  grasshopper  previously  given  will 
apply  to  a  large  number  of  the  more  typical  kinds.  There 
are  several  hundred  different  species  of  grasshoppers, 
and  they  occur  in  almost  all  countries  of  the  tropical 
and  temperate  regions  of  the  earth.  We  commonly  find 
considerable  differences  between  the  grasshoppers  of 
different  countries,  and  any  one  country  usually  contains 
several  species.  Grasshoppers  are  very  common  in  mead- 
ows and  grain  fields.  The  Carolina  locust,  or  roadside 
grasshopper,  frequents  roadsides  and  other  bare  patches 
of  ground  where  it  is  difficult  to  detect  on  account  of  the 
similarity  of  its  color  to  that  of  the  soil.  Many  other 
species  are  protectively  colored  when  in  their  natural 
surroundings.  Certain  species  of  grasshoppers  are  mi- 
gratory and  some  of  the  most  destructive  forms  belong  to 
this  group.  In  some  of  the  migratory  species  the  air  sacs 
connected  with  the  tracheae  are  well  developed  and  when 
inflated  with  air  serve  to  buoy  the  insects  up  during  long 
flights.  These  forms  fly  in  swarms  which  sometimes 
consist  of  incredible  numbers.  In  1889  a  swarm  which 
passed  over  the  Red  Sea  was  over  2000  square  miles  in 


THE    GRASSHOPPER   AND    OTHER    ORTHOPTERA  13 

area.  The  swarms  are  sometimes  so  dense  that  the  sun 
is  darkened  and  when  they  alight  they  eat  up  within  a 
short  time  almost  every  green  plant  within  their  reach. 
Plagues  of  locusts  in  the  old  world  have  been  frequently 
recorded,  some  accounts  of  them  being  found  in  the  Bible. 
The  most  destructive  of  the  grasshoppers  of  our  country 
is  the  celebrated  Rocky  Mountain  locust  which  during 
a  series  of  years  1874-6  caused  enormous  damage  in 
Kansas,  Nebraska,  Missouri  and  other  western  states. 
Old  inhabitants  will  never  forget  the  grasshopper  years. 
The  insects  came  down  upon  them  in  such  vast  swarms 


PIG.  9. — The     California    katydid,     Scudderia    furcifera  Scudd.     Male, 
natural  size.     (After  Essig.) 

that  in  many  places  they  ate  up  completely  the  crops  of 
corn  and  grain,  destroyed  the  pastures,  stripped  many 
shrubs  of  their  foliage  and  devoured  the  weeds,  even  down 
to  such  unsavory  ones  as  smart  weed  and  dog-fennel. 
Stock  thus  deprived  of  their  food  perished  in  large  numbers 
and  the  inhabitants  underwent  great  hardships  on  account 
of  their  losses.  Professor  Packard  estimates  that  the 
losses  due  to  grasshoppers  during  four  years  amounted  to 
$200,000,000.  Very  few  of  our  common  grasshoppers 
are  so  destructive  as  the  Rocky  Mountain  locust  although 
several  species  do  considerable  damage.  One  of  the  most 


ANIMAL  BIOLOGY 


common  and  widespread  pests  is  the  red-legged  grasshopper 
which  is  closely  related  to  the  preceding  species. 

Grasshoppers  have  been  held  in  check  by  various  meth- 
ods. Plowing  the  ground  destroys  large  numbers  of  the 
eggs  as  they  seldom  develop  if  covered  with  a  few  inches 
of  soil.  Grasshoppers  are  sometimes  poisoned  by  bran 
mixed  with  Paris  green  or  London  purple.  A  good  deal 
of  success  in  destroying  them  has 
been  attained  by  dragging  over  the 
ground  machines  called  "  hopper- 
dozers"  in  which  the  grasshoppers 
are  collected  and  killed  by  kerosene 
oil.  This  substance  is  a  deadly 
poison  to  grasshoppers  and  most 
other  insects,  a  slight  contact  with 
it  usually  proving  fatal. 

Closely  allied  to  grasshoppers 
such  as  we  have  described  are  the 
so-called  long-horned  grasshoppers, 
katydids  and  their  allies,  all  of 
which  have  long,  slender  antennae. 
The  fore  wings  in  the  males  are 
furnished  with  a  peculiar  apparatus 
at  the  base,  by  which  they  can 
make  a  noise  when  the  wings  are 
rubbed  together.  Only  the  males 
of  the  katydids  and  grasshoppers 
sing.  The  females  have  an  ovipositor,  frequently  very 
long,  by  which  eggs  may  be  affixed  to  or  inserted  into  the 
stems  of  plants. 

Other  relatives  of  the  grasshoppers  are  the  crickets  with 
whose  dark  and  glossy  bodies,  lively  movements  and  cheer- 
ful chirping  we  are  all  more  or  less  familiar.  In  these 
forms  also  it  is  the  male  that  makes  the  song  and  he  does 


FIG.  10. — Eggs  of  the 
angular-winged  katydid 
attached  to  twigs.  The 
holes  have  been  made  by 
the  egg  parasite,  Eupelmus 
mirabilis  (Walsh).  (After 
Essig.) 


THE   GRASSHOPPER  AND   OTHER   ORTHOPTERA  15 

it  by  rubbing  together  the  sound-producing  organs  on  the 
bases  of  the  fore  wings.  The  female  may  be  distinguished 
by  the  absence  of  these  organs  and  by  the  presence  of  an 
ovipositor  which  frequently  is  of  considerable  length. 
The  white  crickets  which  are  usually  found  upon  plants, 
and  the  mole  cricket  which  lives  under  ground  and  has 
its  fore  legs  modified  for  burrowing  are  less  typical  mem- 
bers of  the  cricket  family. 

Less  popular  relatives  are  the  cockroaches,  some  species 
of  which  are  found  under  stones  and  logs  while  others  pre- 
fer to  live  within  houses  where  they  devour  all  sorts  of 


FIG.  ii. — A  common  cockroach,  Blattella  germanica.  a-e,  various 
stages  of  development,  /,  female  carrying  egg  case;  g,  egg  case.  (After 
Riley.) 

food-stuffs  and  make  themselves  a  general  nuisance. 
They  are  very  lively  rascals,  carrying  on  most  of  their 
depredations  at  night,  although  they  are  often  seen  during 
the  day.  Their  flattened  bodies  enable  them  to  crawl 
into  narrow  crevices  which  afford  them  concealment. 
The  eggs  are  laid  in  a  very  peculiar  egg  case  which  is  car- 
ried around  for  a  while  by  the  female. 

More  distant  kin  of  the  grasshoppers  are  the  walking- 
sticks  and  mantids.  The  former  are  remarkable  for  their 
long,  narrow  body  and  slender  legs,  the  whole  insect  being 
readily  mistaken  for  a  twig.  The  leaf  insect  of  the  tropics 


i6 


ANIMAL  BIOLOGY 


is  allied  to  the  walking-stick,  but  it  is  furnished  with  green 
wings  whose  veins  closely  resemble  those  of  a  leaf.  The 
mantids  have  a  long  prothorax  and  strong  fore  legs 


PIG.   12. — Walking- stick. 

fitted  for  seizing  other  insects  on  which  they  feed. 
The  fore  legs  are  held  in  a  devout  attitude  which 
doubtless  suggested  the  name  " praying  mantis"  and 


gave 


FIG.   13. — American  mantis,  Mantis  Carolina. 

rise  to  the  many  superstitions  associated  with  this  insect. 
The  so-called  attitude  of  prayer  is  really  one  of  readiness 
for  quickly  grabbing  any  insect  within  reach. 


CHAPTER  II 
HOW  ANIMALS  ARE  CLASSIFIED 

The  various  insects  we  have  described  resemble  one 
another  in  different  degrees  so  that  it  is  possible  to  arrange 
them  in  groups  according  to  their  degrees  of  likeness. 
This  process  of  grouping  is  called  classification.  For 
many  purposes  it  is  desirable  to  divide  various  kinds  of 
objects  such  as  books  into  classes  and  this  is  especially 
desirable  in  the  case  of  animals  and  plants  of  which  there 
are  such  vast  numbers  of  different  kinds.  Animals  or 
plants  which  very  closely  resemble  one  another,  and  which 
are  commonly  spoken  of  as  belonging  to  the  same  kind 
constitute  what  is  called  a  species.  For  instance,  the  in- 
dividuals of  the  Rocky  Mountain  locust  form  one  species; 
those  of  the  red-legged  locust  another.  The  Grizzly  bear 
is  one  species,  the  black  bear  another  and  the  European 
brown  bear  a  third.  While  species  is  the  last  or  smallest 
group  usually  dealt  with,  we  sometimes  recognize  smaller 
groups  within  the  same  species,  which  are  called  varieties. 
We  commonly  speak  of  varieties  of  corn,  wheat,  cattle,  pigs, 
etc.,  where  the  groups  differ  but  slightly,  and  where  one 
is  known  to  have  been  derived  from  the  other,  or  where  one 
group  shades  into  the  other  one.  It  is  not  possible  to 
draw  a  sharp  distinction  between  species  and  varieties,  as 
Darwin  pointed  out  a  good  many  years  ago,  and  there  is 
often  difference  of  opinion  as  to  whether  a  group  should 
rank  as  a  variety  or  as  a  distinct  species. 

Different  species  that  closely  resemble  one  another  are 
classed  as  members  of  a  larger  group  called  a  genus;  a 
genus  therefore  is  a  group  of  similar  species.  Now  it  is 
convenient  to  give  every  species  a  name  just  as  it  is  con- 

2  17 


1 8  ANIMAL  BIOLOGY 

venient  to  give  every  human  being  a  name.  The  name  of 
each  species  of  animal  or  plant  commonly  consists  of 
two  words,  the  first  designating  the  genus,  the  second  the 
species.  The  Rocky  Mountain  locust  is  named  Mela- 
no  plus  spretus,  Melanoplus  being  the  genus  and  spretus 
indicating  a  particular  species  of  that  genus.  The  red- 
legged  grasshopper  is  closely  related  to  this  species  and  is 
therefore  placed  in  the  same  genus  but  given  a  different 
species  name,  Melanoplus  femur-rubrum.  The  various 
species  of  bears  mentioned  are  members  of  the  genus  Ursus 
which  is  the  Latin  name  for  bear;  the  grizzly  bear  is  called 
Ursus  horribilis;  the  common  black  bear,  Ursus  ameri- 
canus;  and  the  European  brown  bear,  Ursus  arctos.  The 
naming  of  species  of  animals  is  very  much  like  naming 
different  people  John  Jones,  Peter  Jones  and  Mary  Jones 
to  indicate  that  they  are  individuals  of  the  Jones  family. 
Just  as  similar  species  are  grouped  into  genera  so  are 
allied  genera  united  into  a  larger  group,  the  family. 
Melanoplus,  Dissosteira  or  the  genus  of  the  roadside 
grasshopper,  and  other  related  genera  are  grouped  into 
the  family  Acridiidae  which  includes  the  short-horned 
grasshoppers.  Similarly  various  families  such  as  the 
long-horned  grasshoppers  and  katydids  which  constitute 
the  family  Locus  tidae;  the  cricket  family,  Grillidas;  the  cock- 
roach family,  Blattidae,  etc.,  are  grouped  into  a  larger  divi- 
sion, or  order,  called  the  Orthoptera  (orthos,  straight,  and 
pteron  wing).  The  order  Orthoptera,  together  with  other 
orders  such  as  the  Coleoptera  or  beetles,  the  Diptera  or 
flies,  etc.,  constitute  the  class  of  Insecta.  And  the  Insecta 
together  with  other  classes  such  as  the  Crustacea  (crayfish, 
crabs  and  their  allies)  and  the  Arachnida  (spiders,  scor- 
pions, mites,  etc.)  and  some  others  are  united  to  form  a 
still  larger  division  called  phylum,  which  is  the  largest 
subdivision  of  the  animal  kingdom.  The  vast  assemblage 


HOW  ANIMALS   ARE   CLASSIFIED  19 

of  animals  may  be  compared  to  a  tree  whose  largest 
branches  correspond  to  the  phyla,  the  secondary  branches 
representing  the  classes,  the  branches  of  these  the  orders, 
and  so  on,  the  leaves  at  the  tips  of  the  branches  represent- 
ing the  species. 

As  it  is  often  desirable  to  determine  the  group  to  which  a 
particular  animal  belongs,  guides  to  the  proper  group  are 
often  given  in  the  form  of  a  key.  In  using  the  following 
key  to  the  families  of  the  orthoptera  ascertain  first  if  the 
insect  falls  under  the  group  A.  If  not  try  AA.  If  it 
goes  in  the  latter  division  see  whether  it  falls  under  B  or 
BB.  If  it  comes  under  BE,  then  find  whether  it  belongs 
in  C  or  CC.  After  finding  the  family,  the  genus  and  the 
species  to  which  the  insect  belongs  may  be  determined  in 
a  similar  manner.  As  the  genera  and  species  of  Orthop- 
tera are  so  numerous,  it  is  necessary  to  refer  the  students 
to  more  advanced  works  for  this  infomation. 

Key  to  the  Common  Families  of  the  Orthoptera 

A.  Posterior  legs  larger  than  the  others  and  fitted  for  leaping. 

B.  Antennae  much  shorter  than  the  body.     Organ  of  hearing,  when 
present,   on   the  base   of  the   first  abdominal  segment 

Acridiidae,  or  short-horned  grasshoppers. 

BB.  Antennas  longer  than  the  body.  Auditory  organs  generally  in  the 
base  of  the  tibia  of  the  first  pair  of  legs.  Ovipositor  generally 
long. 

C.  Tarsi  four-jointed,  ovipositor  flattened Locustidae,  or  long- 
horned  grasshoppers. 

CC.  Tarsi  three-jointed.  Ovipositor  very  slender  and  somewhat  en- 
larged at  the  tip Grillidae,  or 

crickets. 

A  A.  Posterior  legs  not  much  longer  than  the  others  and  fitted  for 
walking  or  running. 

B.  Body  rather  short  and  broad,  flattened;  head  partly  inserted  in  the 
broad  prothorax Blattidae,  or  cock- 
roaches. 

BB.  Body  elongated. 

C.  Fore  legs  large,  spiny,  fitted  for  grasping  prey,  prothorax  long. 
Mantidae. 

CC.  Fore  legs  not  large,  prothorax  short Phasmidae. 


CHAPTER  III 

THE  LEPIDOPTERA  OR  BUTTERFLIES  AED 
MOTHS 

The  butterflies  and  moths  constitute  the  large  order 
Lepidoptera,  or  scaly-winged  insects.  They  have  sucking 
mouth  parts  and  undergo  a  complete  metamorphosis.  We 
shall  select  as  a  type  of  this  order  the  common  and  widely 
distributed  cabbage  butterfly  which  is  so  frequently 
seen  in  our  gardens.  This  butterfly  was  introduced  from 


FIG.   14. — The  cabbage  butterfly,     a,  larva.     (After  Packard.) 

Europe  in  about  1860  and,  as  it  produces  three  or  more 
broods  a  year,  has  now  spread  over  most  of  the  United 
States  wherever  there  is  a  cabbage  patch  to  afford  food  for 
its  larvae.  The  whitish  scales  which  cover  the  wings  and 
part  of  the  body  are  beautifully  sculptured  objects,  shaped 
much  like  a  paddle  with  a  very  short  handle.  They  are 
modified  hairs  and  various  intermediate  gradations  be- 
tween hairs  and  scales  may  be  found  on  different  parts 
of  the  butterfly.  The  sucking  tube  which  usually  lies 

20 


THE    LEPIDOPTERA    OR  BUTTERFLIES   AND   MOTHS       21 

coiled  up  like  a  watch  spring  under  the  head  may  be 
straightened  out  into  a  long  "  tongue  "  by  which  the  butter- 
fly sucks  the  nectar  from  flowers.  The  sucker  is  formed  of 
the  parts  of  two  modified  maxillae  which  have  been  enor- 
mously lengthened  and  closely  fitted  together.  Their 
inner  faces  are  concave  so  that  a  tube  is  formed  when  the 
two  parts  are  applied.  The  mandibles  in  the  butterflies 
are  either  represented  by  minute  rudiments  or  absent 
entirely.  There  is  little  left  of  the  labium  except  the  two 
labial  palps  which  project  in  front  of  the  head. 

The  butterfly  lays  its  eggs  upon  the  leaves  of  the  cabbage 
or  some  other  related  plant.  Watch  the  butterflies  as 
they  flit  about  in  a  cabbage  patch  and  you  will  probably 
see  them  alighting  for  a  short  time  upon  the  leaves.  Note 
'carefully  the  spot  where  the  butterfly  rested;  look  at  it 
with  a  hand  lens  and  you  may  find  a  small  oblong  egg 
stuck  by  one  end  to  the  leaf.  The  egg  soon  hatches  into 
a  small  green  larva  which  is  colored  so  nearly  like  the  green 
leaves  that  it  is  often  difficult  to  detect.  The  larva  has 
mouth  parts  fitted  for  chewing,  much  like  those  of  the 
grasshopper,  the  mandibles  being  particularly  strong. 
There  are  three  pairs  of  legs  on  the  thorax;  and  on  certain 
segments  of  the  abdomen  there  are  short,  stubby  legs 
called  pro-legs,  whose  ends  are  furnished  with  minute 
hooks  which  aid  the  caterpillar  in  maintaining  its  hold 
on  the  surface  of  a  leaf.  The  larva  sheds  its  skin  a  number 
of  times  during  its  growth,  and  at  its  last  molt  passes  into 
the  pupa  stage.  It  does  not  spin  a  cocoon  as  is  done  by 
many  moth  larvae,  but  the  pupa  is  fastened  to  some  object 
by  a  thread  which  passes  around  the  thorax.  At  the  tip 
of  the  abdomen  of  the  pupa  there  is  an  organ,  the  cremaster, 
which  is  furnished  with  booklets  for  attaching  to  a  small 
pad  of  silk  which  the  larva  spins  just  before  transforming 
into  the  pupa. 


22 


ANIMAL  BIOLOGY 


In  the  pupa  the  sheaths,  or  cases  of  many  organs  of  the 
butterfly,  may  be  made  out;  the  large  wing  cases  lie  at 
the  sides  of  the  body;  ventral  to  these  are  the  cases  of  the 
antennse  which  show  indications  of  numerous  segments; 
next  to  the  antenna  cases  are  the  cases  for  the  first  and 
second  legs,  those  of  the  third  pair  being  overlapped  by 
other  parts.  Finally,  in  the  middle  line  is  the  case  for 
the  tongue.  Aside  from  being  able  to  move  the  abdomen 
when  it  is  irritated,  the  pupa  is  compelled  to  lead  a  sta- 
tionary life.  But  while  outwardly  quiet  the  pupa  is 


PIG.   15. — The  painted  lady  butterfly,    Vanessa  atalanta. 

by    Essig.) 


(From  photo 


undergoing  a  rapid  and  extensive  transformation  of  its 
organs.  Old  organs  are  being  torn  down,  new  ones  are 
being  built  up,  and  extensive  changes  of  form  are  taking 
place  in  other  parts.  So  great  are  these  changes  that 
the  pupa  may  be  compared  to  a  ship  which  has  to  be  laid 
up  for  repairs.  It  is  the  workshop  in  which  the  caterpillar 
is  being  made  over  into  the  very  different  form  of  a  butter- 
fly. Wings  are  grown;  large  compound  eyes  replace  the 
simple  ones  of  the  caterpillar;  the  biting  and  chewing 
mouth  parts  are  modified  into  the  elongated  nectar- 


THE   LEPIDOPTERA   OR  BUTTERFLIES   AND   MOTHS       23 

sucking  proboscis ;  marked  changes  take  place  in  the 
digestive  organs  which  fit  them  for  the  very  different 
diet  of  the  butterfly;  and  changes  equally  great  occur  in 
many  other  parts  of  the  body. 

One  of  our  commonest  and  most  striking  butterflies 
is  the  monarch,  or  milkweed  butterfly.  It  has  reddish- 
brown  wings  with  black  veins  and  a  dark  border  with 
whitish  spots.  It  is  one  of  the  few  butterflies  that  are 
migratory;  it  frequently  travels  southward  on  the  approach 
o.f  winter,  in  large  flocks.  The  larvae  live  upon  milkweed 
and  may  be  recognized  by  their  conspicuous  black  and 
yellow  stripes  surrounding  the  body.  The  pupa  is  green 
and  hangs  suspended  by  its  cremaster.  The  pupa  stage 
lasts  about  two  weeks,  the  species  passing  the  winter  as 
an  imago. 

Closely  resembling  the  monarch  in  the  color  of  its 
wings  is  another  butterfly  of  somewhat  smaller  size, 
called  the  viceroy,  Basilarchia  archippus.  It  can  be 
most  readily  distinguished  from  the  monarch  by  a  black 
bar  across  the  hind  wings.  The  viceroy  is  not  at  all 
closely  related  to  the  monarch;  the  likeness  is  merely  a 
superficial  resemblance  in  color.  As  the  monarch  butter- 
fly is  particularly  distasteful  to  birds  it  is  therefore 
seldom  troubled  by  them.  The  viceroy  is  commonly 
supposed  to  derive  more  or  less  protection  from  its  resem- 
blance to  the  monarch,  since  the  birds  would  readily 
mistake  it  for  the  distasteful  species.  Such  protective 
resemblance  of  one  species  to  another  is  called  mimicry. 
It  is  a  curious  fact  that  most  of  the  other  species  of  Basil- 
archia are  colored  very  differently  from  the  viceroy. 
There  are  a  great  many  cases  among  butterflies  in  which 
a  species  may  resemble  in  a  most  striking  manner  distaste- 
ful species  of  a  quite  unrelated  group.  At  the  same  time 
these  " mimicking"  species  may  depart  in  an  equally 


ANIMAL  BIOLOGY 


striking  manner  from  the  forms  to  which  they  are  very 
closely  allied  in  points  of  structure  and  life  history.     The 


FIG.   1 6. — Mimicry   of  the  monarch  butterfly    (upper  figure)    by  the 
viceroy    (lower   figure).     (After   Lutz.) 

resemblance  to  the  distasteful  species  is  superficial  and 
due  to  color  and  outline  of  wings,  while  in  many  other 
less  conspicuous  features  of  structure  they  are  similar 


THE    LEPIDOPTERA   OR  BUTTERFLIES   AND   MOTHS       25 

to  the  members  of  their  own  genus  or  family.  Similar  cases 
of  mimicry  have  been  described  in  various  other  animals, 
but  nowhere  are  the  resemblances  so  numerous  or  so  strik- 
ing as  in  the  butterflies,  especially  those  of  South  America 
and  Africa.  A  striking  degree  of  protective  resemblance 
is  shown  by  many  moths  which  are  colored  so  as  to  be 
scarcely  distinguishable  when  resting  on  the  bark  of  trees. 


FIG.   17. — Cecropia  moth.     (After  Lutz.) 

The  butterflies,  on  the  other  hand,  are  usually  colored 
so  as  to  make  them  particularly  conspicuous. 

The  moths  constitute  a  very  extensive  group  of  the  most 
varied  sizes  and  colors.  Generally  the  wings  when  at 
rest  are  horizontal  or  held  folded  over  the  abdomen,  often 
sloping  downward  on  either  side.  Usually  the  moths 
fly  at  night  or  in  the  evening,  while  the  butterflies  are 
lovers  of  the  sunshine.  Some  of  the  largest  and  most 
conspicuous  of  our  species  belong  to  the  giant  silk-worm 


26  ANIMAL  BIOLOGY 

moths.  One  of  these  is  Samia  cecropia.  The  larva 
lives  on  the  leaves  of  several  kinds  of  trees;  preparatory  to 
going  into  the  pupa  stage  it  spins  a  cocoon  of  silk  which  is 
secreted  by  a  pair  of  large  glands  opening  upon  the  small 
lower  lip.  The  cocoons  are  attached  by  one  side  to  a 
twig  and  are  formed  of  very  tough  material  which  is 
admirably  adapted  to  keep  out  cold  and  moisture.  The 
pupa  passes  the  winter  within  this  cocoon  and  the  mature 
moth  emerges  in  the  spring.  With  no  biting  mouth  parts 
the  moth  would  be  utterly  unable  to  get  out  of  its  tough 
envelope,  were  there  not  left  at  one  end  an  opening  filled 
only  with  loose  webby  material  through  which  it  can  push 
its  way.  A  related  species  spins  its  cocoon  against  the 
side  of  a  leaf  so  that  the  leaf  becomes  partially  wrapped 
around  it;  and,  as  if  to  guard  against  its  cocoon  falling 
off  the  tree  when  the  leaves  are  shed  in  the  fall,  the  larva 
spins  along  the  leaf  stem  a  number  of  threads  of  silk 
connecting  leaf  and  cocoon  with  the  twig. 

Perhaps  the  most  beautiful  of  our  moths  is  the  large 
luna  moth,  easily  recognized  by  its  pale  green  color  and 
by  the  swallow  tails  on  its  hind  wings.  Its  larva  feeds 
on  the  leaves  of  the  hickory,  walnut  and  other  trees  and 
forms  a  cocoon  in  which  leaves  are  interwoven  with  the 
silk. 

The  moth  most  valuable  to  man  is  undoubtedly  the 
silk- worm  moth,  Bombyx  mori,  which  is  a  native  of  China 
where  silk  culture  has  been  carried  on  for  many  centuries. 
The  larvae  preferably  feed  upon  the  leaves  of  the  mulberry 
although  they  will  eat  the  common  osage  orange  and  a 
few  other  plants.  The  white  or  yellowish  cocoon  which 
the  larva  spins  is  constructed  of  a  single  thread  which  is 
generally  over  1000  feet  long.  This  thread  is  wound  off 
on  reels  by  the  silk  grower  and  then  put  through  various 
processes  of  preparation  according  to  the  kind  of  silk 


THE   LEPIDOPTERA   OR  BUTTERFLIES   AND   MOTHS       27 

product  which  it  is  desired  to  make.     The  moth  makes  its 
escape  from  the  cocoon  after  moistening  the  end  with  a 


FIG.   1 8. — Silk-worm    moth    eggs    and    cocoons. 

secretion  which  softens  the  cementing  substance  between 
the  fibers.  It  is  a  very  sluggish  sort  of  creature,  scarcely 
able  to  fly,  and  takes  no  food. 


FIG.   19. — A  sphynx  moth.     (After  Lutz.) 

Toward  evening  one  often  sees  the  sphinx  moths  or 
hawk  moths,  (Sphingidae)  flying  about  in  search  of  flowers 


28 


ANIMAL  BIOLOGY 


out  of  which  they  suck  nectar  with  their  very  long  pro- 
boscis. Some  are  called  humming-bird  moths  on  account 
of  the  resemblance  of  their  flight  to  the  flight  of  the  hum- 
ming bird.  One  of  the  largest  and  best  known  of  the  numer- 
ous species  of  this  family  is  the  tomato-worm  moth.  It 
has  a  large,  smooth,  green  larva  with  oblique  white  mark- 


-vf^^sf  ^ 

FIG.   20. — Tobacco  worm.     This  gives  rise  to  a  sphynx    moth.      (After 

Howard.) 

ings  on  the  side  and  a  curved  horn  at  the  posterior  end 
of  the  body.  It  feeds  on  tomato  and  potato  vines  and 
upon  tobacco. 

The  very  large  group  of  owlet  moths  or  Noctuidae 
include  many  of  the  most  injurious  species.  The  army 
worms  which  attack  corn  and  grain,  the  cut  worms  of  our 
gardens,  the  cotton  boll  worm  which  is  estimated  to  cause 

over  $2,000,000  damage  a  year 
to  the  cotton  growers,  and  many 
ether  species  which  live  upon 
the  kind  of  vegetation  that  man 
happens  to  be  interested  in  be- 
long to  this  family.  Belonging 
borer,  with  larva,  /.  and  pupa,  p.  to  a  related  family  is  the  gipsy 

moth,  Porthetria  dispar,  which 

was  brought  from  Europe  into  Massachusetts  in  1868.  It 
spread  with  such  rapidity  and  its  larvae  did  so  much 
damage  to  shade  trees  and  forest  trees  that  the  state  or- 
ganized a  systematic  attempt  to  exterminate  it,  spending 
over  $1,000,000  in  spraying,  destroying  the  eggs,  and  in 
other  methods  of  warfare.  Meanwhile  the  gipsy  moth 
thrives. 


FIG.   21. — Imported  currant- 


THE    LEPIDOPTERA    OR  BUTTERFLIES   AND   MOTHS       2Q 

Every  boy  who  has  eaten  apples  has  doubtless  come 
across  the  larvae  of  the  codling  moth  or  else  the  evidences 
of  its  destructive  activity  upon  his  apple,  although  he  may 
not  have  known  that  the  offending  "worm"  is  the  larva 
of  a  small,  dull-colored  moth  that  lays  its  eggs  at  the 
blossom  end  of  the  developing  fruit.  The  young  larvae 
eat  their  way  toward  the  center  of  the  apple,  and  when 
full  grown  they  gnaw  a  hole  to  the  surface  and  escape; 


FIG.  22. — Codling  moth,  a,  apple  showing  work  of  larva  which  enters 
at  the  blossom  end  b,  where  the  egg  is  laid  and  finally  eats  its  way  to 
the  outside;  e,  larva;  d,  pupa;  i,  cocoon; /and  g,  mature  moths.  (After 
Riley.) 


then  they  crawl  into  some  protected  nook  to  pass  through 
the  pupa  stage.  The  moths  emerge  in  about  two  weeks 
and  deposit  eggs  in  other  apples.  The  second  crop  of 
larvae  usually  pass  the  winter  in  the  apples  and  come  out 
as  moths  the  next  spring.  By  spraying  the  young  fruit 
with  insecticides,  and  putting  bands  of  cloth  around  the 
trees  so  as  to  catch  and  destroy  the  first  brood  of  larvae  as 
they  travel  down  to  pupate  in  the  ground,  and  by  destroy- 


30  ANIMAL  BIOLOGY 

ing  the  windfall  apples,  it  is  possible  to  reduce  very  greatly 
the  ill  effects  of  this  pest. 

The  clothes  moths  may  not  only  destroy  what  the  silk- 
worm moth  has  produced  but  they  will  also  attack  furs 
and  all  sorts  of  woolen  cloth.  There  are  several  species 
of  clothes  moths  all  of  which  are  of  small  size  and  similar 
appearance.  They  lay  their  eggs  preferably  in  woolen  gar- 
ments, carpets,  blankets,  etc.,  the  larvae  feeding  upon  the 
wool.  There  may  be  more  than  one  generation  a  year. 
The  damage  done  is  entirely  the  work  of  the  larvae  since 


FIG    23. — The    clothes    moth,     a,    adult;    b,    larva;    c,   larva   in   case — 
enlarged.     (From  Riley.) 

the  moths  themselves  only  deposit  their  eggs  on  the  cloth. 
The  moths  are  most  active  at  night  and  are.  frequently 
attracted  to  lights.  In  many  places  persistent  vigilance 
is  required  to  keep  these  unobtrusive  creatures  from 
doing  much  damage.  Clothing  that  is  packed  away 
should  first  be  well  brushed  and  exposed  to  light.  If 
pasteboard  boxes  are  used  they  should  be  sealed  by  past- 
ing paper  around  the  edges  of  the  cover.  If  it  is  suspected 
that  eggs  or  larvae  may  still  be  in  the  clothing  it  should 
be  kept  in  a  tight  receptacle  together  with  about  half  a 
cup  of  bisulphide  of  carbon  for  twenty-four  hours.  The 
bisulphide  will  rapidly  evaporate  and  penetrate  all  parts  of 
the  clothing  and  kill  the  eggs  or  larvae  if  any  are  present. 


CHAPTER  IV 

THE  HEMIPTERA,  OR  THE  BUGS  AND  THEIR 
ALLIES 

By  many  unsophisticated  people  the  term  bug  is  applied 
to  almost  any  sort  of  insect  and  even  to  a  number  of 
creatures  which  are  not  insects  at  all.  In  its  stricter  sense 
the  word  is  used  to  designate  any  member  of  a  certain  di- 
vision of  the  order  Hemiptera.  The  Hemip- 
tera  in  general  include  insects  with  a 
gradual  or  incomplete  metamorphosis  and 
sucking  mouth  parts.  In  typical  members 
of  the  division  Heteroptera,  or  true  bugs, 
the  anterior  wings  are  thickened  at  the 
base,  and  the  terminal  portions  are  more  FIG.  24.— The 
or  less  membranous.  The  second  pair  of  ^*§£^gf 
wings  which  are  membranous  are  folded 
under  the  first  pair  and  constitute  the  chief  organs  of  flight. 

A  good  example  of  a  true  bug  is  furnished  by  the  well- 
known  squash  bug  of  our  gardens.  The  sucking  organ 
which  the  bug  uses  to  pierce  and  suck  out  the  juices  of 
plants  consists  of  an  elongated  under  lip,  or  labium,  which 
is  converted  into  a  tube  or  sheath  enclosing  two  pairs  of 
very  slender  and  sharp  piercing  organs  which  are  com- 
monly held  to  represent  the  highly  modified  mandibles 
and  first  maxillae.  The  squash  bug  is  protected  from  its 
enemies  by  means  of  stink  glands  which  open  on  the  side 
of  the  thorax  and  secrete  an  ill-smelling  substance  which 
is  poured  out  when  the  insect  is  disturbed. 

One  of  the  most  injurious  of  the  bugs  is  the  chinch 

31 


32  ANIMAL  BIOLOGY 

bug  which  sucks  the  juices  of  corn,  wheat  and  other  grains. 
Kellogg  in  describing  the  damage  done  by  this  bug  in  the 
Mississippi  valley  states  that  he  has  "seen  great  corn 
fields  in  this  valley  ruined  in  less  than  a  week,  the  little 
black  and  white  bugs  massing  in  such  numbers  on  the 
growing  corn  that  the  stalk  and  bases  of  the  leaves  were 
wholly  concealed  by  the  covering  of  bugs."  The  United 
States  Entomologist  estimated  that  the  annual  losses 
caused  by  the  chinch  bug  amount  to  $20,000,000  a  year. 
While  numerous  species  of  bugs  are  destructive  to  vege- 
tation there  are  many  which  prey  upon  other  insects. 
Among  these  are  the  "  assassin  bugs,"  and  the  celebrated 
"kissing  bug"  which  occasionally  inflicts  very  painful 
bites  upon  human  beings.  The  cone  nose,  or  "big 
bedbug"  occasionally  attacks  man  also,  but  a  more  fa- 
miliar and  widespread  pest  is  the  ordinary  bedbug  of 
human  dwellings.  While  these  disagreeable  insects 
possess  but  very  small  functionless  rudiments  of  wings 
they  can  run  with  remarkable  quickness.  During  the 
day  they  lie  concealed  in  cracks  and  crevices,  but  at  night 
they  scurry  about  in  search  of  their  sleeping  human  vic- 
tims at  whose  expense  they  gorge  their  bodies  with  blood. 
They  breed  with  remarkable  rapidity,  and  wherever 
they  make  their  appearance  it  is  therefore  advisable  to 
wage  war  upon  them  with  the  greatest  vigor.  For  this 
purpose  a  saturated  solution  of  corrosive  sublimate  in 
alcohol  applied  to  the  crevices  where  they  lie  concealed 
is  an  efficient  remedy,  although  one  which  should  be  used 
with  care  as  it  is  very  poisonous.  Besides  being  disagreea- 
ble on  account  of  their  bites  and  offensive  odor,  bedbugs 
are  the  means  of  transmitting  certain  diseases  from  one 
person  to  another.  A  disease  common  in  India,  and  re- 
lapsing fever  which  sometimes  occurs  in  the  United  States 
are  transmitted  by  these  insects. 


THE   HEMIPTERA 


33 


There  are  many  species  of  bugs  that  live  in  or  on  the 
water,  and  these  forms  show  many  remarkable  and  inter- 
esting adaptations  to  aquatic  life.  The  large  electric- 
light  bugs,  which  are  so  frequently  at- 
tracted by  lights  at  night,  live  normally 
in  the  water  where  they  prey  upon 
small  fishes  and  other  aquatic  organ- 
isms. They  are  fierce  fellows  and  in- 
flict severely  painful  bites.  The  slender 
water  scorpion,  which  superficially  re- 
sembles a  walking-stick  in  the  general 
form  of  its  body,  commonly  lives  near 
the  banks  of  ponds  and  streams  with 
the  tip  of  its  long  posterior  breathing 
tube  protruded  at  the  surface  of  the 
water.  By  its  fore  legs  which  resemble 
somewhat  those  of  the  praying  mantis  FIG.  25.  —A  water 
the -water  scorpion  catches  small  crea- 
tures that  come  near,  and  holds  them  while  it  sucks  their 
blood. 

Among  the  most  interesting  and  easily  studied  of  the 
aquatic  Hemiptera  are  the  back  swimmers 
(Notonecta)  which  have  the  peculiarity  of 
swimming  with  the  dorsal  surface  downward. 
These  insects  commonly  hang  obliquely  down- 
ward with  the  tip  of  the  abdomen  at  the  sur- 
face of  the  water  to  give  them  access  to  air. 
FlG  26  _  Their  backs  are  light  colored,  a  circumstance 
A  back  swim-  which  renders  them  more  nearly  invisible  to 
IMP**  giauca.  animals  below  the  surface.  The  posterior  legs 
are  especially  modified  for  swimming,  being 
long,  flattened  and  furnished  with  marginal  hairs.  When 
swimming  below  the  surface  the  backswimmer  carries  quite 
a  supply  of  air  which  gives  it  a  silvery  appearance  where 


34  ANIMAL  BIOLOGY 

the  light  is  reflected  from  the  bubbles.  Backswimmers 
live  by  sucking  out  the  blood  of  small  animals  of  various 
kinds,  and  they  may  attack  insects  larger  than  themselves. 
They  are  readily  kept  in  aquaria,  but  too  many  of  them 
must  not  be  put  together  as  they  will  sometimes  attack 
and  devour  their  own  kind.  Like  many  other  aquatic 
Hemiptera,  backswimmers  are  strongly  attracted  by  light, 
and  may  be  made  to  follow  a  light  about  in  any  direction. 
Similar  in  habits  to  the  backswimmers  are  the  water  boat- 
men which  also  get  their  supply  of  air  by  placing  the  tip 
of  the  abdomen  at  the  surface  of  the  water. 


FIG.  27. — The  periodical  cicada.     Upper  figure,  adult  female;  6,  beak; 
o,  ovipositor.     Lower  figure,   young  larva  enlarged.     (After  Riley.) 

While  most  of  the  aquatic  Hemiptera  live  within  the 
water,  the  water  striders  of  pond  skaters  are  found  upon 
the  surface,  being  supported  by  the  surface  film  which 
they  are  not  heavy  enough  to  break  through.  Insects 
which  fall  upon  the  surface  are  quickly  attacked  by 
these  watchful  rovers. 

In  the  sub-order  Homoptera  the  fore  wings  when  present 
are  membranous  throughout.  One  of  the  largest  of  this 
group  is  the  harvest  fly  or  cicada,  whose  prolonged  and 
uniform  note  is  often  heard  during  the  hot  days  of  late 
summer.  Another  member  of  the  same  genus  is  the  seven- 


THE   HEMIPTERA  35 

teen-year  cicada  or  locust  which  has  the  longest  period 
of  metamorphosis  of  any  known  insect.  After  seventeen 
years  of  life  spent  in  burrowing  in  the  soil,  feeding  upon 
roots  and  other  vegetable  material,  these  cicadas  make 
their  appearance,  often  in  great  numbers,  in  the  spring 
or  early  summer.  The  history  of  various  broods  in  differ- 
ent parts  of  the  country  is  known,  so  that  it  can  be  pre- 
dicted, years  in  advance,  when  they  will  appear  in  any 
particular  part  of  the  country.  The  cicadas  of  the 
southern  states  may  complete  their  metamorphosis  in 
thirteen  years. 

Many  of  the  smaller  Homoptera  such  as  the  little  green 
leaf  hoppers  are  quite  destructive  to  various  species  of 


FIG.  28. — The  bean  aphis,  Aphis  rumicis  Linn.  Winged  and  wingless 
females  with  enlarged  antennae  of  the  same.  Greatly  enlarged.  (After 
Essig.) 

plants.  Some  of  the  most  injurious,  as  well  as  in  some 
respects  the  most  interesting  members  of  the  group  are 
the  aphids  or  plant  lice.  Many  species  do  considerable 
injury  by  sucking  the  juices  of  plants,  as  they  multiply 
with  such  remarkable  rapidity  that  a  plant  may  soon  be 
literally  covered  by  the  descendants  of  a  single  individual. 
Aphids  have  the  peculiarity  of  producing  young  from  eggs 
which  are  not  fertilized,  a  process  known  as  parthenogene- 
sis, a  word  meaning  virgin  reproduction.  Usually  several 
generations  are  produced  in  this  way.  These  consist 
generally  of  wingless  females,  but  at  times  winged  females 
occur  which  may  fly  to  another  plant  and  give  rise  to  a 
new  colony.  After  a  number  of  parthenogenetic  genera- 


36  ANIMAL  BIOLOGY 

tions,  and  generally  upon  the  approach  of  cold  weather 
in  the  fall,  broods  consisting  of  both  males  and  females 
appear,  constituting  the  so-called  sexual  generation.  The 
females  of  this  generation  produce  eggs  of  unusually 
large  size  which  require  to  be  fertilized  before  they  develop. 
These  eggs  remain  over  winter  and  hatch  out  in  the  follow- 
ing spring  into  females  which  start  a  new  series  of  par- 
thenogenetic  generations.  Aphids  are  frequently  attended 
by  ants  which  imbibe  a  sweet  liquid  called  honey  dew 
which  comes  from  the  aphid's  abdomen. 

One  of  the  most  injurious  of  the  aphid  family  is  the 
Phylloxera  which  attacks  the  grape  vine.  In  France 
especially,  enormous  injury  has  been  done  by  this  insect. 
It  attacks  both  the  leaves  and  the  roots,  producing  peculiar 
galls  in  each,  and  causing  the  deterioration  and  often  the 
death  of  the  vine.  Comparative  immunity  from  these 
insects  has  been  secured  by  grafting  French  vines  upon 
vines  native  to  America.  The  aphis  which  feeds  upon 
roots  of  corn  commonly  lives  in  underground  galleries 
of  ants.  The  ants  uncover  the  roots  in  their  burrowing, 
carry  the  aphids  to  them,  gather  their  eggs  and  carry 
them  to  places  of  safety;  in  return  for  these  services  the 
ants  feed  upon  the  sweet  fluid  derived  from  their  adopted 
companions. 

The  most  degenerate  of  all  of  the  Hemiptera  are  the 
scale  insects  or  Coccidae.  In  a  typical  scale  bug,  such  as 
the  San  Jose  scale,  or  the  apple-tree  bark  louse,  the  female 
is  attached  to  a  particular  spot  on  a  leaf  or  twig  where 
she  sucks  in  sap  through  her  slender  beak.  In  the  scale 
bug,  legs,  wings,  antennae  and  eyes  are  lacking,  and  the 
body  is  covered  by  a  scale,  which  is  formed  by  a  secretion 
from  certain  glands.  The  female  lays  large  numbers  of 
eggs  which  hatch  into  active  young  furnished  with  six 
legs,  antennae,  and  various  special  organs  not  found  in 


THE   HEMIPTERA  37 

the  mature  female.  The  young  crawl  about  for  a  while, 
and  soon  become  attached  to  one  spot  where  they  undergo 
a  series  of  molts  and  change  greatly  in  structure.  At 
first  the  male  and  the  female  scale  insects  are  very  much 
alike,  but  after  the  first  molt  the  male  scale  may  be  dis- 
tinguished by  its  smaller  size  and  narrower  shape.  While 
the  female  remains  attached  and  becomes  more  degenerate 
with  age,  the  male  scale  insect,  after  passing  through  a 
pupal  stage,  transforms  into  a  small,  graceful,  winged  in- 


FIG.   29. — Black  olive  scale,     la,  scale  enlarged.      (After  Comstock.) 

sect  which  flies  from  one  plant  to  another.  It  has  only 
one  pair  of  functional  wings,  and  owing  to  its  imperfectly 
developed  mouth  parts  it  is  incapable  of  taking  in  food; 
after  fertilizing  the  female  it  soon  dies.  Males  are  in 
general  more  rarely  seen  than  the  females,  and  in 
some  species  of  scale  bugs  they  have  never  been  dis- 
covered, the  female  probably  reproducing  exclusively  by 
parthenogenesis. 

The  San  Jose  scale  does  a  large  amount  of  injury  to 
fruit  trees.     It  is  a  particularly  bad  pest  in  California, 


ANIMAL  BIOLOGY 


but  despite  efforts  to  check  its  spread  it  has  become  scat- 
tered through  most  of  the  United  States.  An  allied  species 
is  a  destructive  enemy  of  orange  and  lemon  trees.  In 
some  species  the  female  retains  the  power  of  locomotion 
throughout  life  and  possesses  eyes,  antennae  and  legs. 
One  of  the  less  degenerate  scale  bugs  is  the  cottony-cush- 
ion scale  which  secretes  a  cottony  mass  of  fibers  within 
which  it  deposits  its  eggs.  This  insect  was  introduced 
into  California  from  Australia,  and  spread  with  such  great 

rapidity  that  it  threatened  to 
exterminate  the  orange  groves. 
An  entomologist,  Mr.  Koebele, 
was  commissioned  to  search  for 
the  enemies  of  the  cottony- 
cushion  scale  in  its  native 
country  and  to  import  any 
species  which  might  prove  a 
means  of  checking  the  alarming 
spread  of  this  pest.  This  search 
FIG.  30.— Scurfy  bark-louse,  resulted  in  the  importation  of  a 

d,    male;    c,   female.     (After  .         ,   _ . 

Howard.)  beetle,  Novius  (Vedaha)  cardi- 

nalis,  which  thrived  and  mul- 
tiplied to  such  a  degree  that  it  effectively  exterminated 
nearly  all  of  the  scale  bugs  of  this  species.  Other  scale 
bugs  are  combatted  by  spraying  trees  with  kerosene  emul- 
sions and  other  insecticides,  and  by  covering  the  trees  with 
tents  in  which  poisonous  gases  are  generated  in  sufficient 
quantity  to  prove  fatal  to  the  insects  without  severely 
injuring  the  trees.  All  of  these  measures  are  expensive, 
but  they  are  less  costly  than  the  damage  done  by  the  in- 
sects. Directly  or  indirectly  the  scale  insects  entail  a  loss 
of  many  millions  a  year.  On  the  other  hand  there  are  a 
few  species  which  are  of  economic  value,  such  as  the 
cochineal  insect  which  feeds  upon  cactus  in  Mexico  and 


THE   HEMIPTERA  39 

yields  us  the  coloring  matter,  cochineal;  and  the  tropical 
Carter  ia  lacca  from  which  we  derive  shellac. 

Lastly  we  must  mention  what  are  in  some  respects  the 
most  disagreeable  of  the  Hemiptera,  the  lice,  many  spe- 
cies of  which  infest  the  lower  animals  and  a  few  of  which 
are  peculiar  to  man.  Fortunately  they  are  not  so  preva- 
lent as  formerly,  as  they  are  not  tolerated  very  long  by 
people  of  the  present  average  standards  of  cleanliness. 

The  Hemiptera  are  remarkable  for  their  great  diversity 
of  form  and  habit.  Active  plant  feeders,  fierce  assassins 
of  other  insects,  degenerate  and  almost  shapeless  parasites 
of  plants,  denizens  of  the  water,  skaters  on  the  surface 
film  of  ponds  and  streams,  and  the  despised  parasites  of 
the  human  body,  they  nevertheless  show  certain  features  in 
common  which  indicate  their  kinship. 


CHAPTER  V 
THE  DIPTERA  OR  FLIES 

The  true  flies  or  Diptera  are,  as  the  name  implies,  two- 
winged  insects,  although  they  have  what  really  corre- 
sponds to  the  hind  pair  of  wings  of  other  insects  in  the 


FIG.  31. — Head  of  housefly.     (After  Herms.) 

small  club-shaped  halteres  or  balancers  which  are  joined 
to  the  sides  of  the  metathorax.  All  of  the  flies  have 
sucking  mouth  parts  which  include  in  many  cases  slender 

40 


THE    DIPTERA    OR    FLIES  41 

piercing  organs.  All  flies  also  pass  through  a  complete 
metamorphosis  with  sharply  differentiated  stages.  If 
familiarity  always  implied  accurate  knowledge  it  would  be 
unnecessary  to  say  anything  concerning  the  common  house 
fly  (Musca  domestica),  but  even  entomologists  have 
learned  much  that  was  new  regarding  this  insect  within 
the  past  few  years.  One  of  the  most  striking  features 
of  the  fly's  organization  is  the  proboscis  which  has  long 
been  a  favorite  object  with  the  amateur  microscopist. 
Most  of  this  structure  consists  of  the  labium  or  lower  lip. 
Its  end  is  flattened  and  divided  into  two  lobes  which 
can  be  folded  together  when  not  in  use  or  spread  apart 
and  applied  to  a  surface  when  the  fly  is  sucking  in  food. 
The  lower  surface  of  the  lobes  is  roughened  so  as  to  serve 
as  a  rasp  or  grater. 

The  antennae  of  the  fly  are  short  and  consist  of  three 
joints  of  which  the  last  is  much  the  largest.  Examination 
of  this  joint  with  a  microscope  will  reveal  thousands  of 
olfactory  pits,  the  organs  concerned  with  the  sense  of 
smell.  This  sense  is  very  acute  in  flies,  especially  the  blow 
flies  and  flesh  flies.  The  foot  of  the  fly,  another  favorite 
object  of  microscopists,  shows  in  addition  to  two  claws, 
a  two-lobed  flap  which  is  furnished  below  with  minute 
hairs  at  the  end  of  which  a  sticky  secretion  is  poured  out, 
that  enables  the  fly  to  walk  up  vertical  surfaces  and  upon 
the  ceiling. 

House  flies  produce  many  broods  a  year.  Their  eggs 
are  laid  in  horse  manure  and  other  refuse  where  they  hatch 
in  less  than  a  day  into  white  maggots.  In  about  six  days, 
the  precise  time  depending  upon  temperature  and  food, 
the  larvae  pass  into  the  pupa  stage,  from  which  the  mature 
insect  emerges  in  about  five  days.  Besides  making  them- 
selves an  inordinate  nuisance  in  the  house  where  it  is 
apparently  the  height  of  their  ambition  to  die  in  some  arti- 


42  ANIMAL  BIOLOGY 

cle  of  food,  house  flies  are  a  particularly  dangerous  means 
of  spreading  disease.  The  old  contention  that  they  are 
useful  insects  because  they  act  as  scavengers  is  a  mis- 
chievous doctrine;  as  a  matter  of  fact  they  possess  no 
redeeming  virtues.  Since  they  wade  about  in  all  sorts 
of  filth,  they  get  germs  of  various  diseases  on  their  feet 
and  may  carry  them  to  food.  In  many  cases  typhoid 
fever  is  definitely  known  to  have  been  carried  by  flies, 
and  it  is  quite  probable  that  other  diseases  are  carried  in 


FIG.  32. — Common  house  fly,  Musca  domestica.  Puparium  at  left; 
adult  next;  larva  and  enlarged  parts  at  right — enlarged,  a,  antenna. 
(After  Howard.) 


the  same  way.  To  a  certain  extent  flies  may  be  gotten 
rid  of  by  traps,  fly  poison  and  sticky  paper,  but  as  they 
are  continually  being  bred  in  such  enormous  numbers  it  is 
best  to  check  them  by  keeping  covered  the  manure  and 
other  refuse  in  which  they  breed. 

Closely  related  to  the  house  fly  are  the  blow  flies  and  flesh 
flies  whose  larvae  live  upon  decaying  flesh.  The  fly  whose 
larva  is  known  as  the  screw  worm  sometimes  lays  its  eggs 
in  wounds  and  in  the  nostrils  of  men  and  animals;  the  larvae 
may  devour  the  nasal  membrane ,  and  get  into  deeper 


THE   DIPTERA    OR   FLIES 


43 


passages  connected  with  the  nose  and  sometimes  produce 
fatal  results. 

The  larvae  of  hot  flies  commonly  inhabit  the  stomach  or 
intestine  of  horses,  cattle  and  sheep,  attaching  themselves 
to  the  mucous  membranes  of  the  walls  and  often  causing 
great  distress  to  the  afflicted  animal.  The  eggs  of  the 
horse  bot  fly  are  laid  usually  upon  the  hairs  of  the  fore 
legs  of  the  horse  and  gain  access  to  the  stomach  when  the 
horse  licks  itself.  The  larvae  remain  in  the  alimentary 


FIG.  33. — Larvas  of  bot  flies  attached  to  the  walls  of  the  stomach  of  a 
horse.     (After     Osborn.) 


canal  during  the  fall  and  winter  and  pass  out  in  the  spring 
when  they  go  through  their  pupa  stage  in  the  ground. 
The  related  warble  flies  cause  much  discomfort  to  cattle 
since  the  larvae  spend  most  of  their  life  just  beneath  the 
skin.  The  full  grown  larva  may  reach  a  length  of  an  inch. 
When  ready  to  pupate  it  gnaws  a  hole  through  the  skin 
of  its  helpless  host  and  drops  down  and  burrows  in  the 
ground.  In  this  country  the  damage  done  to  hides  is 
estimated  at  $50,000,000  per  year. 


44  ANIMAL  BIOLOGY 

The  family  Tabanidae,  including  horse  flies,  green  heads 
and  their  allies,  is  formed  mainly  of  blood  suckers  which 
pierce  the  skin  with  the  sharp  stylets  of  their  proboscis. 
The  larvae  generally  live  in  the  water  or  in  damp  situations; 
this  is  why  the  flies  themselves  are  usually  more  abundant 
in  low  swampy  regions. 

Few  of  the  Diptera  are  more  annoying  than  the  small, 
fiercely  biting,  black  flies  or  buffalo  gnats  (Simulium) 
which  occur  in  such  numbers  in  certain  parts  01  the 
United  States  and  especially  in  Canada,  as  to  make  life 
almost  intolerable  at  times  for  man 
and  beast  alike.  The  larvae  inhabit 
running  water,  attaching  them- 
selves to  rocks  and  other  objects  by 
the  posterior  end  of  the  body. 

A  large  family  of  the  Diptera,  the 
Tachinidae,  make  their  living  during 
their  larval  state  as  parasites  with- 
FIG.   34.— Black  gadfly  m  the  bodies  of  other  insects.     The 
—  enlarged.      (After  female  fastens  her  eggs  upon   the 
skin  of  some  insect  and  when  the 

young  grubs  are  hatched  they  bore  into  the  body  of  their 
victim  and  proceed  to  devour  its  internal  organs.  In 
general  the  Tachinidae  deserve  our  gratitude  because  they 
afford  a  means  of  holding  in  check  the  ravages  of  de- 
structive caterpillars,  grasshoppers  and  other  injurious 
insects. 

Other  scourges  of  the  insect  world  are  the  robber  flies, 
Asilidae,  which  swoop  down  upon  their  prey,  carrying  it 
off  and  sucking  its  blood.  We  can  no  more  than  mention 
the  hover  flies,  Syrphidae,  that  have  the  curious  habit  of 
hovering  over  one  spot  during  the  summer  days ;  the  fuzzy 
bee  flies,  Bombyliidae,  that  are  often  mistaken  for  bees; 
the  long-legged,  awkward  crane  flies,  Tipulidae;  the  beauti- 


THE   DIPTERA   OR   FLIES 


45 


ful  and  graceful  midges;  and  the  gall  gnats,  Cecidomyiidse, 
which  include  the  destructive  Hessian  fly  which  causes 
so  great  a  damage  to  wheat  fields. 

It  is  desirable,  however,  to  treat  of  the  mosquitoes  a 
little  more  fully,  since  these  insects  are  perhaps  the  most 
important  of  all  the  insect  enemies  of  man.  Mosquitoes, 
like  house  flies,  produce  several  broods  a  year.  The  fe- 
males deposit  their  cigar-shaped  eggs  upon  the  surface  of 
quiet  water,  some  species  placing  them  side  by  side  with 
their  pointed  ends  upward  form- 
ing a  sort  of  "raft"  that  floats 
on  the  water.  The  egg  at  ordi- 
nary summer  temperature 
hatches  in  less  than  a  day  into 
a  small,  large-headed  wriggler 
which  is  commonly  seen  attached 
at  the  surface  of  the  water  by 
its  breathing  tube  situated  near 
the  posterior  end  of  the  body. 
The  wrigglers  live  upon  minute 
organisms  and  organic  matter  in 
the  water,  and  they  may  often  be  PIG  35,_Culex  pungens. 

found  feeding  near  the  bottom.  Female  above,  male  below. 
m  Feet,  /,  and  scales,  s,  enlarged. 

Iney  are  under  the  necessity  of  (After  Howard.) 
coming    to    the    surface   for    air 

at  rather  frequent  intervals.  After  a  number  of  molts 
the  larva  passes  into  a  pupa  stage  which  is  peculiar  in 
being  active  and  in  suspending  itself,  like  the  larva,  at  the 
surface  of  the  water.  Instead  of  having  a  posterior 
breathing  tube,  however,  the  pupa  has  a  pair  of  such 
tubes  attached  to  the  greatly  enlarged  thorax.  Project- 
ing below  the  thorax  may  be  seen  the  wing  cases  and  leg 
cases  which  are  closely  fused  to  the  body.  The  pupa 


40  ANIMAL  BIOLOGY 

takes  no  food  and  in  a  few  days  gives  rise  to  the  mature 
insect. 


FIG.  36. — Egg  raft  and  larvae  of  the  mosquito  Culex  pungens.     bt,  breath- 
ing   tube;    et    two    eggs    enlarged.     (After    Howard.) 

Mosquito  larvae  are  commonly  found  in  stagnant  water 
which  contains  more  or  less  decaying  vegetable  matter. 
They  are  not  uncommon  in  rain-water  barrels,  cisterns 


FIG.  37. — Pupa   of   Culex    (at  left)    and   Anopheles    (at   right) — greatly 
enlarged.     (After  Howard.) 

and  shallow  wells,  and  may  even  live  in  cesspools.     A  few 
species  live  in  salt  marshes.     The  male  mosquitoes  may 


THE   DIPTERA   OR  FLIES  47 

readily  be  distinguished  from  the  females  by  their  longer 
labial  palpi,  large,  bushy  antennae  and  by  having  clasping 
organs  at  the  posterior  end  of  the  body.  In  the  great 
majority  of  species  they  are  not  blood  suckers  like  the 
females,  but  content  themselves  with  a  vegetarian  diet 
by  sucking  the  juices  of  plants.  For  this  reason  and  also 
because  they  are  short  lived,  they  are  much  less  in  evidence 
than  the  females. 

It  has  been  abundantly  shown  that  the  bite  of  mosqui- 
toes of  the  genus  Anopheles  forms  the  sole  means  for  the 
introduction  of  malaria  into  the  human  system.  As  will 
be  more  fully  described  in  a  later  chapter  the  germs  of 


PIG.  38. — Anopheles    at    left,    Culex    at  right  in  characteristic  resting 

position. 

malaria  are  introduced  into  the  body  with  the  fluid  the 
mosquito  injects  from  its  salivary  glands  while  it  is  suck- 
ing blood.  In  a  similar  way  another  much  dreaded  dis- 
ease, yellow  fever,  is  carried  by  mosquitoes  of  the  genus 
Aedes  (Stegomyia).  By  getting  rid  of  disease-carrying 
mosquitoes,  therefore,  the  liability  of  these  diseases 
to  spread  becomes  greatly  reduced,  and  much  attention 
has  been  given  in  recent  years  to  devising  efficient  means 
of  exterminating  these  insects.  Draining  swamps  and 
marshes  where  mosquitoes  breed  is  often  resorted  to,  and 
where  this  is  not  feasible,  covering  the  surface  with  a  thin 
film  of  kerosene  oil  is  often  tried.  Kerosene  quickly  kills 
the  larvae  when  they  come  to  the  surface  to  breathe,  and 
while  it  may  have  to  be  put  on  the  water  more  than  once 


48  ANIMAL  BIOLOGY 

during  the  summer  it  has  proven  a  very  efficient  remedy 
and  one  not  very  expensive  when  the  area  is  not  too  great. 
Certain  fishes,  especially  sun-fish,  stickle  back  and  min- 
nows devour  enormous  numbers  of  mosquito  larvae,  and 
the  introduction  of  these  fishes  into  waters  where  mosqui- 
toes are  in  the  habit  of  breeding  has  often  nearly  extermi- 
nated the  larvae.  Careful  attention  to  rain-water  barrels 
and  other  stagnant  water  is  also  very  desirable.  In  many 
places,  especially  where  malaria  or  yellow  fever  occurs, 
a  vigorous  campaign  against  mosquitoes  has  greatly  re- 


FIG.  39. — Aedes  fasciata,   the  yellow-  fever  mosquito.      (After   Howard.) 

duced  their  numbers,  and  in  most  situations  the  trouble 
and  expense  of  a  mosquito  crusade  would  be  well  repaid 
by  the  increased  comfort  to  be  enjoyed  in  the  absence  of 
these  irritating  pests. 

THE  FLEAS 

It  was  formerly  customary  among  entomologists  to 
regard  the  fleas  as  Diptera  which  had  lost  their  wings 
through  disuse  owing  to  their  parasitic  habits.  But 
however  they  lost  their  wings,  they  are  now  generally 


THE   DIPTERA    OR   FLIES  49 

ranked  as  a  distinct  order,  the  Siphonaptera,  which  may 
nevertheless  have  its  closest  relatives  in  the  true  flies.  The 
fleas  resemble  most  flies  in  havng  mouth  parts  adapted 
for  piercing  and  sucking,  and  their  long  and  powerful 
legs  give  them  such  effective  powers  of  rapid  movement 
that  wings  would  be  almost  superfluous.  There  are  a 
great  many  species  of  fleas  infesting  different  species  of 
mammals  and  birds,  but  only  a  few  attack  man.  The 
eggs  are  laid  in  hairs  or  among  the  feathers  of  the  host 
and  are  usually  shaken  off.  Hodge  reports  that  "from 
a  lady's  dress  on  which  a  kitten 
had  been  fondled  for  a  short 
time,  fully  a  teaspoonf  ul  of  flea's 
eggs  were,  collected."  The 
larvae  are  slender,  whitish  grubs 
which  feed  upon  dried  animal 
and  vegetable  matter.  There 
is  a  pupa  stage  of  short  dura- 

tion, the  whole  period  from  egg         FIG.    40.—  Female     of    flea, 


to  adult  in  the  common  cat  and    fj£*r  j£^'  infesting  man" 


dog  fleas  being  passed  through  in 
not  more  than  two  weeks.  Fleas,  like  mosquitoes,  are  dis- 
ease carriers;  one  of  the  most  dreaded  diseases  that  afflicts 
mankind,  the  plague,  which  has  carried  off  its  hundreds 
of  thousands  in  various  epidemics  that  have  swept  over 
Europe  and  Asia,  is  carried  by  fleas.  The  disease  attacks 
rats  and  squirrels  as  well  as  man,  and  wherever  there 
are  infected  animals  there  is  constant  danger  of  an  out- 
break among  human  beings.  The  fleas  coming  from  rats 
will  readily  carry  the  disease  to  man  and  from  one  man 
to  another.  Consequently  when  the  plague  was  intro- 
duced into  San  Francisco  a  few  years  ago  a  crusade  was 
made  against  the  rats.  Chinatown  was  subjected  to  the 
strictest  search  for  these  vermin  and  rats  were  trapped 


50  ANIMAL  BIOLOGY 

and  poisoned  in  large  numbers.  Plague  patients  were 
carefully  isolated,  and  the  epidemic  which  had  already 
made  considerable  progress,  was  fortunately  held  in 
check.  Without  the  knowledge  of  the  parts  played  by 
the  flea  and  the  rat  in  the  dissemination  of  this  terrible 
disease  the  country  might  have  been  swept  over  a  scourge 
that  would  have  claimed  many  thousands  of  victims. 


CHAPTER  VI 
THE  COLEOPTERA  OR  BEETLES 

As  the  insects  include  many  more  species  than  any  other 
class  in  the  animal  kingdom,  so  do  the  species  of  beetles 
outnumber  those  of  any  other  order  of  insects.  The  order 
is  not  so  diversified  as  the  Hemiptera,  notwithstanding 
its  enormous  size.  In  ninety-nine  cases  out  of  a  hundred, 


FIG.  41. — The  California  May  beetle,  Lachnoslerna   errans  Lee. 
and   grubs,    enlarged.     (After    Essig.) 


Adult 


one  can  detect  a  beetle  at  first  glance,  with  perfect 
certainty.  All  of  the  beetles  have  biting  mouth  parts 
much  like  those  of  the  Orthoptera,  but  they  differ  from 
the  Orthoptera  in  undergoing  a  complete  metamorphosis; 
that  is,  their  life  history  falls  into  three  well-defined  stages : 
the  active  larva,  the  quiescent  pupa,  and  the  imago. 
The  first  pair  of  wings  are  modified  into  hard  thick  wing 

51 


52  ANIMAL  BIOLOGY 

covers  whose  principal  function  it  is  to  cover  and  protect 
the  abdomen  and  the  membranous  second  pair  of  wings 
which  are  the  true  organs  of  flight.  Some  of  the  most 
common  and  widely  distributed  of  the  Coleoptera  are  the 
June-bugs  or  May-beetles  which  often  come  buzzing  in 
through  the  open  windows  of  lighted  rooms  in  the  summer 
time.  The  larvae  are  fat,  whitish  grubs  which  live  upon 
the  roots  of  grass  and  other  plants,  and  frequently  do  con- 


PiG.  42. — Life    history    of    the     Colorado    potato    beetle,     a,    eggs;    b, 
larva;  c,  pupa;  d,  adult  insect;  e,  wing  case;  /,  leg. 

siderable  damage.  After  spending  two  or  three  years  in 
the  ground  they  pass  through  a  relatively  short  pupa  stage 
before  emerging.  There  are  many  different  species  which 
are  similar  in  form  and  habits. 

The  Colorado  potato  beetle  is  one  of  our  most  serious 
insect  pests.  Its  original  home  was  in  the  regions  lying 
near  the  eastern  slope  of  the  Rocky  Mountains  and,  as 
the  cultivation  of  land  extended  from  the  east  and  the 
potato  gradually  traveled  westward,  the  Colorado  beetle 
found  in  this  vegetable  an  acceptable  food  plant  similar 


THE  COLEOPTERA  OR  BEETLES 


53 


to  the  one  it  formerly  preyed  upon.  The  species  then  be- 
gan to  spread  rapidly  toward  the  east.  In  a  few  years 
it  crossed  the  Mississippi,  and  in  a  few  more  years  spread 


FIG.  43. — The  twelve-spot- 
ted cucumber  beetle,  Diabro- 
tica  i2-punctata  Oliv.  (After 
Essig.) 


FIG.  44. — A   "cut   worm   killer," 
Calosoma  calidum,  and  its  larva. 


throughout  all  the  middle  and  eastern  states.  The  beetle 
is  particularly  destructive,  since  it  feeds  upon  the  leaves 
of  the  potato  in  the  larval  as  well  as  in  the  imago  stage. 
Its  eggs  are  laid  in  masses  on  the  leaves  and  they  soon 


FIG.  45. — The  round-headed  apple-tree  borer,     a,  larva;  b,  pupa;  c,  adult. 
(After  Riley.) 

hatch  into  reddish,  fleshy  larvae  which  eat  and  grow 
rapidly.  There  are  commonly  two,  and  sometimes  three 
generations  a  year.  The  mature  insect  passes  the ,  winter 


54  ANIMAL  BIOLOGY 

buried  in  the  ground.  The  little,  yellow,  black-spotted 
cucumber  beetle  and  the  elm-leaf  beetle  which  has  caused 
so  much  damage  to  the  elm  trees  in  the  eastern  states 
are  other  destructive  pests  belonging  to  the  same  family  as 
the  potat  o  bug. 

The  boring  beetles,  of  which  there  are  large  numbers, 
include  many  destructive  enemies  of  trees  and  shrubs. 
The  larvae,  and  in  many  cases  the  adults  also,  live  upon 
the  wood,  forming  tunnels  which  sometimes  result  in 
completely  girdling  the  tree.  The  pupae  usually  lie  in 
the  burrows  and  the  mature  insect  gnaws  its  way  to  the 
outside. 


FIG.  46. — Female  of  FIG.  47. — A  click  beetle. 

the  Vedalia  beetle. 

Among  the  beetles  which  are  beneficial  to  man  are  to 
be  counted  the  lady  beetles  which  are  of  small  size  and  usu- 
ally hemispherical  in  outline.  In  both  larval  and  adult 
stages  they  prey  upon  plant  lice,  scale  bugs  and  other 
insects.  The  Novius  previously  mentioned  which  prac- 
tically exterminated  the  cottony-cushion  scale  is  a  species 
of  the  lady  beetle  family. 

Less  useful,  but  on  the  whole  beneficial  beetles  are  the 
scavenger  or  carrion  beetles  which  feed  upon  the  decay- 
ing bodies  of  animals,  which  they  can  detect  at  a  consider- 
able distance  through  their  remarkably  acute  sense  of 
smell.  There  are  numerous  water  beetles  belonging  to 
several  distinct  families.  The  Gyrinidae,  or  whirling 
beetles,  which  are  the  analogues  of  the  pond-skaters 


THE  COLEOPTERA  OR  BEETLES  55 

among  the  Hemiptera,  are  frequently  to  be  seen  darting 
about  in  groups  at  the  surface  of  the  water.  Below  the 
water  live  the  Dystiscidae  which  are  active,  predatory 
creatures,  furnished  with  legs  especially  fitted  for  swim- 
ming. They  come  to  the  surface  for  air,  and  carry  more 
or  less  air  down  with  them  under  their  wing  cases.  The 
larvae  have  slender  bodies  and  long,  sharp  jaws  which  are 
perforated,  a  device  that  enables  them  to  suck  the  juices 
out  of  the  forms  on  which  they  prey.  Some  other  large 
water  beetles  (Hydrophilidae)  live  upon  decaying  vege- 
table material  as  well  as  animal  food. 


FIG.  48. — The  Plum  curculio,  Conotrac.helus  nenuphar,     a,  larva;  6,  pupa; 
c,  adult;  d,  weevil  attacking  young  plums. 

The  snout  beetles  constitute  a  peculiarly  specialized 
group,  the  head  being  prolonged  into  a  snout  which  is 
often  of  considerable  length.  The  very  small  mouth  parts 
are  situated  at  the  end  of  this  projection  and  the  antennae 
are  borne  on  its  sides.  The  group  is  a  large  one  and  in- 
cludes forms  known  as  curculios,  and  weevils,  although  the 
latter  term  is  applied  to  some  small  beetles  belonging 
to  other  families.  The  snout  beetles  are  particularly 
destructive  to  fruits,  grains,  nuts,  and  to  many  other  ar- 
ticles of  food. 


CHAPTER  VII 

THE  HYMENOPTERA  OR  BEES,  ANTS,  WASPS 
AND  THEIR  ALLIES 

The  Hymenoptera,  or  membrane-winged  insects,  in- 
clude the  bees,  ants,  wasps  and  a  host  of  less  well-known 
forms,  nearly  all  of  which  are  characterized  by  having 
a  combination  of  biting  aftd  sucking  mouth  parts.  There 
are  four  membranous  wings  in  the  great  majority  of  the 
Hymenoptera,  and  the  females  are  provided  either  with 
a  sting,  or  an  ovipositor  which  is  usually  adapted  for 


FIG.  49. — Honey  bees.    A,  drone;  B,  queen;  C,  worker.      (After  Benton.) 

inserting  the  eggs  into  the  tissues  of  plants  or  the  bodies  of 
animals.  This  order  includes  the  most  highly  developed 
of  the  insects,  many  of  which  are  remarkable  for  the  num- 
ber and  perfection  of  their  instincts. 

Among  the  higher  Hymenoptera  we  find  many  instances 
of  a  highly  developed  social  life  which  is  well  exemplified 
by  our  common  hive  bees.  The  hive  bee  community 
is  composed  of  three  kinds  of  individuals,  the  queens, 
the  drones,  and  the  workers.  These  three  kinds  or  castes 
differ  considerably  in  structure,  and  much  more  in  their 
instinctive  activities,  for  each  caste  has  its  particular 

56 


HYMENOPTERA   OR  BEES,    ANTS,    WASPS,    ETC. 


57 


set  of  duties  to  perform  in  the  economy  of  the  hive. 
The  queen  is  larger  than  the  drones  or  workers  and  has 
a  relatively  larger  and  more  elongated  abdomen.  She 
is  the  fertile  female,  and  her  duties  are  limited  to  laying 
eggs  in  the  cells  made  by  the  workers.  Notwithstanding 
her  name  she  is  in  no  sense  a  ruler.  The  workers  feed  and 


PIG.  50. — Head  and  tongue  of  worker  bee  magnified,  a,  antenna,  or 
feeler;  m,  mandible;  g,  gum  flap,  or  epipharynx;  mxp,  maxillary  palpus; 
pg,  paraglossa;  mx,  maxilla:  Ip,  labial  palpus;  I,  ligula,  or  tongue;  b,  bouton, 
or  spoon  of  the  same.  (Reduced  from  Cheshire.) 

protect  her,  and  become  uneasy  and  demoralized  if  she 
is  taken  away  or  dies,  but  she  issues  no  orders  to  her 
faithful  attendants.  Each  queen  is  actuated  by  a  deadly 
hostility  to  every  other  queen,  and  if  two  queens  happen 
to  come  together  there  is  a  fight  to  the  death.  As  the 
young  queen  flies  out  of  the  hive  she  is  followed  by  a 
number  of  drones  with  one  of  which  she  mates;  she  then 


58  ANIMAL  BIOLOGY 

returns  and  soon  begins  her  duties  of  laying  eggs.  The 
drones  do  not  gather  honey  and  take  no  part  in  the  house- 
hold duties  of  the  hive,  but  live  idly  upon  the  food  col- 
lected by  the  workers.  After  the  queen  is  fertilized  and 
there  is  no  more  use  for  the  drones,  the  workers  fall  upon 
them,  sting  them  to  death  and  drag  out  their  dead  bodies. 
Although  the  worker  bees  are  imperfect  females,  in- 
asmuch as  the  development  of  the  reproductive  system 
has  been  arrested,  there  are  few  insects  which  possess  so 
many  wonderful  adaptations  of  structure  for  their  varied 
activities.  Their  mandibles  are  furnished  with  smooth 
edges,  devoid  of  teeth,  and  especially  fitted  for  moulding 
wax.  The  maxillae  and  lower  lip  are  modified  to  form  a 
sucking  tube,  through  which  nectar  is  drawn  from  flowers. 
This  nectar  passes  into  the  honey-sac  or  crop  which 
is  an  enlargement  of  the  alimentary  canal  just  in  front  of 
the  stomach;  here  it  is  converted  into  honey  which  is 
regurgitated  into  the  cells  of  the  comb. 
.  The  legs  of  the  worker  bee,  in  addition  to  their  adaptation 
for  walking  and  the  pads  and  claws  on  the  feet  which  fit 
them  for  climbing  up  either  smooth  or  rough  surfaces, 
show  a  number  of  interesting  modifications  for  various 
other  functions.  One  of  these  is  the  antenna  cleaner. 
On  the  joint  beyond  the  tibia,  the  metatarsus,  is  a  semicir- 
cular notch  which  is  lined  by  a  very  even  row  of  spines, 
and  at  the  lower  end  of  the  tibia  there  is  a  movable  ap- 
pendage which  can  be  fitted  over  this  notch  so  as  to  form 
a  nearly  circular  space  about  the  diameter  of  the  antenna. 
When  the  antenna  becomes  covered  with  pollen  or  other 
material  the  bee  throws  its  fore  leg  over  it  and  pulls  it 
through  the  antenna  cleaner,  thus  stripping  off  the  for- 
eign material.  The  antenna  cleaner  is  found  also  in  the 
queen  and  drone  and  is  common  among  Hymenoptera  in 
general.  The  middle  leg  of  the  worker  is  fitted  with  a 


HYMENOPTERA   OR  BEES,   ANTS,   WASPS,   ETC. 


59 


peculiar  spine  at  the  end  of  the  tibia  which  is  used  for 
cleaning  the  wings  and  for  prying  off  the  masses  of  pollen 
which  are  carried  on  the  hind  legs.  The  third  leg  has  a 
number  of  interesting  devices  for  gathering  and  trans- 
porting pollen;  on  the  outer  side  of  the  tibia  there  is  a 
concavity  bordered  with  stiff  hairs,  called  the  pollen 
basket,  and  if  one  watches  bees  that  come  in  from  the  fields, 
these  baskets  may  often  be  seen  filled  out  with  their  yellow 
masses  of  pollen.  How  does  the  bee  manage  to  get  the 
pollen  into  the  basket?  This  is  done  by  means  of  the 


FIG.  51. — Legs  of  worker  bee.  A ,  lower  part  of  third  leg  seen  from  the 
outside,  pb,  pollen  basket;  ts,  tarsus;  B,  inner  face  of  metatarsus  showing 
the  pollen  comb  pc  and  the  wax  pincers,  wp\  C,  part  of  first  leg  showing  the 
antenna  cleaner,  ac,  and  the  eye  brush,  eb. 

pollen  combs  on  the  inner  side  of  the  metatarsal  joint. 
These  combs  consist  of  a  number  of  rows  of  spines  which 
are  used  to  comb  out  the  pollen  entangled  in  the  hairs  of 
the  bee's  fuzzy  body,  and  when  they  are  filled  the  bee 
crosses  its  legs  and  rakes  off  the  pollen  from  one  comb  into 
the  basket  of  the  opposite  leg.  Another  ingenious  device 
is  shown  in  the  wax  pincers  which  are  formed  by  the  ex- 
tended edges  of  the  tibia  and  metatarsus  at  the  place  where 
they  come  together;  these  pincers  are  used  for  seizing 


6o 


ANIMAL  BIOLOGY 


the  wax  scales  which  are  secreted  by  the  wax  glands. 

There  is  no  pollen  comb  or  basket  and  no  wax  pincers  on 

the  legs  of  either  queen  or  drone. 

The  wax  glands  are  found  only  in  the  worker.     There 

are  four  pairs  of  these  on  the  lower  side  of  the  abdomen. 

The  wax  is  secreted  in  the  form  of  thin  scales  which  are 

seized  by  the  pincers  and  passed  forward  to  the  jaws 
where  they  are  mixed  with  saliva 
and  kneaded  into  the  proper  con- 
sistency for  making  comb. 

The  sting  which  is  present  in  the 
worker  and  queen  but  not  in  the 
drone  is  composed  of  two  very  fine 
and  sharp  " darts"  which  glide  into 
a  sheath  at  the  posterior  end  of 
the  body.  There  is  a  poison  sac 
within  the  abdomen  whose  contents 
are  forced  into  the  wound  in  the 
process  of  stinging.  The  sting  is 
really  a  modified  ovipositor,  a  fact 
that  explains  its  absence  in  the 
drone.  Near  the  tip  of  the  sting 

of  PcGom5^Wh0ornke"  "£    **  *°™  fine,  recurved  teeth  which 

(Apis  mellifera);  natural     make    the    Sting  difficult  to  pull  OUt 
size.     (After  Benton.)  ,  .,     ,  ,     .         .    J          . 

when  it  has  entered  far  into   the 

flesh.  In  fact,  the  bees  are  frequently  unable  to  pull  out 
the  sting  and  in  freeing  themselves  certain  organs  of  the 
abdomen  are  pulled  away  with  the  sting  so  that  the  in- 
sects pay  the  penalty  of  their  boldness  with  their  lives. 
Gathering  honey,  keeping  the  hive  clean,  feeding  the 
queen  and  young  grubs,  building  the  comb,  and  many 
other  acts  keep  the  worker  bee  well  occupied  during 
the  period  of  its  short  life,  which  lasts  in  the  summer  only 
two  or  three  months.  The  comb  of  the  bee  consists  of 


HYMENOPTERA    OR  BEES,    ANTS,    WASPS,    ETC. 


6l 


six-sided  cells  on  either  side  of  a  central  plate  of  wax.  The 
cells  He  nearly  horizontal  inclining  usually  slightly  up- 
ward. The  whole  arrangement  of  the  cells  is  wonder- 
fully adapted  to  afford  the  greatest  amount  of  storage 
space  with  the  least  amount  of  material;  a  problem  which 
the  bees  have  solved  as  well  as  if  they  had  a  knowledge 
of  geometry.  The  cells  constructed  for  rearing  drones  are 


- VUg1  

PIG.  53. — Comb   showing   eggs,   larvae,   pupae   and   queen   cells.     (After 

Benton.) 


somewhat  larger  than  the  usual  ones,  but  of  the  same 
shape;  the  queen  cells,  however,  are  much  larger  than  the 
others  and  hang  down  at  right  angles  to  the  rest  and  are 
usually  roughened  on  the  outer  surface.  Ordinary  cells 
are  used  either  for  storing  food  or  raising  bees.  Some  of 
the  cells  are  filled  with  a  mixture  of  pollen  and  honey 
commonly  called  "bee  bread"  which  is  used  in  feeding  the 
young  larvae  or  grubs. 


62  ANIMAL  BIOLOGY 

Besides  gathering  honey  or  pollen,  bees  bring  in  a  sub- 
stance called  propolis  or  "bee  glue"  which  they  obtain  from 
the  gums  and  resins  of  trees.  This  substance  is  used  in  stop- 
ping up  cracks,  for  holding  the  combs  in  place,  and  for 
covering  over  offensive  objects,  such  as  dead  slugs  or 
other  creatures  which  are  too  large  to  drag  out  of  the  hive. 
Bees  are  watchful  nurses  as  well  as  good  providers.  The 
cells  in  which  the  queen  lays  eggs  are  supplied  from  time 
to  time  with  honey  and  pollen  as  the  young  grubs  require 
more  food.  Often  one  worker  feeds  another  and  all  are 
ready  and  apparently  eager  to  offer  nutriment  to  the  queen. 
Among  bees  care  for  their  own  interests  means  hostility 
to  enemies,  and  the  valiant  worker  is  ready  to  sting  any 
enemy  that  threatens  the  welfare  of  the  community  even 
though  it  involves  the  loss  of  her  own  life. 

In  the  formation  of  new  communities  or  swarms  of 
bees  the  old  queen  followed  by  a  swarm  of  workers  is- 
sues from  the  hive.  The  swarm  often  settles  on  the  bough 
of  some  tree  from  which  the  bees  hang  in  a  dense  cluster. 
If  left  to  themselves  the  bees  may  finally  take  up  their 
abode  in  a  hollow  tree  or  some  other  protected  situation, 
but  the  thrifty  bee  keeper  usually  transports  the  swarm 
to  a  new  hive  where  they  soon  succeed  in  making  them- 
selves at  home. 

There  are  numerous  species  of  bees  which  differ  greatly 
in  their  mode  of  life.  Many  are  solitary  in  their  habits. 
These  show  no  division  into  fertile  and  worker  castes. 
The  female  in  many  species  makes  merely  a  shallow  hole 
in  the  ground;  this  she  stores  with  honey  and  pollen 
upon  which  she  lays  an  egg;  then  she  fills  up  the  hole  with 
dirt  and  leaves  it.  The  larva,  after  devouring  the  stored 
up  food,  pupates  and  then  emerges  as  a  perfect  insect. 
Some  bees  remain  in  the  nest  and  care  for  the  young  more 
or  less  constantly,  and  thus  form  a  family  group.  From 


HYMENOPTERA   OR  BEES,   ANTS,   WASPS,   ETC.  63 

the  simple  family  there  are  various  gradations  to  the  primi- 
tive social  community  such  as  that  formed  by  the  common 
bumble  bees.  Here  the  queen,  which  is  the  only  member 
to  survive  the  winter,  starts  a  nest  during  the  spring 
in  a  hole  or  some  depression  in  the  earth,  which  she  often 
covers  over  by  bits  of  moss  or  grass.  Then  she  makes 
a  few  waxen  cells,  stores  them  with  honey  and  pollen, 
and  lays  in  them  eggs  which  hatch  into  worker  bees.  The 
workers  are  of  relatively  small  size,  but  otherwise  in 
appearance  they  are  very  similar  to  the  queen.  They 
busy  themselves  with  making  new  cells, 
storing  .them  with  honey  and  pollen, 
and  feeding  the  young  grubs.  Later 
in  the  season  queens  and  drones  ap- 
pear; the  queens  after  becoming  ferti- 
lized scatter,  and  those  that  survive  the 
winter  found  new  colonies  in  the  follow- 
ing year. 

The  bumble  bee  community  is  not 

J  FIG.    54. — Nest  of 

a  permanent  one,  but  the  transitory  the  solitary  burrow- 
product  of  a  single  season.  In  its  J^.J^fi!*1  '' 
household  arrangements,  as  in  many 
other  respects,  it  is  simple  and  crude  compared  with  the 
social  life  of  the  hive  bees;  the  wax  cells  are  rounded 
capsules  arranged  in  no  very  definite  order,  and  there  is 
only  one  kind  of  cell  produced.  The  queen  at  first,  as  in 
the  solitary  bees,  performs  all  the  labors  of  making  a  nest 
and  rearing  young,  and  only  later  devotes  herself  exclu- 
sively to  laying  eggs.  Division  of  labor  is  not  carried  very 
far  and  the  castes  are  specialized  only  to  a  slight  extent. 
There  are  other  bees  whose  social  life  is  more  complex  than 
that  of  the  bumble  bees;  they  form  connecting  stages  be- 
tween the  latter  and  the  hive  bees  whose  social  arrange- 


64  ANIMAL  BIOLOGY 

ments  represent  the  culmination  of  a  long  life  of  evolution 
from  the  solitary  species. 

In  the  wasps,  as  in  the  bees,  there  are  both  solitary  and 
social  species.  The  solitary  wasps  commonly  prey  upon 
insects  and  spiders  which  they  store  in  their  nests  as 
provision  for  their  young  larvae.  The  habits  of  a  number 
of  species  have  been  carefully  studied  by  Dr.  and  Mrs. 


FIG.   55. — Solitary    wasp,    Ammophila,    stinging    a    caterpillar.      (After 

Peckham.) 

Peckham  who  have  written  a  most  interesting  book  upon 
the  results  of  their  investigations.  Each  species  generally 
hunts  a  particular  kind  of  prey  and  constructs  a  particu- 
lar kind  of  nest.  In  many  cases  the  prey  is  stung  so  as 
to  paralyze  it  without  destroying  its  life,  thus  providing 
the  larvae  with  a  supply  of  fresh  food.  The  digger 
wasp  Psammophila  makes  a  little  hole  in  the  earth,  and 
then  goes  in  search  of  a  caterpillar  which  it  proceeds  to 
sting  on  the  ventral  side  of  the  body  near  the  nerve  cen- 
ters. Then  the  wasp  flies  across  the  fields  with  her  bur- 


HYMENOPTERA   OR  BEES,   ANTS,   WASPS,   ETC.  65 

den  to  her  inconspicuous  little  hole,  and  after  dragging 
her  prey  in  she  lays  an  egg  upon  it  and  covers  it  over 
with  earth.  Often  several  caterpillars  are  put  into  the 
same  hole  and  after  the  last  one  is  disposed  of,  the  wasp 
fills  up  the  hole  and  leaves  it.  The  mud  daubers  fre- 
quently build  their  nests  on  the  sides  of  buildings;  they 
make  cells  of  mud  and  commonly  store  them  with  para- 
lyzed spiders. 

In  the  social  wasps  we  have  a  worker  caste  consisting 
of  sterile  females  which  show  few  external  differences,  ex- 
cept in  size,  from  the  fertile  females.  The  best  known 
species  are  the  yellow  jackets  and  hornets.  Both  these 
forms  build  rather  large  nests  of  a  paper-like  substance 
which  they  make  by  chewing  up  wood.  Out  of  this  paper 
they  construct  remarkably  neat  and  regular  six-sided  cells 
which  are  placed  with  their  open  ends  hanging  downward. 
There  are  commonly  several  tiers  or  stories  of  these  cells 
one  over  the  other,  and  the  whole  is  surrounded  with  a 
paper  envelope  with  a  hole  in  the  bottom.  The  large 
white-faced  hornets  attach  the  nest  to  the  branch  of  a 
tree,  and  it  is  not  safe  to  molest  them  as  the  hornets 
have  a  very  irritable  temper  and  can  sting  with  consider- 
able severity.  The  nests  of  some  species  of  yellow  jackets 
'are  commonly  found  under  the  ground  while  others  may 
be  attached  to  buildings  or  trees.  These  creatures  are 
likewise  very  pugnacious,  but  not  so  formidable  as  the 
hornets. 

ANTS 

One  would  not  at  first  sight  regard  the  ants  as  members 
of  the  order  Hymenoptera  because  most  of  them  are 
wingless,  but  study  of  their  structure  shows  them  to  be 
related  to  the  bees  and  wasps.  It  is  only  the  workers, 
and  these  are  by  far  the  most  numerous,  that  never  de- 


66 


ANIMAL  BIOLOGY 


velop  wings;  the  males  and  fertile  females  are  winged  as 
they  emerge  from  the  pupa  state,  when  they  are  commonly 
spoken  of  as  "flying  ants."  Like  the  bees  the  ants  fly 
out  of  the  nest  to  mate;  after  the  breeding  period  the  males 
soon  die  and  the  females  strip  off  their  wings  and  spend 
the  greater  part  of  their  life  in  the  wingless  state.  Sir  John 


FIG.  56. — The  little  black  ant  (Monomorium  minuluni).  a,  female;  b, 
same  with  wings;  c,  male;  d,  workers;  e,  pupa;/,  larva;  g,  egg  of  worker — 
all  enlarged.  (After  Marlatt.) 

Lubbock  records  having  kept   a   queen   ant   for  nearly 
fifteen  years. 

In  some  species  there  are  more  than  three  castes,  be- 
cause the  sterile  females  are  differentiated  into  soldiers, 
workers  proper,  and  more  rarely  other  kinds  of  individuals. 
The  soldiers  are  relatively  large  and  have  big  heads  and 


HYMENOPTERA   OR  BEES,   ANTS,   WASPS,   ETC.  67 

strong  jaws;   they  generally  take  a  prominent  part  in 
the  defense  of  the  community  against  its  enemies. 

Ants  usually  make  nests  by  digging  burrows  or  tunnels 
in  the  earth,  and  heaps  of  material  are  often  accumulated 
around  the  openings  of  the  burrows,  or  "ant  hills" 
with  which  everyone  is  familiar.  The  large,  black  car- 
penter ants  burrow  into  old  stumps  or  rotten  tree  trunks. 
A  few  species  make  nests  in  the  hollowed-out  stems  of 
plants.  The  nests  are  usually  in  places  where  it  is  moist 
and  dark.  Here  the  eggs  are  laid,  the  larvae  tended  and 
fed  by  the  workers,  and  the  pupae  stored  in  suitable 
chambers.  The  pupae  of  many  species  are  enclosed  in 
a  cocoon  spun  by  the  larva.  These  cocoons  are  often 
erroneously  called  "ant  eggs,"  the  true  eggs  being  very 
much  smaller  objects.  Both  eggs  and  pupae  are  objects 
of  much  solicitude  on  the  part  of  the  worker  ants ;  they 
carry  them  about  from  one  chamber  to  another  so  as  to 
keep  them  in  a  favorable  situation,  and  when  a  nest  is 
broken  into  the  workers  may  be  seen  wildly  rushing  about 
with  pupae  or  egg-masses  in  their  jaws  in  the  effort  to  save 
them  from  destruction. 

Most  students  of  ant  life  agree  that  ants  have  a  power 
of  communication  by  means  of  striking  one  another  with 
their  antennae  and  by  making  other  signs  whereby  they 
may  be  warned  of  danger,  or  induced  to  follow  a  particular 
ant  to  obtain  food.  If  one  ant  discovers  a  bit  of  sugar 
it  is  not  long  until  a  train  of  other  ants  is  trooping  to  the 
spot.  The  ant  community  is  closely  bound  together  in 
its  common  interests;  the  members  work  industriously 
for  the  common  good,  and  are  ready  to  engage  in  fierce 
struggles  for  the  defense  of  their  community.  Stir  up 
an  ant  hill  and  you  will  see  with  what  vigor  and  zeal  the 
ants  rush  out  to  attack  the  offender.  War  in  many  species 
is  an  almost  chronic  condition.  This  is  especially  true 


68  ANIMAL  BIOLOGY 

of  the  slave-making  species  which  regularly  make  excur- 
sions against  other  communities,  and  after  killing  off 
or  driving  away  the  inhabitants,  seize  the  pupae  and  carry 
them  back  to  their  own  nests.  Here  when  the  young 
ants  emerge  they  are  adopted  by  their  captors  and  take 
part  in  the  household  and  other  duties  as  if  to  the  manner 
born.  In  some  cases,  as  in  the  Amazon  ant,  Polyergus 
rufescens,  the  ants  have  come  to  be  dependent  upon  their 
slaves  for  their  subsistence.  The  Amazons  have  large 
curved  jaws  especially  fitted  for  fighting,  but  they  have 
lost  the  power  of  food  gathering  and  would  perish  were 
they  not  fed  by  their  faithful  slaves.  They  have  become 
so  specialized  as  warriors  that  they  have  become  useless 
for  all  other  tasks.  In  addition  to  their  slaves,  ants 
sometimes  harbor  in  their  nests  a  motley  assemblage 
of  other  creatures  which  are  often  spoken  of  as  " guests" 
or  commensals.  We  have  already  spoken  of  the  aphids 
or  "ant  cows"  from  which  the  ants  obtain  a  sweet  juice. 
Ants  also  harbor  many  species  of  beetles  including  several 
blind  forms;  these  are  cleaned  and  fed  by  their  hosts  with 
as  much  care  as  is  bestowed  upon  members  of  their  own 
family.  In  return  the  ants  obtain  a  secretion  from  these 
guests.  In  many  cases  the  inmates  of  the  nest  seem  to 
be  simply  tolerated  without  affording  the  ants  any  com- 
pensation for  their  board  and  lodging.  There  are  known 
to  be  over  one  thousand  species  of  insects  which  live  for 
all  or  a  part  of  their  lives  in  the  nests  of  ants,  and  many 
of  them  show  very  curious  adaptations  to  this  mode  of  life. 
Ants  are  sometimes  a  source  of  considerable  annoyance 
to  man.  The  little  red  ants  that  come  into  houses  and 
delight  in  getting  into  the  sugar  and  other  articles  of  food 
are  often  difficult  to  deal  with  on  account  of  their  small 
size.  The  best  way  to  check  them  is  to  follow  up  their 
runway  to  the  nest  and  then  flood  the  insects  with  kero- 


HYMENOPTERA   OR  BEES,    ANTS,    WASPS,    ETC.  69 

sene,  gasoline  or  bisulphide  of  carbon.  In  the  south  and 
in  California,  the  Argentine  ant  which  was  recently  intro- 
duced from  Argentina  is  proving  a  serious  pest  to  the 
fruit  growers,  and  there  are  several  other  species  which 
which  make  themselves  more  or  less  of  a  nuisance. 

The  species  of  ants  are  very  numerous  and  they  are 
found  in  nearly  all  parts  of  the  earth.  It  would  require 
a  volume  to  treat  of  the  peculiarities  of  these  interesting 
insects,  and  we  can  no  more  than  mention  the  remarkable 
honey  ants,  the  harvesting  ants,  the  leaf-cutting  and 
fungus-growing  ants,  and  the  ferocious  driver  ants;  all 
of  these  it  would  well  repay  the  student  to  look  up  in 
larger  works. 

Besides  the  ants,  bees  and  wasps,  the  Hymenoptera  in- 
clude a  number  of  less  well-known  families.  The  ich- 
neumons and  their  relatives  lay  their  eggs  on  or  in  the 
bodies  of  insects  or  insect  larvae,  and  the  young  feed  upon 
the  tissues  of  their  host,  thereby  proving  of  great  value 
in  checking  various  insect  pests.  The  members  of 
the  family  Cynipidae  are  commonly  known  as  the  gall 
flies.  When  the  eggs  of  these  insects  are  deposited  on 
or  in  the  tissues  of  plants  a  peculiar  growth  of  the  vege- 
table tissue  results,  which  is  called  a  gall.  The  shapes 
of  these  galls  are  very  characteristic;  the  gall  caused  by  a 
certain  kind  of  insect  in  a  particular  species  of  plant  differs 
from  the  gall  produced  by  another  insect  in  the  same  plant 
and  also  from  that  produced  from  the  same  insect  in 
a  different  kind  of  plant.  Galls  may  be  produced  by 
members  of  various  other  families  of  insects,  such  as  the 
aphids  and  certain  flies.  They  represent  an  abnormal 
growth  of  plant  tissue  caused  by  the  presence  of  some  ir- 
ritating material,  but  they  are  of  use  to  the  insects  pro- 
ducing them  because  they  afford  both  food  and  shelter 
for  the  young. 


CHAPTER  VIII 

THE  DRAGON  FLIES,  DAMSEL  FLIES,  MAY  FLIES, 
STONE  FLIES  AND  CADDIS  FLIES 

All  of  the  insects  described  in  this  chapter  spend  their 
early  or  larval  life  in  the  water,  and  the  adult  insects 
are  frequently  seen  near  the  water,  although  they  may 
at  times  fly  to  a  great  distance  from  it.  The  dragon  flies 
have  four  wings  of  similar  shape  and  nearly  equal  size, 
which  are  held  out  horizontally  when  the  insect  is  at  rest. 
They  have  strong  biting  mouth  parts  and  enormous  com- 
pound eyes  which  cover  over  a  large  part  of  the  surface 
of  the  head  and  enable  the  insect  to  see  in  almost  all 
directions  at  once.  Vision  in  the  dragon  flies  is  very  acute, 
as  it  must  be  to  enable  them  to  catch  the  small  flying 
insects  which  furnish  their  food.  Their  powers  of  flight 
are  developed  in  proportion  to  their  keenness  of  vision. 
Watch  a  dragon  fly  darting  through  the  air  in  the  hunt 
for  prey,  or  better  still  attempt  to  catch  one  in  a  net,  and 
you  will  appreciate  the  efficiency  of  its  eyes  and  wings. 
Although  dragon  flies  are  called  " snake  feeders,"  "devil's 
darning  needles,"  and  other  uncomplimentary  names,  and 
are  associated,  like  the  praying  mantis,  with  a  lot  of  foolish 
superstitions,  they  are  entirely  harmless,  and  indeed  very 
useful  creatures,  since  they  devour  many  other  insects, 
including  a  considerable  number  of  mosquitoes.  The 
eggs  of  dragon  flies  are  laid  in  the  water,  and  hatch  out 
into  dull-colored,  inconspicuous,  slow-moving  larvae,  which 
prowl  along  the  bottom  after  prey  or  lie  in  wait  for  it  to 
come  near.  The  larva  is  furnished  with  a  peculiar 

70 


THE   DRAGON   FLIES  71 

organ  for  seizing  prey,  the  so-called  mask,  which  is  really 
the  labium,  or  second  maxillae.  It  is  furnished  with  mov- 
able hooks  at  the  end  and  is  capable  of  being  extended  for 
a  considerable  distance  in  front  of  the  head.  If  an  un- 
wary insect  ventures  too  near,  the  mask  is  shot  out  with 
great  rapidity  and  the  insect  pulled  back  to  the  mouth. 
When  at  rest  the  mask  is  folded  up  under  the  head. 


FIG.  57. — Dragon    fly.     (After    Kennedy.) 

After  a  series  of  molts,  during  which  the  rudiments  of  the 
wings  are  gradually  developing,  the  larva  becomes  ready 
for  the  final  change  into  the  imago  or  mature  insect. 
It  then  crawls  out  of  the  water,  the  skin  splits  down  the 
back  and  the  dragon  fly  pulls  itself  out  of  the  old 
skin,  shakes  its  wings  dry  and  flies  away.  Upon  a  super- 
ficial view  there  is  little  resemblance  between  the  alert 
and  graceful  movements  of  the  one  as  it  darts  through  the 
air  with  the  greatest  quickness  and  precision,  and  the 


72  ANIMAL  BIOLOGY 

sluggish  stealthy  prowling  of  the  other  in  the  bottom  of 
a  pond  and  stream. 

The  damsel  flies  have  a  slender  body,  broad  head  with 
widely  separated  eyes,  and  very  delicate  wings  which  are 
held  longitudinally  over  the  abdomen  when  at  rest.  The 
damsel  flies  are  frequently  conspicuous  on  account  of  their 
beautiful  coloration,  and  they  are  generally  found  flit- 
ting about  near  the  water.  The  larvae  usually  have  long 
flattened  appendages  at  the  end  of  the  body  called  tracheal 
gills  which  are  abundantly  supplied  with  tracheal  tubes 
for  carrying  air  which  is  absorbed  from  the  water. 

The  larvae  of  the  May  flies  resemble  in  many  ways  those 
of  the  dragon  flies,  but  they  may  usually  be  distinguished 
by  a  number  of  tracheal  gills  attached 
to  the  sides  of  the  abdomen,  and  by 
the  long  thread-like  feelers  at  the  end 
of  the  body.  The  gills  are  kept  mov- 
ing back  and  forth,  thus  keeping  the 
water  near  them  in  constant  circula- 
tion. The  larvae  of  some  species  of 
May  flies  live  in  the  water  for  two,  or 


skin  many  times,  their  wing  buds  be- 
coming larger  with  successive  molts.  Finally  they  come 
to  the  surface,  and  the  winged  insect  emerges  from  the 
nymphal  skin.  This  process  may  occur  when  the  larvae 
is  lying  at  the  surface  of  the  water,  the  old  skin  serving 
as  a  sort  of  raft  or  float  which  keeps  the  winged  insect 
from  getting  wet.  The  life  of  the  mature  May  fly  is 
very  short,  some  forms  living  but  one  or  two  days, 
hence  the  term  Ephemeridae  which  has  reference  to  the 
ephemeral  existence  of  the  members  of  this  family.  Soon 
after  the  insects  emerge  they  cast  a  very  delicate  skin, 
mate,  and  then  lay  their  eggs  in  the  water.  They  take 


THE   DRAGON   FLIES  73 

no  food  in  the  imago  state;  in  fact  their  mouth  parts  are 
so  much  reduced  and  atrophied  that  it  would  probably  be 
impossible  for  them  to  do  so  if  they  made  the  attempt. 
The  only  function  which  the  imago  stage  subserves  is 
that  of  reproduction.  May  flies  frequently  appear  in 
vast  numbers  in  the  vicinity  of  bodies  of  water  and  at 
night  they  are  often  attracted  to  lights,  under  which  the 
dead  accumulate  in  great  heaps.  Often  the  dead  May 
flies  drop  into  the  water  and  are  washed  ashore  in  masses 
resembling  large  windrows. 

The  caddis  flies  are  much  better  known  in  their  larval 
than  in  their  adult  state.  The  larvae  are  remarkable  for 
surrounding  themselves  in  a  tubular  case  made  of  various 
materials  which  they  carry  about  with  them.  Some 
species  construct  cases  of  sand,  some  employ  irregular 
sticks  of  wood,  while  a  few  make  their  cases  of  bits  of 
leaves  which  are  cut  out  in  a  regular  rectangular  shape 
and  fastened  together  at  the  edges  in  a  most  neat  'and  or- 
derly manner.  Usually  only  the  anterior  part  of  the  body 
is  protruded  from  the  case.  The  posterior  part  is  soft 
and  generally  furnished  with  outgrowths  which  serve 
as  gills,  and  at  the  tip  of  the  abdomen  there  is  a  pair 
of  hooks  by  means  of  which  the  worm  holds  on  to  its  case. 
When  the  worms  are  removed  from  their  cases  they  will 
readily  construct  new  ones  if  given  the  proper  materials. 
Caddis  worms  pass  through  a  more  or  less  quiescent  or 
pupa  stage  after  the  close  of  their  larval  life.  The  larva 
closes  up  the  end  of  its  tube  and  transforms  into  a  pupa, 
which  lies  within  the  old  case.  The  mature  caddis 
flies  are  somber  colored,  inconspicuous  insects  that  are 
usually  not  much  in  evidence.  They  frequent  places 
near  the  water  in  which  they  lay  their  eggs. 

The  stone  flies  are  similar  in  their  habits  to  the  May 
flies.  The  nymphs  generally  live  under  stones  in  ponds 


74  ANIMAL  BIOLOGY 

and  streams  and  the  adults  usually  fly  near  the  water. 
Another  insect  of  somewhat  similar  habits  is  the  large 
dobson  fly,  Corydalus,  which  reaches  a  length  of  4.5 
inches.  The  males  have  remarkably  long  slender  man- 
dibles. The  large  larva  (dobson  or  hellgrammite)  is 
much  prized  as  bait. 


CHAPTER  IX 
THE  MYRIAPODS  AND  ARACHNIDS 

The  Myriapoda  which  include  the  centipedes,  milli- 
peds  and  their  allies  constitute  a  group  more  or  less 
closely  related  to  the  insects  and  from  which  the  in- 
sects probably  were  developed.  They  have  usually  an 
elongated  body  with  many  segments  and  many 
pairs  of  legs.  There  is  a  well-defined  head 
furnished  with  antennae,  mandibles  and  max- 
illae, but  there  is  no  division  of  the  body  into 
thorax  and  abdomen  as  in  insects,  the  various 
segments  being  remarkably  similar  in  character 
except  near  the  extreme  end  of  the  body. 

The  centipedes  have  a  flattened  body  and 
are  furnished  with  a  strong,  curved  pair  of 
jaws  just  behind  the  head  at  the  tips  of  which 
opens  the  duct  of  a  poison  gland.     These  jaws      F'IG 
are  really  the  modified  legs  of  the  first  seg-  A  small  cen- 

f  .  i       i      i  -,   J  i  tipede,    Lith- 

ment  of  the  body,  and  they  serve  as  a  means  obius. 

of  injecting  poison  into  the  insects  or  worms 

on  which    the    centipede  commonly  preys.     The  larger 

centipedes  are  capable  of  inflicting  very  painful  bites  upon 

man. 

The  millipeds  or  " thousand  legged  worms"  are  mostly 
cylindrical  in  form  and  have  two  pairs  of  legs  attached  to 
each  ring  in  most  of  the  segments  of  the  body.  There 
are  no  poison-bearing  jaws  as  in  the  centipedes,  but  many 
species  secure  protection  by  means  of  stink  glands  which 
open  along  the  sides  of  the  body  and  pour  out  an  evil- 

75 


7  6  ANIMAL  BIOLOGY 

smelling  secretion.  The  millipeds  are  mostly  vegetable 
feeders,  and  some  species  are  more  or  less  destructive 
to  crops. 

The  myriapods  in  general  are  lovers  of  the  dark  and 
are  commonly  found  under  rocks  and  logs.  Some  species 
are  remarkable  for  the  great  elongation  of  the  body  and 
the  numerous  segments  composing  it.  In  Geophilus  the 
segments  may  be  over  170  in  number.  It  may  have 
been  some  such  creature  that  induced  Professor  Ray 
Lankester  to  write: 

A  centipede  was  happy  quite 

Until  a  toad  in  fun 

Said,  "Pray,  which  leg  moves  after  which?" 

This  raised  her  doubts  to  such  a  pitch, 

She  fell  exhausted  in  the  ditch, 

Not  knowing  how  to  run. 

The  Arachnida  include  scorpions,  spiders,  ticks,  mites 
and  a  number  of  other  forms  which  differ 
very  greatly  in  size,  structure  and  habits. 
We  shall  consider  first  the  spiders  as  they 
are  the  most  familiar  and  the  most  im- 
portant. Spiders  differ  from  insects  in 
possessing  eight  legs  and  in  having  the 

son  gland  of  spider,    head  and  thorax  fused  into  a  single  piece. 

N  eme  si  a,  with    There  are  usually  eight  simple  eyes,  but 

duct  and  fang.  r          / ,» 

no  trace  of  antennae.  The  head  is  fur- 
nished with  a  single  pair  of  jaws  which  end  in  sharp  curved 
hooks  at  the  end  of  which  is  the  opening  of  a  large  poison 
gland.  Behind  the  jaws  are  the  maxillce,  the  bases  of  which 
are  expanded  into  a  sort  of  lip,  the  rest  of  the  organ  consti- 
tuting the  jointed  palp  or  feeler.  Spiders  never  chew  their 
food;  they  simply  suck  out  the  juices  of  the  prey  which  is 
held  by  the  fangs.  On  the  under  side  of  the  abdomen  near 


THE   MYRIAPODS   AND   ARACHNIDS  77 

the  base  are  two  slits  which  open  into  the  pulmonary  sacs 
which  contain  the  organs  of  respiration.  These  organs 
consist  of  a  series  of  flattened  plates  arranged  like  the 
leaves  of  a  book  and  are  therefore  called  the  lung  books. 
In  addition  to  these  organs  spiders  are  furnished  with  tra- 
cheae or  air  tubes  similar  to  those  of  insects,  but  opening 
near  the  posterior  end  of  the  body.  The  sex  opening 
occurs  just  behind  the  slits  leading  to  the  pulmonary  sacs. 
The  organs  which  are  the  most  distinctive  of  spiders 
are  the  spinning  organs  which  produce  the  material  of 


fc's  <ye   py-g 

FIG.  61. — Section  through  the  middle  of  an  orb  weaving  spider,  al.c, 
alimentary  canal  opening  at  a;  E,  eggs  in  ovary;  I,  lung  book;  cy.g,  py.g, 
and  tr.g,  cylindrical,  pyriform,  and  tree-like  spinning  glands  respectively; 
spn.  spinnerets.  (After  McCook.) 

the  spider's  web.  These  consist  of  numerous  glands 
located  in  the  lower  part  of  the  abdomen;  they  open 
through  the  spinnerets  of  which  there  are  usually  three 
pairs  near  the  posterior  end  of  the  body.  There  are  in 
each  spinneret  a  large  number  of  small  tubules  each  of 
which  is  connected  with  a  duct  from  a  spinning  gland. 
The  material  of  the  web  is  at  first  soft  and  sticky.  The 
spider,  after  attaching  its  web  by  placing  its  spinnerets 
against  some  object,  draws  out  the  soft  material  which  rap- 
idly hardens.  As  there  are  numerous  spinning  tubes  the 
web  of  the  spider,  fine  as  it  is,  consists  of  a  large  number 
of  strands.  The  web  of  spiders  is  used  for  many  pur- 
poses. It  is  employed  to  make  the  cocoon  with  which 
the  female  surrounds  the  eggs,  in  making  nests  of  various 


ANIMAL  BIOLOGY 


sorts,  and  in  the  construction  of  snares  for  the  capture  of 
prey.  The  snares  may  consist  of  irregular  masses  of  web, 
broad  funnels  which  lead  into  a  tubular  retreat,  or,  as  in 


FIG.  62. — Female  Drassus  in 
the  act  of  dropping  eggs.  (After 
Emerton.) 


FIG.  63. — Orb  weaving  spider  spin- 
ning, bs,  beaded  spiral  of  sticky  web ; 
R,  rays;  55,  smooth  spiral.  (After 
McCook.)] 


the  orb  weavers,  of  a  beautiful  circular  orb  of  remarkable 
regularity  and  beauty  of  construction.  The  orb  weaving 
spider  commonly  hangs  downward  in  the  center  or  hub 


FIG.  64. — Diagram  of  an  orb  web.    je,  dc,  ec,  scaffolding  of  web;  x,  x,  x, 
foundation  lines  to  which  the  rays  are  attached.     (After  McCook.) 

of  the  web  with  its  legs  spread  out  upon  the  radiating 
strands,  ready  to  hasten  to  any  part  which  is  disturbed  by 
the  struggles  of  an  entangled  victim.  In  their  efforts  to 


THE   MYRIAPODS   AND   ARACHNIDS 


79 


overcome  a  large  insect  caught  in  their  snares,  many  orb 
weavers  make  another  use  of  their  web  in  spinning  a 
broad  sheet  of  it  around  their  captive  until  its  struggles 
are  effectually  overcome.  Then  the  spider  sucks  out 
its  victim's  blood  and  frequently  ejects  the  carcass 
from  its  snare. 

Another   interesting   use   of   web   is   in  " ballooning" 

which  is  a  common  prac- 
tice among  young  spiders. 
The  spider  when  preparing 
for  its  journey  through  the 
air  mounts  upon  a  promi- 
nence and  shoots  out  a 
quantity  of  web  which  is 


FIG.  65. — Attitude  of  aeronautic 
spider  just  before  taking  flight.  (After 
McCook.) 


FIG.  66. — Ballooning  spiders 
floating  in  air  by  means  of  masses 
of  web.  The  spider  at  the  right 
is  gathering  in  its  web  in  order  to 
descend.  (After  McCook.) 


caught  by  the  wind  and  pulled  out  further;  finally  the 
spider  lets  go  its  hold  and  is  carried  away  with  the  float- 
ing mass  of  web  that  is  wafted  by  the  wind.  Spiders  may 
travel  for  miles  in  this  way.  When  they  wish  to  descend 
they  haul  in  the  web  until  they  slowly  sink  to  the  ground. 
There  are  many  spiders  which  actively  hunt  for  their 


8o  ANIMAL  BIOLOGY 

prey  instead  of  spreading  snares  for  it.  Among  these  are 
the  so-called  running  spiders  and  the  jumping  or  hopping 
spiders.  The  latter  especially  are  easily  kept  in  confine- 
ment where  one  may  readily  observe  their  alertness, 
pugnacity,  keenness  of  vision,  their  careful  tactics  in 
approaching  their  prey  and  many  other  entertaining 
peculiarities  of  behavior. 

The  adult  males  of  spiders  may  be  distinguished  from 
the  females  by  the  enlarged  terminal  joint  of  the  palps. 
The  palps  serve  as  the  organs  of  sperm  transfer  at  the 
time  of  mating.  The  males  after  having  drawn  the  sper- 
matic fluid  into  the  enlarged  end  of  the  palp  convey  this 
material  to  the  sex  opening  of  the  female  and  thus  effect 
a  fertilization  of  the  eggs.  Fertilization  is  often  preceded 
by  an  elaborate  courtship  in  which  the  males  perform  the 
most  curious  antics  which  are  often  considered  to  be  the 
means  of  displaying  their  charms,  the  female  being  sup- 
posed to  choose  the  most  attractive  male.  In  some  spiders 
the  males  are  many  times  smaller  than  the  females,  and 
courtship  is  attended  with  its  dangers,  since  the  female 
often  pounces  upon  her  small  suitor  and  devours  him  with- 
out the  least  ceremony.  Spiders  in  general  are  creatures 
with  little  sympathy  in  their  composition.  Their  chief 
business  in  life  is  preying  upon  other  creatures,  and  they 
have  an  attitude  of  hostility  to  almost  everything  that 
moves.  They  perform  a  valuable  service  to  man  in  killing 
off  millions  of  injurious  insects. 

There  are  very  few  species  whose  bite  is  at  all  dangerous 
or  even  painful.  It  is  best  not  to  be  too  familiar  with  the 
large  tarantulas  of  the  south  and  west,  as  their  bite  is 
very  poisonous.  There  is  a  small  round-bodied,  black 
spider,  Latrodectes,  common  in  the  south  and  west, 
which  has  a  bad  reputation,  as  many  cases  of  severe  poison- 


THE   MYRIAPODS   AND   ARACHNIDS 


8l 


ing  and  some  fatal  ones  have  resulted  from  its  bites.  As 
a  rule  spiders  are  not  only  harmless,  but  useful  creatures. 
The  scorpions  are  arachnids  which  may  very  easily 
be  recognized  by  their  large  pincers  or  claws,  and  their 
long  jointed  tail  which  ends  in  a  sting.  What  corresponds 
to  the  mandibles  of  the  spiders  are  small,  short  pincers, 
the  large  ones  corresponding  to  the  spider's  maxillae. 


PIG.  67. — A   scorpion,    Vejovis   boreus.     (After    Essig.) 


The  scorpions  are  predatory  animals  and  live  under  rocks 
and  in  other  protected  situations,  commonly  in  warm 
climates. 

The  ticks  and  mites  form  a  more  or  less  degenerate 
group  which  contains  many  parasites  oh  both  animals 
and  plants.  The.  ticks  live  upon  the  blood  of  various 
animals  and  not  infrequently  attack  man.  They  have  a 


82 


ANIMAL  BIOLOGY 


very  quiet  way  of  boring  their  head  into  one's  skin,  and 
they  are  frequently  not  discovered  until  they  have  so 
gorged  themselves  with  blood  that  they  are  many  times 
their  original  size.  After  a  full  meal  they  may  live 
considerably  over  a  year  without  food.  Ticks,  like 
mosquitoes,  are  the  means  of  spreading  disease.  Texas 
fever  which  sometimes  exterminates  many  thousands 
of  cattle  is  carried  from  one  animal  to  another  by  ticks. 
Rocky  Mountain  fever,  a  disease  of  man  prevailing  in 
certain  parts  of  the  west,  is  also  carried  by  ticks.  A  knowl- 


FIG.  68.  FIG.  69. 

FIG.  68. — Tick    that    produces    the    Rocky    Mountain    fever.      (After 

Hunter  and  Bishopp.) 

FIG.  69. — Female  of  Texas  fever  tick  laying  eggs.     (After  Hunter  and 

Bishopp.) 


edge   of   the  mischievous  role  of  ticks  has  resulted  in 
greatly  checking  the  spread  of  both  these  diseases. 

The  mites  form  a  very  large  group  of  usually  very  small 
creatures.  Some  live  in  water,  others  in  damp  soil,  others 
on  plants,  others  attack  animals.  The  chicken  mite 
which  causes  so  much  discomfort  to  our  poultry,  is  a  com- 
mon pest.  The  small  cheese  mites  are  a  frequent  nuisance, 
but  perhaps  the  most  acutely  disagreeable  of  all  are  the 


THE   MYRIAPODS   AND   ARACHNIDS  83 

very  minute  mites  which  produce  the  disease,  now  hap- 
pily becoming  more  rare,  known  as  the  itch. 


FIG.   70. — Sar copies  scabei,  female  FIG.  71. — Demodex  follicu- 

itchmite.     (AfterLeuckart.)  lorum,    follicle    mite.     (After 

Lud  wig-Leunis . ) 

A  degenerate  form,  Demodex,  is  a  common  parasite 
in  the  follicles  of  the  human  face  and  produces  the  ap- 
pearance known  as  black  heads. 


CHAPTER  X 
THE  CRAYFISH  AND  OTHER  CRUSTACEA 

It  is  a  convenient  and  common  practice  to  study  the 
crayfish  as  a  type  of  the  Crustacea,  especially  ever  since 
Professor  Huxley  so  used  it,  and  wrote  his  celebrated 
volume  on  this  animal  which  can  be  heartily  recommended 
to  every  student  of  biology.  The  body  of  the  crayfish 
is  covered  by  a  chitinous  external  skeleton  as  in  insects, 
but  it  is  hardened  by  deposits  of  lime  salts,  except  at 
the  joints  where  it  remains  thin  and  flexible.  The  head 
and  thorax  are  fused  into  one  piece,  the  cephalothorax, 
which  is  covered  dorsally  and  at  the  sides  by  a  sort  of 
foTd  called  the  carapace.  Anteriorly  the  carapace  is 
prolonged  into  the  rostrum  or  beak.  The  part  behind 
the  cephalothorax  is  the  abdomen  and  consists  of  seven 
freely  movable  segments  or  somites,  the  terminal  one 
being  called  the  telson. 

The  eyes  of  the  crayfish  are  compound  and  situated 
on  movable  stalks.  There  are  two  pairs  of  antennae; 
the  first  pair  has  two  slender  flagella,  the  outer  one  of 
which  bears  minute,  club-shaped  bodies  which  are  organs 
of  smell.  The  long  second  antennae  are  mainly  used  as 
organs  of  touch;  the  first  segment,  however,  contains  the 
opening  of  the  "green  gland''  or  organ  of  excretion. 

The  crayfish  is  furnished  with  six  pairs  of  mouth  parts, 
the  first  of  which,  the  mandibles,  are  stout  organs  well 
adapted  for  crushing  food.  The  two  following  pairs  are 
the  maxilla,  and  these  are  followed  by  three  larger  pairs 
of  appendages  called  the  maxillipeds.  The  first  pair  of 

84 


THE  CRAYFISH  AND  OTHER  CRUSTACEA       85 

legs  are  called  chelipeds  because  they  end  in  a  pair  of 
chela  or  pincers.  There  are  small  chelae  on  the  two  follow- 
ing pairs,  but  the  two  posterior  pairs  of  legs  end  in  a  simple 
claw.  The  large  chelipeds  are  used  as  organs  of  defense 
and  in  the  capture  of  prey.  The  other  legs  are  all  employed 
in  walking,  but  the  small  chelipeds  are  used  also  in  clean- 
ing the  body,  and  in  picking  up  small  bits  of  food  and 
passing  them  forward  to  the  mouth  parts.  The  abdomen 
is  capable  of  being  curved  downward  and  extended,  the 
various  segments  being  articulated  by  hinge  joints  at 


/5 


14 


FIG.  72. — Crayfish  with  the  side  of  the  carapace  cut  away  to  show  gills. 
6,  branchiae  or  gills;  r,  rostrum;  I,  eye;  2,  first  antenna;  3,  second  antenna; 
4,  mandible;  6,  second  maxilla;  7,  8,  9,  maxillipeds;  10-14,  bases  of  legs. 
(After  Huxley.) 

the  sides.  On  each  abdominal  segment  except  the  telson 
there  is  a  pair  of  appendages  (swimmerets) .  In  the  male 
the  first  two  pairs  are  modified  into  organs  for  the  transfer 
of  the  sperm  cells;  the  other  appendages  are  nearly  alike 
in  both  sexes.  The  posterior  pair  is  furnished  with  two 
expanded  branches  which,  with  the  telson,  form  a  tail 
fin  used  in  swimming.  When  the  crayfish  is  disturbed 
in  the  water  it  suddenly  bends  the  abdomen  downward 
and  forward,  thus  causing  the  animal  to  dart  quickly 
backward.  In  the  female  the  small  abdominal  append- 
age? are  used  for  carrying  the  eggs  which  become  attached 
to  the  hairs  of  these  organs  by  a  sticky  secretion. 


86  ANIMAL  BIOLOGY 

On  either  side  of  the  thorax,  in  a  space  called  the  bran- 
chial chamber  which  is  covered  over  by  the  sides  of  the 
carapace,  are  the  breathing  organs  or  gills  (branchice). 
The  crayfish  breathes  the  air  which  is  dissolved  in  the  water. 
A  fresh  supply  of  water  is  kept  passing  over  the  gills  by 
the  movements  of  a  lobe  on  the  second  maxilla;  the  water 
is  expelled  from  the  anterior  part  of  the  gill  cavity  and 
passes  into  it  from  the  sides  under  the  edge  of  the  carapace. 
If  one  places  a  little  colored  fluid  in  a  dish  containing  a 
crayfish  the  fluid  can  be  seen  to  be  drawn  into  the  chamber 


br 


FIG.  73. — Anatomy  of  the  crayfish,  a1,  first  antenna;  a2,  second 
antenna;  br,  brain;  d.l.,  duct  of  liver;  e,  eye;  g,  green  gland  or  excretory 
organ  opening  at  gl,  h,  heart;  *,  intestine,  I;  liver;  m,  mouth;  ms,  muscles; 
P,  pericardium  or  sac  surrounding  the  heart;  r,  rostrum;  s,  stomach;  sa, 
sternal  artery;  v.n.,  ventral  nerve  cord.  (After  Hatschek  and  Cori.) 


and  expelled  in  a  stream  in  front  of  the  body.  The  gills 
of  the  crayfish  are  feather-like  structures  consisting  of  a 
large  number  of  filaments  attached  to  a  central  stem  or 
axis.  Some  of  the  gills  are  situated  on  the  bases  of  the 
walking  legs,  others  are  attached  to  the  sides  of  the  body. 
They  are  to  be  regarded  as  complex  and  greatly  branched 
out-pushings  of  the  surface  of  the  body  in  order  to  afford 
a  great  increase  of  surface  exposed  to  the  water;  the  walls 
of  the  filaments  .are  very  thin  in  order  to  facilitate  the 


THE  CRAYFISH  AND  OTHER  CRUSTACEA       87 

exchanges  between  the  blood  within  and  the  surrounding 
medium. 

While  the  crayfish  often  consumes  vegetable  matter  as 
food  it  is  generally  carnivorous  in  its  habits,  living  upon 
worms  and  various  other  living  creatures  that  it  may 
catch,  and  often  devouring  dead  and  partly  decayed  flesh. 
The  food  after  being  passed  to  the  mouth  parts  is  chewed 
mainly  by  the  mandibles  and  is  swallowed  through  a  short 
tube,  the  esophagus,  whence  it  passes  into  the  stomach. 
This  is  a  rather  large  organ  lined  with  chitin  which  is 
thickened  and  hardened  in  certain  places  called  the  ossicles 


FIG.  74. — Stomach  or  "gastric  mill"  of  the  crayfish  cut  through  the 
middle,  c,  cardiac  regions  of  stomach;  d.l,  duct  from  the  liver;  g,  gastro- 
lith,  or  calcareous  disk  secreted  by  the  walls  of  the  stomach;  *',  intestine; 
l.t,  lateral  teeth  of  grinding  apparatus;  m.t.,  median  tooth;  oe,  esophagus; 
py,  pyloric  region;  v,  valve  between  cardiac  and  pyloric  regions  of  stomach. 
(After  Hatschek  and  Cori.) 

which  act  as  a  sort  of  grinding  apparatus.  The  posterior 
part  of  the  stomach  receives  the  ducts  from  two  large 
digestive  glands,  commonly  called  the  liver.  These  pour 
into  the  stomach  a  digestive  fluid  which  acts  upon  the 
ground-up  masses  of  food,  making  them  capable  of  absorp- 
tion into  the  blood.  At  the  posterior  part  of  the  stomach 
there  project  into  the  cavity  a  number  of  hairs  which  act 
as  a  strainer,  allowing  only  the  finely  divided  food  to  pass 
backward  into  the  intestine.  The  latter  is  a  straight  tube 
extending  backward  into  the  abdomen  to  open  at  the  under 
side  of  the  base  of  the  telson. 


88  ANIMAL  BIOLOGY 

Behind  the  stomach  lies  the  large  heart  which  is  enclosed 
in  a  membranous  sac  called  the  pericardium.  From  the 
heart  there  arise  a  number  of  arteries  which  extend  forward 
and  backward  and  carry  blood  to  all  parts  of  the  body. 
Blood  enters  the  heart  from  the  pericardium  through  three 
pairs  of  apertures,  the  ostia,  which  are  provided  with 
valves  to  prevent  its  return.  The  blood  which  has  been 
forced  by  the  beating  of  the  heart,  to  all  parts  of  the  body, 
passes  into  spaces  between  the  tissues,  called  sinuses,  and 
finally  collects  in  a  large  sinus  lying  along  the  ventral  side 
of  the  body.  From  here  it  passes  to  the  gills  and  then 
flows  back  into  the  pericardium.  Thence  it  again  passes 
through  the  ostia  into  the  heart  to  repeat  its  journey. 
The  blood  of  the  crayfish  is  colorless  and  contains  many 
small  bodies  called  corpuscles,  whose  functions  will  be 
discussed  in  another  chapter. 

Much  of  the  waste  matter  in  the  blood  is  got  rid  of  by 
organs  called  from  their  color  the  green  glands.  They 
are  situated  on  either  side  of  the  esophagus  and  open  at 
the  base  of  the  large  antennae.  The  reproductive  organs 
in  mature  individuals  lie  partly  in  the  cephalothorax  and 
partly  in  the  abdomen.  Their  ducts  in  the  male  open  at 
the  base  of  the  last  pair  of  walking  legs,  in  the  female  in 
the  base  of  the  second  pair  in  front  of  the  last.  It  is  not 
difficult  to  distinguish  the  sexes  of  most  of  the  higher  crus- 
taceans by  the  position  of  these  openings. 

The  nervous  system  is  quite  similar  in  its  fundamental 
features  to  that  of  the  grasshopper.  There  is  a  brain  over 
the  esophagus  giving  nerves  to  the  eyes  and  both  pairs 
of  antennae,  and  cords  passing  ventrally  on  either  side  of 
the  esophagus  to  a  large  subesophageal  ganglion  which 
supplies  nerves  to  the  mouth  parts;  from  this  ganglion  a 
double  chain  of  ganglia  extends  along  the  ventral  side  of 
the  cephalothorax  and  abdomen. 


THE  CRAYFISH  AND  OTHER  CRUSTACEA       89 

Crayfishes  are  very  widely  distributed  over  the  United 
States  and  occur  also  in  many  parts  of  the  old  world. 
There  are  many  different  species.  Some  of  them  inhabit 
ponds  and  streams;  others  are  found  in  damp  soil  where 
they  dig  holes  often  to  a  depth  of  several  feet.  Some  of 
the  burrowing  species  heap  up  the  dirt  which  is  brought 
up  in  digging,  so  that  it  forms  a  tube  or  " chimney"  over 
the  hole.  One  species  of  crayfish  which  is  found  in  Mam- 
moth Cave,  Kentucky,  is  blind;  the  eye-stalks  remain, 
but  the  eyes  have  disappeared.  As  a  rule  crayfish  are 
retiring  in  their  habits  and  usually  lodge  under  stones  or 
in  other  dark  and  protected  situations,  although  curiously 
enough  they  may  be  attracted  by  a  strong  light  at  night. 
Boys  often  catch  them  by  letting  down  into  the  water  a 
string  with  a  piece  of  meat  tied  on  one  end.  The  crayfish 
siezes  the  meat  and  it  does  not  occur  to  it  to  let  go  before 
being  pulled  out  of  the  water. 

The  breeding  season  varies  greatly  in  different  species. 
The  young  after  they  are  hatched  have  a  strong  instinct 
to  cling  with  their  chelae  to  any  object  within  reach, 
and  for  some  time  hang  tenaciously  on  to  the  swimmerets 
of  their  mother.  After  a  while  the  young  leave  their 
parent  and  shift  for  themselves.  Like  young  grasshop- 
pers, they  shed  their  skin  several  times  before  reaching 
maturity.  In  the  process  of  molting  the  skin  splits  be- 
tween the  thorax  and  abdomen  and  the  crayfish  slowly 
pulls  its  body  and  legs  out  of  the  old  cases.  Even  the 
lining  of  the  stomach  and  part  of  the  intestine  are  shed 
also.  Molting  is  a  trying  process  for  crustaceans  in  gen- 
eral and  some  die  as  the  result  of  the  ordeal.  As  the  new 
skin  is  very  soft  the  crayfish  is  not  well  able  to  protect 
itself  and  usually  retires  to  some  sheltered  spot.  Its  usual 
pugnacity  disappears  as  if  it  recognized  its  helpless  plight. 
As  the  crayfish  approaches  its  full  size  molting  occurs  much 


QO  ANIMAL  BIOLOGY 

less  frequently.  Concerning  the  age  reached  by  crayfish 
we  know  little  except  that  they  live  at  least  several  years. 
Crayfishes  are  used  for  food  quite  extensively  in  Europe 
and  to  a  considerable  extent  in  this  country. 

Among  the  nearest  allies  of  the  crayfish  are  the  lobsters. 
The  American  lobster,  Homarus  americanus,  which  is 
closely  allied  to  the  European  species,  is  found  on  the 
eastern  coast  of  the  United  States  as  far  south  as  Virginia. 
It  may  reach  a  length  of  two  feet  and  a  weight  of  twenty- 
five  pounds.  As  it  is  a  favorite  article  of  food,  it  is  caught 
in  great  numbers  so  that  the  larger  individuals  are  now 
more  rarely  found.  It  is  usually  caught  in  a  wooden  cage 
called  a  lobster  "pot,"  which  is  so  constructed  as  to  allow 
the  lobsters  to  go  in — which  they  are  induced  to  do  to 
obtain  the  bait — but  which  prevents  their  escape.  Owing 
to  the  decreased  yield  of  our  lobster  fisheries  it  has  been 
made  illegal  to  sell  lobsters  of  less  than  a  certain  length. 
At  various  places  on  the  coast,  lobster  hatcheries  have 
been  erected.  Here  the  eggs  are  kept  in  jars  of  running 
water  until  they  hatch,  when  the  young  are  carried  out  to 
sea.  How  greatly  the  supply  of  lobsters  has  been  increased 
by  this  method  is  a  matter  of  great  uncertainty.  The 
young  lobster  makes  its  first  appearance  in  a  larval  form 
very  different  Jrom  the  adult  and  passes  through  a  long 
metamorphosis  before  attaining  its  final  form. 

Somewhat  more  distant  relatives  of  the  crayfish  are  the 
various  species  of  prawns  and  shrimps.  These,  like  the 
lobsters,  are  caught  in  large  quantities  for  the  gratification 
of  the  human  appetite.  The  hermit  crabs  are  noteworthy 
for  their  common  habit  of  living  in  the  coiled  shells  of 
mollusks  into  which  they  can  more  or  less  completely 
withdraw.  The  anterior  part  of  the  body  and  the  anterior 
appendages  which  are  habitually  exposed  to  the  impacts 
of  the  outer  world  are  hard,  but  the  abdomen  which 


THE  CRAYFISH  AND  OTHER  CRUSTACEA       QI 

remains  protected  within  the  deeper  part  of  the  shell  has 
become  soft  and  fleshy.  The  terminal  appendages  of  the 
abdomen  have  been  modified  into  organs  to  enable  the 
crab  to  retain  its  hold  of  the  shell.  In  front  of  these  the 
appendages  are  generally  absent  on  the  right  side  of  the 
abdomen,  an  indirect  consequence,  probably,  of  the  spiral 
twist  to  which  the  abdomen  is  subjected.  In  the  males 
the  terminal  appendages  of  the  ab- 
domen are  often  the  only  ones 
present.  Hermits  hang  on  to  their 
shells  with  great  tenacity  and  may 
even  allow  their  bodies  to  be  torn 
in  two  before  releasing  their  hold. 
When  the  hermits  outgrow  their 
shells  they  hunt  larger  ones  and  a 
hermit  often  tries  to  take  possession 
of  a  shell  that  is  occupied  by 
another  individual. 

The  true  crabs  usually  have  a 
short,  broad  carapace  and  a  small 
abdomen  which  is  folded  under  the 
cephalothorax  where  it  fits  neatly 
into  a  concave  space.  The  crabs 

.  FIG.  75. — The   common 

which  are  best  known  are  those  shrimp,  Crangon  vuiga- 
prized  for  food,  such  as  the  blue  rts' 
swimming  crab  of  the  Atlantic  coast;  but  there  are  many 
species  which  have  very  interesting  habits.  Among 
these  may  be  mentioned  the  fiddler  crabs,  the  males 
of  which  have  an  enormously  developed  cheliped  which 
is  held  horizontally  across  the  front  of  the  body.  These 
active  creatures  live  in  holes  dug  in  the  sand  or  mud  near 
the  water's  edge.  They  run  with  a  good  deal  of  agility 
and  usually  make  for  their  holes  at  the  appearance  of 


92  ANIMAL  BIOLOGY 

danger,  the  males  holding  up  their  large  claws  in  a  threat- 
ening manner  while  beating  a  lively  retreat. 


FIG.   76. — Pagurus  bernhardus,  hermit  crab.     (From  Emerton.) 

The  spider  crabs,  on  the  other  hand,  are  generally  very 
sluggish  in  their  movements.     They  usually  have  long, 


FIG.   77. — A  crab,  Panopeus  chilensis.      (After  M.  J.  Rathbun.) 

slender  legs  and  a  body  narrowed  and  pointed  in  front. 
In  some  species  the  back  is  covered  with  a  growth  of 


THE  CRAYFISH  AND  OTHER  CRUSTACEA 


93 


seaweed,  sponges,  hydroids,  etc.,  so  that  it  is  difficult  to 
detect  the  animal  in  its  natural  surroundings.  It  is  a 
curious  fact  that  these  growths  may  be  planted  by  the 
crabs  themselves.  A  spider  crab  placed  in  an  aquarium 
with  bits  of  seaweed  will  snip  off  pieces  with  the  pincers, 
reach  back  and  place  them  among  the  short,  hooked  spines 
and  hairs  on  its  carapace  where  they  become  attached  and 
grow.  A  crab  may  deck  itself  out  with  bits  of  paper 
in  a  similar  manner.  It  has  been  found  by  experiment 
that  this  wonderful  instinct  does  not  depend  upon  the 
brain,  as  a  crab  will  proceed  to  disguise 
itself  in  the  same  way  after  the  brain  is 
entirely  destroyed. 

The  foregoing  crustaceans,  however 
much  they  differ  in  external  appear- 
ance, agree  in  having  many  character- 
istics common  by  which  they  are  grouped 
in  one  order,  the  Decapoda.  The  term 
has  reference  to  the  possession  of  ten 
legs  which  is  a  general  feature  of  the 
group.  The  Decapoda  also  have  a 
carapace,  stalked  eyes  and  gills  on  the 
cephalothorax. 

Another  order  standing  somewhat  lower  in  the  scale  is 
the  Isopoda.  In  this  group  the  typical  number  of  legs  is 
fourteen;  there  is  no  carapace,  the  eyes  are  not  stalked  but 
sessile,  and  the  gills  are  formed  by  modifications  of  the 
appendages  of  the  abdomen.  There  are  many  marine 
isopods,  some  of  which  are  parasites  of  fishes,  while  some 
very  degenerate  forms  prey  upon  other  crustaceans. 
One  species,  Limnoria  lignorum,  is  a  serious  nuisance  to 
man,  as  it  bores  into  the  piles  of  wharves  and  so  riddles 
them  with  its  burrows  that  they  soon  become  useless.  A 
few  isopods,  Asellus  and  its  allies,  occur  in  fresh  water, 


FIG.  78. — A  sow 
bug,  Porcellio,  en- 
larged. (After  Es- 
sig.) 


94  ANIMAL  BIOLOGY 

but  the  most  familiar  ones,  our  common  sow  bugs  and  pill 
bugs,  live  in  damp  situations  upon  land  and  have  become 
adapted  to  breathing  air.  These  terrestrial  forms  are 
often  found  under  logs  and  stones,  in  damp  cellars  and 
around  old  buildings.  They  are  mostly  vegetarians,  but 
do  not  disdain  a  little  meat  occasionally.  For  the  most 
part,  however,  they  are  content  to  fill  themselves  up  on 
such  apparently  unattractive  pabulum  as  partially  de- 
cayed wood.  While  they  sometimes  attack  tender  young 
plants  they  are  for  the  most  part  harmless  creatures  and 

may  even  be  of  benefit  in  a  small 
way  as  scavengers. 

The  nearest  allies  of  the  isopods 
are  the  amphipods  which  agree 
with  the  isopods  in  having  sessile 
eyes,  no  carapace  and  the  typical 
number  of  fourteen  legs.  The 

FlG'  rato^^Sf  flea>  gills>  however>  are  attached  to  the 
thorax.       Most     amphipods    are 

marine,  but  there  are  many  fresh  water  species,  and  a 
few  terrestrial  ones  called  sand  fleas  commonly  found  on 
sandy  sea  beaches. 

At  a  first  glance  no  one  would  classify  the  barnacles  with 
the  Crustacea  and  up  to  less  than  a  century  ago  even 
zoologists  classed  them,  along  with  clams  and  snails, 
among  the  Mollusca.  This  was  doubtless  done  on  ac- 
count of  the  hard  shell  with  which  the  body  of  most  bar- 
nacles is  surrounded.  It  was  later  found  that  barnacles 
hatch  from  the  egg  as  a  nauplius,  a  common  larval  form 
in  other  groups  of  Crustacea.  The  nauplius  is  a  free  swim- 
ming larva  with  a  median  eye  and  three  pairs  of  append- 
ages. The  barnacle  nauplius  as  it  grows  undergoes  a 
series  of  molts  accompanied  by  considerable  changes  of 
form,  and  finally  settles  down  and  attaches  itself  by  its 


THE  CRAYFISH  AND  OTHER  CRUSTACEA 


95 


head  to  some  object  and  gradually  assumes  the  form  of  a 
small  barnacle. 

The  older  naturalists  classified  animals  mainly  on  the 
basis  of  external  form  instead  of  internal  structure.  Had 
they  studied  the  organization  of  the  part  of  the  barnacle 
within  the  shell  they  would  have  found  that  the  animal 
really  resembles  other  Crustacea  even  in  its  adult  state.  It 
has  mouth  parts  consisting  of  mandibles  and  maxillae; 
the  feathered  appendages  which  it  continually  thrusts 
out  and  withdraws  into  its  shell  while  it  is  in  the  water 
are  the  thoracic  legs  richly  supplied  with  hairs  for  entang- 


PIG.   80. — A  group  of  barnacles.     (After  Pilsbry.) 

ling  the  small  creatures  used  as  food.  Some  barnacles, 
such  as  the  common  goose  barnacle,  are  provided  with  a 
flexible  stalk,  while  others  such  as  the  acorn  barnacles 
have  the  shell  attached  directly  to  some  other  object. 
Barnacles  are  frequently  attached  to  the  hulls  of  ships 
where  they  may  be  so  numerous  as  to  greatly  impede  the 
vessel's  movements.  Some  species  attach  themselves 
to  the  skin  of  whales,  others  to  sea  turtles.  Some  mem- 


96  ANIMAL  BIOLOGY 

bers  of  the  barnacle  group  have  become  parasitic  and  have 
degenerated  to  such  a  degree  that  the  adults  would  never 
be  taken  for  crustaceans  at  all  were  it  not  for  our  knowl- 
edge of  their  life  history.  One  of  the  most  extreme  cases 
of  degeneration  through  parasitism  that  is  known  is  fur- 
nished by  Sacculina,  a  parasite  on  crabs.  This  parasite 
appears  as  a  fleshy  mass  attached  to  the  body  of  the  crab 
commonly  under  the  abdomen.  The  Sacculina  sends 
rootlets  into  its  host  which  penetrate  and  draw  nourish- 


FIG.  81. — Sacculina  carcini  attached  to  Carcinus  moenas,  whose  abdo- 
men is  extended,  m,  shell  opening;  r,  network  of  roots  ramifying  the 
crab;  s,  stalk;  a,  o,  d,  antennula,  eye  and  anus  of  the  crab. 

ment  from  nearly  all  parts  of  the  body.  The  parasite 
has  no  appendages,  segments,  or  any  external  structures 
characteristic  of  crustaceans,  and  the  alimentary  canal 
and  most  other  organ  systems,  except  the  reproductive 
organs,  have  disappeared.  The  Sacculina  has  been  re- 
duced to  an  apparatus  for  absorbing  food  from  its  host 
and  producing  eggs  and  sperms.  The  eggs  hatch  into 
nauplius  larvae  which  pass  through  early  stages  of  meta- 
morphosis closely  resembling  those  of  typical  barnacles. 


THE  CRAYFISH  AND  OTHER  CRUSTACEA       97 

Finally  the  larva  becomes  attached  by  its  antennae  to  a 
crab.  Then  it  begins  to  lose  its  specialized  organs,  pushes 
its  branches  into  the  host,  and  becomes  a  fleshy  and  almost 
structureless  mass.  Knowledge  of  the  early  development 
of  an  animal  sometimes  affords  a  clue  to  its  true  relation- 
ship which  could  be  ascertained  in  no  other  way. 

There  are  multitudes  of  species  of  the  lower  Crustacea 
which  are  usually  of  small  size.  Some  of  the  most  common 
are  the  water  fleas  (Daphnia  and  allied  forms)  which  are 
frequently  found  in  fresh  water.  The  minute  copepods 
which  are  abundant  both  in  fresh  water  and  in  the  sea 
form  an  important  factor  in  the  food  supply  of  aquatic 
animals,  especially  fishes. 


CHAPTER  XI 
THE  MOLLUSCA 

The  Molluscs  include  such  animals  as  clams,  snails 
slugs,  devil-fish  and  their  allies.  One  of  the  most  widely 
distributed  and  generally  available  of  the  molluscs  is  the 
fresh-water  clam  of  which  there  are  numerous  species  in 
the  lakes,  ponds  and  streams  of  North  America.  We  shall 
therefore  use  it  as  an  introductory  type.  The  two  valves 
of  the  shell  by  which  the  body  of  the  clam  is  enclosed  are 
secreted  by  a  fold  of  the  body  wall  called  the  mantle  which 
hangs  down  on  either  side  of  the  body.  The  shefl  grows 
in  thickness  by  additions  from  the  mantle  to  its  inner  sur- 
face, and  in  area  by  additions  to  the  edge,  the  concentric 
lines  visible  on  the  outside  of  the  shell  indicating  periods 
of  growth.  Where  the  valves  are  joined  together  there  is 
a  thick,  elastic  body  called  the  hinge  ligament  which  acts 
as  a  spring  to  open  the  shell.  The  shell  is  closed  by  two 
muscles  called  adductors  which  run  from  one  valve  to  the 
other.  The  inner  surface  of  the  empty  shell  shows  the 
marks  made  by  the  insertion  of  the  two  muscles  near  either 
end,  and  also  the  line  of  attachment  of  the  mantle  to  the 
shell. 

By  removing  one  valve  of  the  shell  one  may  see  the  gills, 
two  pairs  of  which  hang  in  the  mantle  cavity,  a  pair  on 
either  side  of  the  body.  These  gills  are  made  of  numerous 
fine  filaments  joined  together  so  as  to  form  broad  plates 
or  lamella,  hence  the  term  lamellibranch  which  is  applied  to 
the  group  to  which  the  clam  and  other  molluscs  with  bi- 
valved  shells  belong.  Each  gill  is  composed  of  two  lamel- 

98 


THE   MOLLUSCA 


99 


lae  which  separate  above  to  form  a  canal  opening  outward 
between  the  folds  of  the  mantle  at  the  posterior  end  of  the 
body.  The  surface  of  the  gills  is  covered  by  fine  cilia 
which  beat  so  as  to  cause  a  current  of  water  to  flow  in 
through  small  orifices  between  the  filaments  and  into  the 
canals  above  the  bases  of  the  gills,  and  thence  out  through 


FIG.  82. — Structure  of  the  clam  Anodonta,  a. a,  anterior  adductor 
muscle  for  closing  the  two  valves  of  the  shell;  c.p.g,  cerebropleural  gang- 
lion or  brain;  g,  intestine  coiled  in  the  foot;  g.L,  gill;  k,  kidney;  I. p.,  labial 
palp;  p.g.,  pedal  ganglion;  r,  rectum;  s.t.  stomach;  v,  ventricle  of  heart 
giving  rise  to  arteries  at  each  end;  v.g.,  visceral  ganglion  just  below  the 
posterior  adductor  muscle.  (After  Rankin.) 

the  opening  between  the  mantle  lobes,  called  the  exhalent 
siphon.  Water  flows  into  the  mantle  cavity  through  the 
inhalent  siphon  which  is  situated  just  below  the  exhalent 
one.  Place  some  colored  fluid  in  a  dish  of  water  contain- 
ing a  clam,  and  you  may  see  it  drawn  into  the  one  opening 
and  expelled  at  the  other. 

The  lower  part  of  the  body  projects  in  front  into  a 
muscular  organ,  the/00/,  which  can  be  protruded  between 


100  ANIMAL  BIOLOGY 

the  valves  of  the  shell.  The  clam  makes  use  of  the  foot  in 
burrowing  into  the  mud  where  it  commonly  lives  with  the 
siphons  exposed  to  the  water.  The  water,  which  in  pass- 
ing through  the  gills  subserves  the  function  of  respiration, 
affords  also  the  means  of  bringing  the  animal  its  food  which 
consists  of  microscopic  organisms  and  other  fine  materials 
swept  in  by  the  ciliary  current.  The  solid  bodies  are 
carried  by  ciliary  action  into  the  mouth  which  is  situated 
between  two  pairs  of  flaps  called  the  labial  palpi  at  the 
anterior  end  of  the  body.  The  mouth  leads  by  a  short 
tube  to  the  stomach  which  receives  the  ducts  from  a  large 
greenish  digestive  gland  commonly  called  the  liver.  The 
stomach  leads  to  the  narrow  intestine  which  after  coiling 
about  in  the  body  opens  near  the  posterior  end  of  the  body 
where  its  contents  are  carried  out  through  the  exhalent 
siphon. 

The  clam  is  furnished  with  a  heart  consisting  of  a  median 
ventricle  and  two  lateral  auricles  lying  in  a  space  called 
the  pericardium  in  the  dorsal  side  of  the  body.     The  intes- 
tine passes  through  this  pericardium  and  is  surrounded  by   5  g 
the  ventricle  of  the  heart.     The  beating  of  the    heart   j 
carries  the  blood  through  arteries  to  various  parts  of  the  3  ui 
body.     On  its  return  it  goes  through  the  gills  where  it  '- 
takes  up  oxygen  and  loses  a  part  of  its  waste  products,   - 

and  then  passes  into  the  auricles  and  thence  into  the 

(/)  «jj 

ventricle.  Just  below  the  pericardium  is  a  pair  of  dark- 
colored  excretory  organs  or  kidneys  which  open  at  one  end 
into  the  pericardium  and,  at  the  other,  to  the  outside  of 
the  body. 

The  nervous  system  of  the  clam  consists  of  three  main 
pairs  of  ganglia  connected  by  nerve  cords  or  commissures. 
The  cerebral  or  brain  ganglia  He  over  the  mouth.  These 
are  connected  by  long  commissures  to  a  pair  of  large  vis- 
ceral ganglia  just  below  the  posterior  adductor  muscle. 


THE   MOLLUSCA 


101 


PIG.  83. — Larva  of 
clam  Anodonta.  a, 
adductor  muscle;  b, 
byssus  thread;  s,  sen- 
sory hairs;  t,  teeth 
for  attachment  to 
host. 


There  is  another  pair  of  commissures  extending  from  the 

brain  to  a  pair  of  pedal  ganglia  in  the  foot. 
A  considerable  part  of  the  compact 

body  of  the  clam  is  made  up  of  the 

sex  organs  which  discharge  their  cells 

near  the  opening  of  the  kidney.     The 

eggs  when  set  free  fall  into  the  spaces 

between  the  lamellas  of  the  gills  where 

they  undergo  their  early  development; 

the  young  larvag  are  then  carried  out 

through  the  excurrent  siphon  and  live 

for  some  time  at  the  bottom  of  some 

body  of  water.     For  the  next  stage  of 

its  development  the  young  clam  is  de- 
pendent upon  becoming  attached  to  the  gills  or  fins  of  some 

fish.  When  this  opportunity 
presents  itself  the  young  clam 
closes  the  valves  of  its  shell  over 
the  tissues  of  its  host  and  hangs 
there.  Later  it  becomes  more 
or  less  completely  overgrown  by 
the  surrounding  tissues  of  the 
fish,  much  as  a  gall  insect  is  en- 
closed in  the  tissues  of  a  plant 
gall.  Finally,  the  young  clam 
breaks  out  of  its  enclosure,  settles 
down  in  the  mud,  and  begins  the 
regular  routine  life  of  its  parents. 
The  shells  of  fresh- water  clams  are 
much  used  in  the  making  of  but- 
tons. Occasionally  they  yield 
pearls  of  considerable  value.  A 

pearl  is  a  calcareous  secretion  of  the  mantle  which  accu- 
mulates around  some  foreign  body,  commonly  a  parasitic 


PIG.  84.  — Pearl  oyster 
from  Ceylon,  showing  pearls 
on  inner  surface  of  shell. 


IO2 


ANIMAL  BIOLOGY 


worm.  Pearls  may  be  formed  by  various  kinds  of  mol- 
luscs, and  in  some  places  pearl  fisheries  form  an  important 
industry. 

Several  species  of  clams  found  on  the  seashore  are  much 
used  as  food.  One  of  these,  Mya  arenaria,  the  common 
long-neck  clam,  is  obtained  by  digging  in  muddy  beaches 
at  low  tide.  The  two  joined  siphons  in  this  species  con- 
stitute a  long  tube  which  projects  upward  as  the  clam 
lies  buried  in  the  mud.  When  the  clam  is  disturbed  it 

frequently    reveals    its   presence 

by  squirting  water  out  of  its 
siphon  as  it  closes  the  valves  of 
its  shell. 

Mussels  are  generally  found 
upon  rocks  to  which  they  at- 
tach themselves  by  a  series  of 
threads  called  the  byssus  which 
is  secreted  by  a  gland  in  the  foot. 
The  common  scallop,  Pecten, 
has  the  somewhat  unusual  habit 
of  swimming  by  alternately  opening  and  closing  the  valves 
of  the  shell.  The  most  important  bivalves  are  unquestion- 
ably the  oysters  which  are  extensively  cultivated  in  various 
parts  of  the  world.  In  its  early  stages  the  oyster  is  a  free- 
swimming  larva;  later  it  settles  down  and  becomes  at- 
tached by  the  left  valve  of  its  shell.  Oysters  are  planted 
and  cultivated  in  oyster  beds.  These  beds  are  especially 
numerous  in  Chesapeake  Bay  which  has  provided  over 
25,000,000  bushels  of  oysters  a  year.  A  very  aberrant  bi- 
valve and  one  which  looks  more  like  a  worm  than  a  mollusc, 
is  the  Teredo  which  has  the  habit  of  boring  into  the  piles  of 
wharves  and  bottoms  of  wooden  vessels  where  it  does  a 
great  deal  of  damage  by  riddling  the  wood  with  its  holes. 
One  large  division  of  the  Mollusca,  the  Gastropoda,  is 


FIG.  85.— A  scallop  shell, 
Pecten. 


THE   MOLLUSCA  103 

characterized  by  an  asymmetrical  and  usually  coiled  body. 
Most  of  the  species  live  in  a  coiled  shell,  but  in  some  forms, 
such  as  the  limpets,  the  shell  is  a  sort  of  cap;  in  the  slugs 
it  may  be  reduced  to  a  small  rudiment  imbedded  in  the 
mantle  while  in  some  forms  no  trace  of  the  shell  remains  in 
the  adult  although  a  shell  gland  is  present  in  the  embryo. 
The  Gastropoda  are  common  in  the  sea,  in  fresh  water, 
and  on  land.  One  can  in  most  places  easily  obtain  a 
fairly  typical  gastropod  in  the  familiar  garden  snail, 
Helix.  The  body  is  furnished  below  with  a  broad,  flat, 
muscular  base,  the  foot,  on  which  the  animal  creeps.  The 


f 

FIG.  86. — Body  of  snail  in  creeping  position  after  removal  of  shell. 
/,  foot;  go.  opening  of  sex  organs;  h,  head;  al,  opening  into  lung  cavity; 
mw,  wall  of  mantle;  es,  visceral  sac;  ti,  tn,  and  tin,  tentacles,  the  upper  pair 
with  eyes  at  the  tip.  (From  Meisenheimer.) 

head  bears,  in  addition  to  the  short  feelers  over  the 
mouth,  a  pair  of  long,  retractile  tentacles  at  the  end  of 
which  are  the  eyes.  When  the  latter  are  irritated  they 
may  be  drawn  into  the  tentacles  much  as  a  person  could 
pull  in  the  end  of  a  ringer  of  a  glove  by  a  string  attached 
to  the  inner  side  of  the  tip.  In  the  mouth  of  the  snail 
there  is  a  ribbon-like  structure  armed  with  rows  of  minute 
chitinous  teeth  which  are  used  in  rasping  off  bits  of  food. 
On  the  right  side  of  the  body  near  the  head  are  the  open- 
ings of  the  sex  organs,  and  further  back  a  larger  aperture 
which  leads  to  the  breathing  cavity  or  lung.  While  in 
the  marine  gastropods  this  cavity  contains  gills  which  are 


104  ANIMAL  BIOLOGY 

used  for  respiration  in  the  water,  in  the  land  snails  and 
many  fresh-water  species  the  gills  have  been  lost  and  the 
surface  of  the  cavity  adapted  for  breathing  air.  The 
garden  snail  feeds  mostly  on  the  tissues  of  plants,  but  it 
will  also  devour  meat  and  various  other  kinds  of  food. 
It  travels  most  at  night  leaving  evidences  of 
its  journeys  in  the  form  of  slime  tracks  which 
result  from  the  mucus  secreted  by  the  foot. 
During  the  winter,  and  sometimes  in  periods 
of  drought,  the  snail  draws  into  its  shell  and 
secretes  a  porous  limy  substance  over  the 

A  pond  snan~  mouth  of  tne  she11  called  the  epiphragm.  Thus 
Physa,  hav-  sealed  up,  the  snail  lives  in  a  dormant  state 
spfrai^coli.86  until  the  advent  of  more  favorable  conditions 

of  life. 

Many  of  the  lung-breathing  relatives  of  Helix  live  in 
fresh  water.  The  common  pond  snails,  Limnaea,  Physa 
and  Planorbis  may  easily  be  kept  in  aquaria  where  one 
may  watch  their  many  interesting  peculiarities  of  behav- 
ior. These  forms  usually  come  to  the  surface  for  air, 
and,  after  filling  the  lung,  descend. 
One  curious  habit  of  many  pond 
snails  is  the  spinning  of  mucus 
threads  from  the  bottom  to  the 
surface  film.  The  snails  crawl  up 
and  down  upon  these  threads  in 


their     periodic    excursions    to    the    FlG.  88._ Conus  eburneus. 
surface  for  air. 

The  sea  abounds  in  gastropods  of  the  most  varied  forms, 
sizes  and  habits.  Some  of  these  are  carnivorous  and  prey 
upon  other  molluscs.  One  often  finds  a  bivalve  with  a 
round,  smooth  hole  bored  through  its  shell.  This  tells 
the  story  of  some  carnivorous  gastropod  which  had  bored 
into  the  helpless  bivalve  with  its  rasp  and  devoured  its 


THE   MOLLUSCA 


105 


soft  parts.     One  species  called  the  " oyster  drill"  destroys 
large  numbers  of  oysters  in  this  way. 

The  chitons  which  are  allied  to  the  gastropods  have  a 
broad,  creeping  foot  and  a  dorsal  shell  composed  of  a  row 
of  eight  pieces.  They  are  often  found  on 
rocks  at  low  tide.  The  Cephalopoda  differ 
greatly  in  appearance  from  the  other  mol- 
lusca.  Their  name  is  derived  from  the 
fact  that  the  foot  is  produced  into  a  num- 
ber of  arms  (8  or  10)  surrounding  the  head. 
In  most  cephalopods  these  arms  are  fur- 
nished with  rows  of  suckers  which  are  used 
for  retaining  hold  of  objects.  The  cepha- 
lopods were  represented  in  former  ages  of 
the  earth's  history  by  vast  numbers  of 
varied  forms.  Some  of  these,  the  ammo- 
nites, had  a  coiled,  chambered  shell  which 
was  often  beautifully  sculptured.  The  or- 
thoceratites  had  a  straight,  chambered  shell  which  in  some 
species  reached  a  length  of  fifteen  feet.  Of  the  forms  now 
living  within  a  shell,  the  chambered  nautilus  is  the  only 


FIG.  89. — Tere- 
bra  babylonia. 


FIG.  90. — Limpets,    a    key    hole    limpet    at    the    left. 

survivor.  It  is  found  in  deep  waters  in  the  Pacific  and 
Indian  Oceans,  but  its  much  prized  shell  is  sometimes  cast 
up  on  the  shore.  In  the  so-called  paper  nautilus  there  is 
a  thin  shell  which  is  formed,  not  by  the  mantle,  as  in  the 


106  ANIMAL  BIOLOGY 

chambered  nautilus  and  other  molluscs,  but  by  the  ex- 
panded posterior  arms;  it  occurs  only  in  the  female  where 
it  serves  as  an  egg  case. 

Most  of  the  other  living  cephalopods  have  a  relatively 
small  shell  which  is  overgrown  by  the  mantle.  This  may 
be  calcareous  as  in  the  cuttle  fish  which  furnishes  the 
" cuttle  fish  bone"  that  we  often  give  to  canaries,  or  it 
may  be  chitinous  as  in  the  "pen"  which  lies  along  the  dorsal 
side  of  the  body  of  the  squid.  It  is  commonly  said  that  the 
squid  carries  its  own  pen  and  ink;  the  animal  is  furnished 
with  an  ink-sac  containing  a  black  fluid  which  may  be  dis- 
charged in  times  of  danger,  producing  a  black  cloud  in  the 
water  which  facilitates  the  escape  of  the  animal.  There  are 
many  species  of  squid  living  in  various  parts  of  the  world. 
One  of  the  forms  most  easily  obtainable  for  study  is  the 
small  Loligo  pealii  found  along  our  Atlantic  coast.  Of 
the  ten  sucker-bearing  arms  extending  in  front  of  the  head 
two  are  longer  than  the  others.  In  the  center  of  the  circle 
of  arms  is  the  mouth  with  its  two  strong,  horny  jaws 
resembling  the  beak  of  a  parrot.  As  in  other  cephalopods 
the  head  bears  two  large,  well-developed  eyes.  The 
squid  swims  backward  by  suddenly  expelling  water  from  its 
mantle  chamber  through  the  siphon  which  is  a  short  tube 
below  the  head.  This  siphon  can  be  turned  in  various 
directions  so  that  the  reaction  of  the  expelled  water  may 
cause  the  animal  to  turn  in  different  ways.  The  mantle 
cavity  contains  the  gills  of  which  there  are  two  pairs. 
Squids  are  very  active  animals,  living  on  small  creatures 
which  they  capture  by  means  of  their  arms.  They  are 
remarkable  for  the  rapid  changes  of  color  which  may 
pass  over  the  skin,  especially  when 'they  are  disturbed. 
There  are  a  few  species  called  the  giant  squid  which  attain  a 
very  large  size,  with  a  body  nine  to  ten  feet  long  and  with 
the  longest  pair  of  arms  reaching  a  length  of  forty  feet. 


THE   MOLLUSCA 


107 


Stories  of  these  monsters  attacking  ships  are  quite  without 
foundation . 

Unlike  the  squids,  which  are  very  graceful  and  attract- 
ive animals,  the  devil  fish,  or  octopi,  are  apt  to  inspire  one 
with  a  feeling  of  repulsion.  Nevertheless  they  are  very 
interesting  creatures  and  the  feeling  of  repulsion,  as  in  so 
many  other  cases,  will  tend  to  disappear  upon  closer  ac- 
quaintance. As  the  name  Octopus  implies  there  are  but 


FIG.  91. — The  devil  fish  or  octopus.     A,  at  rest;  B,  swimming;  a,  arms 
with  suckers;   e,   eye;  S,  siphon.     (From  Cooke,  after  Merculiano.) 

eight  feet  or  arms;  these  are  relatively  long  and  very  strong 
and  they  enable  the  octopus  to  overcome  quite  powerful 
adversaries.  The  larger  species  whose  arms  may  reach  a 
length  of  fourteen  feet  might  be  dangerous  to  man  who  is 
a  comparative  helpless  creature  when  in  the  water.  There 
are  many  stories  of  human  beings  being  attacked  and  over- 
come by  devil  fish,  but  they  are  mostly  due  to  the  prover- 
bial mendacity  of  fishermen.  Like  the  squid  the  devil 
fish  are  sometimes  used  as  food,  but  they  have  never  won 
their  way  to  general  favor. 


CHAPTER  XII 
THE  ECHINODERMS 

In  the  Echinoderms,  or  spiny-skinned  animals,  Nature 
has  worked  out  a  peculiar  type  of  organization  very  dif- 
ferent from  what  is  found  anywhere  else  in  the  animal 
kingdom.  One  conspicuous  feature  of  most  echinoderms 
is  their  apparently  radial  symmetry.  The  parts  of  the 
body  are  arranged  about  a  central  axis  instead  of  merely 
on  two  sides  of  a  median  plane  as  in  insects  and  vertebrates. 
This  radial  structure  led  the  older  naturalists  to  class  the 
echinoderms  along  with  the  jelly-fish  and  their  allies  in  a 
group  called  Radiates,  but  it  is  now  known  that  jelly-fish 
and  echinoderms  are  but  very  distantly  related.  Even 
the  radial  structure  on  which  the  alliance  was  based  is 
now  known  to  be  secondary  in  the  echinoderms  and  de- 
rived from  a  primitive  bilateral  symmetry  which  can  still 
be  traced  in  the  position  of  certain  organs  of  the  body. 
Without  exception  the  echinoderms  are  confined  to  the  sea. 

One  large  division  of  the  Echinoderms  consists  of  the 
Asteroids,  or  starfishes,  of  which  there  are  many  species 
of  various  forms  and  colors.  Very  commonly  there  are 
five  rays  which  extend  from  a  central  disk,  but  in  some 
cases  there  may  be  six,  and  in  a  few,  even  over  twenty. 
The  body  wall  is  hardened  by  a  deposit  of  lime,  but  not  to 
such  a  degree  as  to  prevent  more  or  less  movement  of  the 
rays.  The  principal  organs  of  locomotion  are  the  tube 
feet  which  project  in  rows  through  the  under  sides  of  the 
rays  where  they  are  lodged  in  grooves.  In  most  species 
the  tube  feet  end  in  adhesive  suckers.  By  extending,  at- 

108 


THE    ECHINODERMS 


IOQ 


taching,  and  then  contracting  the  tube  feet  the  starfish 
manages  to  pull  itself  along  over  the  bottom,  or  even  to 
climb  up  vertical  surfaces.  The  tube  feet  also  serve  to 
seize  prey  and  carry  it  toward  the  mouth. 


FIG.  92. — Anatomy  of  Starfish,  Asterias  vulgaris.  a.o,  skeletal  pieces 
of  arms;  c.c,  cardiac  cceca  or  pouches  of  stomach;  p.c.,  pyloric  cceca; 
h.c.,  hepatic  or  "liver"  i'ceca;  r.c,  rectal  coeca;  r.m,  muscles;  s.g,  reproduc- 
tive glands;  m.p.,  madreporic  plate  through  which  water  enters  into  the 
water  vascular  system.  (After  Coe.) 

Although  the  starfish  is  a  very  harmless  and  innocent 
looking  creature,  it  is  able  to  overcome  and  devour  quite 
large  animals.  When  an  object  is  brought  near  the  mouth 
the  stomach  may  become  actually  thrust  out  of  the  body 
and  wrapped  around  the  object  which  it  slowly  digests. 


110  ANIMAL  BIOLOGY 

Oysters,  clams,  and  other  mollusks  which  are  too  large  to 
be  taken  into  the  body  are  often  digested  in  this  way,  after 
which  the  stomach  retracts  leaving  the  empty  shells. 
Starfishes  often  do  much  damage  to  oyster  beds,  and  they 
are  very  difficult  to  get  rid  of. 

Scattered  over  the  body  of  many  kinds  of  starfish  are 
numerous  minute  bodies  called  pedicellaricz  which  look 
like  miniature  pairs  of  forceps.  These  organs  have  usu- 
ally two  jaws  which  open  and  close  by  means  of  special 
muscles.  They  frequently  catch 
hold  of  objects  coming  in  contact 
with  the  starfish,  and  are  thus 
serviceable  in  capturing  prey.  A 
live  fish,  longer  than  the  diameter 
of  the  starfish,  has  been  observed 
to  be  held  by  these  minute  organs 
until  it  was  conveyed  by  means  of 
the  tube  feet  within  reach  of  the 
extensile  stomach. 
from  below  showing  the  The  power  of  regeneration  is 

mouth. 

very  well  developed  in  most  star- 
fishes. They  will  easily  restore  missing  rays  and  even 
considerable  parts  of  the  disk,  and  there  are  a  few  species 
in  which  a  single  ray  may  give  rise  to  an  entire  individual. 

The  Ophiurans,  or  brittle  stars,  may  be  distinguished 
from  the  starfishes  by  their  circular  disk  which  is  clearly 
set  off  from  the  slender  arms.  When  an  arm  is  seized 
it  is  frequently  cast  off  by  a  violent  muscular  contraction, 
hence  the  term  brittle  star. 

In  the  Echinoids  or  sea  urchins  the  body  is  generally 
circular  or  oval  in  outline  and  covered  with  movable 
spines.  Generally  also  sea  urchins  are  provided  with  tube 
feet  having  adhesive  terminal  disks  which  are  used  much 
as  they  are  in  the  starfish.  The  spines  are  joined  by  a 


THE   ECHINODERMS 


III 


FIG.  94. — A  sea  urchin,  Arbacia,  and  its  shell  with  the  spines  removed. 
(After  Clark.) 


112 


ANIMAL  BIOLOGY 


FIG.  95. — "Aris- 
totle's lantern,"  the 
chewing  apparatus  of 
the  sea  urchin. 


sort  of  ball-and-socket  joint  to  rounded  prominences  on 

the  shell,  and  they  can  be  moved  in  different  directions 

by  a  short  ring  of  muscle  fibers  attached  near  the  base. 
Both  spines  and  tube  feet  may  be  em- 
ployed in  locomotion,  but  the  spines  also 
serve  as  organs  of  protection.  After 
removing  the  spines  the  shell  of  the  sea 
urchin  may  be  seen  to  consist  of  several 
regularly  arranged  series  of  plates.  The 
plates  are  perforated  where  the  tube 
feet  are  attached.  The  sand  dollars  are 
greatly  flattened  sea  urchins  with  very 
short  spines. 
The  sea  cucumbers,  or  Holothurians,  have  an  elongated 

body  with  a  flexible  and  usually  somewhat  leathery  wall. 

They  are  generally  somewhat  flattened  on  the  side  upon 

which  they  crawl,  and  the  mouth  is  sur- 
rounded by  tentacles  which  are  used  in 

the  capture  of  food.     With  rare   excep- 
tions,    there    are     tube    feet   projecting 

through  the  body,  and  these  are  usually 

arranged  in  five  double  rows.     Some  of 

the  holothurians  are  extensively  used  by 

the  Chinese  as  food. 

The  Crinoids,  or  sea  lilies,  are  usually 

attached  by  a  jointed  stem,  although  there 

are  a  few  species  that  swim  freely  through 

the  water.     The  usually  cup-shaped  body 

bears  several  branching  arms  which  are 

furnished  on  the  upper  side  with  grooves 

which  lead  to  the  mouth.     Very  numerous 

species  existed  in  past  ages  of  the  earth's  history.     Their 

remains  are  common  in  the   older  rocks,  but   there  are 

a  comparatively  few  forms  living  to-day. 

The  eggs  of  echinoderms  are  generally  shed  directly 

into   the  water  where   they  are  fertilized  and  develop 


FIG.  96. — A  cri- 
noid  or  sea  lily. 


THE   ECHINODERMS  113 

in  most  cases  into  free-swimming,  ciliated  larvae,  very 
different  from  the  mature  forms.  There  are  different 
types  of  larvae  characteristic  of  the  different  groups  of 
echinoderms.  In  the  Ophiurans  and  sea-urchins  the  com- 
mon larval  form  is  furnished  with  long,  ciliated  arms 
and  is  known  as  a  pluteus.  After  a  short,  free  life  the 
larvae  settle  down  and  undergo  a  complicated  metamor- 
phosis in  changing  into  the  mature  form. 


CHAPTER  XIII 
THE  RINGED  WORMS  OR  ANNELIDS 

The  term  worm  is  one  of  wide  and  somewhat  indefi- 
nite significance.  The  old  group  called  "Vermes," 
which  is  Latin  for  worms,  constitutes  what  Professor 
Haeckel  has  called  the  great  lumber  room  of  Zoology,  for 
it  includes  animals  of  the  most  diverse  kinds,  with  little 
in  common  except  that  they  do  not  belong  to  other  groups. 
Nowadays  zoologists  parcel  the  Vermes  out  into  a  number 
of  different  phyla.  One  of  the  largest  of  these  phyla 
is  the  Annelida.  These  are  worms  having  the  body  di- 
vided into  more  or  less  similar  annuli  or  segments,  and 
provided  generally  with  a  body  cavity  or  space  between 
the  digestive  tube  and  the  body  wall. 

There  are  a  great  many  marine  species,  some  of  which 
are  free,  active,  carnivorous  creatures;  others  are  seden- 
tary, living  in  tubes  and  generally  subsisting  on  small 
organisms.  There  are  many  annelids  which  inhabit  fresh 
water  or  burrow  in  the  soil.  The  latter  are  commonly 
known  as  earthworms  or  angle  worms.  There  are  a  great 
many  species  of  earthworms  in  various  parts  of  the  globe, 
one  of  the  most  common  and  widely  distributed  being 
Lumbricus  terrestris  which  is  frequently  found  in  gardens 
and  fields  both  in  Europe  and  in  North  America.  In  this 
species,  which  we  may  take  as  a  type,  the  body  is  composed 
of  a  remarkably  uniform  series  of  segments.  Just  over 
the  mouth  there  is  an  incomplete  segment  called  the  pros- 
tomium.  At  about  the  anterior  third  of  the  body  a  few 
of  the  segments  of  the  mature  worm  are  somewhat  thick- 

114 


THE   RINGED    WORMS    OR   ANNELIDS 


.f 


ened,  forming  the  clitellum,  which  has  an  important  func- 
tion in  relation  to  reproduction.  Nearly 
all  the  segments  are  furnished  with  minute 
bristles,  or  setae,  which  are  arranged  in 
four  double  rows.  These  may  be  seen 
with  a  hand  lens,  or  felt  with  the  finger, 
especially  when  it  is  rubbed  from  behind 
forward  over  the  ventral  surface.  These 
setae  can  be  protruded  or  withdrawn  into 


V 


FIG.  97.  FIG.  98. 

FIG.  97. — Earthworm  from  dorsal  side,  cl,  clitellum;  p,  prostomium. 
(After  Hatschek  and  Cori.) 

FIG.  98. — V,  ventral;  L,  lateral  view  of  earthworm,  cl,  clitellum;  o, 
opening  of  oviduct;  sp,  opening  of  sperm  duct;  m,  mouth;  p,  prostromium. 
(After  Hatschek  and  Cori.) 

special  sacs,    and   they   materially   assist   the   worm    in 
locomotion. 


n6 


ANIMAL  BIOLOGY 


The  body  of  the  worm  is  divided  by  a  number  of  septa, 
or  partitions,  extending  from  the  digestive  tube  to  the 
body  wall,  each  septum'  forming  the  boundary  between 
two  segments  of  the  body.  The  digestive  tube  extends 
straight  from  the  mouth  to  the  anus  in  the  last  segment, 
and  is  divided  into  a  number  of  parts.  Behind  the  mouth 


Ph 


FIG.  99. — Internal  organs  of  earthworm,  br,  brain;  c,  crop;  g,  gizzard; 
h,  hearts  arising  from  the  dorsal  blood  vessel;  n,  nephridia;  oe,  esophagus; 
ph,  pharynx;  sr,  seminal  receptacle;  sv,  seminal  vesicles.  (After  Hatschek 
and  Cori.) 

is  a  muscular  pharynx  which  is  used  in  drawing  things  in. 
This  is  followed  by  a  short  esophagus,  leading  to  a  thin- 
walled  enlargement,  called  the  crop,  closely  behind  which 
is  a  thick- walled  muscular  organ,  the  gizzard,  which  serves 
as  a  grinding  apparatus.  Behind  the  gizzard  is  the  in- 


THE   RINGED   WORMS   OR  ANNELIDS  117 

testine  which  extends  with  little  modification  to  the  last 
segment.  Attached  to  the  sides  of  the  esophagus,  and 
really  consisting  of  outpocketings  of  this  organ,  are  the 
calciferous  glands  which  secrete  limy  crystalline  bodies 
supposed  to  neutralize  the  acids  contained  in  the  food. 
Earthworms  swallow  dead  leaves  and  other  organic  sub- 
stances along  with  large  quantities  of  soil,  and  digest  what- 
ever food  there  may  be  contained  in  this  material.  Rich 
soil  with  a  considerable  proportion  of  vegetable  matter  is 
therefore  a  favorite  haunt  for  these  animals.  Absorp- 
tion probably  takes  place  mainly  in  the  intestine. 

The  earthworm  has  a  well-developed  circulatory  system 
containing  red  blood.  The  principal  parts  of  this  system 
consist  of  a  dorsal  vessel  extending  the  length  of  the  body 
above  the  digestive  tube,  a  ventral  blood  vessel  running 
below  the  intestine,  and,  lateral  vessels  extending  from 
these  to  adjacent  parts.  The  dorsal  and  ventral  blood 
vessels  are  connected  in  front  of  the  crop  by  five  pairs  of 
segmentally  arranged  vessels  which  surround  the  esopha- 
gus. These  are  called  " hearts"  because  their  pulsations 
help  to  propel  the  blood.  The  dorsal  vessel  contracts 
from  behind  forward,  forcing  most  of  the  blood  through 
the  hearts  into  the  ventral  vessel  where  it  is  carried  pos- 
teriorly. 

The  earthworm  has  very  odd  organs  of  excretion  called 
nephridia;  these  are  more  or  less  coiled  tubes,  of  which 
there  occurs  a  single  pair  in  most  of  the  segments  of  the 
body.  At  its  inner  end,  the  nephridium  is  furnished 
with  a  ciliated  funnel  which  passes  through  the  anterior 
septum  of  its  segment  to  open  into  the  cavity  in  front. 
The  outer  end  of  the  tube  opens  by  a  small  pore  through 
the  side  of  the  body.  Waste  material  swept  into  the 
ciliated  funnel  or  secreted  by  the  walls  of  the  tube  is  car- 
ried to  the  outside. 


n8 


ANIMAL  BIOLOGY 


The  earthworm's  nervous  system  consists  of  a  small 
brain  over  the  pharynx,  connected  by  commissures  with  a 
double  chain  of  ganglia  extending  along  the  ventral  side 
of  the  body,  there  being  in  each  segment  a  single  pair  of 
ganglia  which  supply  the  adjacent  parts  with  nerves. 
While  earthworms  have  no  well-defined  eyes,  they  are 
very  sensitive  to  light  and  tend  to  keep  in  dark  situations. 


organs 


n.c 


FIG.  100. — A  few  segments  of  the  earthworm  with  the  dorsal  side  cut 
away  and  showing  the  intestine  cut  through,  bv,  blood  vessels;  d,  dorsal 
blood  vessel;  i,  intestine;  n.c.,  nerve  cord;  s,  septa;  ty,  typhlosole  or  fold 
projecting  into  the  dorsal  side  of  the  intestine;  v,  ventral  blood  vessel. 
(After  Hatschek  and  Cori.) 

They  will  crawl  away  from  the  light;  and  when  light  is 
flashed  on  them  at  night  when  they  are  partly  outside  of 
their  burrows  they  very  quickly  withdraw.  Earthworms 
are  very  sensitive  to  chemical  and  mechanical  stimulation. 
A  slight  jar  may  cause  them  to  retreat  quickly  into  their 
burrows. 

The  reproductive  system  of  earthworms  is  very  complex. 
Both  male  and  female  organs  are  located  in  the  same  in- 
dividual but  the  eggs  are  nevertheless  generally  fertilized 
by  sperm  derived  from  another  worm.  The  eggs  are 


THE    RINGED    WORMS    OR   ANNELIDS  I-ig 

laid  in  a  cocoon  secreted  by  the  clitellum.  When  the 
cocoon  is  formed  it  is  slipped  forward  over  the  head,  re- 
ceiving the  eggs  as  it  passes  the  mouths  of  the  oviducts, 
and  deposited  usually  in  a  damp  place. 

Earthworms  retreat  from  places  that  are  very  warm  or 
dry;  they  are  much  more  apt  to  come  to  the  surface  in 
damp  or  rainy  weather  when  they  may  leave  their  bur- 
rows. At  such  times  we  may  find  th,em  strewn  about 
upon  sidewalks  and  various  other  places  much  to  the  de- 
light of  robins  and  many  other  birds  that  prey  upon  them. 
Earthworms  may  be  found  even  on  the  roofs  of  houses 
where  many  people  suppose  that  they  must  have  rained 
down.  As  a  matter  of  fact  they  crawl  up  the  sides  of 
the  house,  as  you  may  readily  see  them  do  if  you  give  them 
the  chance. 

Earthworms  have  remarkable  powers  of  regeneration. 
If  a  considerable  part  of  either  end  is  removed  the  worm 
will  after  a  time  regenerate  the  missing  segments.  Some 
of  the  aquatic  relatives  of  the  earthworm  regularly  mul- 
tiply by  fission  in  addition  to  developing  from  fertilized 
eggs. 

As  Darwin  has  shown  in  his  interesting  book  on  "The 
Formation  of  Vegetable  Mould  through  the  Action  of 
Worms,"  earthworms  play  a  very  important  part  in  the 
production  of  fertile  soil.  They  burrow  to  a  depth  of 
several  feet  and  bring  to  the  surface  a  large  amount 
of  material  that  has  passed  through  their  bodies  in  their 
"castings"  which  accumulate  around  the  mouths  of  their 
holes.  These  castings  may  be  seen  in  any  region  in  which 
the  earthworms  have  recently  been  burrowing.  They 
are  washed  away  by  rains  or  blown  by  winds;  and,  as  Dar- 
win has  estimated,  their  removal  may  produce  consider- 
able change  in  the  surface  of  the  soil.  As  a  consequence 
of  bringing  up  soil  from  below  the  surface,  rocks  and  other 


I2O 


ANIMAL  BIOLOGY 


objects  tend  slowly  to  settle  down  and  eventually  become 
buried.  Darwin  observed  a  stony  field  which  had  thus 
become  changed  "so  that  after  thirty  years  a  horse  could 
gallop  over  the  compact  turf  from  one  end  of  the  field 
to  the  other,  and  not  strike  a  single  stone  with  its  shoes." 
Monuments  and  old  buildings  tend  to  settle  slowly  where 
they  are  undermined  by  earthworms,  and  in  time  may  be- 


PIG.  101. — A  tube-dwelling  marine  annelid.  Note  the  branched  gills 
at  the  anterior  end  and  the  thread-like  cirri  by  means  of  which  the  worm 
entangles  the  small  organisms  that  provide  its  food.  (After  Quatrefages.) 

come  completely  buried.  In  an  average  field  Darwin 
calculated  that  the  amount  of  dirt  carried  to  the  surface 
by  worms  in  one  year  would  form  a  uniform  layer  one- 
fifth  of  an  inch  in  thickness.  Earthworms  are  thus  con- 
tinually plowing  the  ground,  and  although  their  operations 
may  seem  slow  they  may  effect  great  changes  in  the  course 
of  centuries. 

Related  to  the  earthworms,  although  having  very  dif- 
ferent habits  of  life,  is  the  group  of  annelids  called  leeches. 


THE    RINGED    WORMS    OR   ANNELIDS  121 

The  body  of  a  leech  is  generally  flattened  and  provided 
with  a  sucker  at  each  end  by  means  of  which  it  adheres 
to  various  objects.  Leeches  crawl  by  a  looping  motion. 
Some  species  are  furnished  with  teeth,  especially  those 
which  live  by  sucking  the  blood  of  higher  animals.  Of 
the  "blood  suckers"  the  common  medicinal  leech  is  best 
known,  since  it  was  long  used  for  bleeding  patients,  and 
was  extensively  raised  in  swamps  and  ponds  especially 
prepared  for  leech  culture.  After  a  full  meal  of  blood,  a 
medicinal  leech  may  live  several  months  without  food. 
Some  species  of  leech  attack  small  animals  such  as  worms 
and  snails;  others,  and  especially  the  few  that  live  in  the 
sea,  live  upon  the  bodies  of  fish,  and  in  the  tropics  there 
are  land  leeches  which  are  troublesome  pests  to  animals 
and  man. 


CHAPTER    XIV 
THE  ROUND  WORMS  AND  FLAT  WORMS 

The  round  worms,  or  nematodes,  have  an  unsegmented 
and  nearly  cylindrical  body  commonly  tapering  toward 
one  or  both  ends.  Many  species  live  in  the  soil  or  in 
decaying  organic  matter,  while  numerous  others  are 
parasitic  in  the  bodies  of  animals.  Some  of  the  species, 
such  as  the  large  round  worm  of  the  horse,  Ascaris  megalo- 
cephala  and  the  related  species,  Ascaris  lumbricoides 
found  in  pigs  and  sometimes  in  man,  attain  a  length  of 
several  inches.  Others  are  of  almost  microscopic  size,  such 
as  the  vinegar-eels  which  are  very  frequently  seen  in 
cider  vinegar.  These  forms  are  easily  obtained  and  when 
observed  with  a  microscope  the  principal  internal  organs 
may  be  seen  in  their  semi-transparent  bodies.  They  are 
entirely  harmless,  and  there  is  no  need  to  be  fastidious 
about  taking  them  in  with  our  food. 

One  of  the  most  dangerous  of  the  many  nematode 
parasites  of  man  is  the  Trichina  (Trichinella  spiralis). 
The  worms  are  commonly  taken  into  the  body  by  eating 
insufficiently  cooked  pork,  for  the  Trichina  is  a  common 
parasite  of  the  pig.  In  the  pork  the  worms  are  in  an 
encysted  state  in  the  muscle;  when  this  is  digested,  the 
worms  are  liberated,  after  which  they  grow  to  maturity 
in  the  intestine  where  they  produce  new  worms.  These 
young  worms  bore  through  the  intestinal  walls  and  get 
into  the  blood  vessels  where  they  are  carried  to  various 
parts  of  the  body;  they  then  work  into  the  tissues,  com- 
monly the  muscles,  and  there  encyst.  It  is  during  the 

122 


THE  ROUND  WORMS  AND  FLAT  WORMS       123 

invasion  of  the  blood  vessels  and  tissues  that  the  worms 
produce  their  greatest  injury,  and  a  great  many  deaths 
have  been  caused  by  them.  Infected  pork  may  contain  as 
many  as  80,000  encysted  worms  in  a  single  ounce.  As  these 
Trichina  may  produce  many  more  young  in  the  human 
intestine  a  person  may  be  infected  with  millions  of  these  mi- 
nute worms  after  eating  raw  pork.  The  Trichinae  being 
readily  killed  by  heat,  it  is  easy  to  avoid 
these  parasites  by  not  eating  pork  that  is 
insufficiently  cooked.  One  should  be  espe- 
cially cautious  about  eating  raw  salt  pork, 
or  raw  smoked  ham  (both  of  which  are 
eaten  by  many  people)  because  it  has  been 
shown  that  the  Trichinae  are  not  killed 
either  by  the  salt  brine  or  by  the  process- 
of  smoking.  As  in  so  many  parasites  the 
Trichina  requires  two  hosts,  the  eater  and 
the  eaten,  in  order  to  complete  its  life 
history. 

Another  serious  human  parasite  is  the 
hookworm  of  the  southern  states.  The 
young  of  this  form  live  in  damp  earth  and  (From  Leuck- 
gain  access  to  man  by  boring  in  through  the 
skin.  People  who  went  with  bare  feet  in  infected  districts 
often  contracted  what  was  known  as  " ground  itch" 
which  is  now  known  to  be  caused  by  the  young  hookworm. 
When  through  the  skin  the  worms  are  carried  by  the  blood 
throughout  the  body  and  many  get  into  the  alimentary 
canal;  here  they  grow  to  maturity  and  produce  eggs  which 
are  passed  out  of  the  body,  where  they  hatch  into 
young  worms.  The  latter  live  in  the  soil  where  they 
await  an  opportunity  to  get  into  their  host.  When  in 
the  human  intestine  the  worms  produce  considerable  dis- 
turbance to  general  health,  but  they  may  be  expelled 


124 


ANIMAL  BIOLOGY 


by  giving  the  patient  liberal  doses  of  thymol  which  kills 
the  worms,  fortunately  without  greatly  injuring  the  afflicted 
person. 

Besides  the  numerous  nematodes  living  within  animals, 
there  are  several  serious  parasites  of  plants.     From  our 
human  point  of  view  the  nematodes  in  general  are  a  bad 
lot,  for  there  is  scarcely  any  species  for  which  a  useful 
function  has  ever  been  discovered.     One 
form  which  is  sometimes  classed  with  the 
nematodes  may  be  mentioned  here,  viz., 
Gordius,    or    the    so-called   "  horse-hair 
snake."     This  worm  which  is  popularly 
but  wrongly    supposed    to    come    from 
horse-hairs  that  have  fallen  into  the  water 
is  parasitic  during   the  earlier  stages  of 
its  life,  generally  in  the  body  of  some  in- 
sect, and  only  becomes  free  in  the  ma- 
ture state. 

The    flat    worms    comprise    a    large 
phylum    which    is    divided    into    three 
—The  8rouPs>  the  Turbellaria,  the  Trematodes 
hookworm,  a,  male;  Or   flukes,    and   the    Cestodes   or    tape- 

b,  female;  o,  mouth;  „,  ...  , 

v,  opening  for  dis-  worms.  The  most  primitive  group,  the 
charge  of  eggs.  Turbellaria,  are  usually  free-living 

(After   Leuckart.)  * 

animals,  such  as  the  planarians,  which 
are  commonly  found  under  rocks  in  lakes  and  streams. 
The  Trematodes  are  all  parasitic  forms  characterized  by 
having  a  forked  intestine,  and  usually  one  or  more  suckers 
for  attachment  to  the  host.  They  are  found  in  most  verte- 
brate animals  from  fishes  to  man.  One  of  the  most  injur- 
ious species  is  the  common  liver  fluke  Fasciola  hepatica 
which  frequently  infects  sheep  and  sometimes  occurs  in 
human  beings.  The  flukes  may  reach  a  length  of  over  an 
inch,  and  when  they  are  present  in  considerable  numbers 


FIG 


THE   ROUND   WORMS   AND   FLAT   WORMS 


125 


in  the  liver,  which  is  their  usual  abode,  the  host,  whether  a 
sheep  or  a  man,  has  a  very  uncomfortable  time.  The  life 
history  of  the  liver  fluke  requires  two  hosts  in  addition  to  a 
period  of  life  in  the  water.  The  eggs  are  passed  out  of  the 
intestine  and  if  they  gain  access  to  water  they  hatch  into 
ciliated,  free-swimming  embryos.  Should  an  embryo, 
in  the  course  of  its  wanderings,  encounter  a  water  snail 


FIG.  104. — Developmental  stages  of  the  liver  fluke  Fasciola  hepatica. 
a,  free-swimming  larva  which  develops  in  the  body  of  a  snail  into  a 
sporocyst  b.  The  latter  produces  internally  other  larval  forms,  the 
rediae  R.  c,  a  redia  which  contains  still  other  rediae  R  and  a  cercaria,  C 
or  final  larval  form,  d,  a  cercaria.  The  cercarise  escape  from  the 
snail  and  swim  freely  in  the  water.  (After  Leuckart.) 


it  enters  the  body  and  there  undergoes  further  develop- 
ment. The  larval  form  so  produced  may  give  rise  to 
numerous  others  by  a  process  of  parthenogenetic  repro- 
duction. Finally  these  larvae  leave  the  snail,  swim  about 
in  the  water,  and  frequently  attach  themselves  to  grass 
or  weeds  near  the  water's  edge.  Here  they  encyst.  If 
now  a  sheep  comes  along,  eats  the  grass  that  harbors  the 
encysted  larva,  the  latter  develops  into  the  mature  form 


126  ANIMAL  BIOLOGY 

in  the  intestine,  or  liver  of  its  host.  Of  course  the  chances 
are  very  small  that  any  one  embryo  will  make  all  the  con- 
nections necessary  for  a  successful  life  history.  This 
circumstance  is  offset  in  part  by  the  enormous  number  of 
eggs  produced  in  the  beginning,  and  in  part  by  the  fact 
that  each  embryo  may  produce  many  others  provided  it 
makes  the  first  necessary  connection  with  the  body  of 
a  snail.  Truly  this  seems  to  be  a  very  roundabout  and 
wasteful  method  of  perpetuating  the  species,  and  calls 
to  mind  what  the  poet  Tennyson  said  of  Nature: 

"So  careful  of  the  type  she  seems, 
So  careless  of  the  single  life." 

No  matter  how  many  eggs  or  larvae  fall  by  the  wayside 
so  long  as  the  race  of  liver  flukes  makes  the  journey  from 
sheep  back  to  sheep  again.  Each  species  of  animal  solves 
the  problem  of  getting  through  the  world  in  its  own  way; 
and  the  ways  that  are  followed  are  often  very  devious  and 
peculiar. 

The  Cestodes,  or  tape-worms,  are  also  parasitic,  and  they 
have  been  addicted  to  such  a  life  for  so  long  that  they  have 
lost  all  traces  of  an  alimentary  canal.  Instead  of  digesting 
their  own  food  they  live  by  absorbing  the  digested  food 
in  the  alimentary  canal  of  their  host.  With  one  possible 
exception,  the  Cestodes  are  parasitic  in  the  adult  state  in 
the  intestine  of  the  vertebrate  animals. 

Most  Cestodes  are  divided  into  a  number  of  segments, 
or  proglottids.  In  the  larger  human  tape-worms  which 
may  reach  a  length  of  thirty  feet  there  may  be  over  1000 
of  these  segments.  One  end  of  the  body  is  usually  fur- 
nished with  suckers  and  sometimes  also  with  hooks  for 
attachment  to  the  wall  of  the  intestine.  Behind  the  at- 
tached end  new  proglottids  are  continually  formed  and 
they  gradually  increase  in  size  and  become  more  mature 


THE   ROUND   WORMS   AND   FLAT   WORMS 


I27 


as  they  pass  backward.  Finally  the  proglottids  become 
constricted  off  and  pass  out  of  the  body.  The  mature 
proglottids  contain  fertilized  eggs  which  may  be  set  free 
either  before  or  after  the  proglottid  is  expelled. 


FIG.  105. — A  human  tape-worm  Tcenia  solium.  la,  animal  with  a  few 
segments  enlarged  at  the  right  showing  sex  opening  on  one  edge,  o;  16, 
attached  end  with  suckers  and  circles  of  hooklets,  the  latter  enlarged  at 
C.  (After  a  Pfurtscheller  chart.) 

The  eggs  do  not  develop  directly  into  new  worms; 
typically  the  eggs  or  embryos  are  taken  into  the  body 
of  some  other  animal;  here  the  embryo  bores  its  way 
through  the  walls  of  the  intestine  and  becomes  encysted 
in  some  part  of  the  body,  forming  what  is  called  a  bladder 
worm  (cysticercus  or  cysticercoid) .  In  this  state  the  worm 


128  ANIMAL  BIOLOGY 

develops  only  to  a  certain  stage  and  does  not  attain  matu- 
rity until  it  is  taken  into  the  body  of  some  other  animal. 
The  bladder  worm  of  one  kind  of  human  tape-worm,  Tce- 
nia  solium,  occurs  in  the  pig  where  the  cysts  frequently 
attain  the  size  of  a  pea  and  may  become  considerably 
larger.  The  meat  infested  with  these  cysts  is  called 
"measly  pork,"  and  if  such  meat  is  eaten  raw  by  man,  the 
cysts  will  develop  in  his  intestine  into  mature  tape- worms. 
The  bladder  worm  of  another  large  species  infesting  man 


FIG.  1 06. — Development  of  the  bladder  worm  of  the  tape-worm  Tatnia 
saginata.  a,  embryo  within  egg  shell;  b,  free  embryo;  c,  bladder  worm; 
d,  same  with  introverted  scolex.  (After  Leuckart.) 

occurs  in  cattle  and  the  mature  worm  is  acquired  by  eating 
insufficiently  cooked  beef. 

Human  beings  may  carry  the  bladder  worms  in  their 
tissues  and  the  mature  worms  in  their  intestine.  If  a 
person  swallows  the  eggs  of  a  tape-worm  he  may  get 
bladder  worms  in  his  flesh.  These  may  produce  serious 
injury,  especially  if  they  lodge  in  the  brain  or  some  other 
delicate  organ.  One  case  is  recorded  of  a  bladder  worm 
lodged  in  a  woman's  eye  where  its  growth  could  be  watched 
for  several  years. 

While  the  bladder-worm  stage  of  Cestodes  is  usually 
small  there  are  a  few  species  in  which  it  is  quite  large.  In 


THE   ROUND   WORMS   AND   PLAT   WORMS  129 

Coenurus  cerebralis,  which  is  found  in  the  bladder-worm 
stage  in  sheep  where  it  is  often  lodged  in  the  brain,  the  cys- 
ticercus  may  reach  the  size  of  a  hen's  egg.  It  is  a  fre- 
quent cause  of  death  to  sheep. 

Echinococcus  in  the  bladder-worm  stage  may  attain  an 
enormous  development.  Some  specimens  reach  the  size 
of  a  child's  head  and  weigh  several  pounds.  Each  .cyst 
may  produce  a  large  number  of  worms.  The  tape-worm 
stage  of  this  form  is,  curiously  enough,  a  small  worm  of 
only  four  segments,  usually  found  in  the  dog.  The  blad- 
der-worm most  commonly  occurs  in  sheep,  but  there  are 
many  cases  where  it  has  been  found  in  man,  and  has  not 
infrequently  been  the  cause  of  death.  Echinococcus  is 
common  in  Iceland  and  some  parts  of  Australia  where 
sheep  and  dogs  are  kept.  Living  in  too  intimate  relations 
with  dogs  greatly  increases  the  chance  of  becoming  in- 
fected with  this  terrible  parasite. 


CHAPTER  XV 


THE  CCELENTERATES  AND  SPONGES 

The  hydroids,  jelly  fish,  sea  anemones,  coral  polyps, 
and  their  relatives  constitute  the  phylum  Ccelenterata. 
Primarily  the  Ccelenterates  are  radiate  animals  with  their 
organs  symmetrically  disposed  about  a  central  axis,  but 
there  are  some  of  the  higher  members  of  the  group  which 

have  become  to  a  greater  or  less 
extent  two-sided  or  bilateral. 

One  can  secure  in  almost  any 
part  of  the  country  a  living 
representative  of  this  group  in 
the  common  fresh- water  Hydra 
which  is  frequently  found  at- 
tached to  aquatic  plants  in 
ponds  and  streams.  The  tubu- 
lar body  of  Hydra  is  furnished 
at  one  end  with  a  variable 
number  of  tentacles  (6-8  com- 
monly) surrounding  the  mouth. 
At  the  opposite  end  is  the  foot 
which  may  become  attached  to 
objects  by  means  of  an  adhe- 
sive secretion.  The  attachment  is  not  permanent,  how- 
ever, as  the  Hydra  can  break  loose  at  any  time  and  crawl 
by  a  looping  motion  to  another  locality. 

The  internal  structure  of  Hydra  is  very  simple.  The 
body  may  be  regarded  as  a  sort  of  sac  composed  of  two 
layers  of  cells  separated  by  a  thin  membrane.  The  inner 

130 


FIG.   107. — Fresh  water  Hydra. 
Ov,  ovum;  T,  testes. 


THE   CCELENTERATES   AND   SPONGES  131 

layer  is  known  as  the  entoderm,  the  outer  as  the  ectoderm. 
The  entoderm  lines  the  large  digestive  cavity  which  ex- 
tends the  length  of  the  body,  and  is  continued  also  into 
the  tubular  cavities  of  the  tentacles.  Some  of  the  entoderm 
cells  are  furnished  with  lash-like  organs,  or  flagella,  whose 
movements  serve  to  circulate  the  contained  material. 
The  digestive  juices  poured  out  by  the  entoderm  cells  act 
on  the  food  in  the  central  cavity,  but  small  particles  of 
food  may  be  engulfed  within  the  cells  themselves  and 
digested  there.  Digestion  is,  therefore,  extracellular, 
as  it  is  in  higher  animals,  and  at  the  same  time  intra- 
cellular,  as  it  is  in  animals  still  lower  in  the  scale  of  life. 
The  undigested  residue  of  the 
food  is  ejected  through  the 
mouth. 

The  ectoderm  cells  in  addi- 
tion to  forming  an  outer  cov- 
ering for  the  body  are  modi-      FIG.  108.— Cross  section  of  the 
fied    into  gland  cells,   muscle  *«  &S%«&S& 

Cells,  nerve   Cells,  Sex  Cells  and    M>  mesoglcea;  Nc,  nettling  cell; 
•ii  mi  i       V,  vacuole. 

nettling    cells.      The    muscle 

cells  endow  the  Hydra  with  its  extraordinary  contrac- 
tility. At  times  the  animal  may  be  greatly  elongated 
with  its  tentacles  extended  into  fine  threads  several 
inches  in  length.  Touch  the  animal  one  or  more  times; 
the  tentacles  will  be  reduced  to  mere  stubs  and  the  body 
contracted  almost  into  a  ball.  There  is  no  central  nerv- 
ous system  such  as  occurs  in  higher  animals,  but  a  scat- 
tered network  of  nerve  cells  whose  fine  branches  or  nerves 
connect  with  various  other  cells  of  the  body. 

The  most  interesting  cells  of  Hydra  are  the  nettling 
cells  which  contain  oval  bodies  called  nematocysts.  The 
latter  consist  of  a  hollow  capsule  containing  a  long  thread 
spirally  wound  up  on  the  inside.  In  response  to  certain 


132  ANIMAL  BIOLOGY 

stimuli  the  thread  may  burst  out  of  its  capsule  and  be- 
come extended  with  a  good  deal  of  force  so  that  it  may  pene- 
trate the  tissues  of  animals,  even  those  which  are  covered 
with  a  layer  of  chitin.  The  nematocysts  contain  a  pois- 
onous, irritating  fluid  which  serves  to  paralyze  the  small 
animals  that  the  Hydra  fe'eds  upon.  Nettling  cells  are 
commonly  furnished  with  a  pointed  projection,  "the  trig- 
ger/' which  is  supposed  when  irritated  to  set  off  the  dis- 
charge of  the  nematocysts.  Nematocysts  are  especially 
abundant  near  the  tips  of  the  tentacles  where  they  are 
most  apt  to  come  into  contact  with  prey.  The  tentacles 
are  also  adhesive  and  small  animals  which  come  in  contact 
with  them  are  caught  and  drawn  toward  the  mouth. 
The  swallowing  capacity  of  Hydra  is  enormous;  animals 
considerably  larger  than  the  Hydra  itself  are  successfully 
taken  into  the  digestive  cavity. 

Reproduction  in  Hydra  is  effected  in  two  ways,  (i) 
asexually,  by  the  formation  of  buds,  and  (2)  sexually, 
through  the  production  of  eggs  and  sperms.  In  budding, 
an  outpushing  of  both  layers  of  the  body  wall  occurs, 
tentacles  are  pushed  out  and  a  mouth  breaks  through  at 
the  outer  end  of  the  bud.  Finally  the  bud  constricts  off 
at  the  base  and  forms  a  new  free  Hydra.  Often  many 
buds  are  found  on  one  individual. 

Both  male  and  female  sex  cells  are  produced  in  the  same 
individual.  The  eggs  are  produced,  one  or  two  at  a  time, 
on  the  basal  part  of  the  body.  The  sperms  appear  in  a 
number  of  conical  prominences  nearer  the  oral  end.  The 
sperms  are  set  free  in  the  water  and  fertilize  the  large  egg 
cell  while  it  is  still  in  the  ectoderm  of  the  body  wall.  In 
this  situation  also  the  egg  undergoes  its  early  develop- 
ment, but  at  a  certain  stage  there  is  formed  around  it  a 
chitinous  and  often  spiny  shell,  or  capsule,  which  serves 
to  protect  the  egg  after  it  is  discharged,  when  it  comes  to 


THE   CCELENTERATES   AND   SPONGES 


133 


lie  at  the  bottom  of  a  pond  or  stream.  Enclosed  in  the 
shell,  the  egg  can  withstand  periods  of  drought  and  other 
unfavorable  conditions  after  which  it  may  break  out  of 
the  shell  and  complete  its  development. 

Hydra  has  long  been  a  classical  object  for  the  study 
of  regeneration.  It  may  be  cut  in  numerous  pieces  each 
of  which  may  form  a  new  Hydra,  and  pieces  from  different 
individuals  may  be  grafted  together,  much  as  nurserymen 
graft  together  different  trees  or  shrubs.  One  species  of 
Hydra,  Hydra  viridis,  is  remarkable  for  its  green  color. 


FIG.  109. — A,  budding  in  Hydra;  B,  regeneration  of  Hydra  from  a  small 
piece  from  near  the  middle  of  the  body. 

The  green  is  due  to  the  presence  of  small,  unicellular  green 
plants  (algae)  in  the  cells  of  the  entoderm.  The  plants 
ordinarily  are  not  digested,  but  live  on  material  derived 
from  the  host.  As  plants  assimilate  carbon  dioxide  which 
is  a  waste  product  of  animals  and  give  off  oxygen  which 
the  animal  uses  in  respiration,  the  association  between  the 
Hydra  and  the  algae  is  supposed  to  be  to  their  mutual 
advantage.  Thus  we  have  an  illustration  of  symbiosis 
which  was  briefly  considered  in  a  previous  chapter. 

There  are  numerous  marine  relatives  of  Hydra  which  are 
commonly  called  hydroids.  Many  of  these  are  much 
branched  and  form  colonies.  In  some  of  these  there  has 


134 


ANIMAL  BIOLOGY 


come  to  be  a  division  of  labor  between  different  -indi- 
viduals of  the  colony,  some  being  specialized  for  catching 
prey  (feeding  hydroids) ;  others,  richly  furnished  with  net- 
tling cells,  are  set  apart  for  protection  (defensive  hydroids) ; 
while  others  (the  reproductive  hydroids)  are  devoted  en- 
tirely to  reproduction.  Very  commonly  the  marine 
hydroids  give  rise  by  budding  to  a  free-swimming  genera- 
tion of  jelly  fish,  or  medusa.  The  larger  part  of  a  typical 
medusa  consists  of  a  disk,  or  umbrella,  furnished  with  tenta- 


rc 


FIG.   no. — Hydroids    A    and    medusa    B;    m,    manubrium;  mb,  medusa 
buds;  re,  radial  canals;  t,  tentacles;  v,  velum.     (After  Allmann.) 

cles  along  the  outer  margin.  Hanging  down  from  the  middle 
of  the  lower  side  is  the  manubrium,  at  one  end  of  which  is 
the  mouth.  The  latter  leads  to  the  stomach  from  which  a 
number  of  canals  (commonly  four)  radiate  outward  where 
they  open  into  a  circular  canal  near  the  margin  of  the  um- 
brella. Jelly  fish  are  usually  transparent  animals,  fre- 
quently of  very  delicate  and  beautiful  structure;  they 
swim  through  the  sea  by  contractions  of  the  umbrella 
and  live  upon  animals  which  they  catch  by  means  of  their 
tentacles.  Jelly  fish  produce  sex  cells  which  are  dis- 


THE    CCELENTERATES   AND    SPONGES 


135 


charged  from  the  body  and  commonly  develop,  not  into 
jelly  fish,  but  into  hydroids.  We  thus  have  what  is  called 
alternation  of  generations,  jelly  fish  producing  a  hydroid 
(the  asexual  generation)  which  gives  rise  again  to  a  jelly 
fish.  Not  all  species  pass  through  this  alteration  of 
generations.  Just  as  there  are  hydroids  which,  like  the 
fresh-water  Hydra,  have  no 
medusa  stage  but  develop  di- 
rectly from  eggs  produced  by 
other  hydroids,  so  there  are 
medusae  which  produce  eggs 
that  develop  directly  into  me- 
dusae and  have  no  hydroid  stage. 
In  the  group  of  Siphono- 
phores  the  division  of  labor 
which  has  been  noted  among 
certain  hydroids  reaches  an 
extreme  development.  The 
siphonophores  are  all  free-swim- 
ming or  floating  colonies  made 
up  of  numerous  individuals 
modified  in  various  ways,  some 
for  swimming,  some  for  taking 
food,  others  for  protection,  and 
still  others  for  reproduction. 

One  of  the  largest  species  is  the  Portugese  man-of-war 
which  is  furnished  with  a  long  oblong  float  filled  with 
gas,  by  which  the  colony  rides  upon  the  surface  of  the 
waves.  From  the  lower  side  of  the  float  hang  down 
clusters  of  variously  modified  individuals  and  very  con- 
tractile tentacles  which  may  extend  to  a  length  of  fifty 
feet.  These  are  richly  furnished  with  nettling  cells,  and 
the  poison  they  contain  is  so  virulent  that  even  a  slight 
con  tact  with  a  tentacle  may  produce  considerable  irritation. 


FIG.  in. — Two  species  of 
jelly  fish  from  the  Tortugas. 
(After  Mayer.) 


136 


ANIMAL  BIOLOGY 


The  anemones  are  mostly  sessile  animals  attached  at 
the  base  or  foot  to  rocks  or  seaweed.  They  are  common 
on  rocky  parts  of  the  coast  and  some  forms  may  be  exposed 
at  low  tide.  Many  species  are  remarkable  for  their 

beauty  of  form  and  coloring. 
The  free  end,  or  disk,  is  fur- 
nished with  tentacles  which  are 
employed  in  catching  prey  and 
conveying  it  to  the  mouth. 
Anemones  are  more  highly 
organized  than  the  hydroids. 
The  digestive  cavity  is  divided 
by  a  number  of  partitions,  the 
mesenteries,  which  extend  from 
the  body  wall  toward  the  cen- 
ter. In  some  species  the  edges 
of  these  mesenteries  bear  long 
extensile  filaments,  armed  with 
nematocysts,  which  are  capable 
of  being  thrust  out  of  the  body 
when  the  animal  is  irritated. 

Closely  related  to  the  ane- 
mones are  the  corals.  In  a 
typical  coral  the  body  of  the 
individual  animal,  or  polyp,  has 
the  property  of  secreting  about 
its  base,  a  hard  deposit  of  car- 
bonate of  lime,  forming  the  so- 
called  coral  rock.  As  coral 
polyps  commonly  multiply  by  budding  they  may  form  an 
extensive  society  of  individuals  more  or  less  closely  asso- 
ciated with  one  another.  The  masses  of  coral  rock  which 
the  polyps  form  may  be  increased  almost  indefinitely 
by  the  multiplication  of  the  polyps  and  the  accession 


FIG.    112. — Portugese  man-of- 
war.     (After  Agassiz.) 


THE   CCELENTERATES   AND    SPONGES  137 

of  new  ones.  Islands  may  be  formed  by  the  gradual  accu- 
mulation of  the  deposits  of  coral  polyps,  and  even  consider- 
able parts  of  continents  such  as  most  of  the  peninsula 


FIG.   113. — A  group  of  sea  anemones.     (After  Andres.) 


PlG.   114. — A  fringing  reef  with  many  varieties  of  corals.     (After  Saville- 

Kent.) 

of  Florida.  The  red  coral,  much  used  in  making  orna- 
ments, is  derived  from  a  species  which  occurs  in  the  Medi- 
terranean Sea.  Some  forms  allied  to  the  true  coral 


138 


ANIMAL  BIOLOGY 


form  branching  colonies  which  secrete  a  skeleton  of  a 
tough,  horny  substance  resembling  chitin.  These  include 
the  sea-mats,  sea-fans  and  black  corals,  etc.,  many  of 
which  are  commonly  mistaken  for  seaweed.  The  grace- 
ful form  and  vivid  colors  of  many  of  the  colonies  of  coral 


<> 


FIG.  115. — The  common  bath  sponge,  i,  shows  the  sponge  with  parts 
cut  away  to  show  the  channels  through  which  water  flows  in  and  out, 
the  arrows  indicating  the  directions  of  the  flow;  2,  a  part  of  the  surface 
highly  magnified;  3,  a  section  through  the  sponge  showing  the  horny  fibers, 
/,  the  incurrent  orifices,  o,  and  the  chambers  lined  by  ciliated  cells;  4, 
ciliated  chambers  enlarged,  a  single  collared  cell  at  c.  (From  a  Pfurt- 
scheller  wall  chart.) 

polyps  often  give  to  coral  reefs  the  appearance  of  beauti- 
ful submarine  gardens.  Here  thrive  numerous  other  ani- 
mals which  seek  the  shelter  afforded  by  masses  of  coral 


THE    CCELENTERATES   AND    SPONGES  139 

rock;  many  of  these  forms  are  also  conspicuously  colored 
and  present  a  marked  contrast  to  the  transparency,  or  the 
inconspicuous  colors,  of  most  of  the  unprotected  animals 
of  the  open  sea. 

The  Ccelenterates  known  as  Ctenophores,  or  comb- 
bearers  have  a  fairly  pronounced  bilateral  symmetry. 
They  swim  by  means  of  eight  rows  of  comb  plates  which 
act  like  so  many  small  paddles.  They  have  as  a  rule 
two  long  and  very  contractile  tentacles  armed  with  adhe- 
sive bodies  which  aid  in  the  capture  of  prey.  Nearly  all 
of  the  Ctenophores  are  beautiful,  transparent,  jelly-like 
animals,  and  all  of  the  species  are  confined  to  the  sea. 

The  Porifera,  or  Sponges,  were  formerly  regarded  as 
vegetable  growths,  partly  no  doubt  on  account  of  their 
attachment  and  mode  of  growth,  and  partly  because 
they  show  but  a  slight  degree  of  activity.  The  structure 
of  a  sponge  is  best  studied  in  one  of  the  calcareous  sponges 
such  as  Grantia.  The  body  of  Grantia  is  cylindrical 
with  a  central  cavity  which  opens  outward  by  a  mouth, 
or  osculum.  The  sides  are  perforated  by  pores  leading 
to  canals  which  open  into  the  central  cavity.  Through 
these  canals  a  current  of  water  is  carried  from  the  outside 
to  the  central  cavity,  by  means  of  the  beating  of  flagella. 
The  minute  organisms  carried  by  these  currents  supply 
the  sponge  with  its  food  which  is  digested  within  the  bod- 
ies of  the  cells  lining  the  canals  (intracellular  digestion). 
The  sponge  has  no  organs  of  circulation  or  excretion, 
and  no  nervous  system  or  sense  organs.  Like  Hydra, 
the  body  has  an  inner  layer,  or  entoderm,  and  an  outer 
layer,  or  ectoderm;  but  between  these  are  other  cells  some 
of  which  form  the  skeleton,  or  supporting  tissue,  of  the 
body.  In  the  calcareous  sponges  this  consists  of  spic- 
ules  of  carbonate  of  lime.  In  other  sponges  the  skeleton 
may  be  composed  of  silica  as  in  the  beautiful  glass  sponges. 


140  ANIMAL  BIOLOGY 

In  others  it  may  be  formed  entirely  or  in  part  of  a  horny 
substance,  as  in  our  common  bath  sponges. 

Sponges  may  build  up  large  masses  by  budding;  in  this 
way  they  frequently  give  rise  to  detached  individuals; 
but  they  also  reproduce  sexually  by  means  of  ova  and 
spermatozoa.  The  eggs  of  many  species  produce  free- 
swimming  larvae  which  finally  settle  down  and  develop 
into  a  small  attached  sponge.  While  most  sponges  are 
marine,  there  are  a  few  fresh-water  forms  (Spongilla  and 
allied  genera).  The  sponges  of  commerce  are  fished  up 
in  certain  localities,  by  long  rakes,  or  by  means  of  divers. 
The  animal  matter  is  allowed  to  decay,  and  the  horny 
residue  is  bleached  and  cleaned  before  the  sponge  is  ready 
for  use. 


CHAPTER  XVI 
THE  PROTOZOA  OR  THE  SIMPLEST  ANIMALS 

The  lowest  and  simplest  of  all  animals  are  the  Protozoa. 
The  group  differs  from  the  animals  that  have  been  studied 
in  that  the  individual  consists  of  but  a  single  cell.  Most 
of  the  Protozoa  are  of  microscopic  size,  and  some  are  so 
small  that  the  highest  powers  of  the  microscope  are  neces- 
sary to  detect  them.  The  commonly  recognized  classes 
of  the  Protozoa  may  be  separated  by  the  following  key: 

A .  Protozoa,  at  least  at  some  period  of  life,  moving  by 
means  of  cilia ........  Infusoria. 

A  A.  Body  devoid  of  cilia. 

B.  Protozoa  furnished  with  one  or  more  flagella.    .    .    . 

.  .;,  .    *    iJiv'.'-i •    •  Flagella  ta. 

BB.  Body  devoid  of  flagella. 

C.  Usually  free  forms,  with  pseudopodia.    .  Sarcodina. 
CC.  Exclusively  parasitic  forms,  multiplying  by  means 

of  spores  and  generally  devoid  of  pseudopodia  in 
the  mature  state. Sporozoa. 

Of  these  classes  the  Infusoria  have  the  most  complex 
organization.  It  is  easy  to  obtain  a  typical  infusorian  in 
the  common  slipper  animalcule,  Paramcecium,  which 
usually  makes  its  appearance  in  infusions  of  hay  or  other 
vegetable  matter.  If  one  places  a  quantity  of  hay  in  some 
water  coming  from  a  pond  or  stream  that  contains  more 
or  less  plant  life,  it  is  probable  that  Paramcecia  will  make 
their  appearance  in  the  mixture  in  the  course  of  one  or 
more  weeks.  They  may  be  recognized  by  their  uniformly 

141 


142  ANIMAL  BIOLOGY 

ciliated  body  which  has  the  general  shape  of  a  cigar  with 
a  broad  oblique  groove  on  one  side.  At  the  end  of  the 
oblique  groove  is  a  short  gullet  down  which  the  food  of 
Paramcecium  is  swept  by  the  action  of  cilia.  At  the  end 
of  the  gullet  is  a  small  enlargement,  the  crop,  where  the 
food  accumulates  forming  a  sort  of  ball.  When  the  crop 
is  filled  with  food  it  is  pinched  off  by  the  contraction  of 
the  surrounding  substance,  and  the  mass  of  food  with  a 
small  amount  of  water  passes  into  the  semi-fluid  interior 
of  the  body.  The  small  vesicles  with  their  contained  food 
are  called  food  vacuoles.  By  a  circular  movement  of 
the  inner  substance,  or  endoplasm,  the  food  is  slowly 
carried  about  the  body,  in  the  meantime  undergoing  a 


FIG.  116. — Paramcecium.    oil,  cilia;  cv,  contractile  vacuoles ;  /,  food  vacu- 
oles; g,  gullet  with  crop  at  end;  n,  macronucleus;  nf,  micronucleus. 

process  of  digestion.  The  undigested  residue  is  discharged 
at  the  surface  of  the  body  at  a  spot  a  little  behind  the 
mouth.  Surplus  water  and  products  of  excretion  are 
got  rid  of  through  the  hollow  vesicles  called  contractile 
vacuoles,  located  near  either  end  of  the  body.  These 
may  be  seen  to  slowly  swell  from  the  accumulation  of 
fluid  and  then  suddenly  contract,  expelling  the  fluid  to  the 
outside  of  the  body.  Paramcecia  eliminate  through  these 
organs  several  times  their  own  bulk  of  water  every 
day. 

Paramcecium,  like  most  other  Infusoria,  contains  two 
kinds  of  nuclei,  a  large  one,  the  meganucleus,  and  a  small 
one,  the  micronucleus  which  usually  lies  close  against  the 


THE   PROTOZOA    OR   THE    SIMPLEST   ANIMALS  143 

meganucleus.  Reproduction  in  Paramcecium  takes  place 
by  transverse  fission.  Both  meganucleus  and  micro- 
nucleus  divide  and  the  two  parts  pass  toward  either  end 
of  the  body  which  becomes  constricted  in  the  middle  by  a 
transverse  furrow  and  finally  pinches  in  two.  Para- 
mcecium  may  reproduce  in  this  way  for  several  hundred 
generations,  but  finally  it  is  interrupted  by  another  proc- 
ess which  is  called  conjugation.  In  this  process  the  Para- 
mcecia  come  together  in  pairs  and  become  united  by  their 
oral  surfaces.  When  they  are  united  complicated  changes 
in  the  nuclei  occur,  during  which  the  Paramcecia  exchange 


FIG.   117. — Diagram  of  the  course  of  a  Paramoecium  in  a  drop  of  dilute 
acid  surrounded  by  water. 

a  part  of  their  nuclear  material.  After  this  they  separate 
and  continue  dividing  by  fission  until  another  conjugation 
period  comes  about.  It  is  held  by  some  biologists  that 
conjugation  regenerates,  or  puts  new  vitality  into  the 
stock. 

The  body  of  Paramoecium  is  asymmetrical,  and  as  the 
animal  swims  through  the  water  by  the  Keating  of  the 
cilia  it  rotates  on  its  long  axis  and  describes  a  spiral  path. 
When  colliding  with  an  object,  or  when  stimulated  in 
any  other  way,  Paramoecium  swims  backward  by  revers- 
ing the  stroke  of  the  cilia,  turns  toward  the  side  opposite 
the  mouth,  and  then  goes  ahead.  This  reaction  has  been 


144  ANIMAL  BIOLOGY 

called  the  motor  reflex  and  is  performed  by  Paramoecium 
in  response  to  all  sorts  of  stimuli,  in  much  the  same  way. 
In  fact  Paramcecium  does  little  else  except  swim  forward 
and  give  the  motor  reflex  when  it  meets  with  a  stimulating 
agent,  so  that  its  behavior  is  remarkably  simple.  Some- 
times it  tends  to  remain  quiet  with  its  oral  side  in  contact 
with  some  solid  object.  Advantage  is  taken  of  this  trait, 
by  placing  a  bit  of  cotton  wool  in  a  drop  of  water  con- 
taining Paramcecia,  when  we  wish  to  keep  the  creature 
quiet  for  study. 

Many  infusoria  have  the  property  of  secreting  a  coating, 
or  cyst,  about  themselves,  in  which  they  are  able  to  with- 
stand conditions  that  would  otherwise  prove  fatal.  The 
cysts  of  some  infusorians  have  been  kept  dry  for  over  a 
year,  when  they  gave  rise  to  living  Infusoria  after  being 
placed  in  water.  If  ponds  dry  up  in  summer  the  infu- 
sorians, and  many  other  protozoa  also,  may  go  into  an 
encysted  state  until  the  ponds  become  filled  again.  The 
dried  cysts  of  protozoa  may  be  blown  for  miles  in  the  dust 
and  thus  scatter  the  species  very  widely.  The  great  ease 
with  which  these  minute  forms  become  scattered  accounts 
for  the  world  wide  distribution  of  many  species. 

The  flagellate  protozoa  are  devoid  of  cilia  but  they  swim 
by  means  of  one  or  more  whip-like  organs  called  flagella. 
Many  of  them  have  a  mouth  by  which  they  take  in  food 
(holozoic  forms)  as  the  higher  animals  do;  others  imbibe 
food  in  soluble  form  through  the  body  wall.  Of  the  latter 
some  live  in  decaying  substances  (saprophytic  forms), 
some  live  within  the  bodies  of  other  organisms  (parasitic 
forms),  and  others  live  by  the  imbibition  of  inorganic 
substances  (holophytic  forms).  One  of  the  latter  group, 
Euglena  viridis,  combines  many  characteristics  of  both 
plants  and  animals.  This  species  is  provided  at  the  an- 
terior end  with  a  single  flagellum  inserted  in  a  small 


THE   PROTOZOA   OR   THE    SIMPLEST   ANIMALS 


mouth.  Near  the  base  of  the  flagellum  is  a  small  eye- 
spot.  In  the  endoplasm  there  are  numerous  bodies  con- 
taining chlorophyll,  a  compound  which  enables  the  green 
plants  to  utilize  carbon  dioxide  in  building  up  their  living 
substance.  Euglenas  exposed  to  light  take  in  C02  and 
give  off  0,  just  as  the  higher  plants  do.  At  the  same  time 
they  swim  about  like  animals  and  are  said  to  take  in  a 
small  amount  of  solid  food  through  the  mouth.  Like 
Paramcecium,  Euglena  multiplies  by  fission,  but  it  divides 


FIG.  118. — A,  Vorticella;  c,  cilia;  cv,  contractile  vacuole;  fv,  food 
vacuole;  g,  gullet;  n,  nucleus;  5,  contractile  stalk;  v,  cyst  of  Vorticella; 
B,  a  flagellate  Euglena  viridis.  cv,  contractile  vacuoles;  e,  eye  spot;  m, 
mouth;  n,  nucleus. 

longitudinally  as  do  most  other  flagellates,  instead  of  trans- 
versely. At  times  it  may  go  into  an  encysted  state  in 
which  it  sometimes  divides  into  two  or  more  individuals. 
Some  flagellates  are  more  completely  plant-like  than 
Euglena,  while  there  are  others  which  are  more  like  typical 
animals.  In  fact  the  animal  and  plant  kingdoms  seem  to 
draw  together  in  the  flagellates  which  form  a  sort  of 

common  base  from  which  they  both  diverge.     The  plant- 
10 


146  ANIMAL  BIOLOGY 

like  flagellates  lead  up  to  the  simpler  algae  and  thence  on 
to  the  higher  plants;  the  animal-like  flagellates  lead  on 
to  other  groups  of  animals.  There  is  evidence  that  the 
flagellates  are  related  to  the  simplest  of  all  known  organ- 
isms, the  bacteria,  which  we  may  regard  as  standing  at 
the  very  root  of  the  tree  of  life. 

Some  of  the  flagellates  that  live  within  the  bodies  of 
animals  are  the  causes  of  very  severe  diseases.  Chief 
among  these  forms  are  the  trypanosomes  which  are  found 
generally  in  the  blood  of  the  infected  animal.  Nagana, 
which  carries  off  thousands  of  horses  in  Africa,  is  caused  by 

a  species  of  trypanosome.  The 
disease  is  conveyed  by  means 
of  the  bite  of  the  tsetse-fly, 
much  as  malaria  is  carried  from 
one  person  to  another  by  the 
mosquito.  One  of  the  worst 
scourges  of  humanity  that  is 
known,  the  "  sleeping  sickness  " 

FIG.  119. — Trypanosomes.  r    A  r  •  i  •   i     •          ,•  i, 

of  Africa,  which  is  estimated  to 

have  carried  off  in  the  district  of  Uganda  some  one  hun- 
dred thousand  natives  in  four  years,  is  caused  by  another 
trypanosome,  Trypanosoma  gambiense.  The  disease  in  its 
later  stages  is  accompanied  by  extreme  drowsiness  which 
gave  it  its  name,  and  it  almost  always  results  in  the  death 
of  the  patient.  It  is  now  known  that  this  disease  is  con- 
veyed from  man  to  man  by  a  species  of  tsetse-fly,  but  one 
that  is  different  from  the  species  that  carries  nagana. 
In  the  group  Sarcodina  the  body  does  not  have  a  fixed 
outline,  for  it  has  the  power  of  pushing  out  and  with- 
drawing projections  called  pseudopodia  (false  feet)  which 
serve  both  for  locomotion  and  the  capture  of  food.  One 
of  the  simplest  and  best  known  of  the  group  is  the  common 
Amoeba  proteus.  The  organism  appears  like  a  mass  of 


THE   PROTOZOA   OR  THE   SIMPLEST  ANIMALS 

animated  jelly,  with  no  constant  form.  The  outer  part 
of  its  body,  the  ectoplasm,  is  clearer  and  firmer  than  the 
inner  part,  or  endo plasm,  which  is  granular  and  more  fluid. 
There  is  a  single  nucleus  and  a  contractile  vacuole. 
Amoeba  flows  around  its  food  and  takes  it  into  its  endo- 
plasm  where  it  is  digested  in  food  vacuoles.  Multiplication 
is  commonly  by  fission,  although  after  surrounding  itself 


FIG.  120. — Amoeba  proteus.  A,  active  state;  cv,  contractile  vacuole; 
n,  nucleus;  p,  pseudopod;  B,  Amoeba  dividing;  C,  cyst;  1-4,  stages  in 
ingesting  a  particle  of  food,  F. 

with  a  cyst  Amoeba  may  divide  up  into  minute  bodies 
called  spores,  which  ultimately  break  out  and  become  small 
Amoebae. 

The  common  Amoeba  is  generally  found  in  fresh  waters 
and  usually  appears  in  cultures  such  as  those  used  to  ob- 
tain Paramcecium.  There  are  several  kinds  of  Amoeba, 
a  few  of  which  are  parasitic  in  the  bodies  of  animals. 
Certain  inflammatory  diseases  of  the  human  intestine 
(amoebic  dysentery)  have  been  traced  to  Amcebas  and  re- 
lated organisms.  Many  forms  allied  to  Amoeba  live  within 
a  shell  which  is  formed  either  by  secretion  or  by  the  ag- 


148  ANIMAL  BIOLOGY 

gregation  of  foreign  particles.  One  large  group  of  these 
organisms,  the  Foraminifera,  is  abundantly  represented 
in  the  sea,  in  certain  parts  of  which  extensive  deposits  are 
formed  by  the  accumulation  of  their  minute  shells.  Chalk 
is  a  deposit  which  is  mainly  formed  of  the  shells  of  these 
animals.  Another  very  large  group,  the  Radiolaria,  is 
confined  to  the  sea.  Many  species  have  beautiful  silicious 
skeletons  and  in  some  parts  of  the  ocean  there  are  exten- 
sive deposits  formed  from  the  remains  of  these  animals. 


FIG.   121. — Shells  of  Foraminifera  from  the  bottom  of  the  Indian  Ocean. 

The  Sporozoa,  which,  as  the  name  implies,  are  charac- 
teristically spore-producing  organisms,  are  all  parasitic 
in  the  bodies  of  animals.  One  large  division,  the  Grega- 
rines,  are  parasitic  in  invertebrate  animals,  where  their 
favorite  situation  is  in  the  alimentary  canal.  Another 
group,  the  Coccidea,  infest  both  vertebrates  and  inverte- 
brates. The  Haemosporidia  are  blood  parasites  and  in- 
clude the  common  malaria  parasites  (Plasmodium)  which 
have  already  been  mentioned  in  treating  of  the  mosquito. 
The  organism  that  causes  Texas  fever  in  cattle  and  which 


THE   PROTOZOA   OR   THE    SIMPLEST  ANIMALS 


149 


is  conveyed  through  the  bites  of  wood  ticks  is  another 
member  of  this  group.  x 

Many  diseases  of  fishes  are  caused  by  other  species  of 
sporozoans.  The  disease  called  "pebrine,"  which  at- 
tacks silk-worms  and  formerly  caused  very  great  losses 
to  the  silk  industry  of  France,  is  caused  by  a  sporozoan. 

This  is  one  of  the  comparatively  few  diseases  which 
can  be  transmitted  from  parent  to  offspring  through  the 
egg.  Louis  Pasteur,  a  man  famous  for  his  valuable  work 


FIG.   122. — Skeletons  of   Radiolarians.     (After  Hseckel.) 

in  establishing  the  germ  theory  of  disease,  discovered  that 
infected  silk-worm  moths  could  be  distinguished  from 
the  others  by  microscopic  examination  of  the  blood.  This 
fact  made  it  possible,  by  rejecting  the  infected  individuals, 
to  check  the  spread  of  the  disease,  which  has  since  caused 
much  less  damage. 

Although  small  in  size  the  protozoa  by  their  vast  num- 
bers are  important  factors  in  the  life  of  the  world.  As  we 
have  seen  they  produce  many  diseases  in  animals  and  man; 


ANIMAL  BIOLOGY 


they  have  played  an  important  part  in  building  up  cer- 
tain deposits  of  the  earth's  crust;  but  most  important  of 


FIG.  123. — Life  history  of  the  malarial  parasite.  I,  sporozoit  as  it 
enters  the  blood  from  the  bite  of  a  mosquito.  This  sporozoit  becomes 
an  amoeboid  body,  2,  which  enters  a  red  blood  corpuscle  and  grows, 
3-5;  6,  amoeboid  bodies  into  which  the  parasite  breaks  up  and  which 
enter  new  corpuscles  and  repeat  the  same  history  until  the  sexual  cycle 
appears  (7-11);  7-9,  female  cells;  ja-gb,  male  cells;  10,  union  of  female 
cell  with  filamentous  male  cell;  (this  occurs  in  the  stomach  of  a  mos- 
quito); ii,  fertilized  cell;  12,  the  same  when  imbedded  in  the  wall  of  the 
stomach  of  the  mosquito;  13-15,  growth  of  this  cell,  multiplication  of 
nuclei,  and  breaking  up  of  protoplasm  to  form  numerous  spindle-shaped 
sporozoits,  many  of  which  later  get  into  the  salivary  gland  of  the  mosquito. 
(After  Schaudinn.) 

all  is  the  role  they  play  in  the  food  relations  of  other  organ- 
isms.    Protozoa  devour  bacteria  and  other  simple  plants ; 


THE   PROTOZOA   OR   THE    SIMPLEST  ANIMALS          151 

they  prey  upon  other  protozoa  and  even  the  smaller 
many-celled  animals,  and  they  get  rid  of  disintegrating 
animal  and  vegetable  matter  of  various  kinds.  In  turn 
they  are  eaten  by  larger,  organisms.  Together  with  the 
unicellular  plants  they  afford  most  of  the  food  of  that  large 
class  of  animals  which,  like  the  clams,  sweep  in  their  food 
supply  by  the  action  of  cilia.  They  are  eaten  by  hordes  of 
smaller  animals,  such  as  copepods,  free-swimming  larvae, 
etc.  The  smaller  animals  in  turn  supply  food  for  larger 
animals,  such  as  fishes,  and  it  is  proverbial  that  the  big 
fishes  eat  up  the  little  ones.  The  aquatic  world  would  be- 
come a  vast  grave  yard  were  it  not  for  the  unicellular  plants 
and  animals. 

The  protozoa  are  of  much  interest  on  account  of  their 
simplicity  of  structure  and  behavior.  Animal  life  is  here 
reduced  to  its  lowest  terms.  Within  a  single  cell  is  con- 
tained, as  in  germ,  the  power  of  performing  most  of  the 
functions  which  are  discharged  by  the  various  special 
organs  of  the  bodies  of  higher  animals.  In  the  simple, 
almost  structureless  body  of  an  Amoeba,  we  have  locomo- 
tion without  limbs  or  permanent  organs,  digestion  without 
stomach  or  intestine,  respiration  without  lungs  or  gills, 
circulation  without  heart  or  blood  vessels,  contraction  with- 
out muscles,  and  response  to  stimulation  without  sense 
organs  or  nervous  system.  The  living  substance  of  the 
body  performs  all  these  functions,  not  so  readily  as  each 
would  be  performed  by  organs  devoted  solely  to  one  par- 
ticular activity,  but  still  sufficiently  well  to  enable  the 
Amoeba  to  make  its  living  and  propagate  its  kind.  As 
we  pass  up  the  scale  of  life  we  find  these  various  functions 
taken  over  by  different  organs  which  become  perfected 
along  one  special  line,  at  the  same  time  losing  the  ability 
to  do  other  things.  This  process  is  called  the  physio- 
logical division  of  labor,  and  it  is  quite  analogous  to  the 


152  ANIMAL  BIOLOGY 

division  of  labor  in  human  society.  If  everyone  were  a 
jack  of  all  trades  we  should  not  be  able  to  get  on  as  well 
or  have  as  many  different  things  we  want,  as  when  dif- 
ferent people  make  different  articles  and  exchange  their 
products.  Society  profits  by  specialized  labor  and  there  is 
every  reason  to  believe  that  individual  organisms  do  the 
same. 


CHAPTER  XVII 

THE  LOWEST  VERTEBRATES  AND  THEIR 
NEAREST  ALLIES 

The  various  groups  of  animals  thus  far  studied  are  col- 
lectively known  as  the  Invertebrates  on  account  of  the  ab- 
sence of  a  vertebral  column  or  back  bone.  We  now  pass 
to  the  Vertebrates  in  which  a  vertebral  column  is  one  of  the 
most  characteristic  features  of  structure.  In  any  verte- 
brate such  as  a  fish,  frog,  bird,  or  horse  we  find  that  there 
are  several  fundamental  characters  which  are  very  differ- 
ent from  those  prevailing  among  the  in- 
vertebrates; the  central  nervous  system  is 
dorsal  in  position,  the  heart  lies  below 
(ventral  to)  the  alimentary  canal  instead 
of  above  it;  and  the  skeleton  is  an  inter- 
nal one,  although  in  some  vertebrates  as 
in  turtles,  an  outer  skeleton  may  be  FIG.  124.— A 

i  tunicate. 

present  also. 

While  most  animals  may  be  classed  without  hesitation 
as  vertebrate  or  invertebrate  there  are  a  few  of  more  or 
less  intermediate  position.  Some  of  these  are  so  different 
in  appearance  from  the  true  vertebrates  that  their  re- 
lationship to  the  latter  would  never  be  suspected  upon 
ordinary  observation.  Such  is  the  case,  for  instance, 
with  the  tunicates  or  "sea-squirts."  Most  of  these 
animals  are  sac-like  creatures  living  attached  to  rocks  and 
sea-weed,  and  they  derive  the  name  " sea-squirt"  from 
their  habit  of  squirting  out  water  when  they  are  irritated; 

153 


154  ANIMAL  BIOLOGY 

the  .term  tunicate  refers  to  the  usually  tough  tunic  or 
covering  which  envelopes  the  body.  When  the  develop- 
ment of  these  animals  came  to  be  studied,  the  surprising 
fact  was  revealed  that  the  early  embryonic  stages  strik- 
ingly resemble  the  corresponding  stages  of  vertebrate 
animals,  and  it  was  found  also  that  in  the  larval  period  of 
the  tunicate  there  is  a  dorsal  nerve  cord,  gill-slits  which 
open  from  the  pharynx  to  the  outside  like  those  of  fishes, 


FIG.  125. — Internal  structure  of  a  tunicate.  A,  point  of  attachment; 
BC,  branchial  or  gill  chamber  into  which  water  enters  through  the  orifice 
shown  in  the  upper  part  of  the  figure.  After  passing  through  the  numer- 
ous gill  slits  in  the  wall  of  this  chamber  the  water  is  discharged  through  the 
orifice  shown  at  the  right  of  the  figure;  H,  heart;  /,  intestine.  (After 
Herdman.) 

a  ventral  heart,  and  a  notochord,  or  rod-like  structure 
which  corresponds  to  the  primitive  spinal  column  of  the 
vertebrates.  The  tunicate  larva  is  a  free-swimming 
animal  possessing  the  essential  features  of  vertebrate 
structure.  Sooner  or  later  the  larva  settles  down  and 
becomes  attached  by  its  head;  the  tail  is  resorbed,  and  a 
complex  metamorphosis  ensues  in  which  most  of  the 
vertebrate  characters  are  either  lost  or  much  obscured. 
The  adult  tunicate  is  a  degenerate  animal,  and  were  it 


THE   LOWEST  VERTEBRATES  155 

not  for  our  knowledge  of  its  early  stages  its  real  relation- 
ship to  the  vertebrates  would  not  be  apparent.  As  in 
the  barnacles,  and  especially  such  degenerate  forms  as 
Sacculina,  the  clue  to  the  real  affinities  of  these  animals 
was  first  revealed  through  a  study  of  development. 

There  is  another  group  represented  by  Balanoglossus 
and  a  few  related  genera  which  also  show  relationships 
to  the  vertebrates.  Balanoglossus  is  a  worm-like  animal 
which  burrows  in  the  mud  of  the  sea  bottom  by  means  of 
a  muscular  proboscis.  In  the  anterior  part  of  the  body 
there  are  a  number  of  gill-slits  which  lead  from  the  pharynx 
to  the  outside  and  serve  for  the  exit  of  water  taken  in 
through  the  mouth.  There  is  a  dorsal  nerve  cord  and  a 
structure  dorsal  to  the  pharynx  which  is  regarded  as  repre- 
senting the  notochord.  Balanoglossus  also  resembles 
the  vertebrates  in  many  features  of  its  early  development, 
but  its  relationship  is  much  less  close  than  that  of  the 
tunicates. 

In  the  lancelet,  or  Amphioxus,  the  vertebrate  characters 
are  much  more  conspicuous.  This  animal,  which  Pro- 
fessor Haeckel  has  called  the  most  interesting  vertebrate 
next  to  man,  has  a  narrow,  laterally  flattened  body  taper- 
ing toward  both  ends.  It  lives  in  the  sea  partly  buried  in 
the  sand  in  which  it  can  burrow,  when  disturbed,  with 
remarkable  quickness.  Like  the  tunicates  its  food  con- 
sists of  small  bodies  swept  into  the  alimentary  canal 
by  means  of  cilia.  The  water  that  is  taken  into  the  mouth 
passes  out  through  numerous  fine  gill-slits  in  the  wall  of 
the  pharynx,  while  the  solid  particles  are  retained  and 
swept  by  ciliary  action  into  the  intestine.  The  backbone 
is  represented  by  a  firm  rod-shaped  notochord  extending 
above  the  alimentary  canal.  Dorsal  to  the  notochord  lies 
the  nerve  cord,  the  anterior  end  of  which  is  slightly  en- 
larged to  form  a  sort  of  brain.  This  nerve  cord  corre- 


156  ANIMAL  BIOLOGY 

spends  to  both  the  brain  and  spinal  cord  in  ourselves; 
but  how  remarkably  simple  is  the  brain  in  this  low  crea- 
ture compared  with  the  brain  of  even  a  fish  or  a  frog !  A 
pigment  spot  in  the  wall  of  the  brain  marks  the  position 
of  a  rudimentary  eye.  The  heart  is  represented  by  a 
tubular  blood  vessel  on  the  ventral  side  which  propels  the 
blood  forward;  the  blood  then  flows  through  the  vessels 
in  the  gills,  where  respiration  is  effected  and  then  back- 
ward in  a  dorsal  vessel. 

Although  Amphioxus  has  no  limbs  or  skull  and  but  a 
suggestion  of  a  brain  its  vertebrate  characters  are  un- 
doubted, and  it  matters  little  whether  it  is  classed  just 
within  or  just  without  the  vertebrate  group  so  long  as  we 
recognize  its  affinities.  It  is  now  customary  to  group  the 


FIG.  126. — Amphioxus;  c,  nerve  cord;  gs,  gill  slits;  i,  intestine;  /,  liver; 
m,  mouth;  n,  notochord. 

vertebrates,  Amphioxus,  the  tunicates,  Balanoglossus 
and  a  few  other  forms  in  a  large  phylum  called  Chordata, 
the  members  of  which  all  possess  a  notochord  at  some 
period  of  their  life  history.  From  what  group  of  the 
invertebrates  the  chordates  took  their  origin  is  a  question 
to  which  the  few  intermediate  groups  which  now  exist  do 
not  enable  us  to  give  a  certain  answer. 

The  lowest  true  vertebrates,  if  we  except  Amphioxus, 
are  found  in  the  class  of  Cyclostomes,  or  round  mouths, 
which  include  the  lampreys  and  the  hag-fishes.  These 
animals  have  long  eel-like  bodies  without  any  traces  of 
limbs.  There  is  a  cartilaginous  skull  enclosing  a  well 


THE   LOWEST  VERTEBRATES  157 

developed  brain  and  a  notochord  which  is  not  segmented. 
The  gills  lie  in  pouches,  and  the  water  passes  out  through 
one  or  more  pairs  of  apertures  in  the  sides  of  the  body. 

Most  of  the  cyclostomes  live  upon  other  fishes  to  which 
they  attach  themselves  by  a  sucker-like  mouth  which  is 
furnished  with  a  rasping  apparatus  for  abrading  the  flesh. 
The  lampreys  are  mostly  fresh-water  forms  and  the  few 
marine  species  migrate  up  rivers  to  breed,  the  eggs  of 
several  species  being  deposited  in  rude  nests  constructed 
out  of  small  stones.  The  hag-fishes  are  marine;  often 
they  bore  through  the  body  walls  of  fishes  and  devour 
most  of  the  internal  flesh. 


FIG.   127. — A  brook  lamprey.     (Modified  from  Gage.) 

The  vertebrates,  in  the  most  restricted  sense  of  the  term, 
comprise  the  generally  recognized  classes  of  Cyclostomes, 
Fishes,  Amphibians  or  Batrachia^is,  Reptiles,  Birds  and 
Mammals.  Originally  the  vertebrates  were  aquatic 
animals  breathing  by  means  of  gills,  and  the  lowest  classes, 
the  cyclostomes  and  fishes,  still  retain  the  ancient  habit  of 
living  in  the  water.  The  Amphibians,  as  the  name  im- 
plies (amphi,  both  and  bios,  life)  live  both  in  water  and  on 
land,  the  more  fish-like  members  being  aquatic  gill- 
breathers,  while  the  higher  amphibians,  such  as  frogs  and 
toads,  live  upon  land;  but  even  these  tend  to  remain  near 
the  water  or  at  least  in  moist  surroundings.  The  reptiles, 
birds  and  mammals  have  become  primarily  terrestrial 
animals. 


CHAPTER  XVIII 
THE  FISHES 

In  treating  of  fishes  we  shall  describe  first  a  typical  fish 
such  as  a  perch,  sunfish,  trout  or  bass,  some  one  of  which 
is  easily  obtainable  in  almost  every  locality.  One  notable 
feature  of  the  organization  of  the  fish  is  the  adaptation  of 
the  form  of  its  body  for  gliding  through  the  water  with  the 
least  amount  of  resistance.  The  posterior  part  of  the 
body  tapers  into  a  thin,  vertical  tail  fin  which  is  expanded 
to  give  it  a  broad  purchase  against  the  water  and  it  is 
strengthened  by  a  number  of  long,  flexible  rays.  The  tail 


Pel 


FIG.  128. — A  typical  fish.     A,  anal  fin;  c,  caudal  or  tail  fin;  D,  dorsal  fin; 
N,  nostril;  Op,  operculum;  Pec,  pectoral  fin;  Pel,  pelvic*  fin. 

is  the  principal  organ  of  locomotion  in  the  fish  and  the 
bulk  of  the  muscle  of  the  body  is  used  in  effecting  the  to 
and  fro  movement  of  this  organ,  which  results  in  propelling 
the  animal  forward.  As  in  most  vertebrates  a  typical 
fish  has  four  paired  limbs  represented  by  the  anterior,  or 
pectoral,  and  the  posterior,  or  pelvic,  fins.  These,  like  the 
tail  fins,  are  thin,  flattened  organs  strengthened  by  means 
of  rays.  While  the  lateral  or  paired  fins  may  aid  in  swim- 
ming forward,  their  main  uses  are  to  keep  the  body  in  a 

158 


THE   FISHES  159 

state  of  balance  and  to  change  the  direction  of  movement. 
There  are  also  median  fins  consisting  of  one  or  more  dorsal 
fins  above,  and  an  anal  fin  on  the  lower  side.  In  addition 
to  the  flexible  and  frequently  branched  rays,  the  fins 
may  be  strengthened  by  sharper  and  more  rigid  spines 
which  serve  also  as  organs  of  defense.  Many  fish  erect 
these  spines  when  angry  or  in  danger. 

The  surface  of  the  body  is  covered  by  hard  scales  which 
overlap  so  as  to  form  a  uniform  protective  layer.  The 
scales  are  embedded  in  the  skin  and  grow  with  the  growth 
of  the  fish.  Looked  at  through  the  microscope  they  show 
a  series  of  concentric  lines  indicating  successive  stages 
of  growth.  In  some  kinds  of  fish  (catfish)  the  scales  may 
be  absent,  while  in  others,  such  as  the  gar  pike,  they  may 
be  large  and  very  hard,  forming  a  veritable  coat  of  mail. 

On  the  head  of  the  fish  the  large  eyes  are  noteworthy 
on  account  of  the  lack  of  eye-lids,  so  that  they  are  per- 
manently "open."  The  nostrils,  of  which  there  may  be 
two  pairs  in  some  fishes,  do  not  open  into  the  mouth  cavity 
as  they  do  in  higher  vertebrates,  but  they  lead  to  the  or- 
gans of  smell.  At  the  side  of  the  head  is  a  large  flap,  the 
operculum,  which  covers  over  the  gills.  The  jaws  of  the 
fish  are  quite  different  from  our  own  in  that  the  upper  jaw 
is  movable  instead  of  being  firmly  united  to  the  skull. 
The  jaws  are  furnished  with  sharp,  conical  teeth  which  are 
fitted  for  seizing  and  retaining  prey;  for  the  fish  does  not 
take  time  to  chew  its  food,  but  swallows  it  entire.  Teeth 
are  frequently  present  also  on  the  roof  of  the  mouth,  and 
in  some  fishes  in  other  parts  of  the  mouth  cavity  and  even 
in  the  throat.  Back  of  the  mouth  is  the  pharynx,  the  lat- 
eral walls  of  which  are  perforated  by  four  pairs  of  gill-* 
slits,  between  which  lie  the  rows  of  slender,  red  filaments 
which  constitute  the  gills.  Water  is  taken  into  the  mouth, 
passed  through  the  gill-slits,  bathing  the  gill  filaments  on 


160  ANIMAL  BIOLOGY 

its  way,  and  then  is  forced  out  behind  the  edge  of  the  op- 
erculum.  The  more  or  less  regular  movements  of  the  jaws 
and  operculum  have  to  do  with  taking  in  water  and  forcing 
it  out  past  the  organs  of  respiration. 

All  of  the  fishes  mentioned  above  have  a  bony  skeleton 
composed  of  a  large  number  of  separate  bones.  There  is 
a  complex  skull  consisting  of  the  cranium,  or  brain  case, 
the  jaw  bones  and  their  supports,  and  various  other  parts. 
Joined  to  the  hind  end  of  the  skull  is  the  vertebral  column 
consisting  of  numerous  bi-concave  vertebrae;  each  ver- 
tebra has  a  dorsal  arch,  covering  the  spinal  cord,  and  many 
of  the  anterior  vertebrae  are  connected  below  with  ribs 
which  partially  surround  the  body  cavity.  The  rays  of 
the  pectoral  and  pelvic  fins  are  joined  to  bony  frameworks 
called  respectively  the  pectoral  and  pelvic  arches. 

One  of  the  most  peculiar  of  the  internal  organs  is  the  so- 
called  swimming  bladder,  or  "air  bladder,"  which  lies 
in  the  upper  part  of  the  body  cavity.  This  organ  is  filled 
with  gas  secreted  by  the  fish  and  serves  as  a  sort  of  float. 
In  some  species  this  air  bladder  communicates  by  a  duct 
with  the  esophagus.  Among  the  lung  fishes  (Dipnoi) 
the  walls  of  this  body  are  well  supplied  with  blood  vessels 
and  subserve  the  function  of  respiration. 

Most  of  the  bony  fishes  produce  a  large  number  of  eggs. 
During  the  egg-laying  period  the  females  are  usually 
accompanied  by  the  males  and  when  the  eggs  are  extruded 
the  males  discharge  their  sperm,  or  "milt,"  over  them 
and  thus  effect  their  fertilization.  In  the  breeding  season 
the  males  of  many  species,  such  as  our  common  sunfishes, 
are  more  brilliantly  colored  than  at  other  times,  and  dis- 
play themselves  before  the  females  in  a  manner  that  sug- 
gests courtship  similar  to  that  practised  by  the  males  of 
many  birds.  It  is  a  common  practice  among  fishes  to 
lay  their  eggs  more  or  less  indiscriminately  and  then, 


THE   FISHES 


161 


after  they  are  fertilized,  to  leave  them  to  their  fate.  Many 
marine  fishes  like  the  flounders  lay  eggs  that  float  on  the 
surface  and  are  protected  from  their  enemies  by  their 
remarkable  transparency.  Some  species  make  nests  for 
receiving  the  eggs;  it  is  usually  the  male  which  performs 
this  task. 

In  the  common  dogfish,  or  Amia,  of  our  lakes  and 
streams  the  male  constructs  a  rude  nest  by  pushing  about 
some  stones  on  the  bottom  and  then  induces  a  female  to 
enter  the  nest  where  she  deposits  her  eggs  or,  in  the  lan- 


FIG.  129. — Showing  the  nest  of  a  horned  dace  with  the  male  and 
female  fish  on  the  nest.  The  stream  flows  in  the  direction  indicated  by 
the  arrows.  (After  Reighard.) 

guage  of  fishermen,  "  spawns. "  The  male  after  fertilizing 
the  eggs  stands  guard  over  them  and  rushes  out  to  attack 
any  other  fish  that  ventures  too  near  the  sacred  premises. 
Even  after  the  eggs  hatch,  the  male  accompanies  the  young 
brood  until  they  begin  to  scatter  and  shift  for  themselves. 
The  male  of  the  common  stickleback  constructs  a  more 
elaborate  nest  out  of  sticks  and  bits  of  grass  and  weeds. 
The  males  are  irascible  little  creatures  and  defend  the 
nest  with  much  valor.  In  certain  marine  catfishes  the 
male  protects  the  eggs  by  carrying  them  in  his  mouth. 

Those  fishes  which  simply  lay  their  eggs  in  the  water  with- 
11 


1 62  ANIMAL  BIOLOGY 

out  further  care  are  frequently  compelled  to  produce 
enormous  numbers  of  eggs  to  make  good  the  great  loss 
due  to  lack  of  protection.  The  forms  which  lay  their 
eggs  in  nests  or  guard  them  after  they  are  laid  lay  com- 
paratively few  eggs. 

Some  fishes  make  extensive  journeys  before  depositing 
their  eggs.  The  Columbia  River  salmon  during  the  spring 
of  the  year  leaves  the  ocean,  where  it  spends  a  great  part 
of  its  life,  and  entering  the  mouth  of  a  river  quickly  swims 
up  stream.  In  the  beginning  of  their  journey  the  fish 
are  well  fed  and  full  of  vigor ;  they  require  all  their  stored-up 


FIG.   130. — Quinnat  salmon.     (From  the  Report  of  the  Calif.  Fish  and 
Game  Commission.) 

supply  of  energy,  since  they  take  no  food  after  entering 
the  fresh  water.  When  the  salmon  are  "running,"  the 
water  may  be  densely  crowded  with  them,  and  the  fisher- 
men whose  canneries  line  the  banks  of  the  Columbia 
River  reap  a  rich  harvest,  for  they  have  their  nets  spread 
for  the  unwary  travellers  and  haul  them  in  by  hundreds 
of  tons.  Those  fortunate  enough  to  escape  being  made 
up  into  canned  salmon,  press  on  through  rapids  and  often 
leap  over  low  falls  until  they  reach  the  smaller  tributaries 
of  the  stream,  in  many  cases  over  one  thousand  miles 


THE   FISHES 


I63 


trom  its  mouth.  During  their  course  the  males  become 
lean  and  battered,  and  they  acquire  a  peculiar  lengthening 
of  the  lower  jaw  and  an  increased  development  of  teeth 
which  are  of  value  in  their  frequent  combats  with  others 
of  their  own  sex.  When  the  fishes  finally  arrive  at  a  suita- 
ble breeding  place  in  some  shallow  stream,  the  eggs  are 
laid  and  fertilized,  after  which  the  life  of  the  parent  fish 
is  short.  Thenceforth,  the  mission  of  their  long  and  peril- 
ous journey  accomplished,  they  live  only  in  their  posterity. 


FIG.   131. — Stripping  fish  to  obtain  the  eggs. 

The  young  salmon  gradually  works  down  stream,  grow- 
ing in  the  meantime  from  its  diet  of  worms,  flies  and  other 
small  creatures,  and  finally  reaches  the  ocean  where  it 
lives  until  it  in  turn  comes  to  obey  the  mysterious  call  to 
enter  the  river  and  sacrifice  itself  for  the  perpetuation 
of  the  species. 

The  migration  of  the  common  eel  Anguilla  is  the  reverse 
of  that  of  the  salmon,  for  the  adults  go  down  the  rivers 
to  breed  in  the  ocean  and  the  young  migrate  up  the  streams 
and  live  for  most  of  their  lives  in  fresh  water. 

As  the  eggs  of  nearly  all  food  fishes  are  fertilized  outside 


164  ANIMAL  BIOLOGY 

of  the  body,  advantage  is  taken  of  this  fact  in  the  arti- 
ficial propagation  of  many  of  the  more  valuable  species. 
The  United  States  government  and  various  states  support 
fish  hatcheries  where  young  fishes  are  reared  and  then  let 
loose,  to  replenish,  so  far  as  possible,  the  numbers  taken 
by  fishermen.  To  obtain  the  eggs  a  ripe  female  is  taken 
in  the  hands  and  "stripped"  by  slowly  compressing  the  fish 
from  before  backward,  thus  forcing  the  eggs  out  of  the 
body.  The  sperm,  or  milt,  of  the  male,  which  is  obtained 
in  a  similar  manner,  is  mixed  with  the  water  containing  the 
eggs  and  causes  them  to  be  fertilized.  The  eggs  undergo 


FIG.   132. — A  shark,  Squalus  acanthias.     (After  Dean.) 

their  development  in  specially  prepared  receptacles  and 
the  young  are  set  adrift.  Through  the  fish  commis- 
sions, various  lakes  and  streams  are  stocked  with  desired 
species,  sometimes  by  introducing  the  eggs,  in  other  cases 
by  transferring  the  mature  fish. 

Fishes  may  be  divided  into  three  sub-classes:  the 
Elasmobranchs,  or  cartilaginous  fishes;  the  Teleostomi, 
or  bony  fishes;  and  the  Dipnoi,  or  lung  fishes.  In  the 
elasmobranchs  which  are  represented  by  sharks,  skates, 
rays,  etc.,  the  skeleton  is  composed  of  cartilage,  the  gill- 
slits  open  directly  to  the  outside  instead  of  being  covered 
by  an  operculum,  and  the  tail  fin  is  typically  asymmetrical, 
or  heterocercal.  The  mouth  and  usually  the  nostrils  are 
situated  on  the  ventral  surface  of  the  head,  and  the  body 


THE   FISHES 


I6S 


is  commonly  covered  with  placoid  scales  which  are  pecu- 
liar in  having  a  sort  of  prominence,  or  denticle  situated 
upon  a  flattened  base.  Various  transitions  between  these 
scales  and  teeth  can  be  traced  in  some  forms,  so  that  we 
may  regard  teeth  and  scales  as  corresponding  or  homolo- 
gous organs. 

The  elasmobranchs  with  a  single  exception  are  all  marine 
and  carnivorous.     The  sharks  are,  as  a  rule,  active,  preda- 


FIG.   133. — A  skate. 

tory  animals  feeding  mostly  upon  other  fishes.  The  whale 
shark  Rhinodon  may  reach  a  length  of  40-50  feet  and  the 
large,  white,  man-eating  shark,  Carcharias,  25  feet. 
In  the  skates  and  rays  the  body  is  remarkably  flattened, 
and  adapted  to  living  on  the  bottom  where  the  animals 
feed  mainly  upon  shell-fish  and  crustaceans.  In  the  sting- 
rays there  is  a  pointed  spine  near  the  base  of  the  tail,  which 


1 66  ANIMAL  BIOLOGY 

is  capable  of  inflicting  a  painful  wound.  The  torpedo 
which  is  allied  to  the  rays  is  remarkable  in  possessing  a 
highly  developed  electric  organ  which  may  give  rise  to 
very  severe  electric  shocks. 

Most  of  the  elasmobranchs  lay  large,  yolk-laden  eggs 
which  are  fertilized  before  they  are  laid.  In  many  cases 
these  hatch  within  the  body  of  the  mother  so  that  the 
young  are  brought  forth  alive,  but  in  some  forms  the  eggs 
are  enclosed  in  a  horny  shell,  which  is  sometimes  drawn 


FIG.   134. — Lepomis    punctatus.      Chinquapin    perch. 

out  at  the  two  ends  into  four  cords  by  means  of  which 
they  become  attached  to  sea-weeds. 

The  Teleostomi  include  the  fishes  with  a  more  or  less 
bony  skeleton.  The  gill-slits  are  covered  by  an  opercu- 
lum  and  the  body  is  generally  covered  with  flattened  scales. 
The  most  primitive  of  these  are  the  ganoids  which  in 
early  periods  of  the  earth's  history  constituted  a  large 
and  flourishing  group.  Now  they  are  represented  by  a 
comparatively  few  forms,  a  large  proportion  of  which  are 
found  in  the  fresh  waters  of  North  America.  The  large 
sturgeon  of  our  lakes  and  rivers  whose  ovaries  are  sold 
as  caviar;  the  slender,  hard  scaled  gar  pike;  and  the  dog 


THE    FISHES  lj 

fish,  Amia,  are  some  of  the  better  known  representatives 
of  this  ancient  group. 

The  largest  of  the  two  divisions  of  the  bony  fishes,  the 
teleosts,  includes  the  common  fishes,  such  as  cod,  mackerel, 
perch,  bass,  minnows,  catfish,  eels,  etc.— a  vast  and  varied 
assemblage  occurring  in  fresh  water  and  in  the  sea,  at  all 
depths,  and  in  all  regions.  They  present  almost  every 
conceivable  modification  of  structure  consistent  with 
remaining  fishes,  for  what  could  be  more  diverse  than  the 


FIG.   135. — Antennarius  avalonis.      (After  Jordan.) 

puffy  globe-fish,  the  grotesque  sea-horse,  the  thread-like 
pipe-fish,  the  large  headed  "  angler,"  and  the  almost 
impossible  freaks  of  fish  structure  found  in  some  of  the 
denizens  of  the  deep  sea?  Even  a  superficial  treatment  of 
these  varied  forms  would  require  a  whole  volume  and  a 
large  one  at  that. 

The  third  sub-class  of  fishes,  the  Dipnoi  or  lung  fishes, 
are  represented,  like  the  ganoids,  by  only  a  few  scattered 
remnants  of  a  once  more  numerous  group.  In  these  forms 
the  air  bladder  communicates  with  the  ventral  side  of  the 
esophagus  and  functions  as  an  organ  for  breathing  air, 
although  these  fishes  also  breathe  by  means  of  gills.  The 


1 68  ANIMAL  BIOLOGY 

air  bladder  of  fishes  is  frequently  regarded  as  homologous 
with  the  lungs  of  higher  vertebrates,  and  in  the  Dipnoi 


FIG.  136. — Protopterus  annectens,  lung  fish.     (From  Boas.) 

the  air  bladder  approaches  more  closely  to  the  structure 
and  function  of  true  lungs  than  in  any  other  group  of 
fishes. 


FIG.  137. — Flying  fish.     (After  Jordan.) 


CHAPTER    XIX 

THE   AMPHIBIA    (FROGS,   TOADS,  NEWTS  AND 
SALAMANDERS) 

The  Amphibians  or  Batrachians,  as  a  class,  show  a  cer- 
tain proclivity  for  living  in  or  near  the  water,  and  in  almost 
all  cases  where  species,  as  in  frogs  and  toads,  have  taken 
to  living  on  land  they  return  to  their  ancient  aquatic 
habitat  to  breed.  In  general  the  amphibians  have  a 
smooth  skin  devoid  of  scales  or  armor,  and  furnished  with 
numerous  mucous  or  slime  glands  which,  in  terrestrial 
species,  serve  to  keep  the  skin  constantly  moist.  The 
limbs  in  the  amphibia  are  very  different  from  those 
of  fishes  in  that  they  are  typically  of  the  five-toed  type 
and  fitted  for  walking  or  leaping,  like  those  of  higher 
vertebrates. 

The  amphibians  at  present  existing  on  the  earth  may  be 
divided  into  three  groups,  the  Urodeles  or  tailed  am- 
phibians (newts,  salamanders,  etc.),  the  Anura,  or  tailless 
forms  (frogs,  toads),  and  the  Ccecilians  which  comprise  a 
few  legless  worm-like  species  living  in  warm  climates. 
In  some  of  the  lowest  of  the  tailed  amphibians  we  meet 
with  many  interesting  fish-like  characters  such  as  the 
possession  throughout  life  of  external  gills.  These  forms 
naturally  live  permanently  in  the  water,  although  they  are 
generally  furnished  also  with  lungs  for  breathing  air. 
The  mud-puppy,  Necturus,  is  one  of  these  primitive  forms 
which  is  not  uncommon  in  lakes  and  streams  of  the  north- 
eastern United  States.  Another  is  the  peculiar  Proteus 

169 


170  ANIMAL  BIOLOGY 

anguinus  which  lives  in  dark  caves  in  Austria.  Like 
many  other  cave  animals  it  has  become  entirely  blind  and 
the  body  has  lost  nearly  all  of  its  pigment. 

Most  of  the  higher  tailed  amphibians,  such  as  the 
tritons,  newts  and  salamanders,  do  not  have  gills  in  the 
adult  state,  although  gills  are  usually  present  in  the  young. 
Some  species  live  in  the  water  and  some  on  the  land. 
Of  the  land  forms  the  European  spotted  salamander  is 
remarkable  for  its  conspicuous  colors.  The  skin  of  this 
animal  secretes  a  very  poisonous,  milky  fluid  which  affords 
it  a  sufficient  protection,  since  most  animals  which  live  in 
the  same  region  know  that  the  spotted  salamander  is  some- 
thing to  be  left  alone.  Its  conspicuous  colors  are  supposed 
to  be  of  value  in  enabling  it  to  be  easily  recognized  and 
therefore  in  preventing  it  from  being  molested.  Such 
colors  are  commonly  called  " warning  colors"  and  they  are 
not  infrequent  in  animals  which  are  poisonous  or  distasteful. 
Some  of  the  Urodeles,  such  as  Triton,  can  regenerate 
missing  legs  or  tail,  or  even  the  eye,  but  in  the  frogs  and 
toads  this  power  is  very  limited. 

The  tailless  amphibians,  or  Anura,  comprise  the  most 
highly  developed  amphibians.  They  are  generally  found 
on  the  land,  but  in  most  cases  they  lay  their  eggs  in  the 
water  and  the  young  hatch  as  tadpoles  which  resemble 
the  most  primitive  urodeles  in  having  external  gills  and 
well-developed  tails.  The  series  of  forms  which  we  meet 
in  passing  from  the  lowest  to  the  highest  Amphibia  is 
roughly  similar  to  the  stages  passed  through  in  the  devel- 
opment of  an  individual  frog  or  toad. 

The  breeding  season  of  frogs  and  toads  is  in  the  spring 
when  the  animals  repair  to  the  water  to  deposit  their 
eggs.  The  eggs  laid  are  surrounded  by  a  transparent 
jelly  which  affords  them  a  certain  protection.  During  the 
breeding  season  the  females  are  clasped  by  the  males  which 


THE    AMPHIBIA  171 

eject  their  sperm  over  the  egg  masses  as  soon  as  they  are 
extruded  from  the  body  of  the  female.  The  eggs  once 
laid  and  fertilized,  the  frogs  leave  the  water  and  resume 
their  active  predatory  life.  The  long  months  of  hiberna- 
tion, when  life  was  supported  only  by  the  food  materials 
stored  up  in  the  tissues,  leave  the  frogs  lean  and  hungry, 
especially  after  the  additional  burden  of  maturing  the  re- 
productive cells.  Life  in  the  winter  except  in  warm  cli- 
mates is  spent  in  a  dormant  state,  when  the  temperature  of 
the  body  runs  down  and  the  vital  activities  become  very 
sluggish.  Frogs  which  are  partially  frozen  until  their 
legs  are  so  brittle  that  they  can  be  broken  like  icicles  may 
subsequently  revive,  provided  they  are  very  slowly  thawed 
out;  if,  however,  they  are  frozen  solid  throughout  they 
never  regain  life. 

It  is  in  the  spring  that  the  frogs  make  the  most  music. 
Ordinarily  it  is  the  males  that  do  the  croaking  and  it  is 
supposed  that  the  voice  serves  as  a  call,  like  the  chirping 
of  the  male  cricket,  for  bringing  the  sexes  together. 
In  some  frogs  the  males  have  a  pair  of  vocal  sacs  opening 
into  the  throat,  which  become  inflated  during  the  act  of 
croaking.  In  others,  as  in  the  tree  frogs,  the  production 
of  sound  is  accompanied  by  a  distension  of  the  floor  of 
the  throat.  The  male  toad  produces  only  a  relatively 
faint  but  peculiarly  musical  trill. 

Frogs  and  toads  are  not  particularly  choice  of  what  they 
eat,  as  they  devour  all  sorts  of  insects,  worms  and  other 
small  creatures,  but  they  are  very  peculiar  in  their  methods 
of  food  taking.  They  are  furnished  with  an  extensile 
tongue  which  is  joined  to  the  front  of  the  lower  jaw  and  is 
capable  of  being  thrust  out  of  the  mouth  and  withdrawn 
again  with  great  quickness.  Should  an  insect  or  worm  be 
moving  near  by,  the  tongue  may  be  shot  out  and  the  prey 
drawn  back  into  the  mouth,  and  quickly  swallowed.  It 


172  ANIMAL  BIOLOGY 

is  only  moving  objects  that  attract  frogs  or  toads,  for  they 
will  go  hungry  in  the  midst  of  plenty  unless  some  motion 
induces  them  to  respond. 

Frogs  never  drink  as  higher  animals  do  but  they  ob- 
tain water  .by  absorption  through  the  skin.  They  lose 
water  very  rapidly  by  evaporation  when  kept  in  a  dry 
atmosphere  and  present  a  much  shrivelled  appearance, 
but  if  placed  in  water  again  they  soon  become  plump. 
Dryness  is  soon  fatal  to  frogs  and  toads  and  they  conse- 
quently rarely  venture  far  from  water,  or  at  least  they 
seek  a  moist  retreat.  The  skin  of  these  animals  is  an  im- 
portant organ  of  respiration  as  well  as  of  absorption. 
While  under  ordinary  circumstances  respiration  is  carried 
on  by  both  lungs  and  skin,  skin  respiration  alone  may  suffice 
to  maintain  life  if  the  animal  is  at  a  low  temperature. 
Frogs  often  bury  themselves  in  the  mud  at  the  bottom  of 
ponds  during  the  winter  when  respiration  is  naturally 
carried  on  through  the  skin  alone. 

Frogs  (Ranidae)  are  found  in  nearly  all  countries 
of  the  globe  except  in  the  colder  latitudes  where  they  can- 
not escape  being  frozen  in  the  winter.  The  most  common 
of  our  many  North  American  species  is  the  leopard  frog, 
Rana  pipiens,  which  ranges  over  a  large  part  of  the  middle 
and  eastern  sections  of  the  United  States.  Our  largest 
species  is  the  bull-frog,  Rana  catesbiana  whose  very  hoarse 
croak  resembles  the  roaring  of  a  bull.  It  is  generally 
found  in  or  near  water  and  has  been  sought  so  much  for 
food  that  it  has  been  very  much  reduced  in  numbers  and 
is  practically  extinct  in  many  regions  where  it  was  once 
abundant. 

Toads  (Bufonidae)  are  generally  more  terrestrial  in 
habit  than  frogs.  The  rough  warty  appearance  of  their 
skin  is  due  to  the  development  of  large  poison  glands 
whose  secretion  is  quite  irritating  to  sensitive  surfaces. 


THE   AMPHIBIA 


173 


There  is  no  foundation,  however,  for  the  superstition  that 
handling  toads  produces  warts,  for  they  can  be  handled 
with  perfect  safety.  Few  animals  are  more  useful  to  the 
farmer  or  gardener  than  these  humble  creatures  for  they 
devour  large  quantities  of  injurious  insects  which  they 
catch  during  their  nocturnal  wanderings.  Kirkland  has 
estimated  that  in  a  farming  section  in  Massachusetts 


FIG.  138.— The  bullfrog.     (After  Needham.) 

every  toad  is  worth  several  dollars  on  account  of  the  cut- 
worms alone,  which  it  devours  in  a  single  season.  For 
some  reason  many  persons  indulge  in  the  repulsive  pro- 
clivity of  killing  all  the  toads  they  meet  with.  Such  con- 
duct is  not  only  foolish  and  cruel,  but  it  is  quite  opposed 
to  their  own  interests.  The  ugliness  of  the  toad  doubtless 
tends  to  make  people  treat  it  with  contempt  but  like  the 


174  ANIMAL  BIOLOGY 

homeliness  of  people  whom  we  come  to  like,  it  becomes 
transformed  upon  closer  acquaintance  into  a  source  of 
positive  pleasure.  Hodge  remarks,  "I  pick  up  a  toad  a 
hundred  times  a  season  just  to  enjoy  looking  at  its  eye, 
a  living,  sparkling,  ever-changing  jewel,  and  his  music  in 
the  springtime  brings  a  pleasure  that  nothing  else  affords." 
Toads  are  easily  kept  in  confinement  and  make  interesting 
pets. 

The  tree  frogs  (Hylidae)  comprise  an  interesting  family 
of  rather  small  frogs  most  of  which  live  a  large  part  of 


FiG.   139. — A   toad,    Bufo    halephilus.      (From    photo    by    Holliger.) 

their  lives  upon  trees.  The  toes  of  most  species  are  tipped 
with  sucker-like  adhesive  pads  which  enable  them  to  climb 
up  vertical  surfaces.  The  family  in  general  is  remarkable 
for  the  extensive  changes  of  color  which  take  place  in  re- 
sponse to  the  environment.  Hyla  versicolor  is  usually  of 
a  bright  green  color  when  among  green  leaves,  a  dull  gray 
or  brown  when  resting  upon  bark,  and  various  interme- 
diate shades  under  other  conditions.  This  ability  to  change 
color  is  to  a  considerable  extent  protective,  and  is  affected 
by  light,  temperature,  rough  or  smooth  contact,  and  a 
variety  of  other  agencies.  Although  not  commonly  seen 
the  tree  frogs  are  very  frequently  heard,  as  the  males  are 


THE    AMPHIBIA  175 

capable  of  making  a  noise  which  seems  absurdly  out  of 
proportion  to  their  diminutive  bodies.  Their  song  is  more 
apt  to  be  made  in  a  moist  atmosphere  and  this  probably 
accounts  for  the  fact  that  it  is  commonly  regarded  as  pro- 
phetic of  rain. 

Nearly  all  the  tailless  amphibians  undergo  a  metamor- 
phosis, the  early  stages  of  which  are  passed  in  the  water. 
In  our  common  frogs  and  toads  the  larva,  or  tadpole,  as 
it  emerges  from  the  jelly  in  which  it  has  passed  its  em- 
bryonic development,  is  furnished  with  three  pairs  of 
external  gills  and  a  flattened  tail  by  which  it  swims 
through  the  water  much  after  the  fashion  of  a  fish.  The 
young  tadpole  lives  mainly  on  aquatic  plants,  although 
it  may  eat  animal  food  also  when  occasion  offers.  As  the 
tadpole  grows,  legs  bud  out;  first  the  hinder  pair  and  later 
the  anterior  ones.  During  the  development  of  the  lungs, 
the  gills  gradually  disappear  and  the  tadpole  frequently 
comes  to  the  surface  for  air.  With  the  growth  of  the  legs 
the  tail  becomes  shorter  and  is  finally  resorbed  into  the 
body.  While  these  changes  are  going  on  the  young  frog 
or  toad,  as  we  may  now  call  it,  gradually  comes  to  move 
about  on  the  land.  Four  or  five  years  are  required  for 
our  common  species  of  frogs  to  become  sufficiently  mature 
to  produce  young,  and  they  may  live  four  or  five  years 
longer  if  they  are  fortunate  enough  to  be  spared  from  their 
many  enemies. 


CHAPTER  XX 
THE  REPTILES 

The  reptiles,  although  commonly  associated  in  the 
popular  mind  with  the  Amphibia,  nevertheless  constitute 
a  very  distinct  class  which  is  really  more  closely  related 
to  the  birds  than  to  any  other  group  of  vertebrate  animals. 
The  reptiles  are  lung  breathers  at  all  periods  of  their  life 
and  never  have  any  gills,  even  in  the  young  state.  The 
body  is  covered  with  scales  or  encased  in  a  bony  armor. 
Living  reptiles  fall  into  the  groups  commonly  designated 
as  Ophidia  (snakes),  Lacertilia  (lizards),  Crocodilia 


FIG.  140. — A  garter  snake.     (After  Van  Denburgh  and  Slevin.) 

(crocodiles   and   alligators),   and   Chelonia    (turtles   and 
tortoises). 

i  In  the  snakes  the  body  has  become  greatly  elongated 
and  very  muscular.  No  limbs  are  present  in  most  snakes, 
but  in  the  pythons  and  boas  there  are  rudiments  of  hind 
limbs  and  the  pelvic  girdle  (see  Fig.  235).  Snakes  are 
regarded  as  in  some  respects  degenerate  animals  which 
have  lost  the  limbs  possessed  by  their  ancestors.  But 
while  they  may  have  lost  certain  organs  they  have  devel- 

176 


THE   REPTILES  1 77 

oped  a  remarkable  degree  of  strength,  quickness  and  effect- 
iveness which  has  enabled  them  to  become  one  of  the 
dominant  groups  of  reptiles.  By  the  winding  movements 
of  the  body,  snakes  can  progress  with  considerable  rapidity, 
and  they  are  especially  adapted  to  making  headway 
through  masses  of  vegetation  which  would  greatly  impede 
the  movements  of  other  animals.  The  large  overlapping 
scales  of  the  ventral  side  of  the  body  with  their  free 
posterior  edges  serve  to  facilitate  forward  movement  by 
catching  in  the  irregularities  of  the  surface  over  which 
the  animal  glides. 

Snakes  are  carnivorous  and  feed  upon  living  animals. 
The  teeth  of  snakes  are  conical  and  adapted  for  seizing 
and  retaining  prey  which  is 
always  swallowed  entire.  The 
jaws  are  especially  adapted  to 
swallowing  large  animals  in 
being  separable  from  the  skull 
at  the  base,  thus  permitting 
a  great  enlargement  of  the  FIG.  141.— Jaws  of  rattlesnake 

thrnst        'srmlrpc    f  r  P>  mi  P»  rvH  Ar    showing  fang,  F,  and  poison  sac, 

equently  p     (After  Weir  Mitchell.) 
swallow  animals  whose  bodies 

are  much  thicker  than  their  own,  and  when  distended  with 
food  they  may  remain  for  several  days  in  a  dormant  con- 
dition while  their  meal  is  undergoing  digestion. 

Periodically  snakes  shed  their  outer  skin  which  usually 
comes  off  in  a  single  piece.  Even  the  covering  of  the 
eyes  is  shed  along  with  the  rest,  these  organs  being  pro- 
tected by  a  transparent  part  of  the  general  skin  instead 
of  eyelids.  While  most  snakes  lay  eggs,  others,  such  as  our 
common  garter-snakes,  bring  forth  their  young  alive. 
Despite  stories  of  snakes  taking  their  young  into 
the  mouth  to  protect  them  from  danger  there  is  almost  no 
care  for  the  young  on  the  part  of  the  parents;  the  young 


12 


178  ANIMAL  BIOLOGY 

are  left  to  shift  for  themselves  which  they  are  abundantly 
able  to  do  upon  their  first  appearance  on  the  stage  of  life. 
Snakes  in  general  are  useful  animals  since  they  destroy 
large  numbers  of  injurious  insects;  they  are  also  enemies 
of  mice,  gophers,  and  other  destructive  small  mammals. 
The  bite  of  most  species  is  scarcely  painful,  although  there 
are  several  forms  which  have  a  well-deserved  reputation 
for  being  dangerous.  The  most  common  of  the  venomous 
snakes  of  North  America  are  the  rattlesnakes  which  are 
provided  with  a  jointed,  horny  rattle  at  the  end  of  the  tail, 
by  which  they  make  their  peculiar  rattling  sound,  when 
disturbed.  This  sound  serves  as  a  warning  which  all 
creatures  that  know  what  it  means  are  only  too  ready  to 
heed;  it  may  be  a  service  to  the  snake  also  in  frightening 
away  larger  animals  that  might  otherwise  trample  upon  it. 
The  poison  of  the  rattlesnake  is  secreted  by  two  large 
glands  whose  ducts  lead  to  the  base  of  a  pair  of  large 
perforated  fangs  through  which  the  poison  is  injected  into 
the  bite. 

The  bite  of  the  rattlesnake  has  frequently  resulted  in 
death,  and  in  all  cases  it  should  receive  prompt  treatment. 
A  tight  bandage  should  first  be  applied  between  the  wound 
and  the  heart  so  as  to  check  the  return  flow  of  blood  in 
the  veins,  and  the  wound  should  be  induced  to  bleed  freely. 
Blood  should  be  sucked  from  the  wound  and  permanga- 
nate of  potash  should  be  administered  either  by  injecting 
a  solution  into  the  wound  or  by  rubbing  in  the  crystals. 
Brandy  and  whisky  have  been  much  over- rated  as  reme- 
dies for  snake  bites,  although  they  may  be  of  value  in 
stimulating  the  heart  action,  for  snake  venom  acts  as  a 
heart  poison. 

The  only  poisonous  snake  in  the  United  States,  except 
those  belonging  to  the  rattlesnake  family  is  the  coral  snake 
of  the  South,  which  is  black  with  seventeen  rings  of  red, 


THE   REPTILES  179 

bordered  with  yellow.  In  the  old  world,  although  there 
are  no  members  of  the  rattlesnake  family,  there  are  many 
other  snakes  which  are  very  dangerous.  The  cobra  of 
India  is  responsible  for  the  death  of  about  twenty  thousand 
persons  a  year. 

The  copperhead  and  the  water  moccasin  are  members  of 
the  same  family  as  the  rattlesnakes,  but  they  have  no 
rattle.  The  former  is  copper  colored  and  lives  mainly 
in  the  mountain  districts  of  the  Southern  States;  the  latter 
is  aquatic  and,  like  the  copperhead,  is  very  poisonous. 

Some  snakes  reach  a  great  size,  such  as  the  boa  con- 
strictor, anaconda  and  the  pythons  some  of  which  attain 
a  length  of  thirty  feet.  These,  while  non-poisonous, 
swallow  large  animals  after  they  have  coiled  about  them 
and  crushed  them  in  their  coils. 

The  lizards  are  mainly  inhabitants  of  warm  climates 
and  lovers  of  dry  places.  There  are  very  few  species  in 
the  northern  or  eastern  states,  but  in  the  arid  regions  of 
the  southwest  they  are  quite  abundant.  As  a  rule  lizards 
are  very  active  creatures,  running  over  the  ground  and 
up  trees  with  surprising  quickness.  On  hot  days  the  liz- 
ard seems  especially  to  enjoy  life,  and  he  basks  in  the  sun- 
shine ever  ready  to  dart  at  some  insect  that  happens  to 
move  in  his  vicinity.  In  most  lizards  the  long  slender 
tail  breaks  off  on  slight  provocation  and  when  an  individ- 
ual is  seized  by  this  organ  it  is  usually  left  in  the  hands 
of  the  enemy,  while  the  animal  makes  its  escape; 
a  new  tail  is  later  regenerated. 

The  chameleons  of  the  old  world  are  lizards  which  are 
capable  of  striking  and  rapid  changes  of  color.  Commonly 
green,  they  may  change  to  brown  and  various  interme- 
diate shades  owing  to  the  modifications  of  the  pigment 
cells  of  the  skin,  as  in  the  tree  frogs.  They  are  frequently 
kept  as  pets.  The  " horned  toads"  of  the  western  states 


180  ANIMAL  BIOLOGY 

are  lizards  with  flattened  bodies  and  short  tails.  Their 
color  resembles  that  of  the  soil.  They  readily  live  in  cap- 
tivity if  fed  upon  the  living  insects.  One  of  the  largest  of 
North  American  lizards  is  the  Gila  (pronounced  heela) 
monster  which  is  found  in  Arizona,  New  Mexico  and  Mexico. 
It  is  heavy,  stocky  animal  and,  unjike  most  lizards, 
usually  sluggish  in  its  habits.  It  is  the  only  North  Ameri- 
can lizard  whose  bite  is  poisonous,  the  venom  being 
conveyed  to  the  wound  by  grooves  in  a  pair  of  large 
teeth. 

There  are  some  lizards  which  have  lost  their  legs,  like  the 
Ccecilians  among  the  Amphibia,  and  they  are  frequently 


FIG.   142. — Horned  toad,   Phrynosoma   blainvillei.     (After   Bryant.) 

therefore  mistaken  for  snakes.  Such  is  the  case  with 
the  so-called  joint-snake  or  glass-snake  which  receives 
its  name  from  the  fact  that  its  tail  is  readily  broken  into 
fragments.  This  is  because  it  is  a  lizard  and  not  a  true 
snake.  There  is  a  prevalent  myth  that  the  glass  snake 
gathers  together  the  joints  of  its  tail  and  becomes  whole 
again,  but  it  is  perhaps  needless  to  say  that  the  story  is 
without  foundation  in  fact. 

The  Crocodilians  have  the  appearance  of  immense 
lizards,  although  they  are  quite  different  from  the  lizards 
in  structure.  In  the  United  States  they  are  represented 
by  alligators  of  the  southern  rivers  and  by  a  species  of 


THE   REPTILES  l8l 

true  crocodile  found  in  southern  Florida.  They  spend 
most  of  the  time  in  the  water  where  they  lie  in  wait  for 
prey  with  the  nostrils  exposed  at  the  surface.  They  often 
come  out  upon  the  banks  to  bask  in  the  sunshine  but 
they  are  comparatively  awkward  upon  the  land.  Their 
eggs  are  laid  in  the  sand  and  hatch  out  by  the  heat  of  the 
sun.  Crocodiles  occur  in  the  Nile  and  other  rivers  of 
Africa  and  a  related  form,  the  gavial,  inhabits  the  Ganges. 
Both  alligators  and  crocodiles  live  mainly  on  fish,  but  they 
sometimes  overcome  fairly  large  animals  which  come  to 
the  water  to  drink.  The  American  species  have  a  whole- 
some fear  of  man  and  rightly  so,  since  thousands  of  them 
are  killed  every  year  for  their  hides. 

The  most  highly  modified  of  existing  reptiles  are  the 
Chelonians.  The  body  of  most  turtles  is  enclosed  in  an 
armor  of  plates  joined  to  the  ribs  and  the  backbone.  The 
dorsal  piece,  or  carapace,  is  composed  in  part  of  bony  plates 
and  in  part  of  large  horny  scales  overlying  the  plates, 
but  not  corresponding  to  them  in  position.  The  ventral 
piece,  or  plastron,  is  firmly  joined  to  the  carapace  at  the 
sides.  The  head  and  legs  may  be  more  or  less  completely 
withdrawn  into  the  shell,  and  in  the  box  turtles  the  plas- 
tron is  formed  of  two  movable  plates  united  by  a  hinge 
joint  which  permits  the  two  parts  to  be  drawn  up  against 
the  carapace  so  as  to  completely  enclose  the  animal. 
The  jaws  of  chelonians  are  entirely  devoid  of  teeth,  but 
they  are  furnished  with  a  sharp,  horny  rim,  by  which 
they  can  retain  hold  of  prey  as  well  as  inflict  a  severe 
bite.  Most  species  are  carnivorous,  but  there  are  several 
that  feed  upon  vegetation.  Among  these  are  several  spe- 
cies of  land-tortoises  which  live  entirely  upon  the  land. 
One  species  occurs  in  the  desert  regions  of  Arizona  and 
California  and  another  in  Texas  and  New  Mexico.  The 
gopher  tortoise  of  the  southern  states  is  related  to  the  pre- 


1 82  ANIMAL  BIOLOGY 

ceding  and  derives  its  name  from  its  habit  of  making 
long  burrows  in  the  sand.  There  are  many  species  of 
turtles  in  the  ponds  and  streams  of  the  United  States. 
One  of  the  largest  is  the  snapping  turtle  which  sometimes 
reaches  a  weight  of  forty  pounds.  It  is  named  from  its 
habit  of  quickly  snapping  against  an  object  of  attack. 
According  to  Dugmore  the  "  amputation  of  a  finger  by  a 
medium-sized  specimen,  or  a  hand  by  a  very  large  indi- 
vidual would  be  an  accomplishment  of  no  difficulty  to 
the  reptile." 

In  the  sea-turtles  the  limbs  are  in  the  form  of  flippers 
adapted  for  swimming.  The  large  leather-back  turtle 
of  the  Atlantic  may  reach  a  length  of  six  feet  and  a  weight 
of  a  thousand  pounds.  The  green  turtle,  and  to  a  less 
extent,  the  loggerhead,  are  much  sought  after  for  food. 
The  valuable  tortoise  shell  of  commerce  is  derived  from 
another  large  marine  species,  the  hawk's-bill  turtle,  which 
is  widely  distributed  in  the  warmer  seas.  The  eggs  of 
turtles  and  tortoises  are  oblong  and  encased  in  a  calcareous 
shell.  They  are  usually  buried  in  the  sand  near  the  water, 
and  are  hatched  by  the  warmth  of  the  sun. 


CHAPTER  XXI 
THE  BIRDS 

The  birds  are  so  sharply  distinguished  from  all  other 
vertebrate  animals  that  no  one  would  make  a  mistake  in 
assigning  to  its  proper  class  even  the  most  aberrant  mem- 
ber of  the  group.  There  are  other  vertebrates  that  are 
able  to  fly,  such  as  the  bats  among  mammals  and,  in 
former  periods  of  the  world's  history,  some  outlandish 
looking  reptiles  called  pterodactyls;  but  the  resemblance 
of  these  creatures  to  birds,  aside  from  the  possession  of 
wings,  is  quite  remote.  All  birds  are  furnished  with 
feathers;  they  all  have  a  horny  bill;  and  they  all  have  but 
a  single  pair  of  legs  which  are  used  for  walking,  hopping 
or  running.  This  pair  corresponds  to  the  hind  limbs  of 
other  vertebrates,  the  fore  limbs  being  modified  to  form 
the  wings. 

The  aerial  life  of  birds  has  been  one  of  the  chief  causes  of 
their  distinctive  peculiarities  of  structure.  Flight  implies 
strength  of  bone  and  muscle,  and  expanse  of  surface  for 
beating  against  the  air,  or  for  steering  a  course  through  it. 
The  expanse  of  surface  is  mainly  afforded  by  the  feathers. 
While  feathers  are  found  in  no  creatures  except  birds 
they  represent  highly  modified  scales  such  as  cover  the 
bodies  of  reptiles.  Nature  is  continually  adapting  old 
organs  to  new  functions  and,  in  evolving  the  feather  from 
the  scale,  she  has  perfected  a  wonderfully  complex  and 
beautiful  structure  that  seems  at  first  to  have  little  in 
common  with  the  original  source.  Like  scales,  feathers 
are  derived  from  small  papilla?  in  the  skin.  Commonly 

183 


184  ANIMAL  BIOLOGY 

birds  shed  or  molt  their  feathers  in  the  fall,  but  some 
birds  molt  at  other  times  also.  Frequently  the  plumage 
that  replaces  an  older  one  is  of  different  color  and  some 
birds  have  a  regular  alternation  of  summer  and  winter 
plumage.  The  ptarmigan,  for  instance,  is  brown  and 
white  in  summer,  but  after  the  molt  in  the  fall  it  takes  on 
a  coat  of  pure  white  feathers.  In  nearly  all  birds  the 
first  feathers  that  appear  in  the  young  are  very  different 
from  those  that  come  later.  Sometimes  as  in  young 


FIG.   143. — Diagram  of  a  bird  showing  external  parts.      (Drawn  by  Miss 
H.  M.  Gilkey.) 

chickens  the  plumage  is  in  the  form  of  a  soft  coat  of  down 
which  resembles  fine  hairs,  although  it  is  not  composed  of 
hairs  but  of  true  feathers.  Pin  feathers  are  immature 
stages  in  the  development  of  the  plumage  in  which  the 
feather  is  still  surrounded  by  a  sort  of  sac. 

One  function  of  feathers,  like  that  of  the  fur  of  mammals, 
is  to  protect  the  body  from  cold  and  wet.  The  feathers 
on  the  wings  and  tail,  however,  which  are  much  larger  and 
stronger  than  those  elsewhere,  are  used  as  organs  of  flight. 
The  tail  which  can  usually  be  spread  out  and  contracted 
again  like  a  fan  is  employed,  like  a  rudder,  as  an  organ  of 


THE  BIRDS 


steering.  Notice  the  movements  of  the  tail  as  a  bird 
changes  its  course  or  alights  and  you  will  see  how  this  organ 
is  used  to  guide  the  bird  through  the  air.  Feathers 
shed  water  easily;  and  they  are  aided  in  doing  so  by  being 
kept  more  or  less  oily.  There  is  an  oil  gland  situated 
just  over  the  base  of  the  tail,  and  birds  often  take  some 
of  the  oily  secretion  of  this  organ  into  the  bill  and  distrib- 
ute it  over  the  plumage.  Birds  often  preen  their  feathers, 
or  set  them  in  order,  by  working  over  them  with  the  bill 
when  they  become  disarranged. 


FIG.  144. — Feet  of  birds. 


i,  hawk;  2,  woodpecker;  3,  ostrich;  4,  duck; 
5,  grebe. 


The  feet  of  birds  are  covered  with  tough  horny  scales. 
They  have  but  four  toes,  one  of  which  (and  in  some  cases 
two)  is  generally  directed  backward.  The  toes  end  in  a 
claw,  or  nail,  which  varies  in  shape  according  to  the 
habits  of  birds.  Many  birds  which  swim  or  wade  have  the 
three  front  toes  connected  by  a  membrane,  or  web;  or 
else  the  sides  of  the  toes  arc  furnished  with  flattened  lobes. 
In  birds  of  prey,  such  as  hawks,  owls  and  eagles,  the  feet 
are  powerful  and  furnished  with  strong,  curved  claws 
which  adapt  them  for  seizing  prey.  In  many  climbing 
birds,  such  as  the  woodpeckers,  there  are  two  toes  in  front 


i86 


ANIMAL  BIOLOGY 


arid  two  behind.  Birds  which  perch  generally  have  toes 
which  automatically  close  up  as  the  bird  settles  down  upon 
a  limb  or  perch. 

The  jaws  of  all  living  species  of  birds  are  entirely  devoid 
of  teeth  and  constitute  what  is  known  as  the  beak  or 
bill;  this  has  a  tough,  horny  covering,  and  varies  greatly 
in  shape  in  different  species.  Commonly  the  bill  is  more  or 
less  conical  and  sharp  at  the  tip,  which  adapts  it  for  pick- 
ing up  seeds  or  insects.  In  birds  of  prey  the  bill  is  curved 


FIG.  145. — Bills  of  birds.  I,  duck;  ia,  same  from  above;  2,  gros- 
beak; 3,  spoonbill;  4,  snipe;  5,  kingfisher;  6,  hawk;  7,  humming  bird;  8 
crossbill.;  . 

downward  in  front,  forming  a  sort  of  hook  which  is  used 
in  tearing  the  flesh  of  their  victims.  Ducks,  geese  and 
their  allies  have  a  flattened  bill  adapted  for  scooping  up 
objects  in  the  water  or  mud.  The  woodpecker's  bill  is 
strong  and  sharp  like  a  chisel  and  is  used  for  pecking  holes 
in  trees,  which  is  accomplished  by  a  rapid  series  of  strikes 
the  sound  of  which  is  familiar  to  everyone  who  has  been 
long  in  the  woods.  The  narrow,  slender  bill  of  the  hum- 


THE  BIRDS 


I87 


ming  bird  which  is  used  to  probe  the  necks  of  flowers  for 
small  insects  or* honey  represents  another  type  which 
is  strongly  contrasted  with  the  short  bill  of  night  hawks 
and  swallows,  adapted  for  catching  insects  on  the  wing. 
A  curious  modification  is  seen  in  the  crossbills  in  which  the 
tips  of  the  jaws  are  curved  and  crossed.  This  arrangement 
is  peculiarly  adapted  for  extracting  from  open  pine  cones 
the  seeds  upon  which  the  crossbills  feed.  The  largest 


FIG.  146. — The  toucan. 

bills  among  birds  occur  in  the  toucans,  or  horn-bills,  which 
live  in  South  America. 

As  birds  have  no  teeth  they  do  not  chew  their  food; 
while  the  objects  may  be  broken  up  more  or  less  by  the 
bill  they  are  usually  swallowed  whole.  The  function  of 
grinding  up  food  is  performed  by  the  gizzard  which  is  a 
very  strong  muscular  division  of  the  alimentary  canal. 
Usually  birds  that  live  more  or  less  upon  hard  seeds  swal- 
low a  quantity  of  gravel  which  aids  in  the  grinding  process, 
In  many  birds  the  esophagus  expands  below  the  base  of 
the  neck  into  a  thin-walled  crop  in  which  a  quantity  of  food 
is  carried  and  then  gradually  passed  back  to  the  gizzard. 
After  being  ground  up  in  the  gizzard  and  partly  digested 


1 88  ANIMAL  BIOLOGY 

there  the  food  passes  into  the  intestine  where  digestion  is 
completed  and  the  digested  materials  absorbed. 

Not  only  do  birds  have  well-developed  lungs,  but  there 
are  in  most  species,  extensive  air  sacs  connected  with  the 
lungs  and  extending  into  various  parts  of  the  body.  In 
most  birds  many  of  the  bones  are  hollow  and  contain  pro- 
longations of  these  air  sacs.  Air  may  therefore  be  carried  to 
different  parts  of  the  body  in  a  way  that  suggests  a  com- 
parison with  its  distribution  through  the  tracheal  tubes  of 
insects.  A  sparrow  with  a  broken  wing  may  even  take 
air  into  its  lungs  through  the  hollow  of  its  wing  bones. 

Birds  are  warm-blooded  animals,  and  they  have  a  rapid 
respiration  which  is  greatly  facilitated  by  the  large  sur- 
face afforded  by  the  lungs  and  air  sacs.  They  have  a  four- 
chambered  heart  and  a  complete  double  circulation  such 
as  occurs  in  ourselves. 

The  skeleton  and  muscular  system  of  birds  have  become 
highly  modified  in  relation  to  flight.  To  progress  rapidly 
through  the  air  means  that  there  must  be  a  large  amount 
of  muscle  for  moving  the  wings  and  accordingly  we  find 
the  pectoral  muscles,  those  extending  from  the  breast  bone, 
or  sternum,  to  the  wings,  enormously  developed.  And 
to  give  adequate  attachment  for  these  muscles  the  sternum 
is  not  only  of  large  size,  but  in  all  except  a  very  few  kinds 
of  birds,  it  is  furnished  below  with  a  large  median  ridge, 
or  keel.  The  bones  of  the  wings  conform  to  the  same  gen- 
eral plan  of  structure  as  do  those  of  the  legs.  In  the  outer 
part  of  the  wing,  or  what  corresponds  to  the  hand  in  our- 
selves, some  bones  of  the  digits  have  been  lost  and  others 
are  fused  together  so  that  the  fundamental  plan  is  some- 
what obscured.  -  Such  changes  may  be  regarded  as  a 
natural  consequence  of  modifying  a  fore  leg  so  as  to  adapt 
it  to  the  new  function  of  flying. 

All  species  of  birds  lay  eggs,  and  with  rare  exceptions 


THE  BIRDS 


189 


birds  sit  upon  their  eggs  or  incubate  them,  their  develop- 
ment being  dependent  upon  the  warmth  afforded  by  the 
bird's  body.  Birds  as  a  rule  devote  an  unusual  amount 
of  care  to  the  rearing  of  offspring  and  they  afford  many 
striking  and  attractive  exhibitions  of  fidelity  and  devotion 
in  their  family  life.  The  behavior  of  birds  varies  greatly, 


FIG.  147. — A  rookery  of  nesting  birds  on  the  Farallone  Islands.     (From  a 
group  in  the  museum  of  the  California  Academy  of  Sciences.) 

however,  in  this  regard.  Among  the  lower,  or  more  primi- 
tive, birds  the  eggs  are  laid  either  in  simple,  crude  nests, 
or  upon  bare  rocks  or  soil  (see  Fig.  147).  The  labor  of 
incubation  in  these  cases  falls  entirely  upon  the  female  as 
the  associations  of  the  sexes  are  very  temporary  and  thus 
stand  in  marked  contrast  to  the  matings  which  occur  in 
the  higher  forms.  The  young  of  the  primitive  birds  when 


ANIMAL  BIOLOGY 

first  hatched  are  generally  active  and  require  little  atten- 
tion from  their  parents.  Young  ducklings,  for  instance, 
will  swim  in  the  water,  pick  up  food,  flee  from  their 
enemies,  and  perform  many  other  acts  on  the  first  day 
after  being  hatched.  Lloyd  Morgan  tells  of  a  young 
moor  hen  which  swam  almost  as  soon  as  it  hatched  out 
of  the  egg,  and  dived  into  the  water  as  readily  as  an 
older  bird.  Very  young  chicks  have  the  instinct  to  peck 


FIG.   148. — Nest    and    eggs    of    Brewer's    blackbird.     (From    photo    by 

Holliger.) 


at  small  objects  of  about  a  certain  size,  but  they  quickly 
learn  to  avoid  things  with  a  disagreeable  taste.  They  in- 
stinctively respond  to  the  note  of  the  mother  hen  that 
warns  them  of  danger  and  rush  to  the  mother  or  else 
hide.  They  also  give  a  note  themselves,  the  danger  chirr, 
when  any  object  causes  them  to  become  afraid  and  this 
note  serves  as  a  warning  to  the  other  chicks.  One  of  ten 
sees  them  approaching  an  object  such  as  a  large  bug  of 


THE  BIRDS  191 

which  they  are  half  afraid  and,  after  looking  it  over  sus- 
piciously, giving  the  danger  chirr  which  means  " beware!" 
When  one  chick  musters  up  courage  to  peck  at  an  object 
others  usually  follow  its  example.  If  the  chick  picks  up 
a  worm  and  bolts  off  with  it  the  other  chicks  frequently 
take  after  the  successful  one  in  the  endeavor  to  share 
its  prize.  All  these  acts  and  also  many  others  are  per- 
formed very  soon  after  the  chicks  emerge  from  the  egg. 
The  young  chick  has  a  number  of  instincts  which  equip  it, 
without  previous  experience,  for  most  of  the  circum- 
stances of  its  life.  Hudson  relates  how  the  young  of  some 
birds  will  instinctively  respond  to  the  parent's  call  even 
before  they  break  out  of  the  egg  shell.  Birds  which  are 
active  as  soon  as  hatched  flock  about  the  mother  bird 
who  hunts  food  for  them  and  gives  them  a  certain  pro- 
tection. By  imitating  many  of  the  actions  of  the  parents 
the  young  learn  to  avoid  enemies  and  derive  many  other 
advantages  from  their  parents'  experience. 

In  the  higher  birds,  such  as  the  song  birds,  the  nest  is 
built  usually  of  small  sticks,  twigs  and  bits  of  grass  and 
lined  with  down  and  other  soft  materials;  and  the  young 
which  are  hatched  in  a  weak  and  helpless  state  are  fed 
and  tended  by  their  parents  until  ready  to  take  flight. 
The  common  robin,  for  instance,  which  is  a  familiar  visitor 
in  the  early  spring,  builds  a  nest  usually  in  the  bough  of  a 
tree,  and  both  the  male  and  female  birds  take  turns  in 
sitting  upon  the  eggs  which  are  hatched  in  about  three 
weeks.  The  young,  of  which  there  are  usually  from  two  to 
five,  remain  in  the  nest  until  they  acquire  a  coat  of  feathers 
(for  they  have  but  a  scanty  coat  of  pin  feathers  at  first) 
and  are  then  induced  by  their  parents  to  leave,  if  they  do 
not  do  so  of  their  own  accord.  Herrick  in  his  book  on 
the  "Home  Life  of  Wild  Birds"  describes  as  follows  the 
behavior  of  a  family  of  robins  whose  nest  he  had  carried, 


I Q2  ANIMAL  BIOLOGY 

together  with  the  bough  of  the  tree  on  which  it  was  built, 
to  a  convenient  point  for  observation.  "In  exactly 
fifty-five  minutes  from  the  beginning  of  operations  the 
mother  appeared  with  a  large  grasshopper,  which  she  gave 
to  the  young,  and  afterward  cleaned  the  nest.  The  male 
came  also,  when  the  comparative  safety  of  the  new  con- 
ditions had  become  apparent,  but  appeared  with  more 
caution.  At  first  both  birds  flew  to  the  tree  by  their  ac- 
customed paths  and  examined  the  place  where  the  bough 


FIG.   149. — Nest  and  eggs  of  Massachusetts  black  duck.     (After  Forbush.) 

had  been  lopped  off,  and  in  their  admirable  and  fearless 
manner  blustered  about  for  a  while,  taking  no  pains  to 

conceal  their  anger The  absence  of  sound  in 

strange  objects  is  alway  reassuring  and  now  Mother 
Robin  could  be  seen  perched  on  the  top  of  an  apple  tree, 
surveying  the  field.  She  called  seet!  seet!  while  the 
grasshopper  in  her  bill  squirmed  to  get  free,  and  the 
young  chirped  loudly  in  reply Suddenly  down 


THE  BIRDS  IQ3 

comes  one  of  the  old  birds  with  all  its  weight  on  the  limb. 
The  young  have  felt  similar  vibrations  before  and  know 
what  to  expect.  Up  go  three  heads  at  once,  each  mounted 
on  a  slender  stalk,  and  each  bearing  at  its  apex  what  might 
suggest  a  full  blown,  brilliant  flower,  for,  as  is  well  known, 
the  extent  of  their  gape  is  extraordinary  and  the  inside  of 
the  mouth  has  a  bright  orange  hue.  The  young  tremble 
with  violent  emotions  as  they  jostle,  struggle,  and  call 
with  undiminished  zeal  even  after  being  fed." 

"After  the  first  visit  had  proved  successful,  confidence 
was  established  at  once,  the  female  and  later  the  male 


FIG.  150. — Robin  catching  an  earthworm. 

coming  to  the  young  at  intervals  of  about  five  minutes, 
bringing  grasshoppers,  and  occasionally  removing  the 
excreta They  frequently  carried  five  or  six  in- 
sects at  each  load,  when  their  bills  would  suggest  a  solid 
load  of  grasshoppers,  all  struggling  to  get  free." 

After  feeding  the  young  the  parents  carefully  inspected 
the  nest  and  freed  it  of  any  uncleanliness.  "  Then  after  in- 
spection is  over  they  fly  to  the  nearest  perch,  and  make  haste 

to  clean  their  bills  and  set  their  dress  in  order 

One  robin  at  the  age  of  eleven  days  left  the  family  circle 
early  on  August  i3th,  and  at  nine  o'clock  the  two  which 
remained  were  standing  up  and  flopping  their  wings. 

13 


1 94  ANIMAL  BIOLOGY 

The  old  birds  would  come  near,  displaying  tempting 
morsels  in  their  bills  but  with  no  intention  of  feeding 
their  young  so  long  as  they  remained  in  the  nest.  By  such 
tantalizing  methods  they  soon  drew  them  away.  Both 
old  and  young  hung  about  the  apple  tree  for  several 
days,  when  they  disappeared  and  were  not  seen  again." 

Even  after  the  young  leave  the  nest  they  are  accom- 
panied by  the  parents  for  quite  a  while,  and  it  is  not  un- 
common to  see  a  young  robin  two-thirds  grown  begging 
its  indulgent  parents  for  food,  and  being  fed  with  angle- 
worms, when  it  is  quite  able  to  forage  for  itself. 

The  mating  habits  of  birds  are  subject  to  great  varia- 
tion. In  the  more  primitive  species  there  is,  as  a  rule,  no 
permanent  union  of  the  sexes,  the  males  and  females 
separating  after  the  breeding  season  is  over.  Many 
birds  are  polygamous,  such  as  our  domestic  fowl,  a  single 
large,  strong  male  going  about  with  a  flock  of  females, 
and  driving  away  all  weaker  rivals.  In  most  of  the  song 
birds,  however,  there  is  a  more  permanent  union  of  the 
sexes,  in  some  cases  lasting  until  the  death  of  one  of  the 
members  of  the  pair.  The  males  frequently  take  turns 
with  the  females  in  sitting  upon  the  eggs,  an  office  which 
the  rooster  among  our  domestic  poultry  would  never 
condescend  to  perform.  The  males  of  many  song  birds 
also  help  in  bringing  food  to  the  young,  in  cleaning  the 
nest,  and  in  some  cases  in  bringing  food  to  the  female 
while  she  is  incubating  the  eggs. 

Among  the  higher  birds,  nesting  is  usually  preceded  by 
courtship,  a  ceremony  which  is  dispensed  with  among 
the  cruder  and  less  gallant  males  of  the  lower  birds. 

It  is  very  common  for  the  males  to  be  distinguished  from 
the  females  by  more  brilliant  and  beautiful  plumage  and 
superior  powers  of  song.  Both  of  these  characters  are 
brought  into  play  by  the  males  who  attempt  to  display 


THE  BIRDS 


195 


themselves  to  the  best  advantage  before  the  eyes  of  their 
intended  mates.  Darwin  attempted  to  account  for  the 
superior  qualities  of  the  male  birds  by  his  theory  of  sexual 
selection,  according  to  which  the  males  that  were  the 
most  brilliantly  colored,  or  which  sang  most  sweetly,  or 
otherwise  displayed  themselves  to  the  best  advantage 


FIG.   151. — Side  view  of  male  Argus  pheasant,  whilst  displaying   before 
female.     (After  Darwin.) 

would  be  most  likely  to  be  chosen  by  the  females  as  mates. 
Hence  if  this  selection  were  continued  generation  after 
generation,  the  males  would  gradually  be  improved  in 
respect  to  those  qualities  that  appealed  most  strongly  to 
the  sensibilities  of  the  female  birds.  Almost  everyone 
has  observed  the  strutting  of  the  turkey  gobbler  with  his 
erected  feathers  and  expanded  tail,  and  many  are  doubtless 


196  ANIMAL  BIOLOGY 

familiar  with  the  much  more  beautiful  display  of  the 
male  peacock  as  he  spreads  out  his  magnificent,  wonderfully 
marked  tail  feathers  before  the  gaze  of  the  presumably 
admiring  pea  hens.  Darwin  relates  that  during  courtship 
"  the  bull-finch  makes  his  advances  in  front  of  the  female, 
and  then  puffs  out  his  breast,  so  that  many  more  of  the 
crimson  feathers  are  seen  at  once  then  otherwise  would 
be  the  case.  At  the  same  time  he  twists  and  bows  his 
black  tail  from  side  to  side  in  a  ludicrous  manner.  The 
male  chaffinch  also  stands  in  front  of  the  female,  thus 
showing  its  red  breast  and  'blue  bell'  as  the  fanciers  call 

his  head The  common  linnet  distends  his  rosy 

breast,  slightly  expands  his  brown  wings  and  tail,  so  as  to 
make  the  best  of  them  by  exhibiting  their  white  edgings." 

As  Darwin  remarks  "  there  is  an  intense  degree  of  rivalry 
between  males  in  their  singing.  Bird  fanciers  match  their 
birds  to  see  which  will  sing  longest."  Singing  is  most 
common  during  the  breeding  season.  Many  male  birds 
which  are  not  at  all  musical  give  utterances  to  cries  and 
other  noises  during  this  season,  which  possibly  serves 
rather  to  advertize  their  presence  than  to  charm  their 
hearers.  The  gabbling  of  the  strutting  male  turkey, 
the  harsh  screaming  of  male  parrots,  and  the  hoarse  cawing 
of  male  crows  and  rooks  are  certainly  not  musical  to  us, 
however  they  may  appeal  to  the  female  bird. 

It  is  well  established  that  female  birds  often  manifest  a 
decided  preference  for  certain  males.  Audubon  states 
that  female  turkeys  prefer  the  males  of  wild  turkeys  to 
those  of  their  own  domestic  breed.  There  are  several 
cases  in  which  females  have  rejected  their  mates  after 
they  had  lost  their  brilliant  tail  feathers  or  become  other- 
wise mutilated,  and  female  pigeons  sometimes  desert  their 
own  mates  and  take  up  with  other  males.  How  far  an 
appreciation  of  beauty  occurs  in  birds  it  is  difficult  to  say. 


THE   BIRDS 


IQ7 


Crows  and  magpies  often  carry  away  bright  and  colored 
objects.  Some  birds  weave  colored  feathers  into  their 
nests,  but  the  most  remarkable  exhibition  of  fondness  for 
colored  objects  occurs  in  the  bower  birds  of  Australia. 
These  birds  erect  a  bower  or  tent-like  structure,  built 
of  sticks  and  leaves.  Around  the  entrance  to  the  bower, 


FIG.   152. — Humming    birds,    Spathura    underwoodi,    male    and    female. 
(From  Darwin,  after  Brehm.) 

and  often  woven  into  its  walls  also,  may  be  found  bright 
feathers,  leaves,  colored  shells,  and  various  other  objects 
of  conspicuous  appearance. 

After  mating  comes  the  preparation  for  the  young. 
Here  again  we  meet  with  great  variation;  the  night  hawk 
builds  no  nest  at  all,  and  the  plover  brings  together  but  a 


i98 


ANIMAL  BIOLOGY 


few  sticks  on  which  to  deposit  its  eggs;  robins,  sparrows, 
warblers,  and  many  other  song  birds  build  a  more  elaborate 
nest  which  is  usually  lined  with  soft  materials  which  tend 
to  preserve  the  warmth  of  the  eggs  and  young.  As  a 
rule,  primitive  birds  build  crude  nests,  while  birds  of  a 
higher  type  take  more  care  in  providing  for  the  safety 
and  comfort  of  their  progeny. 

There  are  a  few  birds  such  as  the  cuckoos  and  cow  birds 
whose  young  live  at  the  expense  of  other  species.  The 
eggs  of  the  European  cuckoo,  for  instance,  are  laid  along- 


FIG.   153. — Male  bluebird  with  grasshopper.     (After  Forbush.) 

side  of  the  eggs  of  other  birds  and  the  young  cuckoo  is 
fed  by  the  rightful  owners  of  the  nest  like  one  of  their  own 
young.  When  the  young  cuckoo  develops  sufficient 
strength  it  has  the  peculiar  instinct  of  pushing  its  com- 
panions out  of  the  nest,  where  they  frequently  perish. 
Notwithstanding  this  conduct,  which  seems  like  the  basest 
of  ingratitude  to  its  benefactors,  the  birds  continue  to 
care  for  the  young  interloper  until  it  is  ready  to  take  flight. 
One  of  the  most  pleasing  associations  with  the  advent 


THE   BIRDS  199 

of  spring  is  the  appearance  of  our  feathered  friends  that 
are  returning  from  the  warmer  climes  in  which  they  have 
passed  the  winter.  Scarcely  is  the  snow  off  the  ground, 
and  sometimes  even  before,  when  flocks  of  birds  may  be 
seen  on  their  northward  journey.  Not  all  birds  migrate. 
Some  of  the  birds  of  a  given  locality,  like  the  English  spar- 
rows, are  permanent  residents.  Some,  on  the  other  hand, 
appear  only  in  winter,  having  migrated  from  colder 
climates;  these  are  the  winter  residents.  In  most  places  of 
the  United  States  a  large  proportion  of  the  birds  pass 
through  the  country  during  their  journeys  to  and  from  the 
north;  these  are  the  migrants.  The  distances  travelled 
by  different  species  of  migratory  birds  is  subject  to  great 
variation.  Many  species  (robin,  bluebird,  meadow  lark) 
winter  in  the  Gulf  States  or  in  Mexico,  and  nest  in  the 
northern  states  or  in  Canada.  Large  numbers  pass  the 
winter  in  Cuba  and  the  West  Indies,  while  many  species 
go  as  far  south  as  the  southern  part  of  South  America. 
The  golden  plover  has  one  of  the  longest  migration  routes 
known.  After  passing  the  winter  from  Patagonia  to 
southern  Brazil  it  does  not  stop  in  its  northward  journey 
until  it  reaches  its  breeding  grounds  within  the  Arctic 
Circle,  a  distance  of  nearly  ten  thousand  miles.  Migrating 
birds  frequently  keep  near  prominent  landmarks,  sucli  as 
coast  lines,  mountain  chains  or  rivers.  T,he  Mississippi 
valley  forms  a  great  highway  for  hosts  of  birds,  and  the 
same  is  true  only  to  a  less  degree  of  smaller  streams. 
The  timbered  tracts  along  the  streams  form  excellent 
guides  for  birds  flying  at  any  considerable  height.  Mi- 
grating birds  commonly  fly  very  high,  in  some  cases  at 
least  a  mile  above  the  earth,  and  with  their  acute  vision 
they  are  able  to  survey  an  immense  territory.  They  have 
a  marvellous  ability  to  find  their  way  back  to  their  old 
breeding  grounds.  It  is  not  uncommon  for  the  same  birds 


200 


ANIMAL  BIOLOGY 


to  nest  year  after  year  near  the  same  spot,  sometimes  in 
the  same  nest.     In  fogs  and  during  stormy  nights  it  is 


FIG.  154. — Route  of  migration  of  the  Golden  Plover.  Breeding 
range  in  north  finely  checkered;  winter  home  in  south  shown  by  parallel 
lines. 

true  that  birds  sometimes  lose  their  way;  at  such  times 
they  are  especially  prone  to  be  attracted  to  light-houses 


THE   BIRDS 


201 


where  many  are  killed  by  flying  against  the  walls.  In 
most  cases,  however,  a  bird's  memory  for  a  route  it  has 
once  followed  is  far  better  than  that  of  the  average  human 
being. 

The  tendency  to  migrate  is  doubtless  instinctive,  but 
the  particular  route  followed  is  mainly  a  matter  of  experi- 
ence and  tradition.  Birds  commonly  migrate  in  flocks, 
and  it  is  probable  that  it  is  the  older  and  more  experienced 
birds  that  lead  the  way.  While  it  may  seem  curious  that 


FIG.   155. — Red  winged  blackbird. 

birds  should  leave  a  genial  clime  and  fly  thousands  of 
miles  to  the  cold  and  barren  regions  of  the  Arctic  Circle 
to  rear  their  young,  it  must  be  borne  in  mind  that  this 
northern  region  is  one  in  which  during  the  short  summers 
that  occur,  there  is  an  abundance  of  food  in  the  form  of 
berries  and  insects  (especially  mosquito  larvae)  and  com- 
paratively few  enemies  to  molest  the  young.  The  migra- 
tion of  birds  affords  a  means  of  taking  advantage  of  these 


2O2 


ANIMAL  BIOLOGY 


things.     Nature  allows  few  opportunities  for  making  a 
living  to  go  to  waste. 

With  relatively  few  exceptions  most  birds,  in  one  way  or 
another,  are  of  value  to  man.  There  are  the  game  birds 
such  as  ducks,  geese,  plovers,  snipe,  quail  and  many  others 
whose  value  is  obvious.  There  are  scavengers,  such  as 
the  sea  gulls  which  devour  all  sorts  of  refuse  that  floats  on 
the  water,  and  the  vultures  and  buzzards  which  eat  de- 


FIG.   156. — Yellow-bellied  sapsucker. 

caying  flesh.  The  accumulated  excreta  of  birds,  which  is 
called  guano  and  which  occurs  in  great  quantities  on  cer- 
tain islands  on  which  the  birds  congregate,  is  much  em- 
ployed as  a  fertilizer  of  the  soil.  The  plumage  of  birds  is 
greatly  in  vogue  for  purposes  of  decoration,  as  well  as 
for  various  other  purposes  of  a  more  practical  nature. 
But  by  far  the  greatest  value  of  birds  lies  in  their  whole- 
sale destruction  of  insects  and  other  injurious  forms  of 
animal  life.  Much  study  has  been  devoted  to  the  food 


THE  BIRDS 


203. 


habits  of  different  species  birds,  especially  by  the  Biological 
Survey  of  the  United  States  Department  of  Agriculture, 
which  has  issued  numerous  bulletins  upon  the  subject.  A 
large  part  of  the  data  on  the  food  of  birds  has  been  ac- 
cumulated by  the  examination  of  the  contents  of  stomachs. 
By  the  laborious  counting  of  the  different  kinds  of  insects, 
grains,  weed  seeds  and  other  bodies  which  are  found  in 


FIG.   157. — California  valley  quail.     (From  Rep.  of  Calif.  Fish  and  Game 
Commission.) 

the  stomachs  of  many  thousands  of  birds  of  all  sorts  a 
great  many  very  valuable  facts  have  been  discovered 
concerning  the  utility  or  harmfulness  of  various  species. 
Were  it  not  for  the  destruction  of  insects  by  birds  it  would 
be  difficult  for  man  to  raise  many  of  his  crops.  The 
common  bob-white,  or  quail,  of  the  eastern  and  middle 
states  lives  mainly  on  insects  and  weed  seed,  and  is 


204 


ANIMAL  BIOLOGY 


especially  destructive  of  insects  such  as  grasshoppers, 
Colorado  potato  beetles,  chinch  bugs,  army  worms,  cotton 
worms,  and  striped  cucumber  beetles.  Forbush  in  his 
valuable  book  on  " Useful  Birds  and  Their  Protection" 
says  of  the  quail  that  "it  is  probably  the  most  effective 
enemy  of  the  Colorado  potato  beetle."  Certain  species 
of  birds,  such  as  owls  and  some  kinds  of  hawks,  perform 
a  valuable  service  in  destroying  micej  ground  squirrels, 
gophers  and  other  small  mammals  that  are  a  nuisance  to 
the  farmer.  Other  birds  are  helpful  to  the  farmer  by 
destroying  large  quantities  of  weed  seeds.  And  while 


7  DAYS  OR  LESS  ADULT 

FIG.   158. — Diagram    showing    proportions    of   food    of    American    crow 
(Corvus  americanus) ,  young  and  adult.     (After  Judd.) 

many  species  are  destructive  to  grains  and  fruits,  the 
damage  they  do  is  usually  outweighed  by  the  benefit  they 
confer  in  destroying  weed  seed  and  insects.  Careful 
investigation  has  shown  that  several  kinds  of  birds  com- 
monly deemed  injurious  are  on  the  whole  beneficial. 
The  larger  owls  which  are  often  shot  for  their  occasional 
attacks  upon  poultry  are  on  the  whole  very  valuable 
birds  for  reasons  above  named.  There  are  several  hawks 
which  are  beneficial  since  their  food  consists  almost 
exclusively  of  small  mammals  and  insects.  Others  are 
of  more  doubtful  utility,  since  they  prey  upon  birds  as 


THE  BIRDS 


205 


well  as  upon  small  mammals.  But  there  are  a  few, 
such  as  the  goshawk,  the  sharp-shinned  hawk  and  Cooper's 
hawk,  that  live  mainly  upon  birds,  and  hence  are  an  un- 
doubted nuisance. 

There  are  but  a  few  non-pre- 
datory birds  that  are  not  on  the 
whole  valuable  to  man.  A  notable 
exception  is  the  English  sparrow 
which  was  introduced  into  this 
country  from  England  at  first  un- 
successfully, in  1850  and  again 
with  very  manifest  success  in  1853. 
The  species  has  thrived  and  mul- 
tiplied so  that  there  is  scarcely  a 
village  in  the  United  States  that  is 
free  from  the  nuisance.  English 
sparrows  eat  large  quantities  of 

grain  while  destroying  relatively  few  insects;  but  their  worst 
offense  is  their  crowding  out  and  destruction  of  other  birds. 
They  demolish  the  nests  of  other  species,  break  their  eggs, 


ADULT 
FIG.   159. — Diagram 


erythrogastra.  This  bird  is 
almost  entirely  insecti- 
vorous. 


NESTLING  LESS  THAN  ONE  WEEK  OLD  ADULT 

PIG.   160. — Diagram   showing   proportions   of  food   of   English  sparrow, 
Passer  domesticus,  young  and  adult.     (After  Judd.) 

kill  their  young  and  by  their  continued  fighting  drive 
away  the  older  birds.  The  result  is  that  many  more 
valuable  birds  have  been  expelled  from  towns  and  villages 


206  ANIMAL  BIOLOGY 

and  considerably  limited  in  numbers  in  the  country. 
Efforts  to  exterminate  English  sparrows  have  met  here 
and  there  with  success,  but  to  rid  the  whole  country  of 
the  pests  seems  now  a  hopeless  task. 

The  great  value  of  most  kinds  of  birds  has  led  to  the 
passage  of  various  laws  for  their  protection.  For  game 
birds  there  is  usually  a  "closed  season"  during  which 
hunters  cannot  shoot  them  without  incurring  a  legal 


FIG.   161. — A  screech  owl.     (From  photo  by  Mr.  Tracy  Storer.) 

penalty.  In  several  states  the  song  birds  and  many 
other  kinds  are  protected  at  all  times.  But  notwith- 
standing these  protective  measures  there  is  a  vast  slaughter 
of  bird  life  that  is  leading  to  a  marked  reduction  in  the 
number  of  birds.  The  robbing  of  birds'  nests  by  boys 
destroys  many  valuable  birds,  and  the  still  more  extensive 
collection  of  the  eggs  of  ducks,  gulls  and  other  birds 
which  commonly  nest  upon  islands  or  near  rocky  shores 
destroys  many  more.  Aside  from  the  hunting  of  recog- 
nized game  birds  there  is  in  many  places  a  wholesale 


THE  BIRDS  2O7 

destruction  for  food  of  such  birds  as  meadow  larks,  robins, 
blackbirds,  and  even  many  birds  of  smaller  size.  Laws 
prohibiting  the  sale  of  game  birds  prevent  the  systematic 
hunting  for  the  market  which  is  so  destructive  of  bird  life. 
Birds  are  still  sacrificed  to  provide  ornaments  for  ladies' 
hats,  but  the  combined  forces  of  legislation  and  public 
sentiment  have  diminished  the  fearful  slaughter  of  our 
most  beautiful  birds  for  this  purpose. 

One  of  the  most  destructive  of  the  enemies  of  birds  is 
the  common  house  cat.     It  is  unfortunate  that  this  familiar 


FIG.  162. — Great  grey  owl.     (From  photo  by  Holliger.) 

object  of  affection  and  fostering  care  should  prove  so  mis- 
chievous a  malefactor,  but  recent  investigations  have 
made  the  case  against  pussy  a  very  strong  one.  Forbush 
estimates  that  a  mature  cat  kills  on  the  average  more 
than  fifty  birds  a  year  and  John  Burroughs  says  that  cats 
kill  more  birds  than  all  other  animals  combined.  Ordi- 
narily the  depredations  of  cats  escape  notice,  since  they 
hunt  in  a  quiet  manner  and  do  much  of  their  prowling 
around  at  night.  Cats  are  especially  destructive  to  nest- 
ing birds  and  their  young.  It  is  true  that  cats  perform 


208  ANIMAL  BIOLOGY 

a  certain  service  in  catching  mice  and  that  many  indi- 
vidual cats  catch  few  or  no  birds,  but  there  can  be  no 
doubt  that,  aside  from  their  value  as  pets,  the  harm  they 
do  in  destroying  annually  millions  of  birds  makes  them 
on  the  whole  a  serious  nuisance. 


Nesting  box.     (After  Forbush). 


CHAPTER  XXII 
THE  MAMMALS 

The  class  Mammalia  takes  its  name  from  the  possession 
of  mammary  glands  which  produce  milk  for  the  young. 
All  mammals  possess  these  glands  and  they  are  found  in  no 
other  group  of  animals;  consequently  their  presence 
serves  to  define  quite  precisely  this  class  of  vertebrates. 
Mammals  may  in  most  cases  be  recognized  by  their 
covering  of  hair,  just  as  birds  may  be  distinguished  by 
their  feathers.  In  a  few  forms,  such  as  the  elephant  and 
rhinoceros,  the  hair  is  very  scarce;  and  in  the  whales  it  has 
almost  entirely  disappeared.  Porcupines  and  hedgehogs 
have  many  of  the  hairs  modified  into  large,  stiff  spines 
or  quills,  which  are  efficient  organs  of  protection.  Hair 
is  a  product  of  the  outer  layer  of  the  skin,  the  epidermis, 
and,  like  feathers,  it  is  commonly  shed  more  or  less  period- 
ically. New  hairs  are  grown  from  a  papilla  at  the  base 
of  the  older  hairs  that  fall  out.  The  nails  and  hoofs  of 
mammals  as  well  as  the  outer  covering  of  the  horns  of 
cattle  and  related  forms  are  also  epidermal  structures. 

Unlike  birds  and  reptiles,  mammals  usually  have  well- 
developed  external  ears,  or  pinnag,  which  are  generally 
shaped  so  as  to  catch  sound,  and  are  freely  movable,  as 
may  be  seen  readily  by  watching  a  dog,  horse,  or  rabbit. 
The  sense  of  smell  is  generally  acute  and  enables  many  spe- 
cies to  track  their  prey  and  others  to  detect  their  enemies 
even  at  a  considerable  distance.  The  least  whiff  of  a 
human  being  may  send  a  bear  or  deer  scampering  through 
the  forest  long  before  its  pursuer  appears  in  sight.  By 
smell  mammals  may  recognize  their  own  kind  and  dis- 

14  209 


210  ANIMAL  BIOLOGY 

tinguish  friends  from  foes  within  their  own  species;  so 
the  world  of  smells  is  one  of  great  importance  to  them. 
The  keen  interest  which  the  dog  takes  in  the  various  odors 
encountered  along  his  path  is  doubtless  a  trait  inherited 
from  his  wild  ancestors  for  whom  the  detection  of  odors 
often  meant  the  prevention  of  starvation  or  escape  from 
being  eaten  by  some  larger  animal.  It  is  perhaps  because 
of  the  keen  sense  of  smell  in  mammals  that  there  have 
been  developed  scent  glands  in  many  species  which  doubt- 
less enable  individuals  to  find  one  another  with  greater 
readiness.  Musk  which  is  the  product  of  the  scent 
glands  of  the  musk  deer  is  used  as  a  perfume  and  also 
in  medicine.  In  the  skunk  the  scent  glands  which  are 
situated  near  the  base  of  the  tail  are  developed  to  a  very 
unusual  degree  and  constitute  an  efficient  means  of 
defense.  The  animal  can  discharge  the  fluid  secreted  by 
the  glands  to  a  distance  of  several  feet;  consequently  there 
are  few  creatures  that  care  to  molest  him,  and  he  can 
go  about  with  the  impudent  boldness  which  is  one  of  the 
prominent  traits  of  his  character. 

Mammals  are  found  in  most  parts  of  the  earth  except 
upon  oceanic  islands  where  there  are  none  except  bats 
which  may  have  flown  there,  or  more  rarely  very  small 
species,  such  as  mice,  which  may  have  been  transported  on 
floating  trees  or  other  drift.  Mammals  have  very  limited 
powers  of  migration,  so  that  those  inhabiting  cold  coun- 
tries cannot  escape  the  winter  like  the  birds.  Some  species 
have  developed  a  remarkable  aptitude  for  finding  food 
even  when  the  ground  is  thickly  covered  with  snow;  some, 
such  as  many  kinds  of  squirrels,  store  up  food  during  summer 
which  is  used  during  the  winter;  while  others,  such  as  the 
ground  hog,  undergo  what  is  called  hibernation,  remaining 
in  a  dormant  condition  in  which  they  subsist  mainly  on 
their  own  fat. 


THE   MAMMALS  211 

The  demand  for  many  animals  on  account  of  their  hides 
and  fur  has  led  to  a  great  decrease  in  their  numbers;  some, 
such  as  the  pumas,  bears,  wolves  and  wild  cats  have  been 
rapidly  killed  off,  partly  because  of  their  attacks  upon 
domestic  animals,  partly  for  the  sport  of  hunting.  The 
species,  such  as  the  deer,  which  supply  food  are  rapidly 
going.  But  among  the  most  efficient  of  the  destructive 
agencies  is  the  wanton  killing  by  hunters  for  mere  sport. 
For  years  there  has  gone  on  in  Africa  a  fearful  slaughter 


FIG.  163. — Platypus  or  duck-bill,  Ornithorhynchus  anatinus.   (After  Gould.) 

of  elephants,  rhinoceri,  antelopes,  zebras,  giraffes,  hippo- 
potimi,  gorillas,  etc.,  that  has  greatly  reduced  the  number 
of  these  fine  species,  so  that  several  of  them  are  threatened 
with  extinction.  Many  of  our  finest  North  American 
mammals  such  as  the  moose,  elk,  and  grizzly  bear  are  com- 
paratively few  in  numbers  and  much  restricted  in  range. 
The  class  Mammalia  is  divided  into  several  orders. 
The  lowest  of  these,  the  Monotremes,  have  the  remarkable 
peculiarity  of  laying  eggs,  like  the  birds  and  most  reptiles, 
instead  of  bringing  forth  living  young.  The  order  com- 


212 


ANIMAL  BIOLOGY 


prises  but  three  genera,  the  duck  bills  (Ornithorynchus) , 
which  live  in  ponds  and  streams  of  Australia,  the  spiny 
ant  eaters  (Echidna),  which  are  found  in  Australia,  and  a 
related  genus  (Proechidna) ,  from  New  Guinea.  The 
duck  bills  have  peculiar,  flattened,  protruding  jaws  like 
the  bill  of  a  duck,  and  webbed  feet.  The  body  is  covered 
with  a  fine  fur.  The  eggs  are  laid  -in  burrows.  The  spiny 
ant  eaters  have  very  narrow  jaws;  the  body  is  armed  with 
numerous  pointed  spines  amid  the  hairs,  and  on  the  lower 


FIG.   164. — Echidna,  the  spiny  ant  eater. 

side  of  the  female  there  is  a  sort  of  pouch  in  which  the  eggs 
are  carried,  and  then  the  young,  for  some  time  after  they 
are  hatched.  Aside  from  the  habit  of  laying  eggs,  there 
are  various  other  features  which  indicate  the  relationship 
of  the  Mohotremes  to  the  reptiles;  the  group  may  be 
regarded  therefore  as  in  part  bridging  over  the  gap  between 
the  higher  mammals  and  the  reptile-like  ancestors  from 
which  they  were  derived. 

In  the  next  higher  order,  the  Marsupialia,  the  young  are 
brought  forth  alive,  but  in  a  very  immature  condition. 


THE   MAMMALS  213 

As  soon  as  born  they  are  placed  by  the  mother  in  a  pouch, 
or  marsupium,  on  the  under  side  of  the  body.  Here  they 
receive  nutriment  from  the  mammary  glands  and  are 
kept  warm  and  protected  from  enemies.  The  marsupials 
are  remarkable  for  their  geographical  distribution.  With 
the  exception  of  the  opossum  family  they  are  all  confined 
to  Australia  and  neighboring  islands,  although  remains  of 
their  skeletons  occur  in  "the  deposits  of  past  geological  ages 
in  all  the  continents  of  the  globe.  Where  the  marsupials 
have  been  brought  into  competition  with  the  higher  mam- 


FIG.   165. — Kangaroo. 

mals  they  have  had  to  succumb;  only  in  Australia  which 
has  been  isolated  from  the  rest  of  the  world  and  kept 
free  from  serious  invasion  by  other  mammals,  do  we  find  the 
marsupials  holding  their  own. 

Among  the  largest  of  the  marsupials  are  the  kangaroos 
which  are  remarkable  for  their  long  hind  legs  adapted  for 
jumping,  and  their  short  fore  legs.  There  is  a  great  diversity 
among  the  marsupials ;  some  are  herbivorous,  some  like  the 
"Tasmanian  tigers"  are  carnivorous,  some  burrow  in  the 
ground  like  the  moles,  and  still  others  are  arboreal.  Nature 
has  adapted  them  to  various  modes  of  life  very  much  as  she 


214  ANIMAL  BIOLOGY 

has  done  in  the  case  of  the  higher  mammals.  The  opossum 
family  is  represented  by  several  species  confined  to  North 
and  South  America.  The  common  Virginia  opossum  is 
prized  in  certain  localities  for  food.  Its  habit  of  feigning 
death,  or  " playing  possum,"  when  captured  or  cornered 
doubtless  often  serves  it  a  good  turn  by  deceiving  its 
enemies.  The  young  after  leaving  the  maternal  pouch 
are  carried  about  on  the  back  of  the  mother,  re- 
taining their  hold  not  only  by  their  claws,  but  by  winding 
their  tails  around  the  tail  or  limbs  of  their  parents. 


PIG.  166. — Virginia  opossums.     (Prom  Baker.) 

The  remaining  orders  of  the  Mammalia  are  often  termed 
the  placental  mammals,  because  the  young  are  retained  in 
the  uterus  until  a  comparatively  late  stage  of  development, 
being  attached  to  the  uterine  wall  by  a  vascular  organ, 
the  placenta,  which  serves  to  convey  nourishment  and 
oxygen  to  the  embryo  and  to  carry  away  its  waste  matter 
into  the  circulation  of  the  mother. 

Among  the  lowest  of  these  orders  are  the  Edentata, 
which  include  the  sloths,  armadillos,  and  the  ordinary 
ant  eaters.  The  teeth  are  either  absent,  as  the  name  of  the 
order  implies,  or  else  very  poorly  developed.  The  sloths 
are  inhabitants  of  Central  and  South  America  where  they 


THE   MAMMALS  215 

live  among  trees  in  which  they  commonly  move  about 
along  the  lower  side  of  the  branches,  with  their  backs 
downward.  The  armadillos  have  a  peculiar,  hard, 
scaly  armor.  If  threatened  with  danger  the  Armadillo 
rolls  up  into  a  ball,  like  a  pill  bug,  and  then  becomes  quite 
effectively  protected  by  its  horny  covering.  Most  of  the 
armadillos  live  in  South  America,  but  the  nine-banded 
armadillo  ranges  from  Paraguay  to  sou  them  Texas.  The 
ant  eaters  are  ungainly  creatures  with  long,  narrow  head 
and  slender  extensile  tongue.  The  giant  ant  eater 
of  South  America  may  reach  a  length  of  seven  feet,  but 


PIG.   167. — Nine-banded  armadillo. 

this  is  mainly  due  to  its  long  head  and  very  long,  bushy 
tail.  The  creatures  live  upon  ants,  tearing  open  ant 
hills  with  their  strong  claws  and  then  throwing  out  their 
long,  sticky  tongues  among  the  disturbed  insects  which 
adhere  to  it  and  are  then  drawn  into  the  mouth.  As  the 
tongue  is  worked  with  great  rapidity  the  ant  eater  will 
devour  a  populous  community  of  ants  in  a  short  time. 

The  odd  lot  of  creatures  which  constitute  the  living 
species  of  Edentates  represent  the  few  survivors  of  an 
order  of  animals  once  numerous  and  widely  distributed 
over  the  earth's  surface.  One  of  the  best  known  of  the 
fossil  forms  is  the  gigantic  Megatherium  of  South  America, 
which  reached  a  length  of  eighteen  feet.  The  Glyptodon 
which  sometimes  reached  a  length  of  twelve  feet  had  a 
solid  rounded  armor  of  bony  plates  resembling  the  shell 
of  a  huge  tortoise. 


2l6  ANIMAL  BIOLOGY 

The  order  Insectivora  includes  mostly  small  animals 
which  (as  the  name  implies)  feed  mainly  upon  insects. 
The  best  known  forms  are  the  moles  and  shrews.  The 
moles  are  characterized  by  their  soft  fur,  small  eyes  and 
ears  and  powerful  fore  legs  with  broad  hands  and  strong 
claws  fitted  for  digging  in  the  earth.  Moles  spend  nearly 
all  their  life  underground,  where  they  make  long  burrows, 
occasionally  throwing  up  mounds  of  earth,  or  "mole 
hills,"  above  their  chief  habitations.  The  shrews  are 
small  mouse-like  animals  which  lead  a  very  active  and 
mostly  underground  life  in  search  of  insects,  snails  and 
earthworms.  The  European  hedgehog  has  its  back  cov- 
ered with  a  coat  of  spines,  much  like  the  porcupines  which 
belong  to  a  quite  different  order  of  mammals,  and  are 
often  improperly  termed  hedgehogs  in  this  country. 

The  order  Rodentia,  or  gnawers,  is  a  very  large  group  of 
mostly  small  mammals  including  the  rats,  mice,  squirrels, 
gophers,  and  numerous  others.  Canine  teeth  are  lacking 
in  the  rodents,  and  the  incisors  are  chisel-like  and  capable 
of  continuous  growth  so  as  to  compensate  for  the  wear  that 
results  from  their  frequent  use.  The  rodents  are  largely 
vegetable  feeders,  consequently  many  species  are  very 
destructive.  Some  of  the  worst  offenders  are  the  common 
domestic  mouse  and  the  house  rat,  both  of  which  were 
introduced  into  this  country  from  Europe.  The  rat,  in 
addition  to  its  depredations  upon  grain  and  all  sorts  of 
stored  food,  is  an  important  agent  in  the  spread  of  the 
plague,  as  has  already  been  described  in  treating  of 
the  flea  which  may  carry  this  dangerous  disease  from  rats  to 
man.  Among  the  largest  of  the  rodents  are  the  porcu- 
pines. The  American  species  ranges  over  a  considerable 
part  of  North  America.  Among  the  most  valuable  and 
interesting  of  the  rodents  are  the  beavers  which  have 
been  much  sought  for  on  account  of  the  value  of  their  fur. 


THE   MAMMALS 


217 


Their  webbed,  hind  feet  and  broad,  flat  tail  adapt  them  for 
their  semi-aquatic  habits.  One  of  their  most  remarkable 
performances  is  the  construction  of  dams  across  streams. 
This  is  accomplished  by  cutting  down  trees  which  are  cut 
into  pieces  and  dragged  into  the  water  where  they  form 
the  basis  about  which  the  industrious  animals  gather 


FIG.   168. — A  beaver.     (After  Baker.) 

stones,  sticks  and  various  other  materials,  thus  damming 
up  the  water.  In  the  water  thus  backed  up  the  beavers 
usually  construct  their  mounds,  or  lodges,  which  sometimes 
rise  three  feet  above  the  surface.  These  lodges  are  formed 
of  sticks  and  stones  plastered  together  with  mud  and  are 
entered  only  through  the  water.  In  these  retreats  the 
beaver  passes  the  winter  in  security  from  ordinary  enemies. 


218 


ANIMAL  BIOLOGY 


The  group  Cheiroptera,  or  bats,  have  fore  limbs  modified 
into  wings.  The  second,  third,  fourth  and  fifth  digits  of 
the  fore  feet  are  enormously  lengthened  to  form  the  sup- 
port of  a  thin  membrane  stretched  between  them  and 
extending  from  the  fifth  digit  to  the  hind  leg  and  thence 
usually  to  the  tail.  The  first  digit,  or  thumb,  is  short, 
and  modified  into  a  sort  of  hook.  Our  common  bats  live 
mainly  upon  insects  which  they  catch  while  flying  during 
the  night  or  toward  evening.  Many  of  the  bats  of  the 
old  world  are  fruit  eaters,  and  certain  bats  of  Mexico  and 


FIG.  169. — Skeleton  of  a  bat. 

South  America  live  by  sucking  the  blood  of  mammals. 
They  attack  their  victims  while  the  latter  are  asleep;  and, 
after  making  incisions  with  their  very  sharp  teeth,  quietly 
suck  the  blood.  Many  bats,  but  by  no  means  all,  have 
very  small  eyes.  While  the  popular  notion  that  bats  are 
blind  is  incorrect,  these  animals  when  blinded  may  fly 
about  a  room  full  of  objects  or  even  strung  with  wires 
without  encountering  any  of  the  obstructions.  They 
apparently  have  other  very  acute  senses  which  warn  them 
of  the  proximity  of  obstacles  to  their  flight.  Bats  gener- 


TflE   MAMMALS 


219 


FIG.  170. — A  zebra.     (After  Baker.) 


FIG.   171. — Hippopotamus.      (After/  Baker.) 


22O  ANIMAL  BIOLOGY 

ally  hibernate  in  caves,  hollow  trees  or  other  dark  places 
to  which  they  commonly  retreat  during  the  day. 

The  order  Ungulata,  the  hoofed  animals,  constitutes 
one  of  the  largest  and  most  important  groups  of  mammals. 
In  general  ungulates  are  herbivorous;  their  molar  teeth 
are  fitted  for  grinding  and  the  canines  are  usually  small 
or  wanting.  The  order  is  commonly  divided  into  the 


FIG.   172. — African  elephant.     (After  Baker.) 

odd- toed  ungulates  (Perissodactyla),  such  as  the  horse, 
tapir  and  rhinoceros;  the  even-toed  ungulates  (Artio- 
dactyla),  such  as  the  ox,  sheep,  deer,  camel,  pig,  hippo- 
potamus; and  the  Proboscidea,  or  elephants. 

Some  of  the  even-toed  ungulates  such  as  the  deer, 
sheep  and  oxen  are  called  ruminants  on  account  of  their 
habit  of  chewing  a  cud.  Most  of  these  animals  have  a 
four-chambered  stomach,  one  division  of  which  receives 


THE   MAMMALS 

the  food  when  first  swallowed,  and  later  regurgitates  it  into 
the  mouth  where  it  is  thoroughly  chewed  at  leisure. 
Watch  a  herd  of  cattle  when  they  are  standing  quietly 
after  feeding  and  you  will  probably  see  them  engaged  in 
the  satisfying  operation  of  ruminating.  We  use  the 
term  ruminate  in  a  figurative  sense  signifying  to  ponder 
quietly  over  any  subject,  but  though  cattle  look  as  if 


PIG.   173.^— American  bison  and  calf.      (After  Allen.) 

they  might  be  engaged  in  solemn  reflective  thought  it  is 
reasonably  certain  that  the  appearance  is  quite  deceptive. 
Most  ruminants  are  provided  with  horns  which  may  be 
either  hollow  and  fitted  over  a  permanent  bony  core,  as 
in  the  ox  family,  or  Bovidae;  or  solid,  as  in  the  deer 
family,  or  Cervidae.  The  solid  horns,  or  antlers,  are 
generally  shed  annually,  breaking  off  at  the  base.  While 


222 


ANIMAL  BIOLOGY 


they  are  being  renewed  the  horns  are  covered  with  a 
furry  skin,  or  " velvet,"  which  becomes  dead  or  dried 
when  the  horns  are  full  grown  when  it  becomes  peeled  off. 
Antlers  are  generally  found  only  in  the  male,  but  the 
reindeer  has  them  in  both  sexes.  Their  usual  limitation 
to  the  male  sex  may  be  correlated  with  the  fact  that  the 
males  employ  them  frequently  in  fighting  with  one 
another,  especially  during  the  breeding  season.  In  the 


FIG.  174. — California  valley  elk.      (From  a  group  in  the  museum  of  the 
California  Academy  of  Sciences.) 


United  States,  deer  and  the  larger  related  forms,  the 
moose  and  elk,  have  rapidly  diminished  in  numbers,  and 
game  laws  are  enacted  for  their  protection  from  hunters. 
Related  to  the  deer  family  are  the  antelopes  which  are 
represented  in  North  America  by  the  beautiful  prong- 
horn  antelope  of  our  western  plains.  Of  the  hollow- 
horned  ruminants  the  once  abundant  but  now  nearly 


THE   MAMMALS 


223 


extinct  buffalo  and  the  Rocky  Mountain  sheep  are  the  best 
known  of  our  native  species.  None  of  the  odd-toed 
ungulates  are  native  to  the  United  States.  The  wild 
horses  and  asses  of  both  North  and  South  America  are 
descendants  of  animals  brought  over  from  the  old  world. 
The  order  Carnivora  includes  the  flesh  eaters,  viz.,  tigers, 
lions,  wolves,  dogs,  cats,  bears  and  many  other  related 


FIG.   175. — The  American  prong  horn  antelope.     (From  a  group  in  the 
museum  of  the  California  Academy  of  Sciences.) 

forms.  They  have  soft,  padded  feet  and  four  or  five  well- 
developed  toes,  with  strong  claws  which  in  the  cat  family 
are  curved  and  retractile  and  adapted  for  seizing  prey. 
The  teeth  are  fitted  for  tearing  flesh  rather  than  for  grind- 
ing, and  there  are  usually  well-developed,  pointed  canines. 
The  cat  family,  Felidae,  includes  some  of  the  largest  of 
the  flesh  eaters,  such  as  the  lions,  tigers  and  leopards  of 
the  old  world,  and  the  jaguars  and  pumas  of  the  new.  The 


224  ANIMAL  BIOLOGY 

puma  formerly  ranged  over  a  larger  part  of  temperate 
North  America,  but  in  the  United  States  it  is  now  limited 
to  the  west.  Formerly  it  inspired  much  fear  in  the  early 
settlers  who  commonly  called  it  the  panther  and  related 
many  thrilling  stories  of  its  ferocity.  As  a  rule,  however, 
it  is  exceedingly  shy  of  man  and  is  only  rarely  seen.  The 
somewhat  larger  South  American  jaguar  ranges  north 
through  Central  America  and  Mexico  into  southern  Texas. 
While  the  cat  family  is  exclusively  carnivorous,  the  bears 
and  their  smaller  allies,  the  raccoons,  will  eat  many  other 


FIG.   176. — African  leopard.          PIG.    177. — A  raccoon.     (From 

Baker.) 

things  besides  flesh,  such  as  nuts,  berries,  acorns  and  the 
leaves  of  plants.  The  largest  species  of  bear  in  the  United 
States,  the  grizzly,  is  now  found  only  in  a  few  remote 
localities  in  the  west. 

The  animals  of  one  division  of  the  carnivora,  the  Pinni- 
pedia,  have  taken  to  an  aquatic  life.  These  are  the  seals, 
sea-lions  and  walruses.  While  resembling  other  carnivores 
in  fundamental  features  of  structure,  the  pinnipeds  have 
undergone  striking  changes  of  external  form  in  adaptation 
to  living  in  the  water.  The  fore  legs  are  modified  into 


THE   MAMMALS 


225 


fin-like  flippers  fitted  for  swimming,  and  the  hind  limbs 
are  flattened  and  directed  backward.  Most  of  the  pinni- 
peds are  inhabitants  of  the  colder  parts  of  the  ocean. 
The  seals  especially  are  much  sought  after  for  their  fur 
and  they  have  consequently  decreased  considerably  in 
numbers,  so  that  it  has  been  found  necessary  to  protect 
their  breeding  places  by  law. 

The  most  exclusively  aquatic  of  the  mammals  are  the 
Cetacea  which  include   the  whales,   dolphins,  porpoises 


PIG.  178. — Habitat  group  of  Steller's  sea  lions  showing  large  male, 
females  and  young.  (Prom  a  group  in  the  museum  of  the  California 
Academy  of  Sciences.) 


and  their  allies.  The  whales  are  by  far  the  largest 
of  the  mammals,  the  largest  whale,  the  sulphur  bottom 
of  the  Pacific  Ocean,  reaching  a  length  of  ninety-five 
feet  and  a  weight  of  two  hundred  and  ninety-four 
thousand  pounds.  The  general  form  of  a  whale  is 
more  or  less  like  that  of  a  fish;  the  fore  legs  are  modified 
into  flattened  flippers  and  the  tail  is  expanded,  but  it 
differs  from  the  tail  of  a  fish  in  being  flattened  horizontally 
instead  of  vertically.  The  hind  limbs  of  whales  have  al- 
most disappeared,  being  represented  by  minute  rudiments 

15 


226  ANIMAL  BIOLOGY 

buried  deep  within  the  flesh.  In  the  whalebone  whales  the 
teeth  have  entirely  disappeared  in  the  adult,  but  they  ap- 
pear during  the  early  development  of  the  embryo,  thus 
indicating  the  descent  of  these  whales  from  toothed  ances- 
tors. What  is  commonly  called  whalebone  is  not  really 
bone,  but  a  horny  substance  that  occurs  in  the  form  of  a 
fringe  of  plates  attached  to  the  upper  jaws.  This  fringe 
serves  as  a  strainer  to  hold  in  the  creatures  the  whale 
catches  in  its  capacious  mouth  while  allowing  the  water  to 
pass  through.  Whales  feed  upon  fish,  squid  and  various 
small  animals  that  swim  in  the  open  ocean.  Hairs  in  the 
whales  are  almost  entirely  absent.  Heat  is  retained  in  the 
body  by  means  of  the  very  thick  layer  of  fat,  or  blubber, 
beneath  the  skin.  It  is  this  fat  that  yields  whale  oil,  the 
pursuit  of  which  led  to  an  extensive  whaling  industry  which 
was  carried  on  until  the  supply  of  whales  became  greatly 
reduced.  Spermaceti  is  a  product  of  an  oil  which  comes 
from  a  large  cavity  in  the  head  of  the  sperm  whale.  The 
latter  differs  from  the  whalebone  whales  in  having  numer- 
ous conical  teeth  instead  of  plates  of  whalebone.  The 
nostrils  of  whales  are  united  to  form  a  single  aperture  on 
the  upper  surface  of  the  head.  As  air  is  blown  out  of  this 
opening,  from  the  lungs,  a  column  of  spray,  the  con- 
densed moisture  of  the  breath,  appears  which  has  given 
rise  to  the  erroneous  notion  that  the  whale  spouts  out  the 
water  taken  in  through  the  mouth.  Whales  may  remain 
under  water  for  a  long  time,  but  like  all  animals  that  de- 
pend upon  their  lungs  for  their  supply  of  air  they  are  com- 
pelled to  come  to  the  surface  to  breathe. 

The  sea  cows  constitute  a  small  order  of  aquatic  mam- 
mals, called  the  Sirenia.  These  animals  live  in  rivers  or 
near  the  shore  of  the  ocean  where  they  feed  upon  aquatic 
vegetation.  One  of  the  largest  species,  Steller's  sea  cow, 
was  an  animal  of  twenty  to  thirty  feet  in  length,  inhabiting 


THE   MAMMALS  227 

the  Behring  sea.  As  the  animals  showed  little  fear  of  man 
they  were  entirely  exterminated  in  the  eighteenth  century 
by  hunters  who  killed  them  for  food.  Another  species 
occurs  on  the  coast  of  Florida  and  a  few  others  in  the  old 
world. 

The  Primates  which  comprise  the  lemurs,  monkeys, 
apes  and  man  constitute  the  highest  of  the  mammals. 
The  higher  primates  approach  man  in  the  general  form 
of  the  body,  the  occasional  upright  position,  opposable 
thumb  which  permits  the  foot  to  be  used  as  a  hand,  and 
in  many  other  features  of  structure.  The  lower  primates, 
the  lemurs,  generally  go  on  all  fours  and  have  a  protruding 
muzzle  like  that  of  a  dog.  The  lemurs  are  confined  to 
Africa,  the  Orient  and  Madagascar,  being  most  numerous 
in  the  latter  island  where  they  constitute  a  large  part  of 
the  mammalian  fauna. 

The  primates  of  the  new  world  have  a  broad  nose  and 
usually  a  long  tail  which  is  employed  to  wrap  around  the 
branches  of  trees  from  which  the  monkeys  frequently 
suspend  themselves.  There  are  many  species  of  rather 
small  size  confined  to  South  and  Central  America,  but 
none  occur  native  in  the  United  States. 

The  old  world  primates  are  much  more  varied  in  char- 
acter. While  they  include  many  interesting  forms,  the 
chief  interest  attaches  to  the  large,  anthropoid  (man-like) 
apes  which  are  of  all  animals  the  most  closely  related  to 
man.  The  anthropoids  include  the  gorillas,  chimpanzees, 
orangutans  and  the  gibbons,  the  latter  being  the  lowest 
and  most  monkey-like  of  the  group.  The  orangs  are  con- 
fined to  Borneo  and  Sumatra  where  they  live  mainly  in 
trees.  The  chimpanzees  are  natives  of  Africa  living  mostly 
in  wooded  regions.  While  commonly  walking  on  all  fours 
chimpanzees  are  capable  of  walking  erect  and  they  use  their 
hands  in  a  very  human  way.  They  are  known  to  throw 


228 


ANIMAL  BIOLOGY 


FIG.  179. — A  South  American  arboreal  monkey,  Cebus.     (From  photo 
by  Sanborn,  with  permission  of  the  New  York  Geological  Society.) 


THE   MAMMALS 


229 


sticks  and  stones  at  their  enemies,  and  to  use  sticks  for  pull- 
ing in  objects  otherwise  out  of  reach.  Trained  chimpanzees 
have  been  taught  to  ride  a  bicycle,  skate  on  roller  skates, 


FIG.   1 80. — Young  chimpanzee. 

eat  at  a  table  with  knife,  fork  and  spoon,  and  to  select  one 
of  a  bunch  of  keys  and  unlock  a  lock.  Although  savage 
fighters,  chimpanzees  are  very  fond  of  their  mates  and 
offspring,  and  often  manifest  intense  grief  over  the  loss 


230  ANIMAL  BIOLOGY 

of  one  of  their  family  group.  The  father  and  mother  of  a 
family  appear  to  remain  together  permanently.  Either 
sex  may  carry  the  young  offspring  about  in  the  arms  much 
as  human  beings  carry  their  babies. 

The  largest  and  strongest  of  the  apes  is  the  gorilla,  a 
native  of  Africa.  The  gorilla  lives  in  forests,  often  con- 
structing a  sort  of  nest  in  the  branches  of  a  tree  where  it 
spends  the  night.  Powerful,  brutal,  ferocious,  the  gorilla 
is  a  formidable  foe;  but  one  which  rarely  if  ever  attacks 
man  unprovoked.  Gorillas  have  never  been  kept  very 
long  in  captivity.  They  sulk,  lose  their  spirit,  and  if  they 
do  not  succumb  to  tuberculosis,  which  kills  so  many  of  the 
apes  in  captivity,  they  languish  and  die,  apparently 
through  sheer  mental  depression. 

The  older  naturalists  set  man  apart  in  a  group  by  him- 
self, but  as  Huxley  conclusively  showed  by  a  very  thorough 
comparison  of  the  structure  of  man  with  that  of  the  apes, 
man  differs  less  in  structure  from  the  higher  apes  than  the 
latter  differ  from  the  lower  members  of  the  order  of 
primates.  Man  differs  greatly  from  the  apes  in  the  size 
of  the  'brain,  which  is  a  certain  though  inadequate  index 
of  his  greatly  superior  intelligence.  There  is  abundant 
evidence  that  the  apes  are  by  far  the  most  intelligent  of 
the  animals  below  man;  but  it  is  quite  certain  that  the 
intellect  of  the  lowest  savage  stands  very  high  above  that 
of  his  highest  simian  relative.  There  are  no  "connecting 
links"  between  man  and  ape  at  present  living  on  the  earth, 
but  in  ancient  deposits  fossil  bones  of  human  beings  have 
been  discovered  which  probably  belonged  to  a  type  of  man 
more  primitive  than  any  existing  race. 

Man  is  regarded  as  constituting  a  separate  family,  the 
Hominidas,  and  a  single  genus,  Homo.  The  various  kinds 
of  men,  notwithstanding  their  marked  differences,  are 
commonly  considered  as  members  of  a  single  species, 


THE    MAMMALS  231 

Homo  sapiens.  Man's  permanently  upright  walk,  hairless 
body,  and  large  brain  are  among  the  more  conspicuous 
differences  in  structure  separating  him  from  the  apes,  but 
there  is  nevertheless  an  astonishing  similarity  in  many 
other  structural  peculiarities  as  well  as  in  embryological 
development.  In  a  later  chapter  some  of  these  character- 
istics will  be  briefly  described. 


CHAPTER  XXIII 
THE  CHEMICAL  BASIS  OF  LIFE 

The  division  of  Biology  which  deals  with  the  activities 
or  functions  of  the  parts  of  a  living  organism  is  known 
as  physiology,  as  distinguished  from  morphology  which 
deals  with  the  structure  of  organisms.  The  activities 
of  an  organism  are  in  part  physical  and  in  part  chemical. 
The  material  world  both  living  and  non-living  is  made  up 
of  a  limited  number  (about  eighty)  of  substances,  called 
elements  which  cannot  be  separated  further  into  substances 
of  different  kinds.  Different  -elements  may  be  grouped 
together  to  form  compounds  and  compounds  may  be 
separated  into  their  elements.  Thus  common  salt  is  a 
compound  composed  of  two  elements  sodium  and  chlorine, 
but  the  elements  themselves  cannot  ordinarily  be  de- 
composed further.  Changes  which  involve  the  combina- 
tion, separation  or  rearrangement  of  elements  are  known 
as  chemical  changes.  The  rusting  of  iron  is  a  chemical 
change.  Iron,  an  element,  combining  with  the  oxygen 
of  the  air,  another  element,  produces  a  substance,  iron 
oxide,  which  is  very  different  in  appearance  and  properties 
from  either  of  its  constituents.  Other  chemical  changes 
are  the  burning  of  wood  and  coal,  the  action  of  acid  on 
soda  and  the  fermentation  of  sugar.  In  all  these  cases 
there  are  changes  between  the  elements  of  the  substances 
involved  in  the  process,  resulting  in  the  production  of 
very  different  kinds  of  substances.  Changes  which  do 
not  involve  any  alteration  of  the  elementary  composition 
of  bodies  are  called  physical.  The  conversion  of  water 

232 


THE   CHEMICAL  BASIS   OF   LIFE  233 

into  steam  or  ice,  the  solution  of  sugar  in  water,  the 
mechanical  movement  of  bodies,  and  the  propagation 
of  sound,  light  and  electricity  are  physical  changes  and 
their  treatment  belongs  to  the  science  of  physics. 

One  striking  peculiarity  of  chemical  changes  is  that  they 
occur  between  certain  definite  proportions  of  the  elements 
involved.  This  principle  is  called  "the  law  of  definite 
proportions."  Thus  sodium  and  chlorine  always  combine 
in  a  certain  definite  ratio  by  weight,  23  parts  of  sodium 
to  35.5  parts  of  chlorine  to  form  common  salt,  or  sodium 
chloride.  If  more  of  one  or  the  other  element  is  present 
it  simply  remains  uncombined.  Sometimes  different 
elements  may  combine  with  each  other  in  more  than  one 
ratio,  but  the  different  ratios  have  a  simple  relation  to 
one  another.  Thus  carbon  and  oxygen  may  combine 
in  the  ratio  of  twelve  parts  of  carbon  to  sixteen  parts 
of  oxygen  to  form  a  gas,  carbon  monoxide  (CO),  and  also 
in  the  ratio  of  twelve  parts  of  carbon  to  thirty-two  of 
oxygen  to  form  carbon  dioxide  or  carbonic  acid  gas 
(C02)  which  has  properties  very  different  from  those  of 
carbon  monoxide.  In  carbon  dioxide  there  is  just  twice 
as  much  oxygen  in  the  compound  as  in  carbon  monoxide. 
The  definite  numerical  ratios  in  which  elements  unite 
into  compounds  form  one  of  the  several  considerations 
that  have  led  men  of  science  to  the  view  that  chemical 
elements  are  made  up  of  minute,  indivisible  bodies  called 
atoms.  The  atoms  may  be  united  into  groups  called 
molecules,  a  molecule  being  the  smallest  part  into  which 
a  compound  may  be  divided  without  losing  its  properties. 
The  division  of  a  substance  into  molecules  may  involve 
nothing  but  physical  changes,  but  to  divide  a  molecule 
into  its  constituent  atoms  would  constitute  a  chemical 
change. 

In  order  to  express  the  chemical  constitution  of  bodies 


234  ANIMAL  BIOLOGY 

in  a  convenient  form  chemists  have  given  the  elements 
certain  symbols,  H  for  hydrogen,  O  for  oxygen,  C  for 
carbon,  N  for  nitrogen,  S  for  sulphur,  K  for  potassium 
(kalium),  Na  for  sodium  (natrium),  etc.  The  chemical 
composition  of  bodies  may  be  indicated  by  groups  of 
symbols  representing  their  constituent  elements:  salt, 
NaCl;  water  H2O;  carbon  dioxide,  C02;  sulphuric  acid, 
H2SO4;  etc.  Each  molecule  of  common  salt  is  supposed 
to  contain  one  atom  of  sodium  and  one  atom  of  chlorine; 
each  molecule  of  water  two  atoms  of  hydrogen  to  one  of 
oxygen;  and  each  molecule  of  sulphuric  acid,  two  atoms 
of  hydrogen,  one  of  sulphur  and  four  of  oxygen. 

Chemical  changes  or  reactions  are  expressed  in  the  form 
of  an  equation;  thus  the  formation  of  water  by  the  ad- 
dition of  oxygen  and  hydrogen  is  indicated  by  2H  +  O  = 
H2O  and  the  decomposition  of  calcium  carbonate  by  heat, 

CaCO3  •=  CaO  +  CO2 

Calcium        Calcium        Carbon 
carbonate          oxide  dioxide 

Besides  the  chemical  changes  resulting  from  the  simple 
combination  or  dissociation  of  elements  as  in  the  two 
illustrations  just  given,  we  may  have,  in  bringing  together 
two  compounds,  an  exchange  of  certain  of  their  elements. 
Thus  putting  sodium  chloride,  NaCl,  and  sulphuric 
acid  together,  the  sodium  and  the  hydrogen  of  the  two 
compounds  exchange  places. 

2NaCl  +  H2SO4  =  Na2SO4  +  2HC1 

Sodium          Sulphuric  Sodium         Hydrochloric 

chloride  acid  sulphate  acid 

Living  matter  is  composed  of  comparatively  few 
elements.  Certain  of  these  are  found  in  all  organisms 
while  the  occurrence  of  others  is  less  widespread.  De- 
scriptions are  here  given  only  of  the  more  important  ones. 


THE  CHEMICAL  BASIS  OF  LIFE  235 

OXYGEN 

Oxygen  is  a  transparent,  odorless  gas  which  unites 
readily  with  a  large  number  of  elements  and  compounds. 
It  is  one  of  the  most  abundant  elements,  as  it  occurs 
in  water,  and  forms,  in  combination  with  various  minerals, 
about  one-half  of  the  earth's  crust.  Air  is  composed  of 
about  one  part  of  oxygen  to  four  of  nitrogen  together  with 
small  quantities  of  water  vapor  and  other  gases.  The 
oxygen  of  the  air  is  simply  mixed  with  nitrogen  and  not 
chemically  combined  with  it.  Oxygen  in  a  pure  state 
may  be  obtained  by  the  decomposition  of  water  by  the 
electric  current  or  by  heating  various  substances  that 
contain  it  in  chemical  combination.  In  its  pure  state 
it  acts  very  vigorously  upon  many  substances  that  it 
attacks  but  feebly  in  the  air.  Thus  a  steel  watch  spring 
will  burn  in  pure  oxygen  and  a  glowing  match  thrust 
into  pure  oxygen  will  quickly  burst  into  flame.  Most 
of  what  is  called  combustion  or  burning  is  the  combination 
of  substances  with  oxygen.  When  wood  and  coal  are 
burned  they  combine  with  the  oxygen  of  the  air  giving 
rise  mainly  to  carbon  dioxide  and  water.  The  combina- 
tion of  substances  with  oxygen  is  called  oxidation,  a 
process  which  may  be  a  rapid  chemical  change  such  as 
takes  place  in  the  explosion  that  occurs  when  oxygen 
and  hydrogen  are  mixed  and  ignited,  or  a  very  slow  one 
such  as  the  gradual  rusting  of  iron.  Oxidation  plays  an 
essential  role  in  the  living  body.  Oxygen  occurs  in  all 
living  tissues,  and  it  is  found  in  all  foods. 

CARBON 

Carbon  is  a  solid  devoid  of  taste  or  odor.  It  may  be 
seen  in  almost  pure  form  in  charcoal.  When  burned  it 
combines  with  oxygen  to  form  a  gas,  carbon  dioxide. 


236  ANIMAL  BIOLOGY 

This  gas  is  a  common  product  of  living  bodies,  since  it 
results  from  the  action  of  oxygen  on  the  carbon  contained 
in  living  tissue.  Carbon  occurs  in  all  tissues  and  in  all 
foods. 

HYDROGEN 

This  element  naturally  occurs  in  all  organisms  since  it 
is  one  of  the  constituents  of  water,  but  it  is  found  also 
in  other  combinations  in  all  living  substance.  It  is  a 
very  light,  transparent,  odorless  gas  that  enters  very 
freely  into  composition  with  oxygen,  chlorine,  carbon  and 
a  number  of  other  elements. 

NITROGEN 

This  element  is  a  rather  inert  gas,  transparent  and 
odorless,  as  we  might  infer -from  its  constituting  about 
four-fifths  of  the  atmosphere. 

Other  elements  contained  in  living  bodies  are  sodium, 
potassium,  calcium,  sulphur,  phosphorus,  chlorine,  iron, 
iodine,  and  in  some  cases  silicon,  manganese  and  copper. 
Many  of  these  elements  occur  in  the  form  of  salts  which, 
while  not  commonly  classed  as  foods,  are  nevertheless 
necessary  to  maintain  the  life  of  the  body.  The  elements 
of  the  living  body  are  for  the  most  part  combined  to  form 
substances  of  a  good  deal  of  complexity.  Most  of  the 
compounds  formed  are  not  found  elsewhere  in  nature, 
and  they  are  consequently  known  as  organic  compounds. 
It  was  formerly  held  that  organic  compounds  could  be 
formed  only  through  the  agency  of  life,  but  chemists 
have  succeeded  in  making  a  good  many  of  them  artificially 
in  the  laboratory.  The  very  complex  and  unstable  com- 
pounds more  immediately  associated  with  the  phenomena 
of  life  it  is  still  impossible  to  fabricate.  The  body  of  the 
simplest  organism  is  a  chemical  laboratory  in  which 


THE   CHEMICAL  BASIS   OF   LIFE  237 

processes  go  on  that  are  far  more  complex  than  those 
which  the  chemist  has  been  able  to  control. 

Animals  differ  from  most  plants  in  requiring  organic 
compounds  for  their  food.  Most  plants  are  able  to 
manufacture  their  living  substance  from  the  inorganic 
constituents  of  the  air  and  soil,  but  animals  are  compelled 
to  live  upon  plants  or  other  animals  which  furnish  food 
in  the  form  of  organic  matter.  Organic  food  substances 
fall  into  three  principal  classes:  proteins,  carbohydrates 
and  fats.  Proteins  are  complex  compounds  containing 
C,  H,  O,  N,  and  frequently  other  elements.  The  white 
of  egg,  cheese,  and  the  lean  fiber  of  meat  consist  almost 
entirely  of  protein.  All  living  matter  contains  protein 
material  which  alone  can  supply  the  nitrogen  for  the 
animal  body.  Fats  are  more  or  less  oily  substances 
containing  C,  O,  and  H.  They  are  quite  readily  oxidized 
and  yield  a  considerable  quantity  of  heat.  Butter,  olive 
oil,  suet,  lard  and  tallow  are  common  examples  of  fatty 
substances. 

Carbohydrates  are  composed  of  C,  H  and  O,  there  being 
twice  as  many  atoms  of  H  as  O  in  the  molecule.  They 
include  such  substances  as  sugar,  starch  and  cellulose. 
Starch  is  commonly  stored  in  the  cells  of  plants  in  the  form 
of  grains  with  concentric  layers  like  the  coats  of  an  onion. 
When  treated  with  iodine  it  turns  blue.  It  is  insoluble  in 
water,  but  it  may  be  converted  into  sugar  by  fermentation. 

This  process  of  fermentation  is  one  of  the  most  common 
kinds  of  chemical  action  that  takes  place  in  organisms. 
It  may  be  illustrated  in  the  fermentation  of  sugar  or 
molasses.  If  a  small  amount  of  yeast  is  added  to  a  solu- 
tion of  sugar,  after  a  time  small  bubbles  of  gas  (CC^)  may 
be  seen  to  arise  from  it,  and  its  temperature  increases. 
After  the  process  has  run  its  course  the  sugar  in  the  solu- 
tion disappears  and  in  its  place  there  is  found  a  certain 


238  ANIMAL  BIOLOGY 

amount  of  alcohol.  The  conversion  of  grape  juice  into 
wine  depends  upon  the  fermentation  of  the  sugar  of  the 
fruit  into  alcohol  and  carbon  dioxide.  The  fermenting 
agent  is  here  the  yeast  plants,  minute  plant  organisms 
which  rapidly  multiply  in  the  liquid.  Alcohol  itself  may 
be  fermented  by  other  organisms  that  convert  it  into  acetic 
acid  which  is  the  acid  of  vinegar. 

There  are  a  great  many  kinds  of  fermentation  caused 
by  different  species  of  yeast  and  bacteria.  Fermentation 
may  be  caused  also  by  certain  substances  called  ferments  or 
enzymes.  Ferments  are  produced  by  organisms  and  they 
have  the  remarkable  property  of  converting  a  great  many 
times  their  own  bulk  of  other  substances.  A  very  small 
amount  of  an  enzyme  may  convert  a  very  large  amount 
of  a  material  without  suffering  any  appreciable  loss.  Hu- 
man saliva  contains  a  ferment,  ptyalin,  that  converts 
starch  into  sugar.  In  the  gastric  juice,  which  is  a  secre- 
tion of  the  stomach,  there  is  another  ferment,  pepsin, 
which  converts  proteins  into  simpler  compounds  called 
peptones.  By  fermentation  complex  substances  are 
split  up  into  simpler  ones  and  these  again  may  be  further 
split  up  by  other  ferments.  Heat  is  liberated  during 
fermentation  and  energy  is  thus  supplied  to  the  body. 
Under  certain  conditions  enzymes  may  build  up  more 
complex  compounds  out  of  simpler  ones,  thus  affording  a 
means  of  keeping  up  the  supply  of  complex  substances  in 
the  body. 

The  real  living  substance  of  an  organism,  or  in 
Huxley's  phrase  "  the  physical  basis  of  life, "  is  commonly 
called  protoplasm.  This  is  a  semifluid  substance  of  a 
great  chemical  complexity,  and  it  differs  somewhat  in 
composition  in  different  species  of  animals  and  plants.' 
It  contains,  C, H,  O,  N,  and  frequently  S,  P  and  K.  Unlike 
the  substances  just  described,  protoplasm  has  the  power 


THE   CHEMICAL  BASIS   OF   LIFE  239 

of  active  growth,  taking  up  food  materials  of  various  kinds 
and  converting  them  into  its  own  substance.  This 
process  which  is  known  as  assimilation  is  an  essential  at- 
tribute of  all  living  material.  The  assimilated  material 
is  not  added  to  the  outside  as  in  the  growth  of  stones  and 
most  crystals,  but  permeates  the  entire  mass.  An  animal 
may  live  upon  various  other  kinds  of  protoplasm,  but  the 
foreign  protoplasm  is  broken  down  and  absorbed,  and  then 
worked  over  in  the  wonderful  chemical  laboratory  of  the 
living  tissues  into  the  peculiar  protoplasm  of  the  devouring 
animal. 

Along  with  the  assimilation  of  food,  protoplasm  is 
continually  undergoing  a  process  of  breaking  down  or 
waste,  and  the  materials  so  formed  are  got  rid  of.  This 
process  is  called  excretion.  A  living  organism  may  thus 
be  compared  to  a  vortex  through  which  matter  is  con- 
tinually passing;  the  food  taken  in  is  broken  down  and 
built  up  into  living  substance  which  after  a  time  is  broken 
down  again  and  eliminated.  The  form  of  the  organism, 
like  that  of  a  vortex  or  a  waterfall,  may  remain  constant, 
but  the  matter  of  which  it  is  composed  is  subject  to  a  con- 
tinual change. 

All  protoplasm  requires  oxygen.  The  oxidation  of  pro- 
toplasm supplies  heat  and  other  forms  of  energy  just  as 
the  oxidation  or  burning  of  coal  in  a  furnace  supplies 
heat  for  the  running  of  an  engine.  Among  the  most 
common  products  of  oxidation  in  living  matter  are  car- 
bon dioxide  and  water  which  are  the  same  compounds 
that  result  from  the  burning  of  a  candle  or  a  piece  of  wood. 
The  union  of  organic  substance  with  oxygen  and  the  giving 
off  of  the  products  of  this  union  (CO2  and  H^O)  is  called 
respiration.  The  cessation  of  respiration  results  in  the 
death  of  an  organism  just  as  the  withdrawal  of  oxygen 
will  quickly  put  out  a  fire. 


CHAPTER  XXIV 
CELLS  AND  TISSUES 

One  of  the  most  remarkable  of  the  properties  of  "the 
physical  basis  of  life"  is  its  tendency  to  build  itself  up  into 
a  definite  form  and  structure.  Cattle,  sheep,  insect  larvae, 
and  even  parasite  fungi  and  bacteria  may  all  live  upon 
the  tissue  of  the  same  kind  of  plant,  each  organism  con- 
verting the  plant's  tissue  into  its  own  peculiar  kind  of  pro- 
toplasm. We  ourselves  eat  many  kinds  of  meat  and  vege- 
tables, but  these  foods  are  all  converted  into  our  own  living 
substance.  The  form  assumed  by  each  creature  depends 
very  little  upon  the  food  it  assimilates,  but  very  much  upon 
the  chemical  and  physical  properties  of  the  protoplasm 
that  is  peculiar  to  its  species.  Each  kind  of  protoplasm 
tends  to  produce  its  own  particular  kind  of  organization, 
be  it  man,  dog,  worm  or  plant. 

The  body  of  a  higher  animal  such  as  man  is  a  wonderfully 
complex  mechanism,  and  in  order  to  carry  on  its  many 
kinds  of  activities  it  is  divided  up  into  different  parts  or 
organs  each  of  which  is  especially  fitted  for  its  peculiar 
work.  Thus  we  have  organs  of  locomotion,  organs  such 
as  the  stomach,  liver,  etc.,  for  the  work  of  digestion, 
organs  of  circulation  for  propelling  and  conducting  the 
blood,  organs  of  respiration,  excretion,  and  many  others. 
In  a  very  simple  animal  such  as  the  Amoeba  these  various 
activities  or  functions  are  carried  on  by  all  parts  of  the 
jelly-like  body.  There  are  no  especial  organs  for  the  func- 
tion of  respiration  or  digestion  or  any  other  activities. 
Food  is  taken  in  anywhere  and  digested  anywhere  in  the 

240 


CELLS   AND   TISSUES  241 

interior  of  the  animal.  Respiration  takes  place  all  over 
its  surface  and  there  is  a  constant  circulation  of  the  living 
substances. 

As  we  pass  up  the  scale  to  an  animal  such  as  the  fresh- 
water Hydra  we  find  digestion  carried  on  in  the  interior 
cavity  of  the  body;  there  are  definite  organs,  the  tentacles, 
for  the  capture  of  food;  there  are  muscle  fibers  which  by 
their  contraction  change  the  form  of  the  body;  and  there  are 
special  nettling  cells  set  apart  for  the  purpose  of  protection. 
Nevertheless  respiration  is  carried  on,  not  by  special  or- 
gans, but  over  the  entire  surface  of  the  body;  all  parts  of 
the  body  apparently  eliminate  waste  products;  there  is  no 
blood,  nor  are  there  organs  of  circulation.  Special  or- 
gans have  been  set  apart  for  some  kinds  of  work,  while 
other  functions  are  discharged  by  the  body  in  general 
much  as  in  the  Amoeba. 

When  we  come  to  higher  animals  there  are  organs  es- 
pecially fitted  for  respiration,  such  as  the  gills  of  fishes 
and  the  lungs  of  mammals;  special  organs  are  adapted 
for  excretion,  such  as  the  kidneys;  and  other  organs  are 
exclusively  concerned  with  the  circulation  of  the  blood. 
Passing  up  the  scale  of  life  more  and  more  organs  are  added ; 
each  becomes  especially  fitted  for  its  work  and  at  the  same 
time  less  able  to  do  the  work  of  other  parts. 

The  organs  of  a  higher  animal  are  formed  of  different 
kinds  of  materials  called  tissues,  and  most  tissues  are  in 
turn  composed  mainly  of  small  bodies  called  cells  which 
bear  somewhat  the  same  relation  to  the  organism  as  a 
whole  as  bricks  bear  to  a  brick  house.  Cells  are  masses  of 
protoplasm,  commonly,  though  not  always,  surrounded 
by  a  membrane  or  cell  wall,  and  containing  a  small  vesicle 
known  as  the  nucleus.  The  latter  structure  is  an  essential 
element  in  the  life  of  the  cell.  Cells  multiply  by  a  process 
of  fission,  the  nucleus  dividing  along  with  the  protoplasm 

16 


242 


ANIMAL  BIOLOGY 


of  the  cell  body.  In  a  certain  sense,  cells  may  be  regarded 
as  little  organisms,  capable  of  growth,  and  multiplication; 
the  body  being,  as  it  were,  a  society  of  cells.  As  cells  have 
such  varied  things  to  do  in  the  work  of  the  body  it  is  very 
natural  that  they  have  different  shapes  and  structures, 
and  the  several  varieties  of  tissues  owe  their  differences 
largely  to  the  different  kinds  of  cells  of  which  they  are 
composed.  The  more  common  tissues  fall  into  the  follow- 
ing classes: 

Epithelium. — Epithelial  tissues  occur  commonly  in  the 
form  of  layers,  the  cells  of  which  fit  very  closely  together. 


FIG.  181. — Forms  of  epithelium. 
A,  flattened  or  squamous;  B,  cili- 
ated; C,  columnar. 


FIG.  182. — Fibrous 
connective  tissue  show- 
ing fibers  and  a  few  cells. 


Such  tissue  is  found  covering  the  outer  surface  of  the  body 
and  lining  its  various  cavities  such  as  the  alimentary  canal, 
the  ccelom,  or  body  cavity,  the  interior  of  blood  vessels, 
etc.  Sometimes  the  cells  are  very  thin  and  flattened 
(squamous  epithelium),  or  sometimes  nearly  cubical 
(cuboid  epithelium),  and  very  often  elongated  (columnar 
epithelium).  In  the  variety  known  as  ciliated  epithleium 
the  free  edges  of  the  cells  are  covered  with  cilia  or  short 
hair-like  processes  which  beat  to  and  fro  creating  a  current 
in  the  liquid  bathing  the  cell. 

Connective  tissue  is  composed  usually  of  scattered  cells 


CELLS   AND   TISSUES 


243 


between  which  occurs  more  or  less  intercellular  substance. 
The  general  function  of  connective  tissue  is  to  hold  various 
parts  together  and  to  act  as  a  supporting  substance.  It 
occurs  in  bone  and  in  cartilage  (gristle),  in  ligaments  and 
tendons,  and  in  the  form  of  membranes  and  networks 
binding  together  the  cells  of  various  organs. 


A  B 

FIG.   183. — Cartilage.  FIG.   184. — A,   part   of  a  striated 

muscle   fiber;  B,  fibers   of  unstriated 
or  involuntary  muscle. 

Muscular  tissue  is  composed  of  elongated  cells  which 
have  the  property  of  contracting  strongly  when  they  are 
stimulated.  In  striated  muscle  which  composes  the  great 


FIG.   185. — Nerve  cell,     d,  branching  dendrites;  n,  process  forming  the 
axis  cylinder  of  a  nerve  fiber. 

mass  of  the  muscles  of  our  limbs  and  body  the  cells  are 
marked  with  longitudinal  striations  due  to  the  pressure  of 
very  fine  thread-like  structures  called  fibrillce.  There  are 


244  ANIMAL  BIOLOGY 

also  cross  striations  running  across  the  cell,  and  generally 
several  nuclei  in  each  fiber.  In  unstriated  muscle  the 
cells  are  generally  smaller,  and  have  no  cross  striations  and 
there  is  one  nucleus  to  a  cell. 

Nervous  tissue  is  composed  of  cells  and  fibers  which  make 
up  the  nervous  system. 

Most  organs  of  the  body  are  composed  of  several  tissues. 
The  heart  for  instance  consists  mainly  of  muscle  fibers, 
but  these  fibers  are  held  together  by  connective  tissue. 
There  is  a  coat  of  epithelium  lining  the  cavity  of  the  heart 
as  well  as  its  outer  surface,  and  there  are  nerve  cells  and 
fibers  embedded  in  the  heart  muscle. 


CHAPTER  XXV 
DIGESTION 

What  we  call  living  embraces  a  multitude  of  different 
activities.  In  your  bodies  while  you  are  reading  this 
paragraph,  muscles  are  contracting,  nerves  are  conducting 
stimuli,  air  is  being  drawn  into  and  expelled  from  the  lungs, 
the  blood  is  surging  through  the  blood  vessels,  absorption 
is  taking  place  through  epithelial  membranes,  waste 
matter  is  being  eliminated  from  the  blood,  every  cell  is 
being  built  up  and  torn  down,  chemical  changes  are  tak'ng 
place  in  every  bit  of  living  matter.  It  is  these  chemical 
changes  that  keep  your  body  warm  and  supply  the  energy 
for  its  various  activities.  Were  the  chemical  changes  to 
stop,  everything  else  would  stop,  and  the  body  would 
become  inert  and  cold.  We  might  compare  our  bodies  to  a 
steam  engine  whose  supply  of  energy  comes  from  the 
burning  of  coal  in  the  furnace,  or  in  other  words  the 
chemical  union  of  carbon  and  perhaps  a  certain  amount  of 
hydrogen  with  the  oxygen  of  the  air.  The  movement  of 
levers  and  wheels  depends  on  the  expansion  of  steam  which 
is  caused  by  the  heat  generated  by  chemical  changes. 
Without  the  burning  coal  the  engine  would  be  inert  and 
cold.  To  keep  the  engine  running,  more  coal  is  continually 
added  to  the  furnace,  the  ashes  or  unburned  waste  are 
removed,  and  there  are  arrangements  for  removing  the 
smoke  and  carbon  dioxide  resulting  from  the  burning  of  the 
fuel. 

What  fuel  is  to  the  engine  food  is  to  our  bodies.  Our 
food  supplies  not  only  the  material  from  which  our  bodies 

245 


246 


ANIMAL  BIOLOGY 


are  built,  but  it  furnishes  the  energy  for  performing  the 
work  of  the  body.  In  order  to  yield  this  energy  the  food 
must  undergo  chemical  decomposition.  It  is  split  up  by 
ferments,  and  then  oxidized  or  burned  in  the  various  tis- 
sues. Some  of  these  chemical  changes  result  in  the 
building  up  of  living  matter  out  of  simpler  substances. 
Others  result  in  its  tearing  down  or  decomposition. 

J 


FIG.  186. — A,  the  heart;  B,  the  lungs  drawn  aside  to  show  the  internal 
organs;  C,  diaphragm;  D,  liver;  F,  gall  cyst;  E,  stomach;  G,  small  intes- 
tine; H,  large  intestine.  (After  Le  Pileur.) 

In  vital  activity  we  therefore  have  a  twofold  process 
of  waste  and  repair — a  process  known  as  metabolism — 
which  goes  on  continually.  Metabolism  is  the  very  care 
and  essence  of  vital  activity;  all  other  processes  are  depend- 
ent upon  it.  But  as  it  always  involves  waste,  it  always 
requires  new  material  or  food  to  enable  it  to  keep  going. 
In  order  that  the  various  organs  of  the  body  can  re- 


DIGESTION 


247 


ceive  food  material  for  their  growth  and  activities  the 
food  must  be  prepared  for  being  assimilated.  Such  prep- 
aration is  the  work  of  the  organs  of  digestion.  These 
organs  act  upon  the  food  so  as  to  convert  it  into  a  soluble 
form  capable  of  passing  by  osmosis  into  the  tissues  where 


Molars. 


Pre-molars.     Canine.      Incisors. 


PIG.   187. — Human  teeth. 

it  is  assimilated.  The  conversion  of  food  into  soluble 
form  commonly  involves  both  mechanical  and  chemical 
processes.  In  man  and  many  other  animals  food  is 
chewed  so  that  it  is  divided  up  into  smaller  particles 
which  can  be  acted  on  more  readily  by  the  digestive  juices. 
Another  mechanical  process 
consists  in  moving  the  food 
through  the  alimentary  canal 
where  it  is  acted  upon  by 
ferments  and  absorbed. 
These  functions  involve 
various  organs  which  will 
now  be  described. 

The  Teeth. — In  man  there 
are    thirty-two    teeth.     The 


N 


FIG.   1 8 8. —Teeth  of  child  of  six 
and  one  half  years.     /,  incisors;  O, 
canine;  M,  molars;  E,  permanent 
-,      .  incisors;  C,  canine;    R,  bicuspids; 

two  front  pairs  in  each  jaw    N§  moiar.    (After  Marshall.) 
are    the    cutting    or    incisor 

teeth.  Just  outside  of  these  are  the  canine  or  eye  teeth; 
then  come  two  bicuspids  on  each  side,  and  finally  the  three 
molars  or  grinding  teeth.  The  last  of  the  molars  appear 
quite  late  in  life  and  are  commonly  called  the  wisdom  teeth. 
The  first  set  of  teeth,  or  milk  teeth,  which  the  child  begins 


248  ANIMAL  BIOLOGY 

to  get  usually  in  his  first  year,  are  but  twenty  in  number. 
These  are  later  replaced  by  the  permanent  teeth.  Each 
tooth  is  set  into  the  jaw  bone  by  one  or  more  roots. 
There  is  a  cavity  in  each  tooth  filled  with  pulp  which 
contains  blood  vessels  and  nerves  and  is  sensitive  to  pain. 
The  body  of  the  tooth  is  composed  of  a  bony  substance 
called  dentine,  and  the  exposed  part  is  covered  by  a  very 
hard  layer,  the  enamel. 

In  animals  below  man  the  teeth  vary  much  in  number, 
size  and  shape.  In  the  carnivores  they  are  fitted  for 
tearing  flesh,  while  in  the  herbivores  they  are  adapted  for 
grinding  food.  The  incisors  are  well  developed  in  the 
rodents  or  gnawers,  while  in  the  elephant  the  upper 
incisors  are  modified  into  the  enormous  tusks  which  afford 
us  our  ivory.  In  fishes,  amphibians  and  reptiles  the 
teeth  are  generally  conical  and  fitted  for  seizing  prey, 
which  is  their  primitive  function.  These  animals  as  a 
rule  do  not  masticate  their  food  but  swallow  it  whole. 
Teeth  are  subject  to  decay  which  is  usually  caused  by  the 
lodgment  of  particles  of  food  that  undergo  decomposition. 
When  the  decay  reaches  the  pulp  cavity  we  are  generally 
reminded  of  the  fact  and  are  compelled  to  seek  the  services 
of  the  dentist.  Keeping  the  teeth  clean  by  frequent  use 
of  the  tooth  brush  prevents  the  beginning  of  trouble. 

The  Salivary  Glands. — Three  pairs  of  salivary  glands 
pour  their  secretion,  the  saliva,  into  the  mouth  cavity. 
The  saliva  is  an  alkaline  fluid  containing  a  considerable 
amount  of  mucus  and  a  ferment,  ptyalin,  which  con- 
verts starch  into  sugar.  Chewing  food  not  only  divides 
it  into  smaller  particles,  but  it  mixes  it  with  saliva  which 
thus  has  a  better  opportunity  to  act  upon  the  starchy 
constituents. 

The  Stomach  and  Gastric  Digestion. — When  we  swallow 
our  food  it  passes  through  a  long  tube,  the  esophagus,  into 


DIGESTION 


249 


the  stomach.  The  stomach  is  a  muscular  organ  which 
tapers  toward  the  end  away  from  the  esophagus  where 
it  is  furnished  with  a  muscular  constriction,  the  pylorus. 
The  pylorus  when  contracted  serves  to  retain  food  in 
the  stomach  until  it  is  digested.  The  stomach  is  lined 
with  a  mucous  membrane  filled 
with  numerous  gastric  glands. 
These  glands  secrete  the  gas- 
tric juice,  which  is  slightly 
acid  from  the  presence  of  a 
small  amount  of  hydrochloric 
acid  (about  0.2  per  cent.). 
They  also  produce  a  ferment 
called  pepsin  which  acts  upon 
the  protein  substances  of  our 
food,  converting  them  into  a 
soluble  form  called  peptone. 
Pepsin  has  no  action  upon  fats 
or  carbohydrates,  and  it  acts 
upon  proteins  only  in  an  acid 
medium.  The  presence  of 
food  in  the  stomach  excites 
the  secretion  of  the  gastric 
juice,  and  the  contractions  of 
the  muscular  walls  of  the 
stomach  which  are  set  up  by 
the  same  cause  produce  a  sort 
of  churning  motion  which  mixes  the  gastric  juice  with  the 
food  and  indirectly  aids  in  the  process  of  digestion.  When 
the  food  has  been  acted  on  for  a  time  in  the  stomach,  the 
pylorus  relaxes  and  allows  the  more  or  less  fluid  mass  to 
escape  into  the  small  intestine.  The  latter  is  a  long,  coiled 
tube  with  rather  thin,  muscular  walls  and  an  inner  lining  of 
mucous  membrane  which  contains  numerous  glands.  It  is 


PIG.  189. — Diagram  of  stom- 
ach and  intestines.  O,  esoph- 
agus; S,  stomach;  p,  pylorus;  i, 
small  intestine;  co,  colon  or  main 
part  of  large  intestine;  R,  rec- 
tum or  terminal  division  of  large 
intestine;  A,  appendix  vermifor- 
mis  attached  to  the  cecum,  c. 
The  arrows  indicate  the  direc- 
tions taken  by  the  food. 


2  5° 


ANIMAL  BIOLOGY 


the  contraction  of  the  muscular  walls  that  forces  along  the 
food.  The  inner  surface  of  the  small  intestine  is  thrown 
into  many  folds,  and  these  are  beset  with  numerous  minute 


FIG.  190.  FIG.  191. 

FIG.   190. — Gland  of  stomach.     M,  mucus  forming  cells;  C,  chief  cells; 

P,  parietal  cells. 
FIG.   191. — Part  of  small  intestine  cut  open  to  show  folds  in  lining. 

finger-like  projections  called  mill  whose  function  it  is  to 
increase  the  surface  available  for  absorption.     The  villi 

are  richly  supplied  with  blood 
and  lymph  vessels  which  carry 
away  the  soluble  food  materials 
absorbed  from  the  intestines: 

The  small  intestine  leads  to 
the  large  intestine.  Near  the 
point  where  the  latter  begins 
there  is  a  short  pocket,  the  c&cum, 
at  the  end  of  which  is  a  small 
tubular  organ,  the  vermiform  ap- 
pendix. Whatever  may  be  the 
function  of  the  latter  organ  it  is 
often  the  seat  of  inflammation 
(appendicitis)  which  frequently 
necessitates  an  operation  for  the  removal  of  the  offending 
part. 

Two  large  and  important  glands,  the  pancreas  and  the 
liver,  pour  their  secretions  by  a  short  common  duct  into  the 
small  intestine.  The  pancreas  secretes  an  alkaline  fluid, 


FIG.  192. — Villi,  v,  of  small 
intestine;  c,  capillaries  of 
blood  vessels;  gl,  gland;  /, 
lacteals  or  lymph  vessels. 


DIGESTION  251 

the  pancreatic  juice,  which  contains  three  ferments; 
one,  amylopsin,  which  converts  starch  into  dextrose,  a 
form  of  sugar;  another,  trypsin,  which  digests  proteins; 
and  a  third,  lipase,  which  acts  upon  fats  transforming 
them  in  part  into  soap  and  converting  them  into  an  emul- 
sion. The  materials  which  escaped  digestion  in  the  stomach 
are  acted  upon  by  the  pancreatic  juice  in  the  small  intestine. 

The  liver  is  a  very  large,  reddish  organ  lying  near  the 
stomach  in  the  right  side  of  the  abdomen.  Its  secretion, 
the  bile  or  gall,  may  accumulate  in  a  small  sac  called  the 
gall  bladder  before  it  is  discharged  into  the  intestine.  The 
bile  consists  in  part  of  waste  products,  and  it  plays  little 
part  in  digestion,  but  it  facilitates  the  absorption  of  food 
through  the  walls  of  the  intestine.  Besides  the  secretion 
of  bile  the  liver  performs  another  important  function  in 
storing  up  a  sort  of  reserve  food  supply  in  the  form  of 
glycogen.  This  substance  is  a  carbohydrate,  allied  to 
starch.  The  carbohydrates  which  are  absorbed  by  the 
blood  in  the  form  of  sugar  (dextrose)  are  in  part  converted 
by  the  liver  into  glycogen  which  accumulates  in  the  liver 
cells.  At  other  times,  especially  during  hunger  or  severe 
exercise,  glycogen  is  converted  into  sugar  which  is  given 
off  into  the  blood.  The  liver,  therefore,  serves  as  a  sort 
of  temporary  storehouse,  converting  the  excess  of  carbo- 
hydrate into  the  comparatively  insoluble  form  of  glycogen 
which  is  given  out  again  in  times  of  greater  need. 

The  small  intestine,  which  is  the  seat  of  important  proc- 
esses of  digestion,  is  an  organ  especially  adapted  for  the 
absorption  of  digested  food.  A  certain  amount  of  absorp- 
tion occurs  in  the  stomach,  and  also  in  the  large  intestine, 
but  most  of  it  occurs  in  the  small  intestine  whose  numerous 
villi  and  folds  with  their  rich  supply  of  blood  and  lymph 
vessels  afford  a  large  surface  through  which  the  soluble 
products  of  digestion  have  ready  access  to  the  blood  and 
lymph. 


CHAPTER  XXVI 
FOODS  AND  THEIR  USES 

After  the  food  is  digested  and  absorbed  it  is  carried  by 
the  blood  and  lymph  to  various  parts  of  the  body  where  the 
different  organs  convert  it  into  their  own  peculiar  sub- 
stance. This  conversion  is  the  process  of  assimilation, 
to  which  digestion  and  absorption  were  merely  prepara- 
tory. It  is  one  of  the  most  wonderful  as  well  as  one  of  the 
least  understood  of  the  activities  which  take  place  in  the 
living  organism.  Assimilation  not  only  compensates 
for  the  waste  that  is  always  being  produced  by  the  body, 
but  it  enables  the  body  to  increase  in  size.  When  waste 
is  exceeded  by  repair  as  in  the  normal  small  boy  there  is 
growth.  In  a  fever  when  the  tissues  are  rapidly  consumed, 
or  burned,  there  is  loss  of  weight;  this  may  be  very  marked 
if  the  fever  is  severe.  Growth  is  rapid  in  the  early  years 
of  life  and  a  relatively  large  amount  of  food  is  required  as 
is  evinced  by  the  keen  and  frequently  recurring  appetite 
of  healthy  youth. 

The  many  articles  of  diet  which  we  consume  are  quite 
different  in  their  chemical  composition  and  they  are  put  to 
different  uses  in  the  economy  of  the  body.  The  true  living 
substance,  or  protoplasm,  requires  for  its  formation  foods 
which  contain  all  the  necessary  chemical  elements.  Since 
proteins  contain  nitrogen  (this  element  is  absent  in  carbo- 
hydrates and  commonly  in  fats)  a  certain  amount  of  pro- 
tein is  absolutely  necessary  for  the  continued  maintenance 
of  life.  Fat  in  the  body  may  be  derived  from  carbo- 
hydrates or  from  other  fats.  Many  people  find  sugar  and 

252 


FOODS   AND   THEIR  USES  253 

starchy  foods  fattening.  But  no  amount  of  starch  or  fat 
would  prevent  a  man  from  dying  of  starvation,  because  he 
requires  some  food  which  contains  nitrogen. 

The  carbohydrates  and  fats,  while  they  do  not  alone 
suffice  to  form  the  living  protoplasm  of  our  body,  never- 
theless supply  us  with  the  energy  that  maintains  our  bodily 
heat  and  enables  us  to  do  muscular  work.  Proteins  also 
supply  us  with  energy  in  addition  to  affording  all  the  ele- 
ments necessary  for  building  up  living  tissue.  We  might 
live  on  protein  food  alone,  but  in  order  to  supply  the  energy 
we  need  we  should  have  to  eat  so  large  a  quantity  of 
protein  that  there  would  be  an  abnormally  large  amount 
of  nitrogenous  waste  products  to  be  eliminated  and  the 
organs  of  elimination  would  be  subjected  to  an  undue  strain. 
A  varied  diet  is  therefore  best.  Along  with  meats  there 
should  be  eaten  fruits,  vegetables  and  cereals  in  order  to 
supply  the  carbohydrates  which  afford  the  main  source  of 
our  energy.  Milk,  the  sole  food  of  the  infant,  contains 
proteins,  fats  and  carbohydrates  in  about  the  proper 
proportions.  Most  of  the  proteins  of  milk  may  by  proper 
methods  be  converted  into  cheese.  After  the  milk  stands 
the  fat  rises  as  cream  to  the  surface  and  may  be  made  into 
butter.  The  carbohydrates  are  mainly  in  the  form  of 
milk  sugar  or  lactose. 

The  kind  and  amount  of  food  needed  depends  upon 
climate,  habits  of  life  and  the  peculiarities  of  the  individual 
person.  The  Esquimaux  may  eat  much  more  fats  and 
carbohydrates  than  would  be  good  for  men  in  a  temperate 
climate  because  they  need  food  that  can  be  utilized  as  fuel. 
A  man  at  hard  labor  may  likewise  utilize  more  of  these 
kinds  of  food  than  the  gentleman  of  leisure.  Perhaps 
most  of  us  eat  rather  more  than  is  necessary,  and  it  is 
certain  that  overeating  is  a  fruitful  source  not  only  of 
disturbances  of  digestion,  but  of  various  other  bodily 


254  ANIMAL  BIOLOGY 

disorders.  When  we  eat  too  much,  consider  what  must 
happen.  The  digestive  organs  are  overstimulated  in  the 
effort  to  dispose  of  the  extra  food.  Constipation  fre- 
quently follows.  Materials  which  should  have  been  got 
rid  of  undergo  decomposition,  producing  injurious  sub- 
stances that  are  absorbed  by  the  blood  and  poison  the 
whole  body.  Excess  of  food  commonly  leads  also  to  the 
torpidity  of  the  liver.  One  of  the  functions  of  this  much 
abused  organ  is  the  breaking  up  of  various  products 
resulting  from  the  metabolism  of  the  tissues.  If  the  liver 
is  sluggish,  injurious  substances  may  accumulate  in  the 
blood  and  produce  very  disagreeable  feelings.  Practically 
all  of  the  carbohydrates  that  are  absorbed  from  the 
stomach  and  intestines  pass  through  the  liver  cells.  Many 
people  who  eat  too  much  rich  candy  or  other  sweets  at  all 
sorts  of  unseasonable  times,  and  suffer  from  headache 
and  general  lassitude  as  a  result,  are  apparently  unaware 
that  they  bring  these  unpleasant  consequences  on  them- 
selves, by  imposing  upon  the  poor  liver  greater  burdens 
than  it  can  well  endure. 

The  welfare  of  the  liver  is  of  especial  value  for  the  main- 
tenance of  health,  because  this  organ  performs  so  many 
indispensable  functions.  It  destroys  poisonous  substances 
in  the  blood  by  converting  them  into  less  injurious  mate- 
rials. It  eliminates  various  materials  which  are  discharged 
through  the  bile  duct  into  the  intestine,  while  it  secretes 
other  substances  whose  presence  in  the  intestine  facilitates 
the  absorption  of  food  and  checks  the  undue  decomposition 
of  waste  matter.  It  also  acts  on  dextrose  (the  substance 
into  which  carbohydrates  are  converted  when  they  are 
absorbed  into  the  blood),  converting  it  into  glycogen. 
There  are  other  functions  ascribed  to  the  liver  but  these 
are  the  best  known.  The  ills  that  arise  from  the  mal- 
treatment of  the  liver  are  numerous,  and  in  many  cases 


FOODS  AND  THEIR  USES  255 

the  patient  never  suspects  that  the  liver  is  responsible 
for  their  production. 

The  fate  of  the  different  classes  of  food  in  the  economy 
of  the  body  may  be  summarized  as  follows: 


Proteins. 


produce  energy; 

build  up  living  tissue; 

may  give  rise  to  fat  in  the  body. 


Fats..  I  Produce energy; 

I  are  converted  into  bodily  fat. 


Carbohydrates. . 


produce  energy; 

are  converted  into  fats; 


may  be  stored  up  as  glycogen. 

All  foods  produce  energy  for  the  performance  of  muscular 
work  and  the  production  of  bodily  heat.  Carbohydrates 
and  fats  are  chiefly  energy  producers  and,  although  they 
may  be  stored  for  a  time,  they  may  be  oxidized  later  as 
occasion  demands,  and  hence  used  up  for  the  production 
of  energy  in  the  end. 

Besides  the  three  classes  of  foods  that  have  been  de- 
scribed there  are  several  other  substances  that  are  essential 
for  the  maintenance  of  life.  Conspicuous  among  these 
is  water,  as  it  forms  about  %o  of  the  material  of  the  blood 
and  about  59  per  cent,  of  the  substance  of  the  body. 
Since  water  is  constantly  being  given  off  from  the  body 
through  the  secretory  activities  of  the  kidneys,  by  the  skin 
in  the  form  of  perspiration  or  sweat,  and  by  the  lungs  in 
the  breath,  it  must  be  supplied  in  considerable  quantity. 
While  more  or  less  water  is  contained  in  all  our  foods,  it  is 
necessary  to  drink  water  or  some  beverage  such  as  tea  or 
coffee,  etc.,  consisting  mainly  of  water,  in  order  to  supply 
our  bodily  needs.  A  man  may  do  without  food  for  several 
days  and  in  exceptional  cases  for  some  weeks,  but  he  will 


256  ANIMAL  BIOLOGY 

not  live  nearly  so  long  if  he  is  deprived  of  water.  Men 
under  the  hot  and  dry  climate  of  the  desert  crave  a  large 
amount  of  water  and  soon  succumb  if  they  cannot  obtain 
it. 

In  both  our  food  and  drink  we  consume  small  amounts 
of  various  kinds  of  salts.  Comon  table  salt  or  sodium 
chloride,  NaCl,  is  one  of  the  most  common  of  these, 
and  while  it  occurs  in  small  quantities  in  animal  foods  and 
often  in  drinking  water,  it  is  usually  added  as  seasoning 
to  much  of  the  food  we  eat.  Carbonate  and  sulphate  of 
lime  are  common  in  drinking  water,  the  so-called  hard 
water  containing  an  unusually  large  amount  of  one  or 
both  of  these  salts.  These,  with  phosphate  of  lime,  are 
used  in  the  formation  of  bone,  as  well  as  in  supplying 
calcium  to  other  tissues  of  the  body.  Salts  of  potassium 
and  magnesium  are  also  important,  and  iron  is  required 
for  the  formation  of  the  red  coloring  matter  of  the  blood. 
While  salts  are  needed  only  in  small  quantities,  they  are 
absolutely  essential  for  the  maintenance  of  life;  the  pres- 
ence of  several  different  kinds  of  salts  is  of  even  greater 
importance  than  the  consumption  of  different  classes  of 
foods. 

There  are  several  substances  which  are  consumed  not  so 
much  on  account  of  their  value  as  food,  but  because  they 
gratify  the  sense  of  taste.  Spices  add  to  the  piquancy  of 
various  dishes,  but  they  have  practically  no  value  as  food 
and,  although  they  may  serve  a  good  purpose  by  stimulating 
the  appetite,  some  of  them  may  produce  bad  effects,  espe- 
cially when  taken  in  large  amounts.  There  are  several 
substances  called  stimulants  which  may  or  may  not  be  of 
value  as  food.  A  stimulant  is  a  substance  that  increases 
the  metabolic  activity  of  the  organism.  Frequently  the 
excitement  produced  by  the  stimulant  is  followed  by  a 
period  of  depression  in  which  the  vital  energy  of  the  body 


FOODS  AND  THEIR  USES  257 

is  diminished.  Contrasted  with  stimulants  there  are 
other  substances  called  narcotics  which  have  a  quieting 
effect,  often  associated  with  pleasurable  feeling.  Common, 
narcotics  are  tobacco,  opium,  chloroform  and  cocaine, 
whose  influences  will  be  discussed  in  a  later  section. 
Tea  and  coffee  have  a  mild  stimulating  influence  which 
they  owe  to  alkaloids  (thein  and  caffein)  of  similar  if  not 
identical  composition.  Both  of  these  beverages,  and 
especially  tea,  contain  tannin  which  is  extracted  if  water 
is  allowed  to  stand  too  long  on  the  grounds.  Both  tea  and 
coffee  are  better  when  freshly  made,  not  only  because  they 
contain  less  tannin,  but  because  they  retain  more  of  their 
delicate  aroma  which  soon  disappears  if  either  beverage 
is  allowed  to  stand.  Tannin  is  especially  injurious  to  the 
stomach,  and  tea  and  coffee  should  be  so  prepared  that 
most  of  this  substance  is  not  extracted.  Tea  and  coffee 
may  produce  bad  effects  if  used  to  excess,  and  there  are 
some  individuals  in  whom  coffee,  especially,  produces 
disturbances  of  digestion,  but  perhaps  the  majority  of 
people  experience  little  harm  from  the  use  of  these  drinks. 
Chocolate,  likewise  a  mild  stimulant,  is  more  nutritious 
than  tea  or  coffee. 

The  most  widely  used  of  the  beverages  taken  to  gratify 
the  sense  of  taste  are  the  various  drinks  which  contain 
alcohol;  such  as  beer,  wine,  whisky,  brandy  and  numerous 
others  in  almost  endless  variety.  While  it  has  been  shown 
experimentally  that  alcohol  is  a  food — i.e.,  it  may  be 
oxidized  in  the  body  with  the  production  of  energy — 
it  has  practically  little  nutritive  value  as  compared  with 
other  foods,  and  its  other  effects  more  than  outweigh 
whatever  nutritive  value  it  may  possess.  The  effect  of 
alcohol  on  digestion  when  taken  in  large  quantities  is  bad, 
as  it  gives  rise  to  cirrhosis  of  the  liver,  inflammation  of  the 
stomach,  dyspepsia,  and  a  variety  of  other  disturbances. 

17 


258  ANIMAL  BIOLOGY 

In  smaller  quantities  its  effect  on  digestion  is  less  marked, 
and  more  difficult  to  determine.  As  people  addicted  to  a 
moderate  use  of  alcohol  live,  on  the  average,  a  less  number 
of  years  than  those  who  are  temperate,  the  general  effect 
of  small  quantities  of  alcohol  on  the  body  in  general,  and 
probably  also  on  the  digestive  organs,  is  not  good.  People 
who  take  alcohol  with  their  meals  are  apt  to  take  more  than 
is  good  for  them,  and  it  is  quite  certain  that  the  digestion 
of  normal,  healthy  persons  is  better  without  alcohol  than 
with  it.  Those  whose  digestion  is  impaired  should  take 
alcohol,  if  at  all,  only  as  prescribed  by  a  good  physician. 


CHAPTER  XXVII 
THE  BLOOD  AND  CIRCULATION 

When  the  soluble  products  of  digestion  diffuse  through 
the  walls  of  the  alimentary  canal  they  pass  directly  or  in- 
directly into  the  blood,  and  are  carried  by  this  fluid  to  all 
parts  of  the  body.  The  blood  comprises  about }{ 3  of  the 
weight  of  the  body,  although  it  varies  greatly  in  amount  at 
different  times  and  with  different  people.  It  is  composed 
of  a  fluid  called  plasma  and  numerous  very  minute  corpuscles 
which  are  so  small  that  as  many  as  5,000,000  are 
estimated  to  occur  in  a  cubic  millimeter.  The  plasma 
of  blood  is  a  very  complex  fluid.  It  contains  many  food 
products,  proteins,  fats,  sugar  and  various  salts  which  may 
be  taken  up  by  the  cells  of  the  body;  it  contains  also  the 
waste  matter  derived  from  the  destructive  metabolism  of 
cells.  And  there  are  various  other  substances  in  it  which 
have  a  number  of  different  functions.  Blood  is  the  great 
medium  of  transport  of  food,  oxygen  and  waste.  Each 
cell  takes  out  of  it  the  material  needed  for  its  life  and  gives 
off  into  it  the  broken  down  products  of  its  vital  activity. 
The  blood  has  to  keep  in  circulation  in  order  to  supply  all 
the  parts  of  the  body  which  are  dependent  on  it.  And  in 
the  normal  life  of  man  it  never  stops  for  a  moment  from 
before  birth  to  old  age. 

When  blood  is  withdrawn  from  its  vessels  it  has  the 
curious  property  of  forming  a  solid,  jelly-like  mass,  the 
clot.  This  clot  is  composed  of  a  substance  called  fibrin, 
a  form  of  protein  which  is  supposed  to  be  derived  from 

259 


260  ANIMAL  BIOLOGY 

a  soluble  substance  called  fibrinogen  by  a  process  of  fer- 
mentation. Clotting  is  therefore  analogous  to  the  forma- 
tion of  cheese  (casein)  from  a  protein  which  was  previously 
dissolved  in  the  milk.  Exposure  to  air  and  especially 
contact  with  solid  objects  causes  the  blood  to  clot,  and 
the  process  may  be  hastened  by  adding  fine  powder  to  the 
blood  or  beating  it  with  a  stick.  The  clotting  of  blood 
performs  the  very  useful  function  of  checking  bleeding; 
otherwise  bleeding  would  be  very  difficult  to  control  and 
even  slight  wounds  might  produce  fatal  results.  The  yel- 
lowish fluid  which  remains  after  the 
fibrin  has  been  removed  by  clotting  is 
called  serum. 

The  corpuscles  of  the  blood  which  are 
true  cells  are  of  two  kinds,  the  red  and 
the  white  corpuscles  or  leucocytes.  The 
red  corpuscles  are  round  biconcave  disks; 
they  do  not  contain  a  nucleus,  although 
cies.  /,  leucocytes  a  nucleus  occurs  in  the  early  stages  of 

or  white  corpuscles;    ,-,.,,  mi     • 

r,  red  corpuscles;  s,  their  development.     Their  most  import- 
red  corpuscles  seen       t   ingredient  is  hemoglobin,  the  sub- 

on  edge. 

stance  which  gives  the  blood  its  red  color. 
Haemoglobin  is  a  protein  containing  iron  and  having  the 
property  of  combining  readily  with  oxygen,  and  also  of 
giving  up  its  oxygen  again  with  equal  readiness.  This 
curious  property  enables  haemoglobin  to  perform  its 
important  function  of  a  carrier  of  oxygen,  since  when 
oxygen  is  abundantly  supplied  to  the  blood  as  it  circulates 
through  the  lungs  the  haemoglobin  becomes  oxidized; 
whereas  when  the  blood  passes  into  a  region  where  the 
cells  of  the  body  use  all  the  oxygen  that  is  available  the 
haemoglobin  gives  up  its  oxygen  or,  as  the  chemists  wrould 
say,  becomes  reduced.  Haemoglobin  combined  with  oxy- 
gen is  red  in  color,  while  the  reduced  haemoglobin  is  bluish ; 


THE   BLOOD   AND    CIRCULATION  261 

a  fact  which  accounts  for  the  difference  between  the  red 
color  of  blood  fresh  from  the  lungs,  and  the  bluish  color 
of  blood  in  veins  from  other  parts  of  the  body.  Blue 
blood  is  therefore  blood  with  little  oxygen. 

While  the  red  corpuscles  are  specialized  for  the  function 
of  carrying  oxygen,  the  white  cells  or  leucocytes  perform 
very  different  functions.  These  leucocytes  are  very  active 
cells  with  irregular,  changing  form.  They  have  the  prop- 
erty of  creeping  about  much  like  Amcebas  which  indeed 
they  closely  resemble  in  form  and  general  behavior.  They 
engulf  and  digest  many  foreign  materials  and  they  are 
known  to  devour  bacteria  and  other  minute  organisms 
that  gain  access  to  the  blood.  By  means  of  this  property 
they  guard  the  body  against  many  disease  germs  that 
might  otherwise  have  an  opportunity  for  unrestricted 
multiplication.  This  appetite  of  the  leucocytes  for  bac- 
teria renders  the  body  more  or  less  immune  to  various 
diseases.  Leucocytes  tend  to  congregate  around  centers 
of  bacterial  infection,  and  they  may  even  pass  through 
the  walls  of  delicate  blood  vessels  and  creep  about  in  the 
tissues,  especially  in  regions  of  injury  or  bacterial  invasions. 
If  small  tubes  containing  cultures  of  certain  bacteria  are 
introduced  under  the  skin  of  a  rabbit  it  is  found  that 
leucocytes  creep  into  the  tubes,  while  other  tubes  similarly 
prepared,  but  containing  no  bacteria  are  not  entered.  Ap- 
parently, therefore,  the  leucocytes  are  drawn  into  the 
tubes  with  bacteria  on  account  of  the  fact  that  the  bacteria 
produce  some  substances  that  attract  these  wandering 
cells.  In  regions  where  swelling  occurs  there  are  generally 
large  numbers  of  leucocytes.  Pus,  which  is  a  common 
product  of  inflammation,  is  composed  largely  of  leu- 
cocytes together  with  broken  down  cells  of  other  kinds. 
Leucocytes  wander  through  the  walls  of  the  alimentary 
canal  and  they  may  also  be  found  in  the  mouth.  The 


262  ANIMAL  BIOLOGY 

whitish  color  of  the  coated  or  furred  tongue  is  caused  mainly 
by  these  outwandering  cells  which  are  especially  abundant 
under  certain  abnormal  conditions. 

The  organ  that  keeps  the  blood  in  constant  circulation 
is  the  heart,  which  is  situated  near  the  middle  of  the  chest 
with  its  pointed  lower  end  lying  on  the  left  side  between 
the  fifth  and  sixth  ribs,  where  we  can  plainly  feel  its 
beating.  To  understand  how  the  beating  of  the  heart 
causes  the  flow  of  blood  we  must  study  its  inner  mechanism. 
The  heart  is  composed  mainly  of  muscular  fibers  whose 

periodic  contraction  affords  the 
energy  for  propelling  the  blood. 
It  is  divided  into  four  chambers, 
the  two  auricles  above  and  the 
two  ventricles  below.  The  auricle 
and  ventricle  of  one  side  are  sepa- 
rated from  the  corresponding 
chambers  on  the  other  side  by  a 
median  partition  which  com- 
pletely shuts  off  all  communica- 
tion between  the  two  sides.  Each 
auricle  communicates  with  the 
FIG.  i94.-The  heart  seen  ventricle  of  the  same  side  by  a 

from   in    front.     AO,    aorta;  J 

LA,  left  auricle;  LV,  left  ven-  valve  which  allows  blood  to  paSS 

tricle;  PA,  pulmonary  artery;  ,.  . -i  •   i       •    A       ji 

PV,     pulmonary    veins;    RA,  *™m    the    auricle    into    the    VCn- 

right  auricle;  Rv,  right  ven-  trjcie  but  prevents  its  flow  in  the 

tncle;  VC,  superior  vena  cava. 

reverse  direction.    The  ventricles 

are  connected  with  the  outgoing  blood  vessels  or  arteries, 
while  the  auricles  receive  the  incoming  vessels  or  veins. 
The  muscular  walls  of  the  ventricles  are  considerably 
thicker  than  those  of  the  auricles  as  they  have  to  force 
the  blood  through  the  organs  of  the  body,  whereas  the 
auricles  simply  propel  the  blood  they  receive  into  the 
ventricles.  The  valves  which  are  present  where  the  arte- 


THE  BLOOD   AND   CIRCULATION 


263 


ries  leave  the  heart  prevent  the  backward  flow  of  the 
arterial  blood. 

There  are  two  main  arterial  trunks,  (i)  the  pulmonary 
which  leads  from  the  right  ventricle  and  soon  divides  nto 
the  pulmonary  arteries  which  supply  the  lungs;  and  (2) 
the  aorta  which  passes  from  the  left  ventricle  and  carries 
the  blood  which  supplies  the  greater  part  of  the  body. 
Corresponding  to  the  arteries  which  pass  out  from  the 
ventricles  are  two  sets  of  veins  emptying  into  the  auricles, 


SVC 


FIG.  195. — Diagram  of  inside  of  heart.  AO,  aorta;  IVC,  inferior  vena 
cava;  LA,  left  auricle;  LV,  left  ventricle;  PA,  pulmonary  arteries;  PV, 
pulmonary  veins;  RA,  right  auricle;  RV,  right  ventricle;  SVC,  superior 
vena  cava. 

(i)  the  pulmonary  veins  which  bring  blood  from  the  lungs 
to  the  left  auricle,  and  the  two  vena  cava  which  discharge 
blood  from  the  general  circulation  into  the  right  auricle. 
There  are  two  systems  of  circulation  connected  with  the 
heart,  the  pulmonary  which  carries  blood  to  and  from  the 
lungs,  and  the  systemic  which  carries  blood  to  and  from 
the  rest  of  the  body.  Nevertheless  the  same  blood  must 
pass  through  both  systems. 

In  order  to  illustrate  its  course  let  us  start  with  the 


264  ANIMAL  BIOLOGY 

blood  as  it  passes  from  the  left  ventricle  through  the  aorta. 
From  this  large  vessel  it  may  flow  into  any  of  the  branch 
arteries  which  supply  the  arms,  legs,  liver  or  any  of  the 
numerous  organs  of  the  body.  As  it  passes  through  the 
fine  capillaries  it  is  collected  into  veins  which  ultimately 
lead  into  the  two  venae  cavae  which  discharge  into  the  right 
auricle.  From  here  it  passes  through  a  valve  into  the 
right  ventricle  whence  it  is  forced  out  through  another 
valve  into  the  trunk  that  supplies  the  pulmonary  arteries 
leading  to  the  lungs.  After  passing  through  the  capil- 
laries of  the  lungs,  it  is  returned  by  the  pulmonary  veins 
to  the  left  auricle,  whence  it  flows  through  a  valve  into 
the  left  ventricle,  thus  completing  the  entire  circuit  of 
both  the  pulmonary  and  the  systemic  circulations. 

The  vessels  which  carry  the  blood  to  and  from  the  organs 
of  the  body  fall  into  three  classes,  the  arteries,  carrying  the 
blood  from  the  heart;  the  "veins  which  return  the  blood  to 
the  heart;  and  the  minute  capillaries  which  connect  the 
arteries  with  the  veins.  Both  arteries  and  veins  have 
muscular  walls,  but  the  walls  are  thicker  in  the  arteries  in 
adaptation  to  the  greater  pressure  to  which  they  are 
subjected  by  the  pumping  action  of  the  heart.  As  the 
arterial  walls  are  elastic  they  expand  somewhat  as  blood 
is  forced  into  them  by  each  contraction  of  the  ventricles. 
This  periodic  expansion  forms  the  pulse  which  can  plainly 
be  felt  in  the  arteries  of  the  wrist  and  neck.  The  rapidity 
of  the  pulse,  normally  about  75  beats  per  minute,  is  an 
index  of  the  activity  of  the  heart.  As  one  may  readily 
demonstrate  upon  himself,  the  pulse  is  quickened  by  exer- 
cise and  excitement;  it  is  also  quickened  during  a  fever, 
its  rate  often  affording  the  physician  a  clue  to  the  condi- 
tion of  the  patient.  In  other  conditions  of  illness  the 
pulse  may  be  unusually  slow  and  weak. 

As  the  arteries  branch  into  smaller  and  smaller  vessels 


THE   BLOOD   AND    CIRCULATION 


265 


their  walls  become  thinner  and  finally  lose  their  muscular 
coat  altogether  as  they  pass  into  the  minute  capillaries. 
If  the  web  of  a  frog's  foot  be  examined  with  a  compound 
microscope  one  may  witness  the  fascinating  spectacle  of 
the  veins,  arteries  and  capillaries  with  their  flowing  cur- 
rents of  blood,  and  follow  the  red  and  white  corpuscles 
as  they  pass,  single  file,  in  their  course  from  the  arteries 
to  the  veins.  It  is  through  the  thin  and  delicate  walls 
of  the  capillaries  that  the  principal  exchanges  of  material 


FIG.  196.  FIG.  197. 

FIG.  196. — Diagram  of  circulation  through  the  capillaries  of  a  frog's 
foot  showing  corpuscles  in  capillaries,  p,  pigment  cells. 

FIG.  197. — Valves  in  a  vein.  A,  valves  as  they  appear  when  a  vein  is 
cut  open;  B,  section  of  vein  to  show  closing  of  valve  to  prevent  backward 
flow  of  the  blood;  C,  section  showing  position  of  valve  when  blood  is  flow- 
ing normally. 

occur  between  the  blood  and  the  tissues.  Food  and  oxygen 
diffuse  from  the  blood  into  the  tissues  and  carbon  dioxide 
and  other  waste  products  diffuse  from  the  tissues  into 
the  blood.  The  white  corpuscles  may  pass  through  these 
delicate  walls  also,  as  may  sometimes  be  seen  in  the  web 
of  the  frog's  foot.  The  veins,  whose  function  it  is  to 
carry  the  blood  back  to  the  heart,  are  furnished  with  cup- 
shaped  valves  which  allow  blood  to  flow  past  them  toward 
the  heart  while  they  fill  and  block  its  passage  if  it  should 
be  forced  in  the  opposite  direction.  Many  veins  lie 
nearer  the  surface  than  the  arteries  and  they  may  be 


266 


ANIMAL  BIOLOGY 


easily  seen  in  such  places  as  the  back  of  the  hand.  If  the 
wrist  is  grasped  tightly  so  as  to  check  the  return  flow  of  the 
blood  the  veins  of  the  hand  may  be  seen  to  swell. 

Most  of  the  blood  sent  to  the  stomach  and  intestines 
is  not  returned  at  once  toward  the  heart,  but  is  collected 
by  the  portal  vein  which  distributes  it  to  the  liver.  The 
portal  circulation  is  therefore  peculiar  in  that  it  both  begins 
and  ends  in  capillaries.  Much  of  the  food  material  ab- 
sorbed from  the  stomach  and  intestines  passes  into  the  capil- 
laries that  lead  to  the  portal 
vein.  Sugar  in  the  form  of 
dextrose  passes  into  the 
portal  circulation  and  is  con- 
verted into  glycogen  in  the 
cells  of  the  liver. 

Besides  the  blood,  the 
body  has  a  similar  but 
colorless  fluid,  the  lymph. 
The  lymph  contains  leuco- 
cytes, but  no  red  corpuscles. 
It  flows  in  numerous  ves- 
sels, the  lymphatics,  which 
pour  their  fluid  into  the 
blood.  Lymph  vessels  are 
abundantly  supplied  to  the 
intestines  where  they  are 
called  lacteals  on  account 
of  the  milky  appearance  (lac,  milk)  of  the  lymph  in  this 
region  caused  by  the  presence  of  fatty  substances  absorbed 
from  the  intestine.  The  intestinal  lymphatics  converge 
into  the  thoracic  duct  which  empties  into  a  vein  near  the 
left  side  of  the  neck. 

The  lymph  does  not  have  a  complete  circulation  like  the 
blood.     It  carries  material  from  the  surface  of  the  body 


FIG.   198. — Lymphatic  system, 
lacteals;    T,  thoracic    duct. 


L, 


THE  BLOOD   AND   CIRCULATION  267 

and  the  various  organs  into  the  blood  vessels.  It  is 
replenished  by  fluid  which  diffuses  from  the  finer  blood 
vessels  into  the  surrounding  tissues.  One  of  the  chief 
functions  of  lymph  vessels  is  the  absorption  and  transfer 
of  materials  into  the  blood  system. 

Closely  associated  with  the  lymph  vessels  are  the  lymph 
glands.  Some  of  these  may  be  felt  in  the  groins  or  under 
the  jaw.  They  are  centers  in  which  leucocytes  arise,  and 
they  often  become  enlarged  in  disease.  Infections  often 
travel  from  their  point  of  origin,  along  the  course  of  the 
lymph  vessels  and  frequently  cause  swelling  and  suppura- 
tion of  the  neighboring  lymph  glands.  The  tonsils  contain 
much  lymphatic  tissue  they  are  very  apt  to  become  in- 
fected and  often  have  to  be  removed  because  the  in- 
fection may  spread  from  these  organs  and  produce  a 
variety  of  ill  effects. 

The  organs  of  circulation  are  to  a  certain  extent  under 
the  control  of  the  nervous  system.  The  peripheral  arteries 
may  contract  upon  nervous  stimulation,  as  when  one  sud- 
denly grows  pale,  or  they  may  become  relaxed  and  filled 
with  blood  under  other  circumstances,  as  in  blushing. 
The  exercise  of  a  part  causes  it  to  receive  an  increased 
blood  supply,  and  after  a  meal  there  is  an  unusually  large 
amount  of  blood  sent  to  the  organs  of  digestion.  Hard 
thinking  brings  an  increased  blood  flow  to  the  brain. 
Serious  mental  work  after  a  heavy  meal  when  the  blood 
is  occupied  with  the  business  of  digestion  is  therefore  an 
uphill  task,  as  doubtless  most  of  you  have  already  found 
out. 

The  proper  working  of  the  organs  of  circulation  is  very 
important  for  the  maintenance  of  physical  vigor.  The 
heart  may  be  weakened  by  over  exercise,  but  moderate 
exercise  strengthens  it  as  well  as  gives  tone  to  the  blood 
vessels.  The  heart  is  more  frequently  injured  by  bad 


268  ANIMAL  BIOLOGY 

habits  and  disease  than  by  overwork.  The  continued 
use  of  alcohol  in  excess  generally  leads  to  cardiac  weakness. 
Under  the  stimulus  of  a  moderate  amount  of  alcohol  the 
peripheral  blood  vessels  become  dilated;  more  blood 
goes  to  the  surface,  and  a  feeling  of  warmth  may  be  pro- 
duced which,  however,  soon  passes  away.  Alcohol  proba- 
bly produces  disorders  of  circulation  mainly  through 
its  influence  on  the  nervous  system,  thereby  causing  an 
impairment  of  the  proper  nervous  control  of  the  heart  and 
blood  vessels.  Tobacco,  especially  when  used  by  the 
young,  leads  to  heart  weakness  and  palpitation,  the 
" tobacco  heart"  being  a  frequent  result  of  the  use  of 
tobacco  in  excess. 


CHAPTER  XXVIII 
RESPIRATION 

If  we  hold  our  breath  for  a  short  time  we  soon  experience 
a  sense  of  discomfort  which  increases  the  longer  our  breath- 
ing is  interrupted,  until  it  becomes  quite  intolerable. 
While  we  can  go  without  water  for  some  time  and  without 
food  for  a  much  longer  time,  we  would  very  quickly  suc- 
cumb (it  would  be  a  matter  of  a  very  few  minutes  at  best) 
if  deprived  of  air.  The  element  in  the  air  upon  which 
we  are  so  closely  dependent  for  our  life  is  oxygen,  the 
nitrogen  being  simply  so  much  inert  substance  that  plays 
no  important  part  in  respiration.  While  we  may  be  prone 
to  think  of  breathing  or  respiration  as  drawing  air  into  the 
lungs  and  forcing  it  out  again,  these  processes  are  merely 
subsidiary  to  the  essential  part  of  respiration  which  con- 
sists in  the  assimilation  of  oxygen  and  the  giving  off  of 
carbon  dioxide.  Liquids  tend  to  absorb  gases  when  the 
latter  are  present  in  considerable  quantities,  and  they  give 
off  gases  when  there  is  nothing  to  check  their  escape. 
If  a  liquid  such  as  water  is  separated  from  the  air  by  a 
permeable  membrane  it  may  absorb  air  through  it  and  give 
off  any  gas  which  it  may  contain  in  excess.  Blood  has 
this  property,  like  other  liquids,  and  it  has  an  especial 
aptitude  for  absorbing  and  giving  off  unusually  large 
amounts  of  oxygen  and  carbon  dioxide,  the  chief  gases  con- 
cerned in  respiration.  Gases  have  the  general  property 
of  tending  to  become  uniformly  distributed.  If  a  bladder 
is  filled  with  oxygen  and  suspended  in  an  atmosphere  of 
carbon  dioxide  the  oxygen  will  diffuse  out  of  the  bladder 

269 


270  ANIMAL  BIOLOGY 

while  the  carbon  dioxide  will  diffuse  into  it  until  the  two 
gases  are  evenly  distributed  on  either  side  of  the  mem- 
branous wall. 

The  ability  of  the  blood  to  take  up  large  quantities  of 
oxygen  is  dependent  upon  the  fact  that  the  haemoglobin 
of  the  red  corpuscles  forms  a  chemical  combination  with 
this  element.  When  supplied  with  oxygen  the  blood 
turns  red  as  may  be  demonstrated  by  shaking  up  bluish 
venous  blood  with  oxygen  or  even  with  air,  when  it  takes 
on  a  bright  reddish  color.  Similarly  red  blood  becomes 
bluish  when  shaken  up  in  an  atmosphere  of  carbon  dioxide. 
As  we  have  already  seen,  the  blood  returning  from  the 
lungs  where  it  becomes  exposed  to  the  air  is  red  in  color 
and  remains  red  in  the  arteries  that  supply  the  organs  of 
the  body.  After  it  has  passed  through  the  capillaries 
and  is  returned  through  the  veins  it  acquires  a  bluish  tint. 
As  chemical  tests  show,  it  has  lost  a  considerable  part 
of  its  oxygen  and  has  received  a  larger  amount  of  carbon 
dioxide.  The  constant  need  for  oxygen  to  keep  up  the  life 
of  the  tissue  and  the  necessity  for  the  removal  of  carbon 
dioxide,  which  is  produced  where  vital  changes  are  going 
on,  make  it  so  very  important  that  the  activity  of  breath- 
ing should  go  on  unchecked. 

While  we  speak  of  the  lungs  as  the  organs  of  respiration 
it  must  be  remembered  that  respiration  occurs  in  all  the 
cells  of  the  body.  They  all  take  oxygen  from  the  blood 
and  give  off  carbon  dioxide.  This  process  is  often  distin- 
guished as  internal  or  tissue  respiration.  But  as  the  blood 
circulates  through  the  lungs  it  absorbs  oxygen  from  the  air 
and  gives  off  its  carbon  dioxide,  a  process  which  we  may 
designate  as  external  respiration.  The  blood  acts  as  a 
carrier  between  the  tissues  and  the  respiratory  organs,  a 
function,  as  we  have  seen,  for  which  it  is  admirably  adapted. 
Oxidation  is  essentially  a  process  of  burning,  and  the  con- 


RESPIRATION 


271 


sumption  of  oxygen  by  the  tissues  affords  an  important 
source  of  our  bodily  heat.  And  the  main  products  of  this 
oxidation,  water  and  carbon  dioxide,  are  precisely  those 
which  are  formed  by  the  burning  of  a  candle  or  a  stick 
of  wood. 

As  the  lungs  are  the  principal  organs  from  which  the 
blood  gets  its  oxygen  we  may  now  consider  their  structure, 


s.c 


FIG.  199. — Median  section  through  nasal  cavity,  mouth  and  throat. 
C,  cavity  of  nose;  E,  opening  of  Eustachian  tube  from  the  ear;  ep,  epiglottis; 
f,s,  frontal  sinus;  g,  glottis;  hy,  hyoid  bone;  j,  lower  jaw;  /,  larynx;  oe, 
esophagus;  p',  hard  palate;  p,  soft  palate  ending  posteriorly  in  the  uvula, 
u\  s.c,  bones  of  spinal  column;  s.s,  sphenoidal  sinus;  t,  t,  turbinated  bones; 
tl,  tonsil;  ton,  tongue;  tr.  trachea;  u,  uvula. 

and  see  how  they  are  adapted  to  the  performance  of  their 
functions.  In  order  to  enter  the  lungs  the  air  has  to  flow 
through  a  number  of  passages.  First  it  is  taken  into  the 
nasal  cavity  where  it  is  exposed  to  a  wide  surface  of  moist 
mucous  membrane.  Here  the  air  is  not  only  warmed 
before  passing  to  the  lungs,  but  dust  and  other  particles 


272 


ANIMAL  BIOLOGY 


are  caught  and  prevented  from  interfering  with  respira- 
tion. Posteriorly  the  nasal  cavity  leads  to  a  space  called 
the  pharynx;  at  the  lower  end  of  this  is  a  cartilaginous  box, 


PIG.  200.  —  Vocal  cords,     a,   closed;   b,   open. 

the  larynx,'  which  you  can  feel  in  the  front  part  of  your 
throat  (Adam's  apple).  The  opening  of  the  larynx  lies 
just  in  front  of  the  opening  of  the  esophagus,  but  it  may 
be  covered  by  a  fleshy  lid,  the  epiglottis,  which  normally 

closes  it  during  the  act  of 
swallowing.  Sometimes  food 
"goes  down  the  wrong  way" 
when  it  sets  up  the  act  of  cough- 
ing by  which  it  is  usually  ex- 
pelled. 

The  larynx  contains  the 
vocal  cords  whose  function  it 
is  to  produce  the  voice,  and  it 
leads  below  to  a  tube  called  the 
trachea  or  windpipe  through 
which  air  passes  to  the  lungs. 
The  trachea  is  furnished  with 
a  series  of  C-shaped  cartilages 

7 

or  nearly  complete  rings  which 
keep  its  walls  from  collapsing 

and  thus  impeding  the  passage  of  air.  The  inner  lining 
consists  of  mucous  membrane  containing  many  cells  with 
fine  cilia  whose  constant  beating  creates  a  current  toward 


•FiG'       « 

windpipe  *B  with  its  branches 

r,  bronchial  tubes. 


RESPIRATION  273 

the  mouth.  Fine  particles  which  may  lodge  in  the 
trachea  are  therefore  carried  outside  instead  of  being  al- 
lowed to  accumulate  in  the  lungs.  Nature  has  furnished 
us  with  a  number  of  admirable  contrivances  by  which  the 
lungs  are  shielded  from  injury.  The  broad  nasal  cavity 
for  warming  the  air  and  collecting  dust,  the  epiglottis 
which  closes  the  opening  to  the  air  passages  at  the  very 
moment  when  materials  are  apt  to  pass  into  them,  the 
tracheal  cartilages  to  keep  open  the  trachea  and  thus  to 
insure  access  of  air  to  the  lungs,  and  the  fine  tracheal  cilia 
beating  in  the  right  direction  to  carry  away  offending  par- 
ticles— all  these  structures  act  so  as  to  pro- 
vide the  lungs  with  air  devoid  of  solid 
matter. 

At  its  lower  end  the  trachea  divides  into 
two  bronchi,  one  for  each  lung,  and  these 
two  tubes  subdivide  into  smaller  and 
smaller  ones.  The  final  subdivisions  lead 
to  minute  pockets,  the  air  cells,  the  walls  of 
which  are  exceedingly  thin  and  abundantly 
furnished  with  capillary  blood  vessels.  A 
large  surface  is  thus  provided  in  which  the  open  showing  the 

-,,,.,  ,  ,    .          .  .  ,     air  cells,  C:  bron- 

blood  is  brought  into  intimate  contact  with  chiai  tubes,  r. 
air,  the  thin  walls  by  which  the  two  are 
separated  facilitating  the  exchange  of  oxygen  and  carbon 
dioxide  which,  as  we  have  seen,  is  the  essential  function 
of  organs  of  respiration.    The  total  surface  of  the  numerous 
air  cells  is  estimated  to  be  about  15,000  square  feet,  an  area 
equal  to  the  floor  space  of  a  fair-sized  dwelling. 

The  lungs  are  fairly  large  organs,  pinkish  in  color  and 
of  very  spongy  texture,  and  they  fill  most  of  the  chest  which 
is  not  occupied  by  the  heart.  They  are  surrounded  by  a 
double  membrane,  the  pleura,  one  layer  of  which  is  closely 
applied  to  the  lungs  while  the  other  forms  the  inner  lining 

18 


274 


ANIMAL  BIOLOGY 


of  the  chest.  The  space  between  the  two  layers  contains 
a  fluid  which  serves  to  prevent  friction  from  the  constant 
movement  of  the  chest  in  breathing.  Pleurisy  is  a  disease 
due  to  the  inflammation  of  the  pleura. 

We  have  now  to  consider  how  the  air  goes  in  and  out  of 
the  ungs.  The  ribs  enclosing  the  chest  are  capable  of 
more  or  less  movement  by  means  of  various  muscles  which 
are  attached  to  them.  By  raising  up  the  sternum  or  bone 
to  which  the  upper  ribs  are  attached  in  front,  and  by 
spreading  the  lower  free  ribs  laterally  the  chest  becomes 

enlarged,  and,  as  the  lungs  ex- 
pand at  the  same  time,  air  tends 
to  rush  in  from  without  to  fill 
the  extra  space — a  process 
which  goes  by  the  name  of  in- 
spiration (literally  breathing 
in).  At  the  lower  side  of  the 
cavity  of  the  chest  is  a  broad 
muscular  sheet,  the  diaphragm, 
forming  a  complete  septum 
across  the  body.  Usually  the 
diaphragm  is  arched  upward  in 
the  center,  but  when  its  mus- 
cular fibers  contract  they  cause  this  arch  to  be  flattened 
downward,  thus  further  enlarging  the  cavity  of  the  chest. 
Relaxation  of  the  diaphragm  and  contraction  of  the 
muscles  that  draw  in  the  ribs  cause  the  air  to  be  forced 
out  of  the  lungs — a  process  which  goes  by  the  name  of 
expiration  (literally  breathing  out).  The  alternate  move- 
ments of  inspiration  and  expiration,  while  to  a  certain 
extent  under  the  control  of  our  will,  go  on  for  the  most 
part  quite  unconsciously.  Their  rapidity  varies  with 
age,  being  greater  in  young  children,  gradually  becoming 
slower  as  they  grow  older.  It  also  varies  with  exercise 


FIG.  203. — Diagram  to  illus- 
trate the  effect  of  depressing 
the  diaphragm  on  the  air  con- 
tent of  the  lungs. 


RESPIRATION  275 

like  the  rapidity  of  the  pulse  and  for  much  the  same  reason. 
When  we  work  hard  more  oxygen  is  consumed  and  more 
carbon  dioxide  is  produced  and  the  lungs,  thus  compelled 
to  become  more  active,  require  air  to  be  pumped  in 
and  out  with  greater  rapidity.  At  the  same  time  the 
blood  must  be  hurried  through  the  lung  capillaries  in 
order  that  it  get  rid  of  its  surplus  of  carbon  dioxide  and 
receive  the  requisite  supply  of  oxygen  for  the  increased 
demands  of  the  tissues.  This  is  why  .when  we  run  hard 
for  a  train  we  find  ourselves  panting  for  breath  and  our 
pulse  beating  wildly;  we  become  heated  too  as  a  result 
of  the  increased  metabolism  that  goes  on  in  our  muscles. 

As  respiration  is  so  intimately  associated  with  the 
maintenance  of  life  it  is  especially  important  that  we  be 
supplied  with  an  abundance  of  fresh  air.  If  we  live  in 
small  rooms  into  which  air  from  the  outside  cannot  freely 
enter,  the  air  supply  soon  becomes  contaminated  with 
carbon  dioxide  and  other  noxious  products.  We  soon 
experience  a  sense  of  lassitude  and  depression,  and  if  we 
habitually  live  under  such  conditions  our  general  health 
will  inevitably  become  impaired.  Colds,  consumption  and 
various  other  diseases  are  more  readily  contracted  by 
persons  who  live  in  impure  air.  Rooms  should  be  ven- 
tilated so  as  to  secure  a  free  circulation  of  air  without 
exposing  their  inmates  to  cold  draughts.  In  order  to 
breathe  properly  the  chest  should  not  be  allowed  to  become 
deformed  as  it  is  in  many  people  with  stooping  shoulders. 
Students  who  sit  at  desks  which  are  too  low  are  par- 
ticularly liable  to  this  deformity.  The  chest  capacity  is 
diminished  and  the  whole  body  consequently  suffers. 

Many  women  through  the  absurd  habit  of  tight  lacing 
compress  their  bodies  so  that  the  lower  part  of  the  chest, 
which  normally  expands  most  in  breathing,  can  scarcely 
expand  at  all.  Consequently  they  breathe  mostly  with 


276  ANIMAL  BIOLOGY 

the  upper  part  of  the  chest  and  greatly  diminish  the  supply 
of  air  which  the  lungs  require.  Not  only  this,  but  the 
abdominal  organs  are  displaced  thus  giving  rise  to  various 
other  harmful  effects. 

Respiration  is  a  function  common  to  all  organisms 
without  exception.  In  many  of  the  primitive  animals 
respiration  takes  place  through  the  whole  surface  of  the 
body.  Only  in  higher  forms  are  there  specialized  organs 
of  respiration  and  these  commonly  consist  of  structures 
by  means  of  which  a  relatively  large  surface  can  be 
brought  into  contact  with  oxygen.  In  aquatic  forms  this 
surface  is  usually  in  the  form  of  outgrowths,  such  as 
filaments  or  plates,  the  walls  of  which  are  very  thin  so  as 
to  permit  the  free  interchange  of  gases.  Gills  of  various 
forms  are  to  be  met  with  in  many  worms,  mollusks,  crus- 
taceans, several  aquatic  insects,  in  all  fishes  and  usually 
in  the  young  of  amphibians.  The  oxygen  which  the  gills 
utilize  is,  as  a  rule,  the  free  oxygen  which  is  dissolved  in 
the  water.  If  animals  are  placed  in  water  from  which 
the  oxygen  has  been  driven  off  they  will  die  of  suffocation. 

In  land  animals  the  increase  of  surface  for  exchange  of 
gases  is  usua  ly  obtained  not  by  outgrowths,  such  as  gills, 
but  by  ingrowths,  such  as  the  tracheal  tubes  of  insects  or 
the  lungs  of  higher  vertebrates.  As  the  thin  membrane 
that  separates  the  blood  from  the  oxygen  must  be  kept 
moist  for  the  proper  transfer  of  gases  the  exposure  of 
delicate  gills  to  dry  air,  to  say  noth'ng  of  dust  and  dirt, 
would  be  very  disadvantageous.  In  all  higher  land 
animals  Nature  has  safely  located  the  organs  of  respira- 
tion within  the  body  where  their  delicate  surfaces  are  al- 
ways moist  and  furnished  with  an  abundant  supply  of 
blood.  All  of  the  varied  organs  of  respiration  in  the  animal 
kingdom  are  devices  for  securing  essentially  the  same  end, 
whether  they  are  gills,  tracheal  tubes,  lungs,  or  simply  the 
general  surface  of  the  body  as  in  the  Hydra  and  earthworm. 


CHAPTER  XXIX 
EXCRETION 

As  living  matter  is  constantly  being  torn  down  and  built 
up,  the  removal  of  waste  is  as  important  as  supplying 
food  or  oxygen.  The  process  of  getting  rid  of  waste 
materials  is  known  as  excretion.  It  is  performed  by  sev- 
eral organs  such  as  the  kidneys,  the  liver  and  the  skin, 
each  of  which  carries  on  its  own  peculiar  kind  of  excretory 
activity.  Every  cell  gives  off  waste  into  the  blood  just 
as  every  cell  respires  and  assimilates  food.  A  part  of 
this  waste  is  CO2  and  is  gotten  rid  of  mainly  through  the 
lungs,  while  other  waste  materials  are  solid  and  escape 
from  the  body  only  by  the  medium  of  water,  in  which 
they  become  dissolved.  As  the  lungs  are  specialized  to 
get  rid  of  the  gaseous  waste,  so  other  organs  are  peculiarly 
adapted  to  get  rid  of  other  forms  of  waste  which  are  given 
off  into  the  blood  by  the  cells  of  the  body.  Chief  among 
these  organs  of  excretion  are  the  kidneys,  two  reddish 
organs  one  on  either  side  of  the  spinal  column  just  below 
and  behind  the  stomach.  Each  kidney  receives  a  large 
artery  from  the  aorta  (the  renal  artery)  and  gives  off  a 
large  vein  (the  renal  vein)  that  joins  the  inferior  vena 
cava.  Passing  from  each  kidney  is  a  duct  called  the 
ureter;  the  two  ureters  pass  downward  to  connect  with  the 
bladder  which  is  a  thin-walled,  elastic  sac  which  serves  as 
a  reservoir  for  the  storage  of  the  fluid  secreted  by  the 
kidneys. 

The  kidney  is  a  gland  consisting  mainly  of  numerous 
uriniferous  tubules.  Each  of  these  structures  begins  in  a 

277 


278 


ANIMAL  BIOLOGY 


Malpighian  corpuscle  which  consists  of  a  thin- walled  capsule 
surrounding  a  knot  of  blood  vessels,  the  glomerulus. 
These  tubules  after  a  tortuous  course  lead  to  a  cavity 
which  is  connected  with  the  ureter.  The  uriniferous 
tubules  which  we  may  call  the  drain  pipes  of  the  body  re- 
move a  considerable  quantity  of  water  and  various  salts 
from  the  blood,  but  their  most  important  function  is  the 
elimination  of  urea  which  is  a  nitrogenous  compound  re- 


PIG.  204. — Vertical  section  through  kidney.  2,  pyramid  showing  the 
renal  tubules  opening  at  the  papillae,  3;  4,  pelvis  or  cavity  of  kidney;  5, 
ureter;  6,  renal  artery;  7,  renal  vein;  8,  branches  of  these  blood  vessels. 
(After  Leidy.) 

suiting  from  the  breaking  down  of  proteins.  The  elimina- 
tion of  water  affords  the  means  of  getting  rid  of  solid 
waste  products  in  the  blood,  because  these  substances 
must  be  in  a  state  of  solution  in  order  to  be  discharged 
from  the  body.  Most  people  would  be  better  off  if  they 
drank  more  water  so  as  to  wash  their  protoplasm  free  from 
its  various  injurious  impurities.  We  are  all  poisonous  to 
ourselves.  When  disease  of  the  kidneys  impairs  their 
activities  poisons  accumulate  in  the  body  and  death  may 


EXCRETION  279 

result.  Some  of  the  diseases  of  the  kidneys  such  as  chronic 
Bright's  disease  are  among  the  most  fatal  of  human  mala- 
dies. One  of  the  most  potent  causes  of  kidney  diseases 
is  a'cohol,  because  so  much  blood  passes  through  these 
organs  that  the  secretory  cells  are  especially  exposed  to 
the  influence  of  this  drug.  Excessive  beer  drinkers  are 
especially  prone  to  kidney  disease  not  only  on  account  of 
the  alcohol  they  consume,  but  because  of  the  strain  im- 
posed on  the  kidneys  to  remove  the  large  amount  of  fluid 
added  to  the  blood. 

The  liver  is  also  an  important  organ  of  excretion  not 
only  on  account  of  the  substances  it  discharges  into  the 
intestine  through  the  bile  duct,  but  because  it  acts  on 
various  products  of  protein  metabolism,  converting  them 
into  urea,  in  which  form  they  are  given  off  into  the  blood 
to  be  removed  by  the  kidneys.  Certain  substances,  es- 
pecially salts,  are  thrown  off  in  the  perspiration  of  the  skin. 


CHAPTER  XXX 

INTERNAL  SECRETIONS  AND  THE  DUCT- 
LESS GLANDS 

We  have  already  given  several  examples  of  ordinary 
secretion  in  which  a  gland  pours  out  certain  substances  to 
the  outside  through  a  duct.  While  salts,  urea  and  other 
materials  are  taken  as  such  out  of  the  blood  and  passed 
through  the  glands  unchanged,  in  many  other  cases  the 
substances  that  are  discharged  are  manufactured  by  the 
glands  themselves.  Such  substances  are  found  in  the 
saliva,  gastric  juice  and  bile.  Hydrochloric  acid  and 
pepsin  do  not  occur  as  such  in  the  blood,  but  are  made  in 
the  cells  of  the  gastric  glands.  Secretion  in  these  cases, 
therefore,  does  not  consist  merely  in  filtering  out  materials 
that  are  present  in  the  body,  but  in  the  formation  and 
discharge  of  new  compounds.  There  are  many  cases  in 
which  the  compounds  formed  by  an  organ  are  not  dis- 
charged to  the  outside  but  are  given  off  into  the  blood. 
This  process  is  known  as  internal  secretion.  We  have 
already  met  with  one  example  of  this  in  the  urea  which  is 
formed  in  the  liver  out  of  various  products  of  protein 
metabolism  and  given  off  into  the  blood  to  be  eliminated 
from  the  body  by  the  kidneys.  This  substance,  there- 
fore, is  an  internal  secretion  of  the  liver  and  an  external 
secretion  of  a  quite  different  organ. 

Many  organs  which  produce  internal  secretions  have  no 
outlet  and  hence  are  known  as  ductless  glands.  The  func- 
tion of  most  of  the  ductless  glands  was  for  a  long  time  un- 
known, but  it  is  now  well  established  that  some  of  these 

280 


INTERNAL    SECRETIONS    AND    THE    DUCTLESS    GLANDS      281 

organs  produce  substances  that  are  essential  to  the  main- 
tenance of  life.  One  of  these  is  the  thyroid  gland  which  is 
situated  in  the  fore  part  of  the  neck  under  the  larynx. 
Complete  removal  of  the  thyroid  results  in  death,  which, 
however,  may  be  obviated  if  the  substance  secreted  by 
this  organ  is  given  to  the  patient.  This  substance  con- 
tains iodine  and  is  now  a  remedy  that  is  regularly  kept  at 
drug  stores.  There  is  a  peculiar  disease  called  cretinism, 
caused  by  impairment  of  the  thyroid,  which  is  associated 
with  certain  bodily  abnormalities  and  especially  lack  of 
mental  development.  Administration  of  thyroid  extract 
has  a  wonderful  curative  power  in  such 
cases,  and  it  often  converts  a  child  who 
is  backward  to  the  point  of  idiocy  into  a 
bright  and  happy  little  person.  There 
was  simply  supplied  the  internal  secretion 
necessary  for  normal  development  which 
its  own  body  failed  to  furnish  in  sufficient 
amount.  Another  disease,  goiter,  is  _ 

caused  by  an  abnormal  enlargement  of    thyroid  gland;  L, 
the  thyroid. 

Other  glands  that  produce  a  substance  essential  to  life 
are  the  adrenals  or  suprarenal  bodies,  small  glands  imme- 
diately over  the  kidneys.  Preparations  made  from  these 
glands  (adrenalin,  epinephrin)  have  the  property  of  con- 
tracting the  blood  vessels  of  a  part  to  which  they  are 
applied  and  they  are  therefore  used  in  minor  surgical 
operations  to  prevent  bleeding;. 

The  pancreas  in  addition  to  the  pancreatic  juice  dis- 
charged into  the  intestine  secretes  a  substance  that  has  to 
do  directly  or  indirectly  with  the  metabolism  of  sugar. 
Removal  of  the  pancreas  results  in  the  accumulation  of 
sugar  in  the  blood  (diabetes)  and  eventually  in  death. 
If,  however,  a  small  part  of  the  pancreas  is  grafted  in 


282  ANIMAL  BIOLOGY 

some  other  part  of  the  body  death  may  be  prevented. 
Although  there  is  no  longer  any  secretion  of  pancreatic 
juice,  the  pancreas  continues  its  internal  secretion  which 
is  the  most  important  of  its  functions.  Other  organs  have 
important  internal  secretions  but  they  cannot  be  described 
here. 


CHAPTER  XXXI 
THE  SKIN 

The  most  obvious  function  of  our  skin  is  that  of  protect- 
ing the  organs  which  it  covers,  but  it  serves  also  as  an 
organ  of  excretion,  a  medium  for  the  regulation  of  bodily 
temperature,  and  a  sensory  surface  adapted  to  receive 
many  kinds  of  impressions  from  the  outer  world.  A  few 
facts  about  the  structure  of  the  skin  will  help  us  to  under- 
stand how  it  performs  its  functions. 

The  skin  is  composed  of  two  layers,  a  deeper  one  the 
corium,  and  an  outer  cuticle  or  epidermis,  which  consists  of 
epithelial  cells  without  blood  vessels  or  nerves.  The  outer 
cells  of  the  cuticle  are  dead  and  as  they  are  shed  or  rubbed 
off,  they  are  continually  replaced  by  cells  from  beneath. 
When  a  blister  is  formed  the  cuticle  is  lifted  away  from  the 
corium  by  serum  which  exudes  between  these  two  layers. 
The  corium  is  a  relatively  thick  layer  of  connective  tissue 
containing  muscle  fibers,  blood  vessels,  glands,  the  end 
organs  of  nerves,  and  various  other  structures.  The 
deeper  part  of  the  cuticle  contains  brownish  pigment  which 
in  colored  races  is  especially  abundant  and  which  in  our- 
selves is  increased  when  we  become  freckled  or  tanned. 

Among  the  most  characteristic  structures  of  the  skin 
are  the  sweat  glands  which  are  coiled  tubes  whose  ducts 
open  through  fine  pores  at  the  surface  of  the  cuticle. 
With  a  good  hand  lens  these  openings  may  be  seen  in 
the  palm  of  the  hand.  As  many  as  2,000,000  of  them  have 
been  estimated  to  occur  over  the  entire  body.  Sebaceous 
or  oil  glands  are  present  wherever  hair  occurs  which  is 

283 


284 


ANIMAL  BIOLOGY 


over  most  of  the  body  except  the  palms  of  the  hands  and 
the  soles  of  the  feet.  Over  most  of  the  surface  of  the  body 
these  hairs  are  inconspicuous;  they  represent  the  mere 
remnant  of  the  coat  that  once  covered  our  hairy  ancestors. 
There  are  usually  two  oil  glands  to  each  hair  follicle  and 
their  secretion  serves  to  keep  the  hair  oily.  The  hair 
of  the  head  may  be  supplied  with  more  oil  if  the  glands  are 
stimulated  by  massaging  the  scalp  or  vigorously  brushing 
the  hair. 


FIG.  206. — Section  of  skin  of  man.  (From  Wiedersheim.)  Co, 
derma  (corium) ;  D,  oil  gland;  F,  fat;  G,  blood-vessels;  GP,  vascular  papilla; 
H,  hair;  N,  nerves;  NP,  nerve  papilla;  Sc,  stratum  corneum;  SD,  SD1, 
sweat  gland  and  duct;  SM,  stratum  Malpighii. 

Each  hair  grows  from  a  little  papilla  at  the  bottom  of 
the  hair  follicle,  where  there  are  many  small  blood  vessels 
and  nerves.  Sometimes  hairs  fall  out,  but  if  the  papilla 
is  uninjured  they  may  be  grown  again.  Hairs  contain 
pigment  which  gives  them  different  colors  in  different 
individuals,  but  all  kinds  of  hairs  tend  to  become  gray 
with  old  age  owing  to  the  central  part  of  the  hairs  being 
filled  with  air.  When  the  scalp  is  ill  nourished  the  hairs 


THE    SKIN  285 

that  fall  out  may  not  be  replaced  and  the  head  becomes 
bald.  Then  the  afflicted  person  generally  resorts  to  hair 
tonics  most  of  which  are  utterly  useless.  The  best  way 
to  avoid  the  dreadful  fate  of  having  a  shiny  bald  head  is  by 
washing  the  hair  occasionally  with  soap  and  water,  by 
brushing  the  hair  well  and  keeping  up  a  good  circulation 
in  the  scalp. 

We  have  said  that  one  function  of  the  skin  is  to  regulate 
the  temperature  of  the  body.  How  does  it  do  this? 
Most  of  the  lower  animals  are,  as  we  say,  cold  blooded. 
Their  temperature  goes  up  and  down  with  the  changing 
temperature  of  their  surroundings.  But  we  are  endowed 
with  a  remarkable  system  of  heat  regulation  which  is  so 
perfected  that  between  the  heat  of  summer  and  the  ex- 
treme cold  of  winter  our  bodily  temperature  scarcely 
fluctuates  more  than  a  degree.  Of  course  what  keeps 
up  our  temperature  is  the  burning  of  fats,  carbohydrates 
and  proteins  in  our  tissues,  but  our  skin  regulates 
the  rapidity  with  which  heat  is  allowed  to  escape, 
and  in  this  way  keeps  our  temperature  uniform.  Our 
blood  vessels  are  under  the  control  of  nerves  which  regu- 
late their  diameter  and  thus  control  the  amount  of 
blood  that  passes  through  them.  When  the  nerves  of 
the  skin  are  stimulated  by  cold  they  generate  impulses 
in  the  nerves  supplying  the  blood  vessels  of  the  skin  caus- 
ing these  blood  vessels  to  contract.  The  blood  is  driven 
from  the  skin  and  hence  does  not  radiate  heat  so  rapidly 
to  the  outside.  When  the  blood  is  too  warm  either  from 
surrounding  heat  or  from  exercise  there  is  an  enlargement 
of  the  blood  vessels  of  the  skin.  More  heat  is  radiated 
and  at  the  same  time  the  sweat  glands  secrete  more  per- 
spiration which  is  poured  out  at  the  surface  where  it  evapo- 
rates. Evaporation  always  produces  a  lowering  of 
temperature.  Wet  your  fingers  and  then  wave  your  hand 


286  ANIMAL  BIOLOGY 

through  the  air  so  as  to  make  the  water  evaporate  more 
rapidly  and  you  will  feel  a  sensation  of  coolness.  The 
more  perspiration  is  evaporated  at  the  surface  the  greater 
the  cooling  effect;  thus  by  means  of  the  changes  in  the 
circulation  of  the  skin  and  the  activity  of  its  glands  our 
skin  is  able  to  act  as  a  self-regulating  mechanism,  keeping 
the  temperature  always  at  a  certain  point. 

In  order  that  our  skin  can  perform  its  functions  properly, 
especially  the  regulation  of  temperature,  it  must  be  kept 
clean  so  that  its  pores  are  prevented  from  becoming  clogged. 
We  not  only  acquire  dirt  from  the  outside,  but  we  sweat 
it  out  from  within,  and  the  waste  matters  in  the  form  of 
salts,  and  various  impurities  accumulate,  some  of  them  to 
undergo  decomposition  to  the  distress  of  our  associates 
if  not  of  ourselves. 

But  bathing  is  desirable  not  only  to  get  rid  of  dirt,  but 
as  a  tonic  to  the  skin  and  incidentally  to  the  whole  body. 
The  cold  dash  or  shower  for  a  moderately  robust  person 
tones  up  the  blood  vessels  of  the  skin  and  renders  him 
much  less  liable  to  colds  and  various  other  forms  of  in- 
fection. If  after  taking  a  cold  bath  a  person  does  not  re- 
spond, after  a  vigorous  rubbing,  so  as  to  feel  an  exhilarating 
glow,  he  had  better  confine  himself  to  warmer  water. 


CHAPTER  XXXII 
THE  SKELETON  AND  THE  MUSCLES 

The  skeleton  has  for  its  general  function  the  support 
and  protection  of  the  organs  of  the  body.  If  we  were  to 
be  deprived  of  our  framework  of  bones  we  should  collapse 
at  once  into  an  inert  and  flabby  mass  of  flesh.  What 
gives  the  bones  the  rigidity  necessary  for  their  functions 
is  the  presence  of  mineral  constituents  consisting  chiefly 
of  phosphate  and  carbonate  of  lime.  These  substances 
may  be  dissolved  out  of  bone  by  means  of  nitric  acid 
leaving  a  tough,  gristly  counterpart  which  may  be 
readily  bent  or  even  tied  in  a  knot.  On  the  other  hand, 
when  bones  are  burned  the  tough  animal  matter  is  con- 
sumed, leaving  only  the  mineral  salts  with  which  it  was 
impregnated. 

A  part  of  our  skeleton  is  formed  of  tough  animal  matter 
called  cartilage  which  has  but  a .  very  small  quantity  of 
mineral  salts.  Cartilage  occurs  when  bones  are  growing 
and  where  flexibility  is  required,  as  at  the  ends  of  the  ribs. 
At  the  joints  the  bones  are  bound  together  by  very  tough 
and  inelastic  bands  of  connective  tissue  called  ligaments. 
In  many  cases  the  bones  are  joined  so  as  to  permit  freedom 
of  movement  in  one  or  more  directions.  We  have  the  so- 
called  hinge  joints  at  the  knee,  and  elbow,  permitting  a 
back  and  forth  motion,  and  ball-and-socket  joints  at  the 
hip  and  shoulder,  enabling  the  limb  to  move  in  any  direc- 
tion. Movable  joints  are  enclosed  in  a  synovial  membrane 
whose  secretion,  the  synovial  fluid,  serves  to  lubricate  the 
surfaces  of  the  united  bones.  Many  of  the  long  bones  like 

287 


288 


ANIMAL  BIOLOGY 


the  longer  bones  of  the  arms  and  legs  are  hollow.     With 
a  given  amount  of  material  the  greatest  strength  is  secured 


Frontal  bone 

Parietal  bone 

Temporal  bone 

Malar  or  cheek  bone 

Lower  jaw 


Clavicle 
Humerus  — 


Nasal  bones 
Upper  jaw 


Carpals 
Metacarpals 

Phalanges 


Sternum 


Pelvis 


Ligaments 


Tarsus 

Metatarsus 

Phalanges 


FIG.  207. — Skeleton. 


if  it  is  in  the  form  of  a  hollow  tube,  and  Nature  has  taken 
advantage  of  this  principle  in  the  formation  of  the  skeleton. 


THE    SKELETON   AND    THE   MUSCLES 


289 


But  she  has  not  wasted  the  space  in  the  interior  of  the 
bones;  they  are  filled  with  marrow,  a  substance  which  does 
not  seem  to  have  any  particular  use,  but  is  really  an  es- 
sential organ  of  the  body,  for  it  forms 
the  greater  part  of  the  red  and  white 
corpuscles  of  the  blood. 

We  commonly  have  a  few  more  than 
200  bones  in  the  body,  the  number 
being  somewhat  variable  because  some 
bones  that  are  separate  in  youth  be- 
come fused  together  in  later  life.  In 
the  skull  many  of  the  bones  of  the  cra- 
nium, or  part  enclosing  the  brain,  are 
united  by  sutures  which  dovetail  to- 
gether in  such  a  way  as  to  prevent 
them  from  becoming  separated  while 
at  the  same  time  affording  a  place  where 
the  bones  can  grow  and  thus  give  more 
space  for  the  growing  brain.  As  the 
bones  of  the  head  are  very  rigid,  if  they 
were  fused  together  at  the  sutures  the 
head  could  no  longer  enlarge.  Growth 
takes  place  at  the  edges  of  the  sutures. 

The  central  axis  or  backbone  of  the 
skeleton  (spinal  or  vertebral  column)  is 
composed  of  24  bones,  the  vertebra. 

' 

separated  from  one  another  by  elastic    column, 
pads  of  cartilage.     Inside   of  a  canal 


coc.- 

.FlG>  2°8-~  Sid<: 

view      of     spinal 

cv,   cervi- 


_ 

running  through  the  vertebrae  is  the  Coc-'  coccygeai  ver-. 
spinal  cord  which  connects  with  the 
brain  above  and  sends  off  nerves  between  the  vertebrae  to 
nearly  all  parts  of  the  body.  Projections  or  processes  of 
the  vertebrae  give  attachments  to  ligaments  and  the 
muscles  of  the  back. 

19 


ANIMAL  BIOLOGY 

Attached  by  movable  joints  to  the  vertebrae  of  the 
trunk  are  the  ribs.  All  but  the  two  lower  pairs  are  joined 
by  cartilage  to  the  flat  sternum  or  breast  bone  which  you 
can  easily  feel  in  the  front  of  the  chest.  The  last  or  float- 
ing ribs  are  free  in  front,  thus  permitting  a  greater  expan- 
sion of  the  chest  cavity. 

Forming  a  support  for  the  arms  are  the  scapula  or 
shoulder  blade,  and  a  narrow  bone,  the  clavicle,  which 
extends  from  the  upper  end  of  the  sternum  to  the  scapula 
near  the  articulation  of  the  arm.  Both  these  bones  give 
attachment  to  muscles  that  move  the  arm  and  to  certain 
other  muscles  of  the  neck  and  trunk.  The  upper  bone  of 
the  arm,  or  humerus,  is  joined  to  the  scapula  by  a  ball- 
and-socket  joint.  At  the  elbow,  one  of  the  bones  of  the 
fore  arm,  the  ulna,  is  joined  to  the  humerus  by  a  hinge 
joint,  while  the  other  bone,  the  radius,  which  lies  on  the 
same  side  as  the  thumb  is  joined  to  the  ulna  in  such  a 
way  as  to  permit  it  to  rotate  about  the  latter  with  the 
greatest  freedom.  The  wrist  composed  of  eight  small 
bones,  or  carpals,  is  followed  by  the  five  metacarpals  in 
the  palm  of  the  hand,  and  these  give  attachment  to  the 
phalanges  of  the  thumb  and  fingers. 

The  hip  bones  which  give  attachment  to  the  lower 
extremities  are  united  into  a  solid  arch,  the  pelvis,  which  is 
firmly  joined  to  the  fused  vertebrae  forming  the  sacrum. 
The  large  size  of  the  pelvis  is  necessary  for  the  attachment 
of  the  large  muscles  that  move  the  legs  as  well  as  the 
various  muscles  of  the  trunk.  There  is  a  close  similarity 
between  the  bones  of  the  legs  and  those  of  the  arms. 
Corresponding  to  the  humerus  is  the  femur,  the  head  of 
which  joins  by  a  ball-and-socket  joint  to  the  pelvis. 
At  the  knee  the  tibia  and  fibula,  corresponding  respectively 
to  the  radius  and  the  ulna,  are  united  by  a  hinge  joint  to 
the  femur.  The  carpals  of  the  wrist  are  the  representa- 


THE  SKELETON  AND  THE  MUSCLES 


291 


tives  of  the  tarsal  bones  of  the  ankles,  and  these  are 
followed  by  the  metatarsals,  and  these  again  by  the 
phalanges  which  are  the  skeletal  elements  of  the  toes. 
At  the  knee  there  is  a  small,  rounded  bone,  the  patella  or 
knee  pan. 

The  kind  of  material  that  is  usually  eaten  as  meat 
consists  mainly  of  muscle,  a  tissue  whose  chief  function 
is  the  production  of  movement.  We  are  able  to  move 
only  because  our  muscles  have  the  property  of  shortening 
or  contracting  under  the  influence  of  stimuli.  Grasp 
the  upper  arm  with  one  hand  while 
you  bend  the  fore  arm,  and  you 
can  feel  the  large  muscle  in  front 
of  the  humerus  (the  biceps)  shorten 
and  thicken.  When  you  straight- 
en the  arm  you  can  feel  an  op- 
posed muscle  (triceps)  contract  on 
the  opposite  side.  In  moving  the 
arm  the  bones  act  as  levers  which 
are  pulled  this  way  and  that  by 
the  muscles  attached  to  them. 
Muscles  never  act  by  pushing,  the 
opposed  movement  being  always 
effected  by  the  contraction  of  an 
antagonistic  muscle.  Accordingly 

we  commonly  find  muscles  in  pairs  the  members  of  which 
have  opposed  functions.  If  a  part  is  pulled  in  any  one  di- 
rection there  must  be  some  other  muscle  to  pull  it  back 
again.  Muscles  are  usually  attached  to  bones,  sometimes 
directly  and  sometimes  by  means  of  strong  inelastic  cords, 
or  tendons.  You  can  easily  feel  the  tendons  of  your  biceps 
muscle  or  the  tendons  of  some  of  the  muscles  behind  the 
knee  or  at  the  wrist. 

The  contractile  tissue  is  made  up  of  fibers,  which  are 


FIG.  209. — Diagram 
showing  the  action  of  the 
biceps  muscle  b,  which  when 
it  contracts  moves  the  fore 
arm  in  the  direction  of  the 
arrow. 


2Q2 


ANIMAL  BIOLOGY 


greatly  elongated  cells.  In  the  so-called  voluntary 
muscle,  or  muscle  which  we  can  control  by  the  will,  the 
fibers  are  marked  with  fine  cross  striations.  In  involun- 
tary muscle  the  fibers  are  smaller  and  usually  devoid  of 
cross  striations.  Such  muscular  tissue  occurs  in  the 
coatings  of  the  stomach  and  intestines,  in  the  walls  of 
blood  vessels  and  ducts,  and  in  various  other  parts  of  the 
body.  Involuntary  muscle  acts  usually 
without  our  being  aware  of  its  contrac- 
tion, and  we  have  very  little  direct 
control  over  its  activity.  In  fact  it  is 
best  that  we  are  not  able  to  control  it, 
because  the  wisest  of  us  would  not 
know  how  to  direct  its  functioning. 

Muscles  increase  in  size  and  strength 
through  exercise,  and  there  is  nothing 
so  good  as  exercise  in  the  open  air,  not 
only  for  muscles,  but  for  the  body  in 
general.  Muscular  exercise  involves 
stimulating  to  greater  activity  practi- 
cally all  parts  of  our  organism.  It 
brings  increased  appetite,  better  tone 
of  the  blood  vessels,  greater  lung  power, 
increased  elimination  of  waste,  better 
feelings  and  clearer  thinking.  When 
exercise  is  carried  too  far,  however,  we 
have  the  feeling  of  fatigue  which  is 
caused  by  substances  in  the  blood  that  result  from  an  ex- 
cessive breaking  down  of  living  tissue,  but  when  we  have 
rested  and  the  fatigue-producing  substances  are  disposed 
of,  Nature  not  only  restores  what  has  been  lost,  but  she 
commonly  adds  a  little  more.  Hence  the  strong  biceps 
of  the  blacksmith,  which  is  in  striking  contrast  to  the 
weak  and  flabby  muscles  of  a  sedentary  clerk  who  never 


FIG.  210. — Muscles 
and  tendons  of  fore 
arm  and  hand. 


THE  SKELETON  AND  THE  MUSCLES        293 

takes  any  vigorous  exercise.  And  it  is  not  for  the  sake 
of  our  muscles  alone  that  we  should  exercise,  but  for  the 
sake  of  our  brains  as  well.  For  clear  thinking  depends 
upon  a  good  body  as  much  as  does  good  digestion,  and 
it  is  just  as  necessary  for  the  student  to  attend  to  exercise 
in  order  to  keep  his  body  and  brain  in  good  working 
condition,  as  it  is  for  the  professional  athlete. 


CHAPTER  XXIII 
THE  NERVOUS  SYSTEM 

We  have  seen  that  the  movement  of  a  part  of  our  body 
is  due  to  the  contraction  of  muscle.  But  muscles  contract 
because  of  a  stimulus  which  they  receive  through  a  nerve. 
Without  nervous  impulses  to  initiate  and  direct  movements 
the  muscles  would  be  inactive  and  useless.  The  nervous 
system  is  one  which  controls  and  regulates  to  a  large  degree 
the  activities  of  the  organs  of  the  body,  and  to  this  end 
its  nerve  fibers  extend  into  practically  all  parts  of  the 
organism.  This  system  affords  also  the  medium  through 
which  we  feel  various  sensations.  Almost  all  parts  of 
our  body  are  sensitive  in  one  way  or  another,  and,  when 
we  feel,  it  is  due  to  the  fact  that  some  of  our  nerve  fibers 
carry  an  impulse  to  the  brain.  The  nervous  system,  and 
especially  the  brain,  is  very  closely  associated  with  the 
mind.  It  is  only  through  this  system  that  the  mind  is 
affected  by  influences  acting  on  the  body,  or  is  able  to 
produce  bodily  movement.  When  I  burn  my  finger  the 
impulse  set  up  in  the  nerves  supplying  this  organ  passes 
to  the  spinal  cord  and  thence  to  the  brain.  In  consequence 
of  this  impulse  I  feel  a  very  unpleasant  sensation.  When 
I  pull  away  my  hand,  as  I  am  pretty  sure  to  do  under  the 
circumstances,  there  is  an  impulse  sent  out  in  the  reverse 
direction,  which  is  carried  by  a  nerve  to  the  muscles  of 
the  arm  causing  them  to  contract.  Our  nerve  fibers 
perform  functions  very  similar  to  those  of  telegraph  and 
telephone  wires  which  carry  messages  to  and  from  a 
central  station.  The  mind  like  the  central  operator 

294 


THE    NERVOUS    SYSTEM  295 

receives  messages  that  come  to  the  brain,  and  the  brain 
sends  out  impulses  which  cause  certain  of  our  muscles  to 
contract;  by  this  means  we  are  enabled  to  act  in  any 
way  we  desire  in  regard  to  objects  in  the  world  about  us. 
Through  the  function  of  the  nervous  system  in  conducting 
impulses  from  one  part  of  the  body  to  another  the  activities 


FIG.   211. — Cerebro-spinal     nervous     system. 

of  different  organs  are  made  to  harmonize  or,  as  physiolo- 
gists say,  become  coordinated.  Were  it  not  for  some 
conducting  system  one  arm  might  act  quite  contrary  to 
the  other  arm,  and  each  leg  might  not  act  in  harmony 
with  the  other  one  in  walking,  and  our  other  organs 


296  ANIMAL  BIOLOGY 

might  work  at  cross  purposes,  so  that  we  would  be  unable 
to  accomplish  anything  that  we  wanted  to  do. 

In  order  to  see  how  the  nervous  system  acts  we  need 
to  gain  some  knowledge  of  how  it  is  formed.  Our  nerves 
are  composed  of  bundles  of  nerve  fibers.  Each  fiber 
consists  of  (i)  a  central  core  of  nervous  substance,  the 
axis  cylinder;  (2)  an  external  very  thin  sheath;  and  (3) 
in  most  nerves  a  layer  of  fatty  substance,  the  medullary 
sheath,  between  the  axis  and  cylinder  and  the  outer  cover- 
ing. Each  nerve  fiber  comes  from  a  nerve,  or  ganglion  cell, 
and  it  terminates  in  various  ways  according  to  its  function; 
some  nerves  supply  muscles  (motor  nerves),  some  end  in 
glands,  and  others  (sensory  nerves)  end  in  some  sense  organ 
and  serve  to  carry  sensory  impulses  to  the  central  nervous 
system.  Nerve  cells  commonly  have  several  branches 
some  of  which  may  subdivide  repeatedly.  In  the  central 
nervous  system  these  branches  meet  and  thus  impulses 
received  by  one  cell  may  be  conveyed  to  other  cells  and 
finally  be  transmitted  to  remote  parts  of  the  body.  Nerve 
cells  are  frequently  grouped  together  into  masses  called 
ganglia  which  are  found  in  various  parts  of  our  organism. 
The  large  masses  of  nervous  tissue  making  up  the  brain 
and  spinal  cord  have  much  the  same  composition  as 
ganglia,  being  composed  of  nerve  cells  and  their  branches, 
together  with  blood  and  lymph  vessels  and  a  framework 
of  connective  tissue  binding  the  whole  together. 

The  nervous  system  is  composed  of  two  principal  parts, 
the  cerebro-spinal  system,  and  the  sympathetic.  The  first 
includes  the  brain,  the  spinal  cord,  and  the  nerves  that 
proceed  from  these  central  organs.  Both  brain  and  spinal 
cord  contain  (i)  gray  matter  which  is  composed  largely 
of  nerve  cells  and  their  branching  processes,  and  (2)  white 
matter  which  is  formed  of  nerve  fibers  with  few  or  no  cells. 
In  the  spinal  cord  the  gray  matter  is  central,  forming  a 


THE    NERVOUS    SYSTEM  297 

mass  which  in  cross  section  has  a  certain  resemblance  to 
the  letter  H.  The  white  matter  that  surrounds  the  gray 
mass  is  composed  almost  entirely  of  fibers  running  length- 
wise of  the  cord.  The  spinal  cord  is  lodged  in  a  canal 
within  the  bones  of  the  vertebral  column  and  sends  of!  a 
pair  of  nerves  between  each  of  the  vertebrae.  Each  spinal 
nerve  arises  from  the  cord  by  two  roots,  a  dorsal  and  a 
ventral,  which  penetrate  the  white  matter  and  extend 
into  the  gray.  The  two  roots  soon  unite  and  pass  out  of 
the  spinal  column  as  a  single  nerve.  Each  dorsal  root 
is  furnished  with  a  ganglion,  the  cells  of  which  give  origin 
to  the  nerve  fibers  of  the  dorsal  root  and  to  others  which 
proceed  outward  and  form  a  part  of  the  spinal  nerve. 

Experiment  has  shown  that  the  fibers  of  the  two  roots 
have  different  functions.  If  the  dorsal  root  is  cut  and  the 
end  in  contact  with  the  cord  is  stimulated  a  sensation  of 
pain  is  felt  that  is  referred  to  the  part  to  which  these 
particular  nerve  fibers  are  distributed.  If  the  other  cut 
end  is  stimulated  no  effect  is  apparent,  and  the  part 
which  the  nerve  supplies  may  be  cut  or  burned  without 
producing  the  least  sensation.  It  is  evident,  therefore, 
that  the  nerves  producing  sensation  pass  into  the  cord 
through  the  dorsal  root.  Cutting  a  ventral  root  destroys 
all  power  of  voluntary  movement  in  the  part  supplied  by 
the  nerve  in  question,  but  the  sensibility  in  that  part 
remains  undiminished.  Stimulating  the  cut  end  of  the 
root  in  contact  with  the  cord  produces  no  marked  result 
while  stimulating  the  outer  cut  end  produces  vigorous 
movement  in  the  part  to  which  the  nerve  is  distributed. 
The  ventral  root  contains  the  motor  fibers,  or  those  having 
to  do  with  the  production  of  motion. 

The  spinal  cord  is  the  center  of  many  reflex  acts.  If 
the  spinal  cord  of  a  frog  is  cut  across  near  the  middle  and 
one  of  the  hind  toes  is  pinched,  the  leg  is  quickly  withdrawn. 


298  ANIMAL  BIOLOGY 

Therbrain  of  the  animal  has  nothing  to  do  with  this  act,  as 
it  no  longer  has  any  connection  with  the  parts  involved 
in  the  reaction.  The  impulse  set  up  in  certain  sense  cells 
of  the  foot  travels  toward  the  cord,  passing  through  the 
dorsal  root  into  the  gray  matter.  Thence  it  passes  out  of 
the  cord  along  the  ventral  or  motor  root  to  the  muscles 
of  the  leg  causing  them  to  contract,  thus  drawing  the  leg 


FIG.  212. — Diagram  of  a  cross  section  of  a  spinal  cord  showing  paths 
taken  by  nerve  impulses  in  a  simple  reflex  act.  A,  afferent  or  sensory 
nerve  fiber  entering  the  dorsal  side  of  the  cord;  DG,  dorsal  ganglion;  DR, 
dorsal  root;  G,  gray  matter  of  cord;  M,  muscle;  SO,  sense  organ;  V,  branch 
of  ventral  or  motor  root  of  spinal  nerve;  VR,  ventral  root;  W,  white  matter 
of  cord. 

away.  If  a  drop  of  acid  is  put  on  the  side  of  the  same  frog 
the  hind  foot  on  that  side  is  brought  forward  to  wipe  away 
the  irritating  substance.  These  are  but  a  few  of  the 
reflex  acts  which  may  be  performed  by  the  spinal  cord. 
Such  acts,  although  involuntary,  are  adaptive  in  that  they 
are  directed  so  as  to  perform  some  useful  function.  They 
are  carried  out  in  ourselves  much  as  in  the  frog.  If  the  sole 
of  the  foot  is  tickled  the  foot  is  quickly  withdrawn  even 
before  we  are  aware  of  our  action.  We  can  check  or  pre- 
vent many  of  our  spinal  reflexes  by  means  of  impulses  sent 


THE   NERVOUS    SYSTEM  2QQ 

down  from  the  brain,  but  none  the  less  many  such  reflexes 
are  often  performed  without  our  knowing  it  and  they  con- 
tinue to  be  performed  if  the  upper  part  of  the  cord  is  injured 
or  paralyzed  so  that  the  lower  part  of  the  body  is  no  longer 
under  voluntary  control.  Reflex  acts  are  performed  by 
way  of  the  brain  and  other  nerve  centers  as  well  as  by  the 


PIG.  213. — Lower  side  of  brain.  A,  C,  lobes  of  the  cerebrum;  B, 
olfactory  tracts;  D,  crossing  of  the  optic  nerves;  H,  M,  cerebellum;  N, 
medulla;  R,  pons.  (After  Leidy.) 

spinal  cord.  Coughing,  sneezing  and  winking  are  some  of 
these  and  they  are  often  performed  quite  independently 
of  our  will. 

Man  is  remarkable  among  animals  for  the  great  size  of 
his  brain.  The  largest  part  of  the  brain  consists  of  the  two 
cerebral  hemispheres  which  are  the  organs  especially  con- 
cerned with  voluntary  action  and  the  power  of  thought. 


300  ANIMAL  BIOLOGY 

Though  separated  from  one  another  by  a  deep  median 
cleft  or  fissure  they  are  broadly  united  by  a  mass  of  trans- 
verse fibers,  the  corpus  callosum.  The  surface  of  the 
hemispheres  is  thrown  into  numerous  folds  or  convolutions 
separated  by  fissures.  The  outer  part,  or  cortex,  of  the 
hemispheres  is  composed  of  gray  matter,  which  consists 
mainly  of  ganglion  cells  and  their  interconnecting  processes. 
There  are  numerous  fibers  which  pass  from  the  cortex 
to  certain  large  ganglionic  masses  at  the  base  of  the  brain 
and  these  in  turn  are  connected  with  the  spinal  cord  and 
with  various  cranial  nerves.  Then  there  are  numerous 
fibers  which  run  from  one  part  of  the  cortex  to  the  other 
so  that  the  whole  structure  may  be  regarded  as  a  great 
mass  of  nerve  cells  closely  united  by  connecting  fibers  and 
intimately  connected  with  other  parts  of  the  brain,  with 
the  spinal  cord,  and  thence  with  other  parts  of  the  body. 
Below  the  posterior  part  of  the  cerebral  hemispheres  is 
the  cerebellum,  an  organ  which  probably  has  to  do  with  the 
control  or  coordination  of  bodily  movements,  but  of  whose 
precise  functions  comparatively  little  is  known. 

.  The  lowest  part  of  the  brain,  the  bulb  or  medulla,  may 
be  regarded  as  an  enlargement  of  the  spinal  cord.  From 
this  part  arise  several  pairs  of  nerves  which  are  mainly 
distributed  to  the  head,  face  and  neck;  one  pair,  however, 
the  vagus  nerve,  sends  branches  to  the  lungs,  heart  and 
organs  of  digestion.  This  nerve  has  an  important  influence 
upon  the  beating  of  the  heart  and  the  movements  of 
respiration.  Destruction  of  a  certain  center  in  the  me- 
dulla results  in  death,  because  respiratory  movements  are 
stopped  and  the  animal  dies  of  suffocation.  An  animal 
can  live  without  a  cerebrum,  although  he  would  be  a  very 
stupid  sort  of  creature,  but  the  medulla  is  absolutely 
essential  to  life. 

When  the  cerebral  hemispheres  are  taken  out  of  a  pigeon 


THE   NERVOUS    SYSTEM  301 

the  bird  is  at  first  dull  and  inactive,  but  after  a  time  it 
regains  its  power  of  spontaneous  movement.  It  can  fly, 
avoid  obstacles,  balance  itself  on  a  perch,  but  it  does 
not  recognize  its  associates,  pays  no  attention  to  its  young 
and  shows  no  evidence  of  any  knowledge  of  the  things  it 
had  previously  learned.  A  German  physiologist,  Goltz, 
has  succeeded  in  the  difficult  operation  of  removing  the 
entire  cerebrum  from  a  dog,  and  in  keeping  the  animal 
alive  for  several  months.  After  recovery  from  the  opera- 


Pic.  214. — Median  section  through  brain.  A,  B,  C,  D,  lobes  of  the 
cerebrum;  E,  cerebellum;  F,  arbor  vitas;  H,  pons  Varolii;  K,  medulla. 
(After  Leidy.) 

tion  the  dog  was  able  to  walk  about  spontaneously  and 
even  became  unusually  active.  It  would  growl  and  snap 
when  its  paw  was  seized  and  it  would  eat  food  placed  in 
contact  with  its  nose,  but  it  would  reject  meat  or  milk  made 
bitter  with  quinine.  While  the  dog  could  hear  and  could 
react  to  light,  it  recognized  none  of  its  old  acquaintances 
either  by  sight  or  sound.  Everything  it  had  acquired 
by  memory  was  lost,  and  it  became  a  creature  of  pure  in- 


302 


ANIMAL  BIOLOGY 


stinct,  without  knowledge  and  without  understanding. 
If  intelligence  is  especially  associated  with  the  cerebral 
hemispheres  can  we  say  that  different  faculties  of  the 
mind  are  located  in  different  regions  of  these  parts  of  the 
brain?  A  number  of  years  ago  several  theorists  elabo- 
rated a  system  called  phrenology,  according  to  which 
various  faculties  of  the  mind  are  located  in  different  parts 
of  the  brain,  and  therefore  in  order  to  determine  what 


FIG.  215. — Left  side  of  a  monkey's  brain  showing  motor  areas.  When 
these  areas  are  stimulated  movements  are  caused  in  the  parts  of  the  body 
designated  by  the  names  upon  the  corresponding  parts  of  the  brain. 

faculties  in  a  person  were  exceptionally  well  developed,  it 
was  only  necessary  to  study  the  shape  of  his  head  which 
was  supposed  to  give  a  fairly  reliable  index  of  the  outline  of 
the  brain.  Phrenology  has  now  fallen  into  disrepute.  Dif- 
ferent parts  of  the  cerebrum,  however,  have  different 
functions,  although  various  faculties  of  the  mind  cannot 
be  mapped  out  as  the  phrenologists  had  them  located. 
Near  the  middle  of  the  cerebral  hemispheres  is  the  so-called 


THE    NERVOUS    SYSTEM  303 

motor  area  containing  a  number  of  centers  which,  when 
stimulated  by  electric  needles,  produce  a  movement  in  a 
particular  part  of  the  body.  There  is  in  the  ape's  brain, 
for  instance,  a  center  for  the  movement  of  the  fingers, 
another  for  the  forearm,  another  for  the  shoulder  muscles, 
others  again  for  various  parts  of  the  hind  leg  and  trunk. 
When  these  centers  are  cut  out  the  animal  has  difficulty 
in  making  movement  in  a  corresponding  part  of  its  body. 
When  brain  tumors  occur  in  the  motor  area  their  precise 
location  is  often  indicated  by  the  inability  of  the  patient 
to  perform  certain  movements.  Many  such  cases  have 
been  cured  by  making  an  opening  through  the  skull  over 
the  area  indicated  and  removing  the  tumor. 

Abnormal  conditions  of  the  brain  are  very  frequently 
correlated  with  epilepsy  and  insanity.  There  is  a  remarka- 
bly close  relationship  between  the  activities  of  our 
brains  and  the  working  of  our  minds.  It  is  not  possible 
to  have  a  healthy  mind  in  a  diseased  brain,  and  as  the 
brain  is  an  especially  delicate  and  sensitive  organ  it 
quickly  feels  the  effect  of  injurious  agencies.  Nearly  a 
fifth  of  the  circulating  blood  goes  to  supply  this  organ. 
Nervous  tissue  absorbs  a  relatively  large  amount  of 
material  from  the  blood  and  it  is  the  seat  of  active 
metabolic  changes.  This  circumstance  accounts  in  large 
part  for  the  necessity  for  sleep  which  is  a  period  of  rest 
and  restoration.  During  childhood,  which  is  a  time  of 
rapid  growth  and  active  exercise,  more  sleep  is  required 
than  later  in  life;  but  in  all  periods  of  life  sleep  cannot  be 
dispensed  with  for  long  without  producing  very  serious 
results. 


CHAPTER  XXXIV 


THE  ORGANS  OF  SENSE 

We  become  aware  of  objects  in  the  outer  world  through 
our  organs  of  sense;  these  when  stimulated  set  up  im- 
pulses which  are  conveyed  by  sensory  nerve  fibers  to  the 
brain  and  arouse  sensations  of  various  kinds  according 
to  the  kind  of  sense  organ  affected.  Each  sensation  that 

we  feel  has  its  own  peculiar 
sense  organ  which  is  especi- 
ally sensitive  to  a  particular 
activity  in  the  outer  world. 
Contact  for  instance  stimu- 
lates the  organs  of  touch, 
sound  waves  the  organs  of 
hearing,  and  light  affects  the 
organs  of  vision.  Were  it 
possible  to  destroy  all  of  our 
sense  organs  or  the  nerves 
which  lead  from  them  to  the 


FIG.  216. — Tongue,  i,  circum- 
vallate  papillae;  2,  circumvallate 
papilla,  large;  3,  toad-stool  (fungi-  central  nervOUS  System,  the 

outer  world  would  make  no 


form)  papillae;  4,  threadform  (fili- 
form) papillae. 


impression  on  us. 

Some  of  our  sense  organs  are  distributed  over  most  of 
the  surface  of  the  body,  while  others  are  limited  to  well- 
defined  areas.  We  may  feel  sensations  of  touch  over  most 
of  the  skin  and  in  various  internal  organs,  but  there  are 
some  areas  such  as  the  tip  of  the  tongue  and  the  ends  of 
the  fingers  where  tactile  sensibility  is  especially  acute. 
Heat  and  cold  are  likewise  felt  over  most  of  the  surface  of 

304 


THE    ORGANS   OF    SENSE  305 

the  body.  These  sensations  doubtless  have  their  own 
separate  nerves  corresponding  to  little  areas  called  heat 
spots  and  cold  spots  which,  when  stimulated,  yield  each 
its  own  sensation  of  heat  or  cold  respectively.  Menthol 
has  the  property  of  stimulating  the  cold  spots  and  of  mak- 
ing the  skin  feel  cold,  although  in  reality  it  may  be  quite 
warm.  Pain  is  a  definite  sensation  which  is  aroused 
when  the  tissues  of  the  body  are  injured. 

The  sensation  of  taste  is  aroused  by  the  stimulation  of 
the  taste  buds  of  the  tongue.     There  are  a  limited  number 


FIG.  217. — Nasal  cavity.  i,  olfactory  nerve  with  its  branches 
shown  in  2;  3  and  4,  turbinated  bones;  5,  fifth  cranial  nerve.  (After 
Marshall.) 

of  true  sensations  of  taste,  i.e.,  sweet,  bitter,  sour,  salt; 
much  of  what  we  call  tastes  are  really  odors  which  are 
caused  by  substances  arising  through  the  pharynx  and 
stimulating  the  olfactory  nerves.  This  is  why  holding  the 
nose  when  certain  substances  are  being  chewed  and  swal- 
lowed, and  thereby  preventing  the  air  from  freely  entering 
the  nasal  cavity  from  behind,  tends  to  make  us  unaware 
of  their  flavor. 

The  eyes  are  among  the  most  complex  and  delicately 
adjusted  organs  of  the  body  and  they  have  long  excited 
wonder  and  admiration  on  account  of  the  perfection  of 
their  mechanism.  The  eyes  are  freely  movable  within 


20 


ANIMAL  BIOLOGY 


their  sockets,  or  orbits,  by  means  of  six  small  muscles. 
Their  outer  exposed  surface  is  kept  moist  by  the  secretion 
of  the  lachrymal  glands.  Normally  this  secretion  is  drained 


FIG.  218. — The    eye.     i,    lachrymal    gland;    2,    tear  duct. 

off  by  the  tear  duct  which  leads  from  the  inner  angle  of 
the  eye  to  the  nasal  cavity,  but  when  the  secretion  is 
unusually  abundant  it  may  overflow  as  tears.  The  eye 


\ 

3  5 

FIG.  219. — Sectiont  hrough  the  eye.  I,  optic  nerve;  2,  vitreous  body; 
3,  sclerotic;  4,  choroid;  5,  retina,.  6,  cornea;  7,  anterior  chamber;  8,  iris; 
9,  pupil;  10,  crystalline  lens. 

is  nearly  spherical  in  form  and  is  furnished  with  a  tough, 
whitish,  fibrous  outer  coat,  the  sclerotic,  which  extends 
over  all  but  the  anterior  surface  where  it  is  replaced  by  the 


THE    ORGANS    OF    SENSE  307 

transparent  cornea.  Behind  the  cornea  is  a  colored,  cir- 
cular partition,  called  the  iris,  which  has  a  central,  circular 
aperture,  the  pupil,  through  which  light  is  admitted 
to  the  back  part  of  the  eye.  Just  behind  the  iris  lies  the 
transparent  crystalline  lens.  This  separates  the  interior 
of  the  eye  into  two  chambers,  (i)  a  small  anterior  one 
filled  with  a  transparent  fluid  called  the  aqueous  humor, 
and  (2)  a  large  posterior  chamber  filled  with  the  trans- 
parent vitreous  humor.  The  back  part  of  the  eye  is  lined 
internally  by  the  sensitive  retina  which  is  really  the 
expanded  end  of  the  optic  nerve.  Between  the  retina  and 
the  sclerotic  is  the  black,  pigmented  choroid  coat  which 
serves  to  absorb  scattered  light  which  enters  the  eyeball. 

The  optical  parts  of  the  eye  are  so  arranged  as  to  throw 
images  of  outer  objects  on  the  retina.  The  eye  has  often 
been  compared  to  a  camera  which,  in  a  very  similar  way, 
is  constructed  so  as  to  throw  images  on  the  photographic 
plate  at  the  back.  The  Jens  of  the  eye  functions  like  that 
of  a  camera  in  forming  an  image;  the  iris,  which  by  con- 
tracting or  relaxing  alters  the  size  of  the  pupil,  corre- 
sponds to  the  shutter  which  regulates  the  amount  of  light 
entering  the  camera;  the  choroid,  like  the  black  inside 
of  the  camera,  absorbs  superfluous  light;  and  the  retina 
on  which  images  are  thrown  is  analogous  to  the  sensitive 
photographic  plate  or  film.  As  images  formed  by  a  lens 
are  clearly  outlined  only  when  the  object  is  a  certain 
distance  away,  if  the  parts  of  the  eye  remained  always 
the  same  we  could  not  see  both  distant  and  near  objects 
with  equal  clearness.  We  are  enabled  to  do  this  because 
the  curvature  of  the  lens  can  be  increased  by  the  con- 
traction of  a  special  muscle  that  surrounds  it,  while  the 
lens  resumes  its  previous  shape  when  the  muscle  is  relaxed. 
The  eye  thus  has  the  power  of  focusing  itself  upon  objects 
at  varying  distances. 


3o8 


ANIMAL  BIOLOGY 


In  many  people  the  eye  is  not  entirely  spherical,  or 
the  lens  has  not  the  proper  convexity,  so  that  the  eye 
does  not  have  the  usual  range  of  vision.  Some  people 
are  near  sighted,  that  is,  they  see  clearly  only  close  at 
hand,  while  others  are  far  sighted  and  can  see  clearly  only 


PIG.   220. — Diagram    to    illustrate    the    adjustment    of    the   crystalline 
lens,  A,  for  distant  objects,  B  for  near  ones.      (After  Huxley.) 

things  that  are  distant.  In  the  first  case  the  clearest 
image  is  formed  in  front  of  the  retina  and  in  the  other  case 
the  image  is  behind  it.  These  defects  are  corrected  by 
proper  eye  glasses. 

A  very  common  eye  defect,  called  astigmatism,  is  caused 
by  the  unequal  curvature  of  the  eye  ball  or  lens.     This  is 


FIG.   221. — Diagram  of  the  position  of  the  retina.     F,  in  far  sight;  N, 
in  near  sight;   and  C,   in  natural   sight. 

corrected  by  lenses  which  have  a  cylindrical  instead  of  a 
spherical  curvature.  Much  eye  strain  is  endured  by  many 
people  without  their  being  aware  of  the  fact;  and  many 
disorders,  such  as  headache,  nervousness,  indigestion  and 
other  ailments  are  directly  traceable  to  this  cause.  Read- 
ing in  dim  light  or  with  the  light  in  front  so  that  we  get 


THE    ORGANS   OF   SENSE 


309 


the  glare  from  the  paper  tends  to  fatigue  the  eyes,  and 
reading  during  convalescence  from  illness  is  especially  apt 
to  leave  the  eyes  in  a  weakened  condition. 

The  ear,  or  organ  of  hearing,  is  composed  of  three  parts, 
the  external,  the  middle  and  the  internal  ear.  The  external 
ears  of  most  of  the  mammals  can  be  turned  so  as  to  catch 
the  sound,  or  else  flattened  against  the  head  for  protection, 
but  in  ourselves  the  ear  muscles  are  mere  rudiments 
capable  of  producing  only  a  slight  amount  of  movement, 


SC 


FIG.  222. — Section  through  the  ear;  a,  anvil;  h,  hammer;  s,  stirrup; 
co,  cochlea;  eo,  external  opening;  Et,  Eustachian  tube;  tb,  temporal 
bone;' tc,  tympanic  cavity;  tm,  tympanic  membrane;  v,  vestibule. 

or  none  at  all.  In  fact  the  aural  appendages  of  man  are 
almost  devoid  of  function  as  they  are  poorly  adapted  for 
catching  sound  and  represent  but  the  vestiges  of  a  struc- 
ture once  valuable  to  the  animal  ancestors  of  man.  The 
passage  leading  toward  the  inner  parts  of  the  ear  is 
furnished  with  numerous  glands  that  secrete  a  waxy 
substance  which  serves  to  protect  the  ear  from  dust  and 
insects.  The  inner  end  of  the  passage  is  closed  by  the 
tympanic,  or  drum  membrane.  On  the  inner  side  of  this 


310  ANIMAL  BIOLOGY 

membrane  lies  the  space  called  the  middle  ear.  This  is 
connected  with  the  pharynx  by  the  Eustachian  tube  which 
serves  to  admit  air  to  the  middle  ear  from  the  throat. 
When  one  swallows  one  can  usually  hear  the  opening  of 
this  tube. 

Connected  with  the  drum  membrane  on  the  one  side 
and  with  the  inner  ear  on  the  other  is  a  chain  of  three  small 
bones,  called  the  hammer,  the  anvil,  and  the  stirrup. 
Sound  waves  set  the  drum  membrane  into  vibrations 
which  are  conveyed  by  these  bones  to  the  inner  ear  where 
they  stimulate  the  end  organs  of  the  auditory  nerve. 
The  inner  ear  is  a  delicate,  complex  structure  lodged  in  a 
cavity  within  the  bones  of  the  .skull.  The  spirally  wound 
cochlea  which  resembles  a  snail  shell  in  shape  contains  the 
delicate  end  organs  of  the  nerves  of  hearing.  Another 
part  of  the  internal  ear  consisting  of  three  semicircular 
canals  has  a  very  different  function,  as  it  forms  an  organ 
for  the  maintenance  of  the  equilibrium  of  the  body. 


CHAPTER  XXXV 
ALCOHOL  AND  TOBACCO 

Human  beings  are  not  satisfied  as  a  rule,  with  wholesome 
food  and  drink,  but  they  manifest  a  perverse  tendency 
toward   the  use  of  artificial   stimulants  and  narcotics, 
whose  influence  on  both  mind  and  body  is  almost  always 
injurious  and  frequently  disastrous.     While  alcohol  has 
been  alluded  to  in  discussing  various  bodily  functions, 
its  use  is  so  deeply  entrenched  in  popular  custom  that  it 
is  desirable  to  give  here  a  fuller  account  of  its  physiological 
effects.     The  influence  of  alcohol  has  been  studied  by  Pro- 
fessor Hodge  by  means  of  experiments  on  dogs,  extending 
over  five  years.     Four  pups  of  the  same  litter  were  chosen 
and  observed  for  some  time  to  see  if  they  showed  any  dif- 
ferences previous  to  giving  them  alcohol.     The  two  most 
vigorous  pups  were  given  a  daily  portion  of  alcohol,  but 
never  enough  to  produce  intoxication.     In  a  few  months 
the  alcoholic  dogs  became  more  sleepy  and  lifeless,  whereas 
the  other  dogs  which  were  given  no  alcohol  were  bright 
and  active.     Experiments  in  which  all  four  dogs  were  given 
a  hundred  trials  in  chasing  a  ball  thrown  to  a  distance  of  a 
hundred  feet  showed  that  the  alcoholic  dogs  secured  the 
ball  only  about  one-half  as  often  as  the  others.     The  al- 
coholic dogs  were  much  more  nervous,  and  when  all  the 
dogs  contracted  the  distemper,   the  disease  was  much 
more  severe  on  those  that  were  given  alcohol. 

These  results  are  quite  typical  of  the  effects  of  alcohol 
on  human  beings.  Dr.  Parkes  had  the  opportunity  of 
testing  the  influence  of  alcohol  on  two  lots  of  soldiers.  The 


312  ANIMAL  BIOLOGY 

men  were  of  the  same  age,  had  the  same  food,  and  lived 
under  the  same  conditions.  The  one  lot  of  men  were 
given  beer  when  they  wanted  it,  which  they  usually  did 
when  tired ;  the  others  had  no  alcohol.  While  the  alcoholic 
lot  outstripped  the  others  at  first,  they  soon  lagged  behind 
and  did  far  less  in  a  day  than  the  others.  When  the  condi- 
tions were  reversed,  the  lot  of  men  who  formerly  drank 
but  now  took  no  alcohol  did  much  more  work  in  a  day  than 
the  other  lot.  The  experiences  of  Kitchener,  Roberts, 
and  others  with  soldiers  has  convinced  them  that  men 
endure  marching  and  other  tasks  much  better  without  al- 
cohol. Count  von  Haeseler,  the  German  commander, 
says  "The  soldier  who  abstains  altogether  is  the  best 
soldier.  He  can  accomplish  more,  can  march  better, 
and  is  a  better  soldier  than  the  man  who  drinks  even 
moderately." 

The  almost  unanimous  testimony  of  mountain  climbers 
is  that  if  arduous  journeys  are  to  be  taken  no  alcohol 
should  be  used.  Athletes  in  training  are  usually  not  al- 
lowed alcohol.  Although  alcohol  is  a  food,  the  trainers 
of  athletes  have  learned  that  it  is  a  very  dangerous  ex- 
periment to  allow  its  use,  even  in  very  small  amounts. 

Alcohol  not  only  reduces  the  capacity  to  perform  tasks  in- 
volving strength  and  endurance,  but  it  has  an  even  greater 
effect  on  performances  that  require  dexterity  and  skill. 
Experiments  with  type  setters  who  were  given  a  moderate 
amount  of  alcohol  on  certain  days  and  no  alcohol  on  others, 
have  shown  that  the  amount  of  work  done  when  no  alcohol 
is  given  was,  on  the  average,  markedly  less  on  the  alcoholic 
days,  although  the  men  were  under  the  impression  that 
they  were  accomplishing  more.  Kraepelin,  who  believed 
that  alcohol  in  small  amounts  increased  the  activity  of 
his  mind  in  adding,  subtracting,  and  learning  figures, 
found,  when  he  came  to  test  the  matter,  that  he  accom- 


ALCOHOL  AND  TOBACCO  313 

plished  these  operations  less  quickly  than  when  he  had  taken 
no  alcohol.  Numerous  experiments  with  Swedish  sol- 
diers under  various  conditions  have  shown  that  accuracy 
in  shooting  at  a  target  was  reduced  from  30  to  50  per  cent, 
when  a  small  amount  of  brandy  was  given. 

In  the  higher  operations  of  the  mind  alcohol  acts  as  a 
depressant  and  inhibitor.  A  person  slightly  under  its 
influence  often  talks  more  rapidly  and  appears  more  lively, 
but  he  acts  with  less  judgment.  Herbert  Spencer  observes 
"  Incipient  intoxication,  the  feeling  of  being  jolly,  shows 
itself  in  a  failure  to  form  involved  and  abstract  ideas." 
Helmholtz,  in  speaking  of  the  inspirations  that  came  to 
him  while  pondering  over  his  problems,  said  "They  were 
especially  inclined  to  appear  to  me  while  indulging  in  a 
quiet  walk  in  the  sunshine  or  over  the  forest-clad  moun- 
tains, -but  the  smallest  quantity  of  an  alcoholic  beverage 
seemed  to  frighten  these  ideas  away." 

Alcohol  in  inhibiting  the  higher  operations  of  the  mind 
causes  the  loss  of  self-restraint  that  only  too  frequently 
leads  to  crime.  Swedish  statistics  show  that  out  of  24,298 
prisoners  committed  to  hard  labor,  17,374,  or  71.2  per  cent, 
attributed  their  crime  to  the  use  of  alcohol.  Dr.  Sullivan 
found  that  "out  of  200  men  convicted  of  murder  or  attempts 
at  murder,  158  were  of  alcoholic  habits,  and  in  120  of 
these,  or  50  per  cent,  of  the  whole  series,  the  criminal 
act  was  directly  due  to  alcoholism."  The  same  inhibition 
of  higher  nerve  centers  accounts  for  the  large  percentage 
of  accidents  that  happen  to  people  influenced  by  drink. 
The  nervous  system  is  a  delicate  mechanism,  and  when 
anything  important  depends  on  its  proper  working,  al- 
cohol had  better  be  left  entirely  alone. 

While  the  evil  effects  of  over  indulgence  in  alcoholic 
drinks  are  evident  enough,  it  is  often  claimed  that  moder- 
ate drinking  can  be  practised  with  no  serious  results. 


314  ANIMAL  BIOLOGY 

Many  people,  it  is  true,  drink  regularly  a  small  amount  of 
alcoholic  beverage  and  live  to  an  advanced  age  in  apparent 
good  health.  But  this  does  not  prove  that  moderate 
drinking  was  not  harmful  to  them,  or  that  in  other  people 
less  able  to  withstand  the  strain  it  may  not  cause  greater 
injury.  One  of  the  worst  effects  of  moderate  drinking 
lies  in  the  danger  that  it  may  lead  to  heavy  drinking. 
Many  people,  once  they  acquire  a  taste  for  alcohol,  soon 
become  victims  of  a  habit  which  is  insidiously  fastened 
upon  them  and  finally  makes  a  wreck  of  their  lives.  That 
many  men  of  fine  intellect  and  excellent  character  become 
the  slaves  of  alcohol  is  a  fact  known  to  everyone,  and 
whoever  takes  to  drink  thinking  that  it  will  be  easy  to 
break  off  is  performing  a  very  dangerous  experiment. 
Habit-forming  drugs  impair  the  will  at  the  same  time  that 
they  increase  desire.  And  before  one  is  aware  *>f  the 
danger,  he  may  be  already  in  the  clutches  of  the  enemy 
that  he  is  powerless  to  shake  off. 

One  of  the  best  evidences  of  the  injurious  influence  of 
moderate  drinking  is  afforded  by  the  statistics  of  life  insur- 
ance companies  which  show  that  the  average  length  of 
life  of  moderate  drinkers  is  less  than  that  of  total  abstain- 
ers. Some  life  insurance  companies  do  not  take  even 
moderate  drinkers.  In  one  of  these,  the  American  Tem- 
perance Life  Insurance  Association,  the  death  rate  of  the 
members  is  26  per  cent,  less  than  that  of  general  risk. 
Users  of  alcohol  are  more  liable  to  contract  infections 
such  as  pneumonia,  tuberculosis,  and  cholera,  and  the 
disease  is,  as  a  rule,  more  severe  with  them. 

TOBACCO 

Ever  since  its  first  introduction  into  the  civilized  world 
by  Sir  Walter  Raleigh,  tobacco  has  been  very  extensively 


ALCOHOL  AND   TOBACCO  315 

used  by  a  considerable  part  of  mankind.  Tobacco  has  a 
narcotic  effect  which  is  due  to  small  quantities  of  nicotine, 
a  substance  so  poisonous  that  only  two  or  three  drops  are 
required  to  cause  the  death  of  a  man.  Habitual  users  are 
affected  but  little  by  this  small  percentage  of  nicotine, 
but  those  just  beginning  the  use  of  tobacco  often  have  a 
very  uncomfortable  time  after  their  first  chew  or  smoke. 

Tobacco,  like  other  habit-forming  drugs,  creates  a 
craving  which  is  frequently  difficult  to  overcome  and 
which  may  lead  to  an  immoderate  use  that  is  decidedly 
injurious  to  health.  Many  people,  however,  may  use 
moderate  amounts  of  tobacco  for  years  with  no  noticeable 
ill  effects.  In  such  cases  one  has  to  reckon  with  the 
possibility  of  less  obvious  injury  which  ordinarily  escapes 
detection.  Where  men  are  in  training  for  an  athletic 
contest  which  requires  all  their  muscular  and  nervous 
energies,  it  is  found  by  athletic  trainers  generally  that  it  is 
best  to  forbid  all  use  of  tobacco. 

The  effect  of  tobacco  on  the  heart  in  producing  the 
condition  known  as  "tobacco  heart"  is  well  known. 
Tobacco  smoke  is  frequently  irritating  to  the  throat,  and 
also  to  the  lungs,  especially  when  it  is  inhaled,  as  it  often  is, 
by  smokers  of  cigarettes. 

All  students  of  the  subject  agree  that  tobacco  exerts  a 
very  harmful  influence  upon  young  boys.  It  stunts  their 
growth,  saps  their  vitality  and  dulls  their  intellect;  a 
school  boy  who  is  addicted  to  its  use  is  almost  sure  to  make 
a  relatively  poor  record.  Even  among  college  students 
the  use  of  tobacco  only  too  frequently  goes  along  with 
idleness  and  poor  scholarship.  Andrew  D.  White,  former 
President  of  Cornell  University,  remarked  that  "I  never 
knew  a  student  to  smoke  cigarettes  who  did  not  disappoint 
expectations;"  and  Dr.  Meylan  of  Columbia  University, 
who  has  made  a  careful  study  of  smokers  and  non-smokers 


316  ANIMAL  BIOLOGY 

among  the  students,  states  that  "the  scholarship  standing 
of  smokers  was  distinctly  lower  than  that  of  the  non- 
smokers." 

There  is  no  reasonable  doubt  that  people  would  be  better 
off  without  tobacco  than  with  it.  The  tobacco  habit  is 
expensive,  often  repugnant  to  others,  decidedly  harmful 
to  youth,  and  frequently  injurious  to  adults.  Many 
derive  solace  from  their  pipe  or  cigar.  They  may  think 
that  whatever  bad  effect  tobacco  may  have  upon  them 
is  more  than  outweighed  by  the  satisfaction  derived  from 
its  use.  If  there  are  people  for  whom  this  is  true — and  ij 
is  by  no  means  certain  that  there  are — it  is  perfectly 
clear  that  it  is  true  only  for  those  who  have  reached 
maturity.  As  Peabody  has  remarked,  "the  ambitious 
boy  who  has  any  regard  for  developing  a  vigorous  body 
fitted  for  athletic  success,  for  training  a  mind  capable  of 
clear  thinking,  and  for  preparing  himself  for  a  successful 
life  work,  will  resist  all  temptations  to  smoke,  at  least 
until  he  has  attained  his  full  growth." 


CHAPTER  XXXVI 
BACTERIA  AND  DISEASE 

For  ages  mankind  has  been  nearly  helpless  before  the 
ravages  of  contagious  diseases.  Ignorant  of  their  real 
cause,  people  have  attributed  such  diseases  to  "effluvia," 
to  poisons  carried  in  the  air,  and  in  former  ages  to  posses- 
sion by  evil  spirits.  We  know  now  that  they  are  produced 
by  some  kind  of  an  organism  that  can  be  transferred  from 
one  individual  to  another.  Many  diseases  are  caused  by 
protozoans,  as  is  the  case  with  malaria,  Texas  fever  and 
amoebic  dysentery.  Some  diseases  (ringworm)  are  pro- 
duced by  fungi.  A  few  diseases,  such  as  filariasis,  trichi- 
nosis and  the  itch,  are  caused  by  higher  animals.  But 
the  greater  part  of  our  contagious  maladies  are  due  to  very 
minute  organisms  known  as  bacteria. 

These  bacteria  are  the  simplest  known  forms  of  life. 
They  are  as  a  rule  exceedingly  minute.  A  great  many 
species  appear  like  short  rods  (Bacilli),  some  are  nearly 
spherical  (Cocci),  while  others  are  spiral  (Spirillum, 
Spirochetes).  Some  of  the  species  are  furnished  with  one 
or  more  flagella  by  means  of  which  they  may  move  .about. 
Bacteria  usually  multiply  by  fission,  and  so  rapid  is  their 
multiplication  that  a  single  bacillus  may  give  rise  to 
16,700,000  individuals  in  twenty-four  hours.  At  times, 
and  especially  under  unfavorable  conditions,  bacteria 
may  produce  small,  rounded  bodies  called  spores  which 
are  unusually  resistant  to  heat,  cold  or  dryness.  When 
better  conditions  occur  these  spores  give  rise  to  other 
bacteria. 

317 


318  '    ANIMAL  BIOLOGY 

There  are  countless  different  kinds  of  bacteria;  they 
live  under  the  most  diverse  conditions,  and  are  capable 
of  subsisting  upon  a  great  many  kinds  of  food.  Many 
forms  cause  the  decay  of  the  bodies  of  higher  organisms. 
Whenever  an  organic  body  putrefies  or  decays,  it  may  be 
found  to  be  teeming  with  multitudes  of  bacteria.  If  these 
minute  organisms  are  excluded  from  an  organic  body  it 
may  be  preserved  for  a  long  period.  Canning  fruits, 
vegetables  and  meats  is  essentially  a  device  for  keeping 
these  articles  free  from  bacteria.  The  heating  of  canned 
goods  kills  whatever  bacteria  may  have  been  present  in 
them,  and  the  sealing  prevents  the  access  of  others. 
Once  introduce  bacteria  and  the  substances  soon  decay. 

Many  articles  are  kept  from  spoiling  by  means  of 
preservatives,  or  substances  which  either  kill  bacteria  or 
check  their  growth.  Up  to  a  point  which  varies  with 
different  species,  bacteria  multiply  more  rapidly  as  the 
temperature  is  increased,  and  they  are  kept  from  multipli- 
cation at  a  temperature  at  or  near  the  freezing  point. 
Cold  storage  therefore  keeps  them  from  attacking  meats 
and  other  articles  of  food;  hence  our  cold  storage  plants, 
refrigerator  cars  and  ice  chests. 

Bacteria  are  usually  not  killed  by  freezing,  however, 
and  many  kinds  will  endure  a  temperature  of  over  ioo°C. 
below  zero  without  losing  their  vitality.  Ice  may  harbor 
the  germs  of  many  diseases  and  in  particular  those  of 
typhoid  fever  which  are  especially  hard  to  kill.  Boiling 
kills  most  bacteria,  but  the  spores  of  many  species  will 
resist  even  boiling  for  a  certain  period. 

Bacteria  are  almost  universally  distributed  in  water, 
soil  and  all  sorts  of  organic  material.  Owing  to  their 
minute  size  they  are  capable  of  being  easily  carried  through 
the  air.  If  a  bit  of  beef  broth  or  vegetable  infusion  is 
left  exposed  to  the  air  for  a  few  moments  it  will  become 


BACTERIA  AND   DISEASE  319 

infected  with  bacteria;  in  fact  they  often  gain  access 
when  it  is  thought  that  they  are  effectively  excluded. 
They  are  especially  liable  to  be  carried  about  on  particles 
of  dust.  Look  at  a  beam  of  light  entering  a  room  and 
you  will  usually  see  myriads  of  small  bodies  floating  in 
the  air.  For  every  particle  that  you  can  see  there  are  thou- 
sands that  are  too  small  to  be  visible.  When  we  remem- 
ber that  even  invisible  particles  may  be  over  a  million  times 
as  large  as  a  bacillus  we  can  gain  some  idea  of  what  it 
means  to  effectively  exclude  the  possibility  of  bacterial 
infection. 

While  many  bacteria  are  harmful,  most  species  are  proba- 
bly beneficial.  The  r61e  of  bacteria  in  causing  decay 
is  one  of  great  importance.  Organisms  are  resolved  back 
into  their  primitive  constituents,  and  their  atoms  may  live 
again  in  the  bodies  of  other  forms  of  life.  On  account  of 
their  causing  the  decomposition  of  organic  material  the 
bacteria  play  an  important  part  in  the  production  of  soil; 
Certain  species  associated  with  the  roots  of  plants  have 
the  property  of  utilizing  the  nitrogen  of  the  air  and  con- 
verting it  into  a  form  that  may  be  subsequently  used  by 
plants  and  animals.  Many  of  the  processes  of  fermenta- 
tion, such  as  the  souring  of  milk  and  the  production  of 
vinegar,  are  the  result  of  bacterial  activity.  In  fact  were 
it  not  for  these  invisible  organisms  higher  forms  of  life 
would  not  be  able  to  exist  in  the  earth. 

That  certain  species  of  bacteria  should  come  to  live  in 
the  tissues  of  plants  and  animals  is  quite  analogous  to  the 
fact  that  many  other  organisms  have  adopted  a  parasitic 
mode  of  life.  The  disease-producing  bacteria  do  not  wait 
until  an  organism  is  dead  before  they  attack  it,  but  like 
the  bacteria  that  effect  the  decomposition  of  the  dead 
body  they  tend  to  bring  about  the  dissolution  of  the 
organism.  Louis  Pasteur,  the  great  French  investigator 


320  ANIMAL  BIOLOGY 

who  did  more  than  anyone  else  to  establish  the  germ  theory 
of  disease,  was  led  to  his  most  important  discoveries  on 
account  of  his  previous  studies  of  the  phenomena  of  fer- 
mentation and  putrefaction.  Once  the  germ  theory  of 
disease  was  established,  contagion  was  no  longer  a  mystery, 
but  a  natural  result  of  the  transfer  of  minute  organisms 
from  one  person  to  another.  Just  as  a  drop  of  decaying 
substance  will  set  up  decomposition  in  fresh  material,  so 
will  a  small  amount  of  matter  from  a  diseased  person  con- 
vey the  disease  to  a  healthy  individual.  It  has  been 
shown  that,  in  a  great  many  diseases,  bacteria  are  uni- 
formly present  in  great  numbers  in  the  tissues  of  the  person 
affected.  In  many  cases  it  has  been  found  possible  to 
cultivate  the  germs  of  certain  diseases  in  artificial  media 
outside  the  body,  and  to  propagate  them  free  from  admix- 
ture with  other  germs.  The  germs  from  such  "pure 
cultures,"  as  they  are  called,  have  been  shown  to  give 
rise  to  the  disease  in  question  when  inoculated  into  the 
body  of  a  healthy  person.. 

When  the  secret  of  contagion  was  known,  it  became 
much  easier  to  check  the  spread  of  contagious  diseases. 
For  this  purpose  much  use  is  made  of  germicides  and  dis- 
infectants, substances  which  kill  the  germs  of  the  disease. 
Rooms  that  have  been  occupied  by  diseased  persons  are 
commonly  fumigated  with  formaldehyde,  a  strong  germi- 
cide, before  they  are  again  occupied.  Articles  used  in 
connection  with  the  patient  are  washed  in  an  antiseptic 
solution  or  boiled.  And  the  patient  is  so  far  as  possible 
kept  free  from  contact  with  healthy  people  until  disease 
germs  are  no  longer  given  off  from  his  body. 

Formerly  surgical  operations  were  commonly  attended 
with  gangrene,  blood  poisoning  and  other  infections 
which  we  now  know  are  caused  by  bacteria.  Surgeons 
now  exercise  the  greatest  care  in  keeping  the  wounds  of 


BACTERIA  AND   DISEASE  321 

their  patients  free  from  bacterial  infection.  All  instru- 
ments used  are  carefully  sterilized  and  everything  con- 
nected with  the  operation  is  made  scrupulously  clean. 
As  a  result  operations  are  now  performed  which  were  un- 
dreamed of  before  the  days  of  aseptic  and  antiseptic  sur- 
gery, and  the  number  of  infections  following  ordinary  op- 
erations has  been  greatly  diminished. 

Cuts,  scratches  and  abrasions  of  the  skin,  while  they 
usually  heal  up  with  no  serious  results,  may  become  in- 
fected and  lead  to  blood  poisoning.  It  is  well  to  wash 
them,  therefore,  with  peroxide  of  hydrogen  or  some  other 
antiseptic,  and  then  bind  them  up  so  as  to  exclude  the 
entrance  of  other  germs.  Boils  and  carbuncles  result  from 
bacterial  infection  and  the  pus  they  contain  may  give  rise 
to  similar  infections  in  other  parts  of  the  body,  or  in  the 
body  of  another  person.  The  common  notion  that  boils 
are  useful  in  eliminating  impurities  from  the  blood  is 
absurd.  On  the  contrary  they  are  a  source  of  actual  poi- 
soning to  the  whole  body. 

The  number  of  diseases  caused  by  bacteria  and  protozoa 
is  very  great.  We  shall  describe,  therefore,  only  a  few  of 
those  about  which  everyone  should  have  some  knowledge 
for  the  sake  of  his  own  safety. 

Colds. — What  we  commonly  call  colds  are  really  infec- 
tions. Almost  everyone  has  noticed  how  colds  tend  to 
run  through  a  family  or  a  school,  and  how  at  times  colds 
are  unusually  prevalent.  People  commonly  believe  that 
they  " catch  cold"  by  sitting  in  a  draught,  getting  their 
feet  wet,  or  exposing  themselves  in  cold  weather.  What 
really  happens  is  that  their  temperature  or  their  resistance 
may  be  reduced  by  these  circumstances,  and  thus  an  op- 
portunity is  offered  for  the  germs  of  the  infection  to  make 
headway,  whereas  otherwise  they  might  have  been  kept 

in  abeyance.     Arctic  travellers  and  people  living  away 
21 


322  ANIMAL  BIOLOGY 

from  contact  with  their  fellows  rarely  take  cold  despite 
their  exposure.  On  the  other  hand,  colds  are  often  con- 
tracted when  there  has  been  no  exposure  to  cold  at  all. 

A  little  attention  to  the  subject  will  bring  home  to  us 
how  many  are  the  ways  in  which  the  germs  of  colds 
and  other  diseases  may  be  transferred  from  one  person 
to  another.  The  afflicted  person  may  cough  or  sneeze 
and  send  into  the  air  a  multitude  of  germs  which  may  be 
breathed  in  by  other  people.  Most  infections,  however, 
are  probably  carried  by  the  hand-to-mouth  method.  A 
person  with  a  cold  for  instance,  by  the  frequent  use  of  a 
handkerchief,  inevitably  transfers  the  germs  that  abound 


FIG.  223. — Forms  of  disease-producing  bacteria,     a,  typhoid;  6,  staphy- 
lococcus;   c,  tuberculosis;   d,   diphtheria;   e,   syphilis;  /,   plague. 

in  his  mucous  secretions  to  his  hands.  He  may  shake 
hands  with  another  person  or  handle  some  object  that 
the  other  person  touches.  The  latter  may  eat  some  food 
that  he  handles  or  otherwise  bring  the  germs  on  his  hands 
in  contact  with  his  mouth  and  thus  the  transfer  is  made. 
Door  knobs,  straps  in  street  cars,  or  any  objects  commonly 
handled  by  several  people  afford  excellent  means  for  the 
transfer  of  the  germs  of  disease.  If  one  has  been  exposed 
to  any  of  these  sources  of  contagion,  especially  during  a 
time  when  colds  or  other  infections  are  prevalent,  care 
should  be  taken  not  to  eat  before  the  hands  are  thoroughly 
washed.  It  is  well  to  avoid  people  with  colds  whenever 
possible,  and  the  sufferer  should  bear  in  mind  the  possi- 


BACTERIA  AND   DISEASE  323 

bility  of  his  infecting  others  and  give  as  little  opportunity 
as  he  can  for  the  transfer  of  his  affliction.  The  term  cold 
is  loosely  applied  to  a  number  of  infections  which  vary 
greatly  in  their  severity.  Colds  often  pave  the  way  for 
tuberculosis,  pneumonia  and  other  ills,  and  they  should 
be  treated  with  promptness  and  vigor  when  first  contracted, 
otherwise  they  are  much  more  difficult  to  deal  with. 

Tuberculosis,  one  of  the  most  frequent  causes  of  death, 
is  a  disease  that  may  attack  any  part  of  the  body,  although 
it  most  commonly  affects  the  lungs  when  it  is  known  as 
consumption.  It  was  proven  by  Robert  Koch,  a  famous 
German  bacteriologist,  to  be  caused  by  a  small  rod-like 
organism,  the  Bacillus  tuberculosis.  Cattle  are  commonly 
affected  with  a  form  of  tuberculosis  and  the  bacilli  fre- 
quently occur  in  milk.  Much  effort  has  been  made  to 
stamp  .out  the  disease  in  cattle,  and  milk  that  is  sold  in 
cities  is  often  put  through  a  process  called  pasteurization 
in  order  to  kill  the  germs  of  tuberculosis  or  other  disease 
germs  that  may  be  contained  in  it.  It  is  now  recognized 
that  tuberculosis  may  be  conveyed  from  one  person  to 
another.  This  may  be  done  by  the  hand-to-mouth 
method  previously  described,  but  a  frequent  source  of 
infection  consists  in  breathing  air  laden  with  tubercle' 
bacilli.  Air  in  dwellings  occupied  by  consumptives  is 
particularly  dangerous,  especially  if  it  contains  much  dust. 
The  sputum  of  consumptives  usually  abounds  in  bacilli, 
and  when  dried  and  reduced  to  powder  it  may  be  readily 
blown  about  in  the  air  and  taken  into  the  lungs.  Con- 
sumptives should  be  particularly  careful  not  to  expectorate 
in  places  where  their  dried  sputum  can  possibly  be  a 
source  of  infection.  The  sputum  should  be  disposed  of  in 
receptacles  especially  devised  for  the  use  of  consumptives. 
Care  should  be  taken,  when  coughing  or  sneezing,  to 
cover  the  mouth  or  nose  with  a  handkerchief,  and  the 


324  ANIMAL  BIOLOGY 

dishes  used  by  consumptives  should  be  carefully  sterilized 
by  boiling. 

The  isolation  of  tuberculous  patients  and  the  care  that 
has  been  taken  to  prevent  the  dissemination  of  the  germs 
of  the  disease  has  resulted  in  a  marked  diminution  of 
tuberculosis  in  recent  years.  With  the  spread  of  knowl- 
edge regarding  the  transfer  of  tuberculosis,  and  with  con- 
tinued efforts  to  prevent  its  spread,  there  is  reason  to 
believe  that  this  " great  white  plague"  will  finally  be 
exterminated. 

Tuberculosis  is  usually  curable  if  treated  in  the  early 
stages.  Rest,  plenty  of  nutritious  food,  such  as  fresh  eggs 
and  milk,  and  living  continually  in  the  open  air  will,  in 
the  majority  of  cases,  effect  a  cure. 

Typhoid  fever  is  a  disease  that  is  carried  mainly  through 
food  and  drink.  The  bacillus  that  causes  it  isunusually 
resistant  to  heat  and  cold,  and  may  live  in  the  water  and 
in  soil  and  sewage  for  a  long  period.  The  germs  are 
especially  abundant  in  the  intestine  and  hence  in  the 
excreta  of  typhoid  patients.  Where  sewage  is  allowed  to 
discharge  into  rivers  or  lakes,  the  germs  are  liable  to  be 
taken  in  in  drinking  water,  and  many  epidemics  of 
typhoid  in  cities  have  been  traced  to  the  contamination  of 
the  water  supply.  Sewage  from  one  town  is  often  allowed 
to  flow  into  a  stream  that  forms  the  water  supply  of 
another  town  farther  down.  Many  cities  profiting  by 
costly  experience,  have  instituted  filtering  plants  for  purify- 
ing their  water.  Some  cities  situated  on  lakes  have  elabo- 
rate plants  for  disposing  of  their  sewage  instead  of  pour- 
ing it  into  the  water  that  they  use  for  drinking.  Country 
places  which  derive  their  water  from  wells  located  so  that 
the  seepage  from  privies  may  flow  into  them  are  often 
afflicted  with  typhoid.  In  all  these  cases  the  elimination 


BACTERIA  AND   DISEASE  325 

of  typhoid  depends  upon  the  purification  of  the  water 
supply. 

Germs  of  typhoid  may  be  carried  in  food.  Several 
epidemics  have  been  traced  to  oysters  grown  in  places 
contaminated  by  sewage.  In  many  instances  the  disease 
has  been  carried  by  flies  which  alight  upon  food  after 
having  walked  over  excreta. 

People  who  have  apparently  recovered  from  typhoid 
are  sometimes  capable  of  spreading  the  disease  for  years 


FIG.   224. — Pollution  of  a  well  by  the  contents  of  a  neighboring  cess  pool. 

afterward.  These  people  who  are  called  "  typhoid 
carriers''  harbor  multitudes  of  typhoid  bacilli  in  their 
intestines  and  are  especially  dangerous  if  they  handle 
food  that  is  to  be  eaten  by  others.  The  case  of  "  Typhoid 
Mary,"  who  served  as  a  domestic  in  several  homes  and 
left  a  trail  of  typhoid  patients  wherever  she  went,  is 
one  of  the  best  known. 

Most  diseases  tend  to  run  a  certain  course  and  end  in 
natural  recovery.     If  the  disease  does  not  prove  fatal,  the 


326  ANIMAL  BIOLOGY 

body  conquers  the  disease  and  very  frequently  one  attack 
protects  the  individual  from  another  attack  of  the  same 
malady.  Typhoid,  scarlet  fever,  smallpox,  are  rarely 
taken  more  than  once,  the  patient  having  acquired  what 
is  called  immunity  to  these  diseases. 

Disease  germs  produce  their  deleterious  effects  by 
generating  some  poisonous  substance,  or  toxin.  The 
cells  of  the  body  have  the  property  of  producing  substances 
which  neutralize  or  destroy  these  poisons,  and  these 
are  called  antitoxins.  The  white  phagocytes  of  the  blood 
also  attack  and  devour  disease-producing  bacteria.  A 
disease  in  the  body  means  a  battle  between  the  bacteria, 
which  tend  to  live  and  multiply  at  the  expense  of  the 
organism,  and  the  cells  of  the  body  with  their  antitoxins 
and  phagocytes.  The  discovery  that  bacterial  poisons 
may  be  destroyed  by  antitoxins  generated  by  the  body 
has  led  to  efforts  to  control  diseases  by  injecting  anti- 
toxins into  the  blood.  One  of  the  first  and  most  note- 
worthy attempts  of  this  kind  is  the  antitoxin  treatment 
of  diphtheria.  This  disease  formerly  had  a  high  death 
rate.  The  rod-like  bacilli  occur  chiefly  in  the  throat 
and  generate  a  toxin  of  extreme  virulence.  The  German 
bacteriologist,  von  Behring,  found  in  1892  that  if  diphtheria 
toxin  is  injected  into  a  horse,  the  blood  serum  of  the  animal 
will  contain  a  substance  that  neutralizes  the  toxin.  In 
the  manufacture  of  diphtheria  antitoxin  healthy  horses 
are  given  several  injections  of  diphtheria  toxins  of  gradually 
increasing  strength.  After  several  months  some  of  the 
animal's  blood  is  removed  and  the  serum  preserved  for 
injecting  into  human  beings.  The  antitoxin  treatment 
of  diphtheria  is  now  regularly  employed  and  it  has  reduced 
the  death  rate  of  this  dreaded  disease  by  75  to  80  per  cent. 

Rabies,  or  hydrophobia,  has  been  successfully  treated 
by  a  method  somewhat  different  from  the  preceding, 


BACTERIA  AND   DISEASE  327 

but  based  on  the  principle  of  rendering  the  body  immune 
to  the  disease.  This  disease  occurs  on  dogs  and  may  be 
communicated  by  biting  to  other  kinds  of  animals  and  to 
man.  Remedies  were  formerly  powerless  against  this 
disease ;  unless  the  germs  were  killed  by  promptly  cauteriz- 
ing the  wound,  the  patient  had  no  hope  of  escaping  one 
of  the  most  horrible  kinds  of  death.  To  the  genius  of 
Louis  Pasteur  the  world  owes  the  discovery  of  a  method 
of  cure  now  known  as  the  Pasteur  treatment.  By  a  series 
of  injections  of  a  preparation  made  from  the  spinal  cord 
of  a  mad  dog  the  patient  may  usually  be  prevented  from 
contracting  hydrophobia,  even  if  the  treatment  is  begun 
several  days  after  the  bite.  A  very  high  percentage 
of  those  bitten  by  rabid  dogs  contract  hydrophobia. 
The  Pasteur  Institute  at  Paris  has  treated  many  thousands 
of  such  cases  with  an  average  mortality  of  less  than  one- 
half  of  i  per  cent.  Since  the  recent  outbreak  of  rabies 
in  California,  641  persons  have  been  treated  by  virus 
supplied  by  the  Hygienic  Laboratory  at  Berkeley,  Calif. 
According  to  Dr.  Geiger,  "  Eliminating  all  persons  treated 
who  were  not  bitten,  the  percentage  of  failures  with 
virus  supplied  by  this  Bureau  was  0.491,  less  than  one-half 
of  i  per  cent."  In  over  98  per  cent,  of  the  persons  bitten, 
the  animals  doing  the  biting  were  found  by  laboratory 
examination  to  have  had  rabies. 

There  is  no  foundation  for  the  belief  that  dogs  are  caused 
to  go  mad  by  the  hot  weather  of  "dog  days."  All  sus- 
pected dogs  should  be  confined  until  the  time  for  symptoms 
of  hydrophobia  to  appear  are  past.  By  muzzling  all  dogs 
whenever  there  is  the  least  danger  of  hydrophobia  this 
disease  could  soon  be  stamped  out,  but  through  care- 
lessness that  is  inexcusable  in  the  light  of  our  present 
knowledge,  hydrophobia  in  many  localities  has  actually 
been  on  the  increase  in  recent  years. 


328  ANIMAL  BIOLOGY 

Another  method  of  securing  immunity  to  disease  is  by 
the  introduction  of  the  germs  of  a  milder  form  of  the 
malady.  This  is  the  procedure  followed  in  vaccination 
to  prevent  smallpox.  In  1796  the  English  physician, 
Edward  Jenner,  found  that  virus  taken  from  cattle 
with  the  so-called  cow  pox  would,  when  inoculated  into 
the  human  body,  prevent  the  individual  from  taking 
smallpox.  A  properly  vaccinated  person,  if  exposed  to 
smallpox,  may  contract  a  much  milder  malady  called 
varioloid,  but  vaccination  decreases  his  chances  of  doing 
even  this.  Since  vaccination  has  become  prevalent 
smallpox  has  very  greatly  decreased.  In  the  i8th  century 
it  is  estimated  that  18,000,000  died  of  smallpox.  In 
Russia  alone  from  1893-1897  there  were  275,502  deaths 
from  this  disease,  while  in  Germany  which  had  compulsory 
vaccination  there  were  no  epidemics.  The  German  army 
has  had  but  two  deaths  from  smallpox  since  1874.  Before 
vaccination  was  introduced  into  Sweden  the  death  rate 
from  smallpox  was  165  per  100,000,  but  since  vaccination 
was  made  compulsory  it  fell  to  18  per  100,000.  Formerly 
undesirable  after  effects  were  sometimes  produced  by 
vaccination,  but  with  improved  methods  of  securing 
pure  virus  the  dangers  are  now  very  slight.  A  form  of 
vaccination  is  now  used  with  remarkable  success  in  typhoid 
fever.  Small  amounts  of  the  toxin  obtained  from  dead 
typhoid  bacilli  are  introduced  at  different  times  and  the 
person  so  treated  is  rendered  comparatively  immune 
from  typhoid  for  a  considerable  period.  In  the  United 
States  army  since  vaccination  against  typhoid  was  required 
the  death  rate  from  typhoid  has  been  less  than  one-fiftieth 
of  what  it  was  before.  The  death  rate  from  typhoid 
during  the  Mexican  war  and  the  civil  war  was  appalling. 
In  the  Spanish  war  "5000  men  in  the  United  States  army 


BACTERIA   AND   DISEASE  329 

died  of  typhoid  or  other  fly-borne  diseases  while  only 
300  were  killed  by  Spanish  bullets." 

Since  contagious  diseases  constitute  so  serious  a  menace 
to  human  welfare  it  is  necessary  to  have  laws  to  regulate 
the  treatment  of  contagious  cases,  so  that  they  may  be 
prevented  from  infecting  others.  People  with  such  dis- 
eases are  often  put  in  quarantine  until  danger  of  spreading 
their  infection  is  past.  Immigrants  are  examined  for  con- 
tagious diseases  and  detained  for  a  certain  period  before 
being  allowed  to  land.  Through  these  means  many 
epidemics  have  doubtless  been  averted  which  otherwise 
would  have  destroyed  thousands  of  lives.  In  cities  and 
towns  boards  of  health  and  health  officers  look  after  the 
enforcement  of  regulations  for  checking  disease,  and 
for  securing  general  sanitary  conditions. 

The  correct  diagnosis  and  treatment  of  disease  demands 
expert  knowledge  and  special  training,  and  states  have 
wisely  framed  laws  requiring  that  those  who  occupy 
themselves  with  the  very  responsible  business  of  the 
physician  or  surgeon  should  have  received  adequate  in- 
struction for  carrying  on  their  work.  Even  the  best 
physicians  sometimes  make  mistakes,  but  the  ignorant 
or  careless  charlatan  does  little  but  harm.  Requirements 
for  obtaining  a  license  to  practice  medicine  are  steadily 
being  raised  but  there  are  still  many  incompetents  in  the 
regular  profession  and  many  quacks  who  contrive  to  evade 
the  law  and  carry  on  a  lucrative  trade.  One  of  the  favor- 
ite devices  of  the  quack  is  advertisement.  Newspapers 
commonly  contain  several  advertisements  of  the  wonder- 
ful skill  and  success  of  various  doctors  who  often  pretend 
to  cure  ills  for  which  no  remedy  has  ever  been  discovered. 
It  is  a  safe  rule  to  avoid  all  so-called  doctors  who  advertise, 
for  the  great  majority  of  them  are  unprincipled  charlatans. 

Numerous  frauds  are  imposed  on  the  public  through 


330  ANIMAL  BIOLOGY 

patent! medicines.  Some  of  these  preparations  are  good, 
but  many  others  which  have  been  widely  advertised  are 
worthless,  if  not  positively  injurious.  The  soothing  syrups 
for  quieting  crying  children  are  among  the  worst  of  these, 
because  they  nearly  always  contain  opium  or  some  other 
drug  which  works  lasting  injury  on  the  helpless  child. 


PART  III 

GENERAL  FEATURES  AND 
ADAPTATIONS 


CHAPTER  XXXVII 
THE  PERPETUATION  OF  LIFE 

All  organisms  have  the  property  of  producing  other  or- 
ganisms similar  to  themselves  and  thus  continuing  their 
race.  In  the  simplest  forms  of  life  new  individuals  com- 
monly arise  by  the  division  or  fission  of  the  parent  form. 
An  Amoeba  or  Paramcecium,  as  we  have  seen,  simply  con- 
stricts in  two  and  the  new  individuals  soon  regain  their 


FIG.  225. — Pandorina  morum.  A,  gametes  formed  by  repeated  divi- 
sions of  the  cells  of  the  colony.  These  gametes  meet  and  fuse  and 
finally  lose  their  flagella  and  become  converted  into  a  spherical  encysted 
zygote,  2. 

normal  size  and  shape.  Other  organisms  reproduce  by 
budding,  such  as  most  hydroids,  sponges,  several  kinds  of 
worms  and  many  other  primitive  animals.  In  some  of 
the  Protozoa  the  body  divides  up  into  a  number  of  bodies 
called  spores  which  scatter  and  develop  new  individuals. 
In  organisms  except  the  very  simplest,  such  as  the  bac- 
teria, the  process  of  reproduction  is  commonly  associated 

331 


332 


ANIMAL  BIOLOGY 


with  the  phenomenon  of  sex.  We  have  already  described 
some  of  the  manifestations  of  sex  in  the  conjugation  of 
Paramcecium  where  after  a  series  of  generations  produced 
by  fission  there  is  a  union  of  individuals  by  pairs,  during 
which  each  individual  receives  a  nucleus  from  the  other. 


FIG.  226. — Volvox  aureus.  (After  Klein  and  Schenck.)  A,  mature 
colony  containing  daughter  colonies;  (£)  and  ova  (o);  B,  group  of  32  de- 
veloping spermatozoa  seen  end  on;  C,  the  same  seen  sideways;  D,  mature 
spermatozoa,  X  824. 

After  the  union  of  one  of  its  own  nuclei  with  the  one  re- 
ceived from  its  partner,  the  individuals  separate  and  con- 
tinue^ to  divide  by  fission  as  before.  More  commonly 
in  primitive  organisms  there  is  a  complete  fusion  of  nucleus 


THE   PERPETUATION   OF   LIFE  333 

and  cytoplasm  so  that  each  conjugating  individual  loses 
its  identity  in  the  resulting  product.  In  some  of  the  one- 
celled  animals  and  plants  the  conjugating  individuals, 
instead  of  being  of  equal  size,  have  become  differentiated 
into  larger,  relatively  passive  individuals  on  the  one  hand, 
and  smaller,  more  active  ones  on  the  other.  In  the  colo- 
nial flagellate  Pandorina  the  conjugating  cells  are  both 
active  and  but  slightly  unequal  in  size,  but  in  the  related 
form  Eudorina  and  in  Volvox  the  conjugating  cells  are 
very  dissimilar.  One  kind  is  large,  spherical  in  form  and 


A .  _  _ 

FIG.  227. — Fertilization  of  the  egg.  A,  egg  entered  by  a  sperm  cell,  s; 
B,  the  nucleus  of  the  head  of  the  sperm  cell,  s,  enlarged  and  approaching 
the  nucleus  of  the  egg,  n ;  C,  sperm  nucleus,  5  more  enlarged  and  in  contact 
with  the  egg  nucleus  n;  D,  egg  nucleus  and  sperm  nucleus  fused  together. 

devoid  of  activity;  while  the  other  is  small,  with  an  ovoid 
head  and  a  lash-like  tail  by  means  of  which  it  swims  through 
the  water.  One  of  the  small  active  cells  meets  and  fuses 
with,  or  fertilizes,  one  of  the  large  ones  which,  after  going 
into  a  resting  stage,  produces  by  repeated  division  a  new 
colony. 

In  all  the  multicellular  animals  the  sex  cells  are  dif- 
ferentiated into  two  very  sharply  contrasted  types,  the 
relatively  large  and  inactive  ova,  or  egg  cells,  and  the  small 
active  spermatozoa,  or  sperm  cells  whose  function  it  is  to 
meet  and  fertilize  the  eggs.  The  eggs  of  nearly  all  animals 
require  to  be  fertilized  before  they  can  develop,  but  in 
exceptional  cases  eggs  may  develop  without  being  fertilized. 
This  process  which  is  called  parthenogenesis  (see  page  35) 
is  well  illustrated  by  the  generation  of  the  aphids  or  plant 


334  !        ANIMAL  BIOLOGY 

lice  in  which  the  females  may  reproduce  by  parthenogene- 
sis for  several  generations,  especially  during  the  summer. 
After  a  time,  however,  different  kinds  of  eggs  are  produced 
which  require  fertilization  before  they  develop.  It  has 
been  found  by  Loeb  that  in  some  animals  eggs  which  nor- 
mally require  fertilization  before  developing,  maybe  stimu- 
lated artificially  by  chemicals  and  other  agencies  so  that 
they  develop  without  fertilization  into  apparently  normal 
embryos.  In  almost  all  forms  in  which  parthenogenesis 
occurs,  reproduction  by  means  of  fertilized  eggs  occurs  also 
after  one  or  more  parthenogenetic  generations. 

While  in  most  animals  sperm  and  egg  cells  are  produced 
by  separate  male  and  female  individuals,  there  are  many 
animals  in  which  both  kinds  of  sex  cells  are  borne  in  the  same 
body.  Such  animals  are  called  hermaphrodites.  Most 
flat  worms,  earthworms,  leeches,  land  snails  and  tunicates 
are  hermaphrodites,  and  there  are  occasional  hermaph- 
roditic species  in  many  other  groups  of  animals,  and 
exceptional  hermaphrodites  which  arise  as  " sports" 
or  monstrosities  in  species  with  normally  separate  sexes. 
It  is  a  curious  fact  that  in  hermaphroditic  animals  the 
eggs  are  very  rarely  fertilized  by  sperms  from  the  same 
individual,  but  instead  there  is  cross  fertilization,  as  we 
have  seen  in  our  account  of  the  earthworm.  In  sexual 
reproduction  in  general  there  is  a  mingling  of  germinal 
material  derived  from  two  separate  individuals. 

After  the  union  of  the  egg  and  sperm  cell  there  begins 
the  process  of  embryonic  development  which  results 
in  the  formation  of  a  new  individual.  This  process, 
which  is  one  of  great  complexity,  forms  the  subject 
matter  of  the  science  of  embryology,  a  subject  which  can 
be  treated  but  very  briefly  in  an  elementary  book.  The 
egg  in  all  animals  consists  of  a  single  cell.  Usually  this 
is  of  minute  size,  but  in  birds  and  many  reptiles  and  in 


THE   PERPETUATION   OF   LIFE  335 

a  few  other  forms  it  may  be  very  large.  In  the  egg  of 
a  bird  the  original  egg  cell  forms  the  part  which  we  call  the 
yolk.  This  yolk  after  its  discharge  from  the  ovary 
receives  first  a  coating  of  albumen,  or  white,  and  then  the 
shell  during  its  passage  down  the  oviduct,  so  that  the 
egg  in  this  case  consists  of  an  enormous  cell,  the  yolk, 
plus  the  surrounding  materials  which  are  secreted  by 
the  glands  of  the  oviduct. 

Animals  which  lay  eggs  are  said  to  be  oviparous,  but 
there  are  many  animals  such  as  all  the  mammals  (with 
the  exception  of  the  monotremes)  in  which  the  develop- 
ment of  the  embryo  takes  place  in  the  body  of  the  mother. 
These  forms  are  called  viviparous  since  they  bring  forth 
living  young,  but  in  all  viviparous  animals  the  embryo 
arises  from  an  ovum  or  egg,  just  as  in  those  forms  which 
lay  eggs.  When  eggs  are  of  large  size  it  is  due  to  the 
presence  of  yolk  or  other  material  which  affords  food  for 
the  developing  embryo.  The  eggs  of  the  viviparous 
mammals  are  very  minute.  They  are  always  fertilized 
within  the  body  of  the  female,  usually  while  in  the  oviduct, 
and  they  undergo  development  within  the  uterus.  In  all 
mammals  higher  than  the  marsupials  the  embryo  becomes 
attached  to  the  wall  of  the  uterus  by  an  organ  containing 
numerous  blood  vessels,  called  the  placenta.  Through 
this  organ  nutriment  is  carried  by  means  of  the  maternal 
blood  to  the  embryo,  whose  own  blood  vessels  extend  into 
the  placenta  and  there  absorb  the  food  material  that 
passes  out  by  osmosis  from  the  blood  of  the  mother.  The 
blood  vessels  that  lead  from  the  embryo  to  the  placenta 
are  contained  in  the  umbilical  cord  which  enters  the 
embryonic  body  at  the  point  called  the  navel.  The 
placenta  is  cast  out  soon  after  birth. 

The  first  clearly  marked  stage  of  development  that 
occurs  after  the  fertilization  of  the  egg  is  the  process  of 


22 


336 


ANIMAL  BIOLOGY 


cleavage  by  which  the  egg  is  divided  into  a  number  of 
cells.  Typically  cleavage  results  in  the  formation  of  a 
hollow  sphere  of  cells,  the  blastula;  this  becomes  pushed  in 
on  one  side  forming  a  double-layered  sac  called  the  gas- 
trula  whose  inner  wall  generally  gives  rise  to  the  lining 
of  the  digestive  cavity  and  the  various  organs  that  arise 
from  it.  In  some  animals,  especially  those  in  which 
the  egg  contains  much  yolk,  the  blastula  and  gastrula 
stages  may  become  very  much  modified,  so  that  they  are 


4 


FIG.  228. — Early  development  of  Amphioxus.  i,  four  cell  stage;  2, 
eight  cells;  3,  16  cells;  4,  32  cells;  5,  blastula;  6,  blastula  cut  through  the 
middle;  7,  early,  and  8,  late  gastrula.  (Prom  Hatschek.) 

not  easily  recognized,  but  in  most  of  the  multicellular 
animals  they  are  nevertheless  represented  in  some  form. 
In  the  gastrula  stage  there  are  formed  the  two  primary 
germ  layers,  an  inner,  the  entoderm,  and  an  outer,  the 
ectoderm.  In  animals  above  the  ccelenterates  a  third 
germ  layer,  the  mesoderm,  arises  between  the  two  others. 
At  first  the  cells  of  the  embryo  are  similar  in  kind,  but, 
as  the  organs  develop  from  the  germ  layers,  the  cells 
become  gradually  differentiated  into  all  the  varied  kinds 
found  in  the  adult  body. 


THE    PERPETUATION   OF   LIFE  337 

In  the  early  stages  of  development  animals  in  general 
are  much  more  alike  than  they  are  later.  As  they  develop 
the  embryos  of  different  groups  become  more  and  more 
dissimilar;  those  of  distantly  related  groups  are  strikingly 
different  in  their  early  stages,  while  the  embryos  of  closely 
related  forms  usually  show  a  strong  resemblance  in  all 
periods  of  development.  The  embryos  of  higher  animals 
are  often  similar  to  the  adult  stages  of  animals  which  stand 
below  them  in  the  scale  of  life.  These  similarities,  as 
we  shall  see  in  a  later  section,  point  clearly  to  a  descent 
of  the  higher  animals  from  more  primitive  forms. 

Some  animals  when  hatched  or  born  bear  a  fairly  close 
resemblance  to  the  adult  condition,  but  in  many  others 
the  young  as  they  first  emerge  are  so  different  from  their 
parents  as  to  appear  to  belong  to  a  quite  different  group 
of  animals.  Such  animals  are  said  to  undergo  a  metamor- 
phosis in  developing  into  the  mature  form.  Instances  are 
furnished  by  the  butterflies  and  moths,  beetles,  flies  and 
many  other  insects,  by  the  transformation  of  tadpoles 
into  frogs,  and  by  the  larval  stages  of  many  marine 
invertebrates.  In  several  cases  larvae  have  been  described 
as  new  types  of  life  before  it  was  discovered  that  they 
represented  the  young  stage  of  some  previously  known 
animal. 

In  higher  animals  a  part  of  the  function  of  perpetuating 
life  consists  in  caring  for  offspring  until  they  are  able 
to  shift  for  themselves.  Among  low  forms  the  young 
receive  no  attention  whatever  from  their  parents,  most 
of  whom  do  not  recognize  their  offspring  as  their  own. 
The  young  spider  is  a  nimble,  active  creature,  that  can 
spin  its  own  web  practically  as  well  as  in  later  life.  Many 
Crustacea  carry  their  eggs  and  for  a  time  their  young  in 
brood  pouches  or  attached  to  appendages  of  the  abdomen, 
but  they  never  care  for  their  offspring  in  any  way,  and 


338 


ANIMAL  BIOLOGY 


are  quite  as  willing  to  devour  them  as  any  other  kind  of 
food.  The  young  of  most  insects  do  not  receive  or  need 
any  attention  from  their  parents,  although  in  some  of  the 

social  Hymenoptera  the  young 
are  fed  and  tended  with  scrupu- 
lous care. 

Among  fishes  the  eggs,  after 
they  are  shed  and  fertilized;  are 
usually  left  to  their  fate;  but 
some  forms  such  as  the  stickle- 
back and  the  dog-fish  Amia  build 
nests  for  the  eggs  which  are 
watched  and  defended,  usually 
by  the  male  who  protects  them  from  enemies,  but  parental 
solicitude  lasts  for  only  a  short  time. 

The  amphibia  and  reptiles  show  little  concern  for  their 
offspring,  but  in  the  birds  and  mammals  we  find  parental 
care  well  developed  especially  in  higher  forms.  The  primi- 


PIG.  229. — Dolomedes  mir- 
abilis  carrying  her  cocoon. 
(After  Black  wall.). 


FIG.   230. — Nestling  marsh   hawks.      (After   Baker.) 

tive  birds  as  a  rule  construct  crude  nests  and  the  young 
are  hatched  so  that  they  are  able  to  look  out  for  them- 
selves, either  at  once  or  at  a  very  early  period.  Among 
the  higher  song  birds  the  nests  are  more  carefully  made. 


THE   PERPETUATION    OF    LIFE 


339 


The  young  which  are  hatched  in  a  weak  and  helpless  condi- 
tion are  fed,  brooded  and  protected  by  their  parents  who 
usually  keep  the  nest  clean  and  often  continue  to  care  for 
their  young  after  they  have  left  the  nest  and  are  appar- 
ently quite  able  to  secure  food  for  themselves.  Among 
primitive  types  which  produce  a  large  number  of  offspring 
there  is  a  great  waste  of  life.  A  codfish  may  lay  over 
9,000,000  eggs  of  which  as  a  rule  only  two  produce  fishes 


FIG.  231. — Bluebird   at   edge   of   nest   with   grasshopper   in   mouth   for 
young.     (After    Baker.) 

that  live  to  a  mature  age.  A  humming  bird  which  care- 
fully rears  its  young  in  a  well-prepared  nest  lays  but  two 
eggs  in  a  season.  With  parental  care  a  species  no  longer 
needs  the  enormous  fecundity  of  the  primitive  forms  which 
leave  their  eggs  and  young  to  the  mercies  of  the  elements 
and  numerous  enemies. 

In  the  mammals  parental  care  is  universal.  The  young 
are  closely  dependent  on  their  parents  for  food  which  is 
supplied  by  the  mammary  glands  and  the  instinct  to 
suckle  and  protect  the  young  is  a  part  of  the  endowment 


340  ANIMAL  BIOLOGY 

of  every  mother.  When  the  need  for  milk  and  protection 
is  past  parental  affection  as  a  rule  soon  passes  into  indiffer- 
ence. The  period  of  relatively  helpless  infancy  increases 
as  we  pass  to  higher  mammals.  This  affords  a  greater 
opportunity  to  learn  by  experience  while  under  the  pro- 
tection and  guidance  of  parents  before  the  young  animal 
has  to  face  the  serious  business  of  life.  Young  birds  are 
taught  to  fear  particular  enemies  and  to  peck  at  certain 
kinds  of  food.  The  danger  chirr  of  the  old  hen  fills  the 
young  chick  with  alarm  and  the  alarm  notes  of  the  par- 
tridge will  send  the  young  into  hiding  places  in  the  grass. 
The  lessons  learned  in  infancy  frequently  are  the  means 
of  saving  life  when  the  young  are  free  from  parental 
guidance. 

Among  the  simplest  organisms,  as  we  have  seen,  the 
perpetuation  of  life  is  effected  simply  by  the  process  of 
fission.  In  somewhat  higher  forms  we  meet  with  phenome- 
non of  sex,  and  the  various  activities  of  mating.  Later  we 
find  that  the  activities  of  reproduction  involve  the  care 
of  eggs  and  young;  and  as  we  ascend  the  scale  of  life  the 
time  and  energy  expended  upon  the  rearing  of  offspring 
becomes  greater  and  greater.  The  perpetuation  of  the 
race  finally  comes  to  mean  not  only  the  production  of 
new  individuals,  but  the  fostering  and  training  of  the 
new  generation  until  it  is  capable  of  leading  an  independent 
life. 


CHAPTER  XXVIII 
THE  EVOLUTION  OF  LIFE 

The  brief  survey  of  the  animal  kingdom  to  which  the 
first  part  of  this  book  is  devoted  gives  some  idea,  inadequate 
though  it  be,  of  the  variety  of  animal  life  on  the  surface 
of  the  earth.  Zoologists  have  described  several  hundred 
thousand  species,  and  the  fact  that  new  species  are  being 
described  at  the  rate  of  about  ten  thousand  a  year  shows  us 
how  far  we  still  are  from  having  a  complete  list  of  the  earth's 
fauna.  The  number  of  species  of  animals  now  on  the 
earth  is  certainly  over  a  million  and  is  possibly  several 
millions.  But  the  number  of  species  now  living  constitute 
but  a  small  fraction  of  the  enormous  number  that  formerly 
peopled  the  earth.  The  science  of  Geology  teaches  us  that 
the  crust  of  the  earth  is  a  great  burial  ground  in  which  are 
interred  the  remains  of  countless  animals  and  plants,  and 
that  new  forms  have  constantly  replaced  the  old  during 
the  many  millions  of  years  involved  in  geological  history. 

The  question  naturally  arises:  How  did  all  this  wealth 
of  plant  and  animal  life  come  into  existence?  Formerly 
it  was  generally  held  that  each  species  was  separately 
created,  but  as  students  of  life  came  to  have  more  extensive 
knowledge  of  the  structure,  distribution  and  relationships 
of  living  forms,  and  as  they  traced  the  succession  of  extinct 
species  buried  in  the  rocky  strata  of  the  earth's  crust,. they 
became  convinced,  almost  without  exception,  that  species 
of  plants  and  animals  arose  by  a  gradual  process  of  devel- 
opment or  evolution.  How  life  first  began  no  one  knows, 
but  the  gap  between  the  non-living  and  the  living  once 

341 


342  ANIMAL  BIOLOGY 

having  been  bridged,  life  gradually  advanced  from  the 
simplest  particles  of  living  substance  to  the  highest  types 
of  plants  and  animals.  The  establishment  of  the  doctrine 
of  evolution  was  one  of  the  greatest  of  the  scientific  achieve- 


FIG.  232. — Charles  Darwin.     (From  Gager.) 

ments  of  the  igth  century;  and  the  credit  for  it  is  due,  more 
than  to  anyone  else,  to  the  great  English  naturalist,  Charles 
Darwin,  whose  epoch-making  work,  the  Origin  of  Species, 
published  in  1859,  first  convinced  the  scientific  world  in 
general  of  the  truth  of  the  evolution  theory. 


THE   EVOLUTION   OF    LIFE  343 

One  of  the  strongest  indications  that  species  are  gene- 
tically connected  is  furnished  by  the  resemblance  in  struc- 
ture which  is  found  among  the  animals  of  any  group.  The 
animals  of  any  division  of  the  animal  kingdom  are  built 
upon  the  same  general  plan  of  structure,  however  diverse 
may  be  the  modifications  which  they  present.  In  the 
mammals  the  limbs,  for  instance,  are  formed  after  much 
the  same  pattern.  In  some  cases  bones  may  be  fused 
together  that  are  separate  in  other  animals,  or  certain 
bones  may  be  missing;  but  nevertheless  it  is  possible  by  a 
comparative  study  of  limb  structure  to  show  how  the 
diverse  forms  may  be  derived  from  a  common  type.  Organs 
which  are  formed  according  to  the  same  fundamental 
pattern  are  called  homologous,  however  diverse  their  form 
and  function.  On  the  other  hand  organs  which  perform 
the  same  function  but  which  are  different  in  their  funda- 
mental plan  of  structure  are  called  analogous.  Examples 
of  the  first  class  are  afforded  by  the  arms  of  man,  the  fore 
legs  of  a  horse,  the  wings  of  bats  and  birds,  and  the  flippers 
of  the  whale.  These  organs  have  been  modified  in  various 
ways  to  subserve  very  different  functions,  but  a  study  of 
their  structure  shows  them  to  bear  a  very  close  resemblance 
nevertheless.  Examples  of  analogous  organs  are  afforded 
by  the  wings  of  birds  and  the  wings  of  insects  which,  while 
they  are  both  used  as  organs  of  flight,  have  very  little 
resemblance  in  structure.  The  resemblance  of  funda- 
mental plan  amid  differences  in  the  way  in  which  the  plan  is 
worked  out  is  the  natural  result  of  inheritance  from  some 
common  ancestral  form,  the  diversity  being  due  to  adapta- 
tions to  varied  conditions  during  the  divergence  of  species 
from  their  common  ancestor. 

Very  striking  indications  of  the  descent  of  animals  is 
furnished  by  the  existence  of  rudimentary  organs.  These 
are  organs  of  small  size  and  degenerate  structure,  and  they 


344  ANIMAL  BIOLOGY 

are  for  the  most  part  apparently  functionless.  In  our 
own  bodies,  for  instance,  there  are  several  small  muscles 
attached  to  the  ear  some  of  which  are  entirely  function- 
less  and  others  practically  so.  These  muscles  we  find 
much  more  highly  developed  in  the  lower  mammals  where 


FIG.   233. — Rudimentary  or  vestigial  and  useless  muscles  of  the  human 
ear.     (From  Romanes,  after  Gray.) 

they  are  of  service  in  moving  the  ears.  On  the  outer  sur- 
face of  the  ear  there  is  in  many  people  a  small  point  which 
represents  the  tip  of  the  ear  of  lower  mammals.  The 
vermiform  appendix  which  is  the  cause  of  such  frequent 
trouble  is  the  rudiment  of  an  organ  found  in  a  much  more 
highly  developed  state  in  the  lower  mammals  where  it 


THE   EVOLUTION   OF   LIFE 


345 


performs  a  useful  digestive  function.     The  fauna  of  caves 

frequently  includes  many  animals  which  are  totally  blind. 

Many  of  these  forms  have  eyes  in  a 

rudimentary     condition.       Among 

the  blind  fishes  of  which  there  are 

numerous  species  in  the  caves  of 

North  America  there  are  various 

degrees  of  degeneracy  to   be  met 

with  in  the  structure  of  the  eyes, 

from  those  in  which  the  eyes  are 

fairly  well  developed,  though  func- 

tionless,    to   those   in    which   they 

have  almost  entirely  disappeared. 

The  blind  crayfish  of  the  Mammoth 

Cave  has  lost  its  eyes,  but  it  still 

preserves  the  eyestalks.     In  the  inner  corner  of  our  eye 

there  is  a  small  semilunar  fold,  a  rudiment  of  the  third 


FIG.  234. — Cecum  and 
appendix  of  man.  A,  ap- 
pendix; C,  cecum;  LI, 
large  intestine;  SI,  small 
intestine. 


FIG.  235. — Rudimentary  hind  limbs  of  Python.     (After  Romanes.) 

eyelid,  which  in  many  reptiles  and  birds  is  capable  of 
being  drawn  over  the  surface  of  the  eye.     Some  of  the 


ANIMAL  BIOLOGY 

reptiles  have  a  rudiment  of  a  third  eye  which  is  located 
as  a  rule  near  the  middle  of  the  roof  of  the  skull.  In 
one  species  of  reptile,  Sphenodon,  this  eye  is  quite  well 
developed,  but  in  all  other  forms  it  exists  in  a  very  de- 
generate condition.  This  third  eye  was  formerly  con- 
nected with  a  part  of  the  brain  known  as  the  pineal 
gland,  a  structure  which  is  present,  although  rudimentary, 
in  nearly  all  vertebrates  including  man.  Weidersheim 
has  recorded  as  many  as  180  organs  which  are  rudimentary 
in  the  human  body. 

ear 


, 

eye  W   V 

fll 


FIG.   236.  —  Very  young  human  embryos  showing  gill  slits,  gs  and  rudi- 
ments    of    limbs,    /.     (After     His.) 

It  frequently  happens  that  organs  which  have  entirely 
disappeared  in  the  adult  are  represented  by  rudiments  in 
embryonic  development.  The  upper  incisor  teeth  are 
absent  in  cattle,  but  rudimentary  teeth  are  nevertheless 
found  in  fcetal  calves.  In  the  whalebone  whales  teeth 
are  no  longer  present,  but  the  embryos  of  these  whales 
have  numerous  teeth  in  a  rudimentary  condition  which 
later  disappear.  All  of  these  rudimentary  organs  are 
very  naturally  explained  as  structures  which  were  useful 
once,  but  which  have  become  dwindled  through  disuse  as 
animals  have  adopted  new  habits  of  life. 

The  evidence  of  the  descent  of  higher  from  lower  forms 
furnished  by  embryology  is  often  very  striking.  The 
higher  vertebrates  without  exception  show  the  gill  clefts 


THE   EVOLUTION   OF   LIFE 


347 


corresponding  to  the  spaces  between  the  gills  of  their 
fish-like  ancestors.  The  arterial  blood  vessels  of  the  gill 
region  have  almost  precisely  the  arrangement  found  in 
the  fishes,  there  being  a  number  of  aortic  arches  corre- 
sponding to  the  clefts.  The  arrangement  is  such  as  to 
carry  blood  to  a  series  of  gills,  although  no  actual  gills  are 


A 


FIG.  237. — Human  embryos.  A,  right  side;  B,  median  section;  C, 
front  view;  a,  arches  of  the  aorta;  b,  brain;  e,  ear  vesicle;  gs,  gill  slits;  h, 
heart;  uc,  umbilical  cord.  (After  His.) 

found.  Later  most  of  the  aortic  arches  disappear,  a  few 
being  more  or  less  completely  retained  in  the  adult  blood 
system.  One  of  the  gill  clefts  is  modified  to  form  the 
Eustachian  tube  which  extends  from  the  pharynx  to  the 
middle  ear.  The  hyoid  which  supports  several  muscles 


348  ANIMAL  BIOLOGY 

of  the  tongue  is  the  homologue  of  part  of  the  bony  frame- 
work of  gill  arches  found  in  the  fishes. 

The  student  of  the  development  of  life  naturally  looks 
with  interest  upon  the  revelations  of  geology  as  to  the 
succession  of  organisms  on  the  surface  of  the  earth.  The 
earth  itself  has  undergone  an  evolution  from  a  relatively 
homogeneous  condition  in  which  it  was  a  heated  mass  of 
molten  rock.  With  the  cooling  and  thickening  of  the 
crust  there  came  the  condensation  of  water  which  formed 
shallow  seas  covering  most  if  not  all  of  the  surface.  As 
the  earth  cooled  further  its  surface  was  thrown  into  folds 
which  gave  rise  to  mountains.  With  the  elevation  of 
land  there  began  the  process  of  erosion  and  the  deposition 
of  sediment  in  the  bottom  of  the  primitive  seas.  Thus 
were  produced  the  stratified  rocks  which  have  been  slowly 
formed  to  a  thickness  of  many  miles.  Subsequently 
many  of  the  strata  deposited  at  the  bottom  of  the  sea 
were  raised  up,  thus  affording  to  the  geologist  an  opportu- 
nity to  study  the  fossils  or  remains  of  living  forms  which 
they  contain.  It  has  taken  a  long  time  to  trace  out  the 
succession  of  strata  that  are  found,  some  here  and  some 
there,  over  the  earth's  surface,  but  the  labors  of  many 
geologists  have  now  given  us  a  fairly  adequate  account 
of  the  history  of  the  earth  and  its  inhabitants.  These 
rocky  strata  are  the  leaves  of  a  great  book  in  which  the 
earth  has  written  its  own  history.  Beginning  with  the 
lowest  and  the  earliest  strata  in  which  remains  of  living 
forms  occur  we  can  follow  the  successive  stages  in  the 
evolution  of  life  as  we  pass  to  more  recent  times.  Most 
of  the  earliest  records  of  life  have  been  obliterated,  but  in 
the  Cambrian  period  living  forms  are  preserved  in  great 
abundance.  Most  of  the  phyla  of  invertebrate  animals 
were  represented,  and  there  were  several  groups,  such  as 
the  trilobites  and  graptolites,  which  have  long  become 


THE   EVOLUTION   OF   LIFE  349 

extinct.  In  the  following  period,  the  Silurian,  we  meet 
with  the  remains  of  fishes  which,  however,  were  very 
different  from  the  fishes  of  the  present  day,  although 
many  of  them  were  related  to  the  primitive  cartilaginous 
fishes  such  as  the  sharks  and  rays.  During  the  Carbon- 
iferous era  there  was  a  great  luxuriance  of  vegetation, 


PIG.  238. — A  pterodactyl,  an  extinct  flying  reptile.     (After  H.  v.  Mayer.) 


mostly  belonging  to  primitive  types  related  to  our  ferns 
and  club  mosses.  Much  of  our  coal  is  derived  from  the 
plants  of  the  old  carboniferous  forests,  and  we  can  often 
trace  in  pieces  of  coal  the  woody  structure  or  the  delicate 
outline  of  leaves  of  the  trees  that  flourished  at  this  time. 
In  this  period  we  find  the  remains  of  insects  and  am- 
phibians, and  in  the  following  period,  the  Permian,  we 
meet  with  those  of  reptiles. 

It  was  not  until  the  next  period  that  the  latter  animals 


350 


ANIMAL  BIOLOGY 


reached  the  colossal  size  and  often  grotesque  form  that 
gave  to  this  epoch  the  name  of  the  age  of  reptiles.  Great 
monsters  stalked  in  the  land,  enormous  creatures  swam 
in  the  seas,  and  numerous  queer  looking  pterodactyls 
flew  in  the  air;  but  in  the  following  epochs  these  great 
creatures  all  became  extinct.  The  earliest  bird  of  which 
there  is  record  is  a  curious  creature  nearly  as  much  reptile 
as  bird,  called  the  Archaeopteryx.  Unlike  all  existing 
birds  it  had  a  long  tail  with  many  vertebrae,  and  its  jaws 


PIG.  239. — Skeleton  of  a  cretaceous  dinosaur,  Triceratops  prorsus  in  the 
U.    S.    National   Museum.     (After   Gilmore.) 


were  set  with  numerous  conical  teeth.  It  was  covered 
with  feathers,  and  had  undoubted  wings,  but  the  wing 
bones  were  much  more  like  those  of  typical  fore  leg 
than  they  are  in  our  modern  birds.  It  had  been  held 
before  that  birds  sprang  from  reptilian  ancestors,  and  the 
discovery  of  the  Archaeopteryx  afforded  a  connecting  link 
which  confirmed  this  opinion.  A  few  other  birds  with 
teeth  are  found  in  later  strata,  but  their  general  structure 


THE   EVOLUTION   OF   LIFE 


351 


FIG.  240. — The  Archaeopteryx.  Note  the  clawed  digits  i,  2,  and  3  of 
the  wings,  the  long  tail  with  many  vertebrae,  and  the  teeth  in  the  jaws. 
(After  Zittel.) 


23 


352 


ANIMAL  BIOLOGY 


approaches  more  nearly  that  of  the  birds  of  the  present 
time. 

During  the  age  when  the  reptiles  were  the  dominant 
animals  on  the  earth  we  find  the  first  remains  of  the  highest 
group  of  vertebrates,  the  mammals.  These  were  repre- 
sented for  a  long  time  by  relatively  small  and  primitive 


"7~''.:^Sffii ^'B^'s^^rr®, 


FIG.  241. — The    Ichthyornis,  a  toothed  bird  of  the  Cretaceous  period. 
(After  Marsh.) 

forms  allied  to  the  present-day  marsupials.  It  was  not 
until  more  recent  times  in  the  Tertiary  period,  often  called 
the  age  of  mammals,  that  the  mammals  became  abundant. 
They  replaced  the  large  reptiles  of  the  previous  period, 
and  their  remains  are  in  some  cases  sufficiently  abundant 


THE    EVOLUTION   OF   LIFE 


353 


Equus:  Qua- 
ternary and 
Recent. 


Pliohippus : 
Pliocene. 


Protohippus  : 
Lower  Plio- 
cene. 


Miohippus : 
Miocene. 


Mesohippus : 
Lower  Mio- 


Orohippus  : 
Eocene. 


FIG.  242. — Feet  and  teeth  in  evolution  of  the  horse;  a,  bones  of  fore- 
foot; b,  bones  of  hind  foot;  c,  radius  and  ulna;  d,  tibia  and  fibula;  e,  roots 
of  a  tooth;  /  and  g,  crowns  of  upper  and  lower  polar  teeth.  (From 
Romanes  after  Marsh.) 


354  ANIMAL  BIOLOGY 

to  enable  us  to  trace  the  gradual  evolution  of  some  of  our 
modern  types.  The  history  of  the  evolution  of  the  horse 
is  especially  complete.  In  our  modern  horses  the  digits 
of  the  feet  are  reduced  to  a  single  one  corresponding  to 
one  middle  digit,  the  hoof  representing  a  greatly  enlarged 
and  thickened  nail.  On  either  side  of  this  middle  digit 
are  two  rudiments,  the  splint  bones,  representing  the 
basal  part  of  the  second  and  fourth  digits.  The  first 
representative  of  the  series  of  horse-like  animals  was  a 
small  creature,  the  Eohippus,  about  the  size  of  a  fox, 
that  lived  during  the  earliest  division  of  the  tertiary 
period.  Its  fore  foot  contained  four  toes  with  hoofs 
and  a  rudimentary  fifth,  and  its  hind  foot  had  three  hoofed 
toes.  This  animal  was  succeeded  in  more  recent  deposits 
by  a  type  with  four  toes  on  the  fore  foot  and  three  on  the 
hind  foot.  Later  appeared  somewhat  larger  horses  about 
the  size  of  a  sheep,  with  three  toes  on  both  fore  and  hind 
feet,  and  a  rudiment  of  a  fourth  toe  on  the  fore  foot; 
while  still  later  forms  had  but  three  toes  on  fore  and  hind 
feet,  the  lateral  ones  being  much  reduced  in  size,  but  still 
bearing  hoofs.  Later  these  lateral  hoofs  and  their  digits 
disappeared  with  the  exception  of  the  rudimentary  splint 
bones.  As  the  horses  increased  in  size,  the  middle  digit 
became  larger  and  came  to  bear  more  and  more  of  the 
weight  of  the  body,  while  the  lateral  ones  became  smaller, 
and  finally  all  but  disappeared.  From  thirty  odd  species 
of  fossil  horses  that  are  known,  we  can  select  a  series  of 
connecting  links  which  afford  the  strongest  evidence  of 
the  descent  of  our  modern  horses  from  a  five-toed  ancestral 
species. 

Only  in  relatively  late  deposits  do  we  meet  with  any 
fossil  remains  of  man,  and  but  very  few  of  the  oldest  re- 
mains have  been  preserved.  The  oldest  of  all  represented 
by  the  top  part  of  the  skull,  a  femur  and  a  few  minor 


THE   EVOLUTION   OF    LIFE  355 

fragments  belong  to  a  creature  called  Pithecanthropus 
erectus  which  was,  so  far  as  its  fragmentary  skeleton  in- 
dicates, a  human  being  decidedly  nearer  the  apes  than 
are  any  existing  races  of  men.  Much  later  we  find  remains 
of  a  more  human  type  along  with  skeletons  of  the  extinct 
cave  bear,  cave  lion  and  mammoth.  We  find  also  the 
stone  implements  of  primitive  man,  such  as  arrow  heads 
and  axes;  at  first  these  were  crude  but  later  they  were 
more  accurately  made.  These  were  made  by  men  of  the 
stone  age,  but  later  there  are  found  implements  of  bronze 
and  still  later  those  of  iron.  Although  man  is  of  recent 
origin,  geologically  speaking,  he  has  been  on  the  earth 
several  hundred  thousand  years,  although  we  cannot 
measure  this  time  with  a  great  degree  of  exactness. 

Taken  as  a  whole,  and  despite  the  gaps  and  imperfec- 
tions of  the  record,  the  history  of  fossil  forms  shows  us  a 
gradual  advance  from  lower  to  higher  types  of  life.  In 
some  cases  where  the  record  is  unusually  complete,  as  in 
the  series  of  fossil  horses  and  elephants,  it  enables  us  to 
follow,  step  by  step,  the  evolution  of  our  modern  forms. 
The  science  of  geology  reveals  to  us  an  almost  immeasur- 
able past  during  which  the  seas,  the  continents,  the  moun- 
tains and  the  valleys  of  our  earth  were  gradually  being 
formed,  and  the  earth's  wealth  of  plant  and  animal  life 
was  gradually  being  evolved. 

From  a  variety  of  sources,  such  as  morphology,  or  the 
science  of  structure,  embryology,  geology,  the  geograph- 
ical distribution  of  life  and  the  observed  facts  of  variation 
there  is  an  overwhelming  mass  of  evidence  for  the  con- 
clusion that  plants  and  animals  including  man  have  arisen 
by  a  gradual  process  of  evolution.  It  is  a  problem  of 
great  importance  to  ascertain  by  what  method  this  great 
change  has  been  effected  in  organic  life.  Ordinarily 
plants  and  animals  give  rise  to  progeny  closely  resembling 


356  ANIMAL  BIOLOGY 

their  parents  whose  qualities  they  inherit.  But  occasion- 
ally organisms  have  been  observed  to  depart  considerably 
from  the  parental  type,  producing  what  are  called  varia- 
tions. It  is  often  remarked  that  no  two  individuals 
are  exactly  alike,  and  this  applies  as  much  to  plants  and 
animals  as  to  human  beings.  Many  of  the  differences 
between  organisms  of  the  same  ancestry  are  due  to  food, 
climate  and  other  environmental  causes,  and  are  probably 
not  inherited;  but  other  variations  which  occur  less  fre- 
quently are  undoubtedly  transmitted.  Thus  there  was 
born  in  Massachusetts  a  peculiar  ram  having  an  unusually 
long  body  and  short,  crooked  legs.  Its  enterprising 
owner  conceived  that  it  would  be  desirable  to  produce  a 
breed  of  sheep  like  this  ram,  and  he  found  that  it  was 
capable  of  transmitting  its  peculiar  qualities  to  its  off- 
spring. There  was  thus  produced  the  Ancon,  or  otter 
variety  of  sheep.  The  Merino  sheep  likewise  originated 
from  a  sudden  variation.  Breeds  of  hornless  cattle 
have  been  produced  in  a  similar  manner,  and  a  great 
many  of  our  cultivated  varieties  of  plants  and  animals 
have  also  originated  from  a  sudden  variation.  These 
sudden  transmissible  variations  are  commonly  spoken  of 
as  sports  or  mutations. 

It  is  owing  to  the  occurrence  of  variations  of  a  trans- 
missible kind  that  breeders  of  plants  and  animals  are  able 
to  effect  such  striking  changes  in  their  stock.  The  breeder 
selects  those  variations  which  are  best  fitted  for  his  purpose 
and  breeds  from  them.  Other  variations  in  the  same  direc- 
tion are  selected,  until  a  race  is  finally  produced  which  is 
often  very  different  from  the  original  one.  Horses  have 
been  bred  for  speed,  for  strength  and  other  qualities  for 
generations,  producing  the  slender  high-spirited  race  horse 
on  the  one  hand,  and  our  heavy  draft  horses  on  the  other. 
Cows  have  been  bred  for  increased  yield  of  milk  with  the 


THE  EVOLUTION   OF   LIFE 


357 


FIG.  243. — Varieties    of   domestic    pigeons.     (After   Romanes.) 


ANIMAL  BIOLOGY 

result  that  now  our  better  breeds  of  cattle  produce  several 
times  as  much  milk  as  did  the  cattle  of  a  few  centuries  ago. 
The  selections  of  the  pigeon  fancier  have  resulted  in  the 
production  of  such  diverse  types  as  the  pouter,  the  fantail, 
the  tumbler  and  numerous  other  varieties,  all  of  which  are 
considered  to  be  the  descendents  of  the  original  rock  pigeon 
Columba  lima.  Our  domestic  dogs  doubtless  sprang  from 
several  varieties  of  wolf,  but  cross  breeding  and  continued 
selection  have  resulted  in  the  production  of  the  greatest 
variety  of  form,  size  and  disposition.  Animals  so  different 
as  the  bull-dog,  the  greyhound,  the  newfoundland,  the 
spaniel,  and  fehe  terrier  would  undoubtedly  have  been 
considered  members  of  very  distinct  species,  if  not  genera, 
had  they  been  met  with  in  a  state  of  nature.  This  process 
of  artificial  selection,  as  it  is  called,  has  resulted  also  in  the 
production  of  many  varieties  of  plants  which  are  of  the 
utmost  value  to  man.  By  its  means  man  has  greatly 
increased  the  quality  and  yield  per  acre  of  his  wheat,  oats, 
corn  and  many  other  grains,  and  produced  countless 
varieties  of  beautiful  flowers.  The  genius  of  Luther 
Burbank  has  given  us  a  stoneless  plum,  a  spineless  cactus, 
the  Burbank  potato  and  a  large  number  of  other  improved 
varieties  of  fruits  and  vegetables,  as  well  as  ornamental 
plants. 

The  possibility  of  improving  our  races  of  plants  and 
animals  depends  upon  the  occurrence  of  variations  which 
are  inherited.  Variations  occur  in  a  state  of  nature  as 
well  as  under  domestication,  and  if  there  were  any  agency 
capable  of  selecting  variations  of  a  certain  type,  organisms 
would  be  modified  in  nature  just  as  they  have  been  under 
domestication  through  the  agency  of  man.  The  existence 
of  such  a  modifying  agency  was  first  pointed  out  by  Charles 
Darwin  and  Alfred  Russel  Wallace  who  independently 
and  at  nearly  the  same  time  worked  out  their  celebrated 


THE   EVOLUTION   OF   LIFE 


359 


V'H    ENGLISH  TERRIER^ 


KING-      CHARLES   SPANIEL 


FIG.  244. — Varieties  of  dogs.     (After  Romanes.) 


360  ANIMAL  BIOLOGY 

theory  of  the  origin  of  species  by  means  of  natural  selection. 
According  to  this  theory  there  is  a  process  of  selection 
continually  going  on  in  nature  producing  results  more  or 
less  analogous  to  those  produced  by  man  by  the  process  of 
artificial  selection.  Natural  selection  is  the  outcome  of  the 
struggle  for  existence  which  is  ever  waging  in  the  organic 
world.  Organisms  tend  to  multiply  so  rapidly  that  if 
their  propagation  were  not  checked  there  would  not  be 
space  enough  on  the  earth  to  support  them.  According  to 
Jordan  a  codfish  may  produce  as  many  as  9,100,000  eggs 
per  year.  "If  each  egg  were  to  develop,  in  ten  years  the 
sea  would  be  solidly  full  of  codfish."  The  elephant  which 
is  reckoned  the  slowest  breeder  of  all  animals  would 
produce  in  800  years,  according  to  Darwin,  19,000,000 
elephants  from  a  single  pair.  In  a  few  years  more  these 
would  increase  until  the  entire  earth  would  be  covered  by 
elephants. 

Now  it  is  obvious  that  animals  do  not  actually  increase 
at  this  rapid  rate.  If  the  individuals  of  a  species  are  not  on 
the  increase,  as  they  generally  are  not,  only  two  individuals 
from  a  single  pair  will  on  the  average  live  to  maturity. 
Their  numbers  are  kept  down  by  various  checks  such  as 
limitation  of  food,  climate,  diseases  and  numerous  enemies. 
It  is  only  occasionally  when  organisms  are  introduced  into 
a  new  country  where  for  a  time  there  is  little  to  check  their 
increase,  that  the  high  rate  of  multiplication,  which  we 
have  described,  is  approximated.  When  rabbits  were 
introduced  into  Australia  and  New  Zealand  they  found  few 
competitors  and  they  multiplied  so  rapidly  that  they  be- 
came a  serious  nuisance  and  much  effort  has  since  been 
expended  to  rid  the  country  of  the  pest.  Similarly  when 
cattle  were  introduced  into  South  America  by  the  Span- 
iards they  increased  in  numbers  to.  such  an  extent  that 
before  many  years  the  plains  of  that  country  were  overrun 


THE   EVOLUTION    OF    LIFE  361 

by  immense  herds  of  these  animals.  The  descendents  of 
the  English  sparrow,  introduced  not  many  years  ago  into 
this  country,  now  number  untold  millions. 

As  only  a  few  of  the  descendents  of  any  organism  can  as  a 
rule  survive,  the  chances  are  that,  on  the  whole,  the  sur- 
vivors owe  their  existence  to  the  possession  of  some 
quality  which  gives  them  an  advantage  over  their  competi- 
tors in  the  struggle  for  existence.  As  organisms  vary, 
those  variations  which  are  best  adapted  to  their  conditions 
of  life  will,  on  the  whole,  survive  and  propagate  their  kind. 
Thus  there  results  in  nature  a  process  of  selection  working 
ever  toward  the  preservation  of  the  better  endowed  indi- 
viduals. This  process  was  called  by  Darwin  natural 
selection  in  contradistinction  to  artificial  selection  which  is 
practised  by  man.  In  natural  selection  we  have  a  modi- 
fying agency  which  is  ever  tending  to  mould  organisms  into 
better  adapted  forms.  In  a  herd  of  wolves  for  instance  it 
would  naturally  work  to  produce  greater  fleetness  of  foot, 
keenness  of  scent,  quickness  of  eyesight,  strength,  intelli- 
gence and  other  qualities  which  would  give  a  wolf  an  ad- 
vantage over  its  neighbors.  According  to  Darwin's  theory 
evolution  has  been  brought  about  mainly  through  natural 
selection  in  a  manner  more  or  less  similar  to  that  in  which 
man,  by  a  process  of  artificial  selection,  in  an  infinitely 
shorter  period  of  time,  has  been  able  to  effect  such  strik- 
ing modifications  in  his  cultivated  plants  and  domestic 
animals. 


CHAPTER  XXXIX 
DIVERGENCE  AND  ADAPTATION 

The  continued  modification  of  organisms  by  the  agency 
of  natural  selection  tends  to  adapt  them  to  diverse  kinds 
of  environment.  The  struggle  for  existence  is  most 
severe  between  animals  occupying  the  same  region  and 
living  on  the  same  kind  of  food.  There  is  little  competi- 
tion between  the  grasshopper,  the  honey  bee  and  the  house 
fly,  because  they  do  not  interfere  much  with  one  another's 
activities.  In  a  small  town  there  is  competition  between 
rival  grocery  stores,  but  comparatively  little  between  the 
grocery  man  and  the  blacksmith.  It  is  advantageous  for 
organisms  as  it  is  for,  tradesmen  to  get  their  living  in 
different  ways;  there  is  a  certain  escape  from  the  rigors 
of  the  struggle  for  existence.  Any  organism  which  adopts 
a  new  mode  of  life  or  is  able  to  subsist  upon  a  different  kind 
of  food  secures  a  certain  advantage  over  its  neighbors.  As 
a  result  of  this,  natural  selection  is  ever  working  toward 
the  production  of  diversity;  it  tends  to  fill  with  a  living 
organism  all  situations  in  nature  which  can  support  an 
inhabitant.  In  looking  over  the  world  one  cannot  avoid 
a  feeling  of  wonder  and  surprise  that  Nature  has  filled  so 
many  different  kinds  of  situations  with  living  beings. 
She  has  adapted  them  to  the  severe  cold  of  the  arctic 
regions,  to  the  blistering  heat  of  arid  deserts,  to  the  depths 
of  the  oceans  where  many  forms  live  in  a  region  of  cold 
and  darkness  under  a  pressure  of  several  miles  of  water. 
She  has  modified  them  often  into  the  most  fantastic 

362 


DIVERGENCE   AND   ADAPTATION  363 

shapes  and  endowed  them  with  most  curious  habits  of 
life. 

We  shall  consider  in  this  chapter  a  few  of  the  many 
adaptations  which  Nature  has  produced  in  order  to  equip 
her  children  for  the  great  battle  of  life.  Many  animals 
are  colored  in  such  a  way  that  they  are  difficult  to  detect 
in  their  natural  environment.  The  fauna  of  the  arctic 
regions  contains  a  very  large  proportion  of  birds  and  mam- 
mals which  are  colored  white  like  the  snow  and  ice  among 
which  they  live.  Animals  which  live  in  deserts  are  very 
frequently  colored  much  like  the  sand.  A  great  many 


FIG.  245. — A  leaf  insect. 

leaf-eating  insects  and  larvae  are  green,  while  species  that 
are  found  upon  the  bark  are  more  commonly  of  a  duller 
hue.  The  celebrated  leaf  insect  of  South  America  has 
wings  which  simulate  not  only  the  shape  and  color  but 
also  the  venation  of  leaves.  One  of  the  most  striking 
cases  of  protective  coloration  is  afforded  by  the  Kallima 
butterfly  which,  when  it  is  at  rest  on  a  twig  with  its  wings 
folded  together,  closely  resembles  a  dead  leaf,  the  tail 
of  its  wing  corresponding  to  the  stem  of  the  leaf,  and  a 
dark  line  extending  across  the  wings  presenting  a  close 
likeness  to  the  midrib.  Only  the  under  side  of  the  wings 


364  ANIMAL  BIOLOGY 

is  colored  like  a  dried  leaf,  the  upper  side  being  bright 
colored  and  conspicuous. 

Contrasted  with  the  protective  coloration  of  many 
forms,  are  the  bright  colors  of  certain  animals  which  are 
poisonous  or  have  a  disagreeable  taste.  Such  animals 
are  said  to  possess  a  warning  coloration.  Examples  are 
afforded  by  the  conspicuous  spotted  Salamandra  macu- 
losa  of  Europe,  whose  skin  produces  a  copious  supply  of  a 
virulent  poison.  Many  poisonous  snakes  are  very  con- 
spicuously colored  and  the  same  is  true  of  many  stinging 
insects.  It  has  been  found  that  certain  non-poisonous 
forms  closely  resemble  species  having  a  warning  colora- 
tion. This  resemblance  is  called  mimicry  k(see  p.  23) 
and  is  commonly  explained  as  having  been  developed 
because  resemblance  to  a  protected  form  is  an  advantage 
in  deceiving  enemies.  A  great  many  species  of  butter- 
flies show  a  remarkably  close  resemblance  to  other  species 
which  are  known  to  possess  a  disagreeable  taste  and  odor. 

A  very  common  kind  of  adaptation  is  shown  by  the 
organisms  called  parasites.  These  creatures  usually  are 
carried  by  others  from  which  they  obtain  their  sustenance. 
We  have  already  become  acquainted  with  many  parasitic 
species  from  various  groups  of  the  animal  kingdom.  In 
the  Protozoa  we  have  parasitic  Amoebae,  parasitic  infusoria 
and  flagellates  and  the  entire  group  of  Sporozoa.  Among 
the  flat  worms  the  trematodes  and  the  cestodes,  or  tape- 
worms, are  entirely  parasitic.  There  are  numerous 
parasitic  round  worms,  or  nematodes.  There  are  large 
groups  of  parasitic  forms  among  the  Crustacea,  such  as 
the  fish  lice,  whale  lice  and  parasitic  barnacles.  The 
arachnids  have  their  parasitic  ticks  and  mites,  and  the 
insect  world  contains  thousands  of  species  parasitic  on 
plants  and  animals. 

Parasitism    forms    a   relatively   easy   way   of   getting 


DIVERGENCE   AND    ADAPTATION  365 

a  living  and  animals  from  a  great  variety  of  classes  have 
taken  advantage  of  this  means  of  obtaining  it.  There  is  a 
natural  check  to  the  number  of  possible  parasites,  for  if 
the  hosts,  or  organisms  preyed  upon,  were  to  be  killed 
off,  the  parasites  would  starve.  As  it  is,  most  animals 
harbor  *a  number  of  these  dependent  creatures.  Man 
for  instance  is  infested  with  a  considerable  number  of 
these  parasitic  Protozoa  to  say  nothing  of  the  numerous 
disease-producing  bacteria.  Of  the  trematodes,  cestodes 
and  round  worms  that  attack  him  there  are  somewhat  over 
fifty  species.  And  then  there  are  various  species  of  ticks, 
mites,  fleas,  lice,  bed  bugs  and  other  creatures  which 
infest  his  person  with  more  or  less  regularity  according 
to  his  location  or  manner  of  life. 

Parasites  are  classed  as  external,  such  as  ticks  and  fleas, 
and  internal  such  as  tape- worms.  They  differ  as  to  the 
degree  of  dependence  upon  their  host,  some,  the  obligatory 
parasites,  being  like  the  tape-worm  entirely  dependent 
on  their  host;  others  called  facultative  parasites  being 
only  occasionally  parasitic,  such  as  mosquitoes  and  biting 
flies.  Parasitism  almost  always  entails  a  certain  amount 
of  degeneration.  Where  parasites  live  in  or  upon  their 
host  there  is  often  a  loss  of  the  higher  sense  organs,  a 
degeneration  of  the  nervous  system,  a  loss  of  organs  of 
locomotion  or  a  conversion  of  them  into  organs  of  attach- 
ment, and  sometimes  a  loss  of  the  organs  of  digestion  where 
the  parasite  lives  upon  the  digested  food  of  its  host.  An 
extreme  case,  as  we  have  seen  in  the  chapter  on  the  crusta- 
ceans, is  furnished  by  the  parasite  Sacculina,  in  which  the 
animal  has  lost  sense  organs,  appendages,  digestive  tract 
and  has  become  converted  into  an  irregular  mass  presenting 
no  recognizable  points  of  similarity  to  the  barnacles  to 
which  it  is  related.  Its  life  history  affords  an  interesting 
illustration  of  the  extent  of  degeneration  to  which  para- 


366  ANIMAL  BIOLOGY 

sitic  habits  may  lead,  as  well  as  the  importance  of 
a  knowledge  of  development  in  order  to  determine  an 
animal's  true  affinities. 

In  the  tape-worms  degeneration  has  not  proceeded  so 
far,  but  higher  sense  organs  are  lacking  and  there  is  no 
trace  of  a  digestive  system.  Digestive  organs  are  quite 
unnecessary  for  the  tape-worms  as  these  animals  absorb 
the  digested  intestinal  contents  of  their  hosts. 

Frequently  parasitic  animals  are  compelled  to  live  in 
the  bodies  of  two  kinds  of  host  before  completing  their 
life  history.  The  common  liver  fluke  of  the  sheep, 
Fasciola  hepatica,  passes  a  part  of  its  life  history  in  the 
body  of  a  snail  before  it  is  taken  into  the  alimentary  canal 
of  a  sheep.  Most  tape-worms,  as  we  have  seen,  live  in  two 
different  animals,  usually  an  herbivore  and  a  carnivore. 
The  same  is  true  of  the  trichina;  and  the  life  history  of  the 
malarial  parasite  is  spent  partly  in  the  mosquito  and  partly 
in  man.  This  change  of  host  makes  the  perpetuation  of 
the  life  of  a  parasite  more  than  usually  precarious.  A 
failure  to  meet  with  either  of  the  hosts  would  naturally 
be  fatal  to  the  parasite's  career,  but  the  increased  dangers 
of  such  a  method  of  propagation  are  offset  by  an  extra- 
ordinary degree  of  fecundity. 

Some  organisms  are  found  more  or  less  constantly  asso- 
ciated, although  neither  subsists  in  any  way  upon  the 
other.  Such  forms  are  called  commensals,  or  messmates. 
An  example  of  the  commensal  relation  is  afforded  by 
the  small  oyster  crab,  Pinnotheres,  which  lives  between 
the  valves  of  the  shells  of  oysters  and  other  bivalves. 
A  third  kind  of  association  is  called  symbiosis;  in  this  case 
each  organism  confers  some  benefit  upon  the  other,  so  that 
the  partnership  is  mutually  advantageous.  Many  primi- 
tive organisms  such  as  the  green  Hydra,  the  flat  worm 
Convoluta,  and  many  species  of  anemones  and  corals 


DIVERGENCE   AND   ADAPTATION  367 

harbor  multitudes  of  unicellular  algae,  which  grow  and 
multiply  within  the  tissues  of  their  hosts.  The  algae  derive 
food  from  the  carbon  dioxide  and  probably  other  products 
of  excretion  from  the  animal's  body,  while  they  give  off 
oxygen  which  is  of  value  to  the  animal.  Each  member 
of  the  partnership  thus  profits  by  its  association  with  the 
other.  Another  striking  case  of  symbiosis  is  afforded  by  a 
species  of  hermit  crab  whose  shell  usually  carries  a  specimen 
of  sea  anemone,  Adamsia.  The  anemone  secures  the 
advantage  of  being  carried  about  in  situations  where  it  can 
obtain  more  food,  while  by  means  of  its  nettling  organs 
it  affords  a  certain  degree  of  protection  to  the  hermit 
crab.  If  for  any  reason  the  shell  of  the  hermit  crab  should 
be  deprived  of  the  anemone  the  crab  hunts  for  another 
specimen  which  it  manages  to  work  loose  from  its  attach- 
ment and  fasten  to  its  shell. 

One  of  the  most  striking  cases  of  mutual  adaptation  is 
afforded  by  the  relations  of  insects  and  flowers  whereby  the 
insects  are  enabled  to  secure  food  and  the  flowers  to  obtain 
the  advantages  of  cross  fertilization.  It  has  been  abun- 
dantly shown  by  the  investigations  of  Darwin  in  his  inter- 
esting work  on  the  effect  of  cross  and  self-fertilization  of 
flowers  that  the  seeds  of  flowers  which  have  been  cross 
fertilized  generally  produce  plants  of  greater  vigor  than 
those  resulting  from  self-fertilization.  In  higher  plants 
fertilization  is  accomplished  by  means  of  pollen  grains; 
in  many  plants  these  are  blown  by  the  wind  from  one  flower 
to  another,  but  in  many  others  they  are  carried  by  insects. 
The  insects  attracted  by  the  honey  of  the  flowers  become 
dusted  with  the  pollen  as  the  result  of  their  visit  and  when 
they  fly  to  another  flower  some  of  this  pollen  may  be 
rubbed  off  against  the  surface  of  the  stigma  and  thus  effect 
cross  fertilization.  Many  flowers  show  remarkable  adap- 
tations for  bringing  the  pollen  in  contact  with  the  body  of 

24 


368  ANIMAL  BIOLOGY 

the  insect  and  also  for  receiving  the  pollen,  which  the  insect 
has  acquired  in  its  previous  visit  to  another  flower  of  the 
same  species.  This  is  very  well  illustrated  by  the  flowers 
of  the  sage  Salvia  pratensis.  At  the  lower  side  of  the 
opening  of  the  flower  there  is  a  sort  of  platform  upon  which 
the  insect  alights.  At  the  base  of  the  flower  is  the  nectar; 
the  anthers  or  pollen-bearing  organs  of  the  flower  are  at 
the  end  of  a  movable  lever  which  swings  on  a  pivot.  As 
the  insect  goes  toward  the  base  of  the  flower  in  the  pursuit 


FIG.  246. — Flower  of  the  sage  (Salvia  pratensis);  I,  lower  lip  of  corolla; 
p',  pistil  when  immature;  p",  mature  pistil;  st',  stamen  when  immature; 
st",  mature  stamen. 

of  honey  it  causes  the  anther  to  be  pushed  down  and  some 
of  the  pollen  becomes- dusted  upon  the  insect's  back.  The 
pollen  and  stigma  mature  at  different  periods  so  that  a 
flower  is  prevented  from  becoming  fertilized  by  its  own 
pollen.  When  the  stigma  is  ready  to  receive  pollen  it 
becomes  extended  in  the  position  shown  in  the  figure. 
When  the  insect  visits  a  flower  which  is  ready  for  fertili- 
zation a  part  of  the  pollen  upon  its  back  becomes  brushed 
off  upon  the  stigma  whose  position  is  now  such  as  to  be 
brought  into  contact  with  it.  This  is  but  one  of  the  very 


DIVERGENCE   AND   ADAPTATION  369 

numerous  and  ingenious  devices  for  effecting  cross  fertili- 
zation, which  we  find  among  flowering  plants.  The  color 
and  scent  of  flowers  serve  to  allure  the  insects  to  the  places 
where  they  may  secure  honey.  Thus  both  insects  and 
plants  profit  by  the  relation.  The  beautiful  color  and 
sweet  scent  of  flowers  have  probably  been  evolved  in  order 
to  take  advantage  of  the  visits  of  insects. 


CHAPTER  XL 
HEREDITY  AND  HUMAN  IMPROVEMENT 

Everyone  is  familiar  with  the  fact  that  among  plants 
and  animals  like  begets  like,  or  in  other  words  offspring 
inherit  the  qualities  of  their  parents.  Everyone  has 
noted  cases  of  family  resemblance  in  which  certain  peculi- 
arities of  form,  or  facial  expression  occur  in  all  the  children 
of  a  family.  The  peculiar  feature  known  as  the  Hapsburg 
lip  has  characterized  for  many  generations  the  members 
of  the  reigning  house  of  Austria.  A  white  tuft  of  hair 
has  frequently  been  transmitted  for  several  generations 
and  there  are  numerous  cases  in  which  supernumerary 
fingers  and  toes  have  likewise  been  inherited  for  a  long 
period.  These  are  among  the  countless  illustrations  of 
the  operation  of  heredity.  Organisms  inherit  from  both 
parents  apparently  to  the  same  degree.  And  they  also 
inherit  qualities  from  their  grandparents  and  more  remote 
ancestors.  Now  and  then  a  peculiarity  which  has  long 
been  latent  or  recessive  suddenly  crops  out  and  it  is  then 
called  a  case  of  atavism  or  reversion. 

The  germ  cells  of  organisms  are  the  bearers  of  hereditary 
qualities.  During  development  these  cells  divide  and 
differentiate  to  form  the  various  parts  of  the  new  indi- 
vidual, but  a  part  of  the  cells  of  the  embryo  give  rise  to 
new  germ  cells,  while  others  produce  body  or  somatic 
cells.  There  is  an  unbroken  series  of  cell  generations 
from  the  germ  cells  of  the  parent  to  those  of  the  offspring. 
It  has  been  supposed  by  many  biologists  that  hereditary 
resemblance  is  due  to  what  Weismann  has  called  the  con- 

370 


HEREDITY  AND   HUMAN   IMPROVEMENT  371 

tinuity  of  the  germ  plasm,  or  the  transmission  of  a  part 
of  the  germinal  substance  relatively  unchanged.  A  part 
of  the  original  germ  plasm  of  the  fertilized  ovum  differ- 
entiates into  the  bodily  organs,  while  a  part  remains 
comparatively  unchanged  and  forms  the  basis  from  which 
the  new  individual  may  arise.  Parent  and  offspring 
resemble  one  another  because  both  sprang  from  a  com- 
mon substance.  Germ  plasm  comes  from  preceding 
germ  plasm,  the  bodies  of  organisms  being  the  carriers 
of  this  substance,  or  as  Gal  ton  .says  the  "  trustees  of  the 
germ  plasm."  Since  it  has  become  customary  to  look 
upon  inheritance  as  coming  not  from  the  bodies  of  parents 
but  from  germ  cells  of  which  the  body  is  both  the  product 
and  the  carrier,  many  biologists  think  that  the  character- 
istics acquired  by  the  body  are  not  transmissible  to  the 
next  generation.  It  was  formerly  held  that  those  char- 
acters which  an  organism  acquires  by  its  own  efforts  or 
through  the  action  of  the  environment  were  in  a  measure 
passed  on  to  its  offspring.  It  was  thought  that  if  a  black- 
smith strengthened  his  arm  by  wielding  the  hammer  his 
son  would  have  a  stronger  arm  as  a  result  of  his  father's 
exercise.  But  the  majority  of  biologists  now  doubt  if 
such  acquired  characters  as  the  increased  or  decreased 
development  of  a  particular  part  are  ever  transmitted. 
Numerous  mutilations  such  as  cutting  off  the  tails  of 
mice  have  been  practised  for  many  generations  without 
producing  the  slightest  effect  upon  the  offspring,  and 
certainly  the  decorative  mutilations  which  many  savages 
have  indulged  in  for  untold  generations  such  as  gashing 
the  cheek,  flattening  the  skull  or  deforming  the  lips,  noses, 
ears  or  feet  have  not  had  the  least  influence  on  the  children 
of  these  peoples  who  are  born  as  free  from  blemishes  as 
those  of  civilized  man.  The  transmission  of  acquired 
characters  is  a  subject  on  which  numerous  experiments 


372  ANIMAL  BIOLOGY 

have  been  performed,  many  of  which  have  been  inter- 
preted in  different  ways,  and  there  is  still  a  difference  of 
opinion  on  the  question  among  students  of  heredity. 

Most  of  the  change  that  has  been  produced  in  domestic 
plants  and  animals  has  been  effected,  not  by  the  trans- 
mission of  characters  acquired  by  the  parents,  but  by 
means  of  the  preservation  of  variations  which  originated 
in  the  germ  cells.  The  appearance  of  six-toed  cats,  Ancon 
sheep,  albinos  and  runnerless  strawberries  is  due  to  some 
change  in  the  germ  plasm,  and  there  is  no  doubt  that  such 
variations  of  germinal  origin  tend  strongly  to  be  trans- 
mitted. The  selection  of  germinal  variations  might  in 
time  effect  very  great  changes,  and  it  is  held  by  many 
biologists  that  the  whole  process  of  evolution  has  been 
brought  about  by  this  method. 

It  was  formerly  a  widespread  belief  that  various  peculi- 
arities can  be  impressed  upon  unborn  children  by  the  ex- 
periences of  the  mother  during  pregnancy.  Sometimes 
children  are  born  with  a  mark  or  blemish  of  some  sort 
which  is  often  attributed  to  a  fright,  desire  or  other  strong 
feeling  on  the  part  of  the  mother.  There  are  skin  markings 
called  naevi  due  to  an  enlargement  of  the  cutaneous 
capillaries  that  sometimes  have  a  certain  resemblance, 
more  often  fancied  than  real,  to  strawberries,  black- 
berries, liver  or  some  other  object  for  which  the  expectant 
mother  may  have  had  a  strong  craving.  When  a  child 
is  born  having  any  sort  of  blemish  the  history  of  the 
mother  is  inquired  into  to  discover  some  experiences 
which  might  account  for  it,  and  out  of  the  numerous 
experiences  that  have  occurred  something  is  frequently 
found  that  satisfies  the  enquirer.  Stories  like  the  follow- 
ing are  typical :  Mrs.  A.  on  putting  her  hand  into  a  flour 
bin  was  frightened  by  a  mouse  which  ran  upon  her  arm. 
Her  child  born  some  weeks  afterward  had  a  reddish  patch 


HEREDITY   AND   HUMAN   IMPROVEMENT  373 

on  its  arm,  resembling  a  mouse.  In  another  case  a 
dentist  raised  up  the  lip  of  a  lady  to  look  at  an  eye  tooth. 
Her  child  born  shortly  afterward  had  a  hare  lip  or  lip 
cleft  at  one  side  like  that  of  a  hare.  The  first  case  was 
probably  a  coincidence  and  the  second  cannot  have  been 
due  to  the  alleged  cause  because  hare  lip,  a  phenomenon 
occurring  in  lower  animals  as  well  as  in  man,  is  due  to 
lack  of  junction  of  two  embryonic  rudiments  and  is  caused 
very  much  earlier  in  development  than  the  period  in 
question.  The  connection  between  mother  and  child  is 
established  through  the  organs  of  circulation  and  while 
anything  such  as  sickness,  starvation  or  alcohol  which 
deteriorates  or  poisons  the  blood  of  the  mother  may  be 
very  unfavorable  to  the  child  there  is  no  good  evidence  that 
the  mother's  imagination  can  paint  pictures  on  the  child's 
body,  or  bring  about  specific  deformities.  Most  of  the 
latter  which  are  attributed  to  maternal  impressions, 
occur  also  in  the  lower  animals  and  are  well  known  to 
pathologists  as  due  to  quite  different  causes. 

Heredity  is  fast  coming  to  be  the  subject  matter  of  an 
exact  science.  This  is  largely  due  to  the  discovery  of  a 
remarkable  law  which  is  named  after  its  discoverer, 
Gregor  Mendel,  an  Austrian  monk.  For  years  Mendel 
had  been  experimenting  by  crossing  varieties  of  sweet 
peas  and  other  flowers;  he  finally  published  his  results  in  a 
rather  obscure  periodical  where  his  papers  remained 
unnoticed  until  the  year  1900  when  they  were  brought  to 
light.  The  rediscovery  of  Mendel's  law  in  1900  made  an 
epoch  in  the  study  of  heredity,  for  those  who  have  followed 
in  Mendel's  footsteps,  verifying  and  extending  the  inves- 
tigations which  he  began,  have  shown  that  Mendel's 
long  forgotten  law  affords  the  key  that  unlocks  many 
mysteries  previously  obscure  and  makes  it  possible  to 


374  ANIMAL  BIOLOGY 

attain  results  in  experimental  breeding  of  the  greatest 
practical  value. 

Let  us  see  what  this  law  is.  In  crossing  varieties  of  peas 
that  differed  in  certain  well-defined  characters  Mendel 
found  that  in  the  first  generation  the  offspring  were  not 
intermediate  in  respect  to  the  characters  in  question,  but 
that  one  character  was  represented  apparently  to  the  com- 
plete exclusion  of  the  other.  Thus  crosses  of  tall  and 
dwarf  peas  produced  nothing  but  tall  peas,  and  crosses  of 


x 


E 

FIG.  247. — Mendelian  inheritance  in  Guinea  pigs.  A  black  animal, 
A,  mated  with  an  albino,  B,  produces  progeny  which  are  all  black  like  C. 
These  progeny  have  albinism  in  a  recessive  state,  and  when  they  are  mated 
produce  blacks,  D,  and  albinos,  E,  in  the  ratio  of  three  to  one. 

yellow  with  green  peas  produced  only  peas  that  were 
yellow.  The  character  such  as  tallness  or  yellowness 
which  appeared  to  the  exclusion  of  its  opposite  was  called 
dominant,  the  suppressed  character  being  called  recessive. 
The  most  striking  results,  however,  were  obtained  in  the 
second  generation  after  the  members  of  the  first  generation 
were  crossed  with  one  another  or  self -fertilized.  The  reces- 
sive character  was  then  found  to  reappear  in  one-fourth  of 
the  progeny,  the  other  three-fourths  showing  the  dominant 


HEREDITY   AND   HUMAN   IMPROVEMENT  375 

character.  The  dwarf  peas  thus  arising  produced  nothing 
but  dwarfs,  the  dominant  character  never  reappearing. 
It  was  found  also  that  one-third  of  the  tall  peas  produced 
nothing  but  tall  plants,  the  recessive  character  never  appear- 
ing. These  were  called  the  pure  dominants;  two-thirds 
of  the  tall  peas,  however,  when  interbred  produced  tall  and 
dwarf  in  the  ratio  of  3  to  i.  Two- thirds  of  the  tails  were 
therefore  mixed  as  regards  the  tall  and  dwarf  characters. 
It  is  customary  to  write  a  formula  for  the  second  genera- 
tion of  hybrid  crosses  in  the  following  way:  iDD  +  2DR 
+  iRR.  In  the  case  of  our  second  generation  of  peas  one- 
fourth  would  be  pure  dominants  or  DD's,  two-fourths 
impure,  DR's,  and  one-fourth  pure  recessives,  RR's. 
Similarly  the  progeny  of  the  yellow  peas  resulting  from 
crosses  of  the  yellow  and  green  varieties  are  found  to 
produce  yellow  and  green  peas  in  the  ratio  of  3  to  i.  Of 
the  yellows  one-third  were  pure  yellows,  and  two-thirds 
produced  both  yellow  and  green  peas,  whereas  the  greens 
being  the  pure  recessives  produced  nothing  but  green  peas. 
The  most  significant  thing  about  Mendel's  law  is  that 
contrasted  characters  come  to  be  segregated  out  in  the 
second  generation  of  hybrids  in  definite  numerical  ratios. 
Characters  such  as  greenness,  yellowness,  tallness,  short- 
ness and  many  others  apparently  behave  as  units  capable 
of  being  combined  and  separated  again  without  losing  their 
identity. 

Where  organisms  differing  in  two  pairs  of  contrasted 
characters  are  crossed  each  pair  behaves  as  a  rule  inde- 
pendently of  the  other.  Thus  when  a  tall,  yellow  pea  is 
crossed  with  a  dwarf  green  variety  the  first  generation  is 
tall  and  yellow;  the  second  generation  is  constituted  as 
follows:  9  tall  yellowy  tall  greeny  dwarf  yellow  :i 
dwarf  green.  Where  several  pairs  of  characters  enter  into 
the  combination  the  ratios  are  still  more  complex. 


376  ANIMAL  BIOLOGY 

Mendel's  law  has  been  found  to  apply  to  a  great  many 
plants  and  animals.  The  breeder  who  knows  the  ancestry 
of  his  stock  is  able  to  anticipate  what  will  be  the  various 
forms  that  will  probably  arise  from  certain  ma  tings.  He 
is  often  able  to  effect  new  combinations  of  qualities  and  the 
practical  value  of  such  knowledge  applied  to  the  improve- 
ment of  grains,  fruits,  vegetables  and  domestic  animals  has 
already  amounted  to  millions  of  dollars  for  farmers  and 
stock  raisers. 

But  one  of  the  most  important  applications  of  Mendel's 
law  is  in  the  field  of  human  heredity.  Heritable  human 
traits  have  been  studied  very  extensively  in  recent  years 
with  the  result  of  throwing  a  flood  of  light  on  many  sub- 
jects hitherto  obscure.  Eye  color  in  man  as  in  animals  is 
one  of  the  many  characters  that  has  been  found,  in  most 
cases  at  least,  to  obey  Mendel's  law.  Dark  colors  are 
dominant  over  lighter  ones.  Matings  of  two  black-eyed 
people  may  produce  only  black-eyed  children  or  again  some 
of  the  children  may  have  brown,  gray  or  blue  eyes.  The 
lighter  colored  eyes  are  due  to  the  fact  that  the  parents 
were  not  pure  dominants,  DD's,  but  mixed,  DR's.  Mat- 
ings  of  dark-  and  light-eyed  people  may  produce  both  dark- 
and  light-eyed  children,  but  matings  of  two  light-eyed 
people  cannot  be  expected  to  produce  a  dark-eyed  child, 
as  the  light  colors  are  recessive  to  dark.  When  both 
parents  have  blue  eyes  all  of  the  children  will  almost 
always  have  blue  eyes  also.  There  is  evidence  of  Mende- 
lian  segregation  in  hair  color,  although  the  latter  is  subject 
to  much  variation  through  environmental  causes.  Dark 
colors  are  dominant  to  light  and  consequently  while 
matings  of  dark-haired  parents  may  produce  some  light- 
haired  children,  light-haired  parents  would  not  be  expected 
to  produce  dark-haired  children.  Albinism,  a  condition 
in  which  hair  and  eyes  are  devoid  of  pigment,  is  recessive 


HEREDITY  AND   HUMAN  IMPROVEMENT  377 

in  man  as  in  animals.  Two  albinos  will  produce  nothing 
but  albino  offspring. 

Deafness  is  sometimes  a  hereditary  and  sometimes  an 
acquired  character.  When  it  is  due  to  accident  or  disease 
there  is  little  danger  of  its  transmission,  but  when  it  is 
caused  by  some  inborn  defect  it  is  very  apt  to  afflict 
the  following  generation,  especially  if  both  parents  are 
congenitally  deaf. 

It  often  happens  that  there  may  be  a  strong  proclivity 
toward  some  defect  or  disease  which  may  be  overcome 


FIG.  248. — Diagram  illustrating  the  inheritance  of  insanity  and 
other  forms  of  mental  defect,  i,  alcoholic;  2,  feeble  minded;  3,  feeble 
minded;  4,  hypochondriac;  5,  had  insane  daughter;  6,  visionary,  drunken 
wreck;  7,  eccentric;  8,  insane;  9,  unbalanced;  10,  crazy,  fits  of  temper, 
gets  wild;  n,  insane;  12,  microcephalic,  defective,  died  in  infancy;  f 
died  in  childhood.  (Prom  data  from  Rosanoff  and  Orr.) 

by  wholesome  living  under  favorable  conditions.  It  is 
commonly  held  that  people  may  inherit  a  tendency 
toward  tuberculosis,  gout,  Bright's  disease  and  numerous 
other  maladies;  but  if  a  person  takes  the  proper  precau- 
tions he  may  avoid  these  impending  dangers.  Knowledge 
of  hereditary  predispositions  is  often  of  great  service 
to  the  physician  in  understanding  his  patient's  case, 
especially  if  he  is  dealing  with  nervous  or  mental  ailm  nts. 
That  heredity  plays  an  important  role  in  the  production  of 
insanity  has  long  been  recognized,  but  it  is  only  recently 
that  evidence  has  been  brought  forward  to  show  that 


378  ANIMAL  BIOLOGY 

insanity  is  inherited  in  accordance  with  Mendel's  law. 
We  should  distinguish  hereditary  insanity  from  insanity 
that  may  be  the  result  of  accident,  disease,  alcoholism 
or  severe  shock,  although  in  many  cases  these  alleged 
causes  only  serve  to  awaken  a  hereditary  proclivity  that 
is  not  strong  enough  of  itself  to  make  the  person  insane. 
Insanity  is  not  inherited  in  so  clear  cut  a  manner  as  albin- 
ism or  eye  color;  what  is  transmitted  is  rather  a  nervous 
condition  that  may  manifest  itself  as  insanity,  epilepsy 
or  other  nervous  disorders.  Insanity  appears  to  behave 
as  a  recessive  or  partially  recessive  character.  Matings 
of  normal  and  insane  frequently  produce  only  normal 
children,  although  if  the  normal  partner  came  from  insane 
ancestry  a  part  of  the  children  would  probably  be  insane. 
When  both  parents  are  afflicted  with  hereditary  insanity 
all  of  the  children  may  be  expected  to  become  insane  or 
have  some  severe  nervous  affliction.  If  both  parents  are 
sane  but  of  insane  ancestry  the  expectation  is  that  one- 
fourth  of  the  children  will  be  afflicted.  While  there 
may  be  no  cases  of  insanity  among  the  immediate  relatives 
of  the  afflicted  person  his  insanity  may  nevertheless  be 
inherited  from  more  remote  ancestors.  From  what  is 
known  of  the  inheritance  of  insanity  it  is  clear  that  people 
in  whom  insanity  is  an  inherited  trait  should  not  marry  and 
incur  the  risk  of  transmitting  this  terrible  malady  to 
their  children. 

Several  careful  studies  have  shown  that  feebleminded- 
ness, like  insanity,  is  inherited  as  a  Mendelian  character. 
Feeblemindedness  is  capable  of  being  detected  in  early 
years,  before  insanity  usually  manifests  itself,  and  in 
the  majority  of  cases  it  is  clear  that  it  is  an  inherited 
character,  although  it  sometimes  results -from  sickness 
or  injury.  A  very  interesting  study  of  the  inheritance  of 
feeblemindedness  is  contained  in  a  little  book  by  Goddard, 


HEREDITY  AND   HUMAN  IMPROVEMENT 


379 


380  ANIMAL  BIOLOGY 

entitled  "The  Kallikak  Family,"  in  which  there  is  traced 
the  pedigree  of  several  hundred  descendants  of  one  feeble- 
minded girl.  Martin  Kallikak,  a  revolutionary  soldier, 
had  by  this  girl  an  illegitimate  and  feebleminded  son, 
who  raised  a  large  family  most  of  whom  were  feebleminded. 
Altogether  there  were  traced  the  histories  of  480  direct 
descendants  of  the  feebleminded  girl.  Of  these  143 
were  definitely  known  to  be  feebleminded  while  the  mental 
condition  of  291  was  doubtful.  Thirty-six  of  the  children 
were  illegitimate  and  82  died  in  infancy;  33  descendants 
were  sexually  immoral,  24  were  confirmed  drunkards, 
8  keepers  of  disreputable  houses;  3  were  criminals  and  3 
epileptics.  Only  46  were  known  to  pass  as  normal.  In 
the  Nam  family  studied  by  Davenport  about  90  per  cent, 
were  feebleminded,  and  about  90  per  cent,  of  the  men 
were  addicted  to  alcohol.  One-fourth  of  the  children 
were  illegitimate  and  the  history  of  the  family  is  one  of 
pauperism,  debauchery  and  crime.  The  cost  of  this  family 
to  the  community  is  estimated  at  a  million  and  a  half 
dollars. 

While  we  cannot  properly  speak  of  crime  itself  as 
inherited,  criminal  tendencies  are  known  to  run  through 
families,  some  being  addicted  to  thieving,  others  to  crimes 
of  violence,  etc.  In  the  notorious  Jukes  family  whose 
members  to  the  number  of  2094  have  been  traced  through 
several  generations  there  were  181  victims  of  intemperance, 
299  paupers,  118  criminals,  378  prostitutes  and  86  keepers 
of  brothels.  In  one  branch  of  the  family  taking  its  origin 
from  a  disreputable  woman  known  as'  Margaret,  the 
Mother  of  Criminals,  there  have  been  over  800  descend- 
ants including  numerous  paupers,  criminals  and  prostitutes. 

A  very  large  proportion  of  the  criminal  class,  but  by  no 
means  all,  are  of  defective  mentality.  Fernald  states  that 
in  Massachusetts  "at  least  25  per  cent,  of  the  inmates  of 


HEREDITY  AND   HUMAN   IMPROVEMENT  381 

our  penal  institutions  are  mentally  defective.'7  Criminals 
show  a  high  percentage  of  epileptics  who  are  especially 
predisposed  to  crimes  of  violence.  Reformatories  and 
homes  for  delinquent  girls  show  that  a  remarkably  large 
number  of  these  offenders  are  of  defective  intelligence, 
the  proportion  in  an  institution  at  Geneva,  Illinois  being 
89  per  cent.  The  Massachusetts  Commission  for  the 
investigation  of  the  White  Slave  Traffic  reports  that  of  300 
prostitutes,  154  or  51  per  cent,  were  feebleminded,  and 
most  of  the  others  "were  of  distinctly  inferior  intelligence." 
Besides  those  who  are  feebleminded  there  is  a  large  element 
of  the  population  who,  born  with  inferior  intellect  and  weak 
will,  cannot  secure  or  retain  positions  of  responsibility,  and 
who  are  unable  to  resist  the  temptations  of  the  evil  sur- 
roundings amid  which  they  are  prone  to  drift,  and  who  are 
apt  to  find  their  way  sooner  or  later  into  the  ranks  of  the 
tramps,  paupers,  chronic  alcoholics  or  criminals. 

Our  defective  classes  are  a  great  drag  upon  society  and  a 
menace  to  its  peace.  They  necessitate  homes  for  the 
feebleminded,  reformatories,  homes  for  delinquent  girls, 
asylums  for  the  epileptics  and  insane  and  they  help  to 
fill  our  jails  and  penitentiaries.  But  the  millions  spent 
upon  those  maintained  in  institutions  is  a  small  part  of 
their  total  cost  to  the  country.  The  larger  part  of  those 
who  are  defective  mentally  are  unconfined  and  they  help 
to  swell  the  number  of  incompetents,  vagrants,  criminals 
and  immoral  women  whose  evil  influence  .through  the 
spread  of  loathsome  diseases  is  beyond  calculation. 
Could  society  rid  itself  of  its  hereditary  defectives  there 
would  result  directly  and  indirectly  untold  benefits;  there 
is  no  social  question  more  urgent  than  how  the  race  can 
purge  itself  of  its  undesirable  stock. 

In  the  production  of  defective  human  beings  we  must 
not  forget  the  direct  influence  of  the  environment.  Where 


382  ANIMAL  BIOLOGY 

children  are  raised  under  conditions  of  extreme  poverty, 
crowded  together  in  unsanitary  tenements  with  a  scant 
allowance  of  poor  food,  and  breathing  impure  air,  the 
deteriorating  effects  upon  both  mind  and  body  generally 
handicap  the  individual  for  life.  Undoubtedly  the 
conditions  under  which  Kallikaks,  the  Jukes  and  other 
notorious  families  have  lived  contributed  much  to  the 
deterioration  of  their  members,  but  it  would  be  a  great 
error  to  attribute  their  degradation  to  environment  alone. 
What  an  individual  becomes  is  a  product  of  his  inheritance 
on  the  one  hand  and  his  environment  on  the  other.  Where 
either  is  very  bad  his  chances  of  amounting  to  much 
are  greatly  reduced;  but  it  better  to  have  a  bad  environ- 
ment than  bad  inheritance,  for  many  individuals  born  with 
good  stuff  in  them  have  risen  to  eminence,  despite  all 
sorts  of  obstacles  that  surrounded  them.  Sanitary 
surroundings,  education  and  a  wholesome  moral  atmos- 
phere might  have  made  passable  citizens  out  of  many  of 
the  Kallikaks  and  Jukes,  but  these  advantages  probably 
would  not  have  made  any  of  them  a  great  discoverer  or 
President  of  the  United  States.  It  is  with  human  beings 
as  it  is  with  varieties  of  corn.  Some  kinds  of  corn  will 
give  rise  in  ordinary  soil  to  large  fine  ears  while  others 
raised  under  identically  the  same  conditions  will  produce 
but  a  scanty  yield  of  small  ears  which  are  poorly  filled. 
The  poor  scrubby  variety  with  superior  cultivation  may  be 
made  to  give  an  increased  yield,  but  no  farmer  would 
think  of  planting  it  if  he  could  get  seed  of  the  better  kind. 
Among  men  as  among  lower  animals  and  plants  it  is 
the  breed  that  tells.  But  among  men  bad  inheritance 
tends  to  make  bad  environment,  for  the  naturally  weak 
and  incompetent  and  the  vicious  tend  to  associate  with 
their  like  and  to  form  a  social  stratum  where  vice  flourishes 
and  crime  is  bred.  Does  bad  environment  in  turn  produce 


HEREDITY   AND   HUMAN   IMPROVEMENT 


bad  inheritance?  This  is  a  very  important  question 
upon  which  it  is  very  desirable  that  more  should  be 
known.  Some  writers  have  answered  it  in  the  negative, 
but  several  recent  experiments  have  shown  that  the  ques- 
tion may  have  to  be  answered  in  the  other  way.  In  his 
experiments  on  the  hereditary  influence  of  alcohol  in 
Guinea  pigs  Stockard  found  that  the  offspring  of  animals 
subjected  for  several  weeks  to  the  fumes  of  alcohol 
were  frequently  undersized  and  of  diminished  vitality. 
The  animals  tested  were  first  bred  together  and  found 
capable  of  producing  healthy  young.  Afterward  they 
were  kept  under  the  influence  of  alcohol,  and  then  bred 
and  the  young  compared  with  those  of  the  former  matings 
of  normal  Guinea  pigs.  Matings  were  made  between 
normal  males  and  alcoholic  females,  normal  females  and 
alcoholic  males  and  alcoholic  males  and  alcoholic  females. 
All  of  these  gave  a  considerable  number  of  offspring  that 
were  dead  at  birth  (still  born)  and  several  young  dying 
soon  after  birth,  the  proportions  in  both  cases  being  highest 
in  those  matings  in  which  both  parents  were  alcoholic. 
The  striking  difference  between  progeny  of  alcoholic 
and  normal  parents  is  shown  in  the  following  table: 


No.  of 
matings 

Neg.  results,  or 
early  abortions 

Young  soon 
dying 

Survivors 

Ale.  cf1  *  X  normal  9    • 

CQ 

25  matings 

8  litters 

•3-1 

Ale  9  X  normal  cT 

j  e 

IO 

Alc.d71  X  ale.  9  
Summary  .    . 

2Q 

ioa 

IS 

A? 

3 
14- 

9 
^6 

Controls 

•if 

2 

I 

s6 

2d  generation: 
Ale.  rf1  X  ale.  9 

10 

7 

o 

1  3 

Normal  9  X  ale.  c/1  

•2 

2 

2 

*  cf1  =  male;   9  =  female. 
25 


384  ANIMAL  BIOLOGY 

Several  of  the  animals  resulting  from  alcoholized  parents 
were  bred  together,  and  although  they  had  themselves 
not  received  any  alcohol,  they  produced  a  high  per- 
centage of  weak  and  defective  offspring.  Apparently 
alcohol  produced  an  effect  on  the  germ  cells  that  caused 
a  hereditary  weakness  in  the  offspring  that  was  handed 
on  after  the  original  cause  was  removed.  The  parent 
animals  showed  little  effects  of  alcohol.  There  was  no 
transmission  of  an  acquired  character,  but  the  production 
of  a  germinal  variation  by  the  action  of  alcohol  on  the 
germ  plasm. 

These  results  make  it  probable  that  in  human  beings 
also  alcohol  may  be  a  potent  cause  of  defective  inheritance, 
as  it  has  long  been  regarded  by  many  physicians  and 
physiologists.  Idiocy,  feeblemindedness  and  epilepsy 
are  found  with  exceptional  frequency  among  the  children 
of  people  addicted  to  alcohol.  On  the  other  hand,  chronic 
alcoholism  is  in  a  large  proportion  of  cases  the  result  of 
inherited  defects,  so  that  the  children  of  alcoholics  may 
show  weakness  because  their  parents  were  defective  quite 
aside  from  their  alcoholism.  What  starts  defective 
strains  of  humanity  in  the  first  place  we  do  not  know, 
but  it  is  probable  that  much  of  the  mischief  must  be  laid 
to  the  score  of  alcohol. 

It  is  of  the  highest  importance  to  our  race  that  we  abolish 
the  sources  of  our  hereditary  feeblemindedness,  insanity, 
epilepsy  and  criminality.  It  is  also  of  the  highest  impor- 
tance and  an  imperative  social  duty  to  prevent  the  propaga- 
tion of  the  hereditary  defectives  that  we  have.  This  class, 
speaking  generally,  is  unusually  prolific.  Although  infant 
mortality  is  high  among  them,  it  is  the  opinion  of  many 
of  the  foremost  students  of  the  problem  that  our  defectives 
are  on  the  increase. 

The  feebleminded  as  a  rule  are  remarkably  prolific. 


HEREDITY  AND   HUMAN  IMPROVEMENT  385 

Speaking  of  conditions  in  England  Whetham  remarks: 
"The  workhouse  records  frequently  note  that  five,  six, 
or  seven  children  have  been  born  before  the  mother  is 
twenty-five  years  of  age,  and  she  herself  may  have  com- 
menced child-bearing  at  fifteen  years  of  age  or  even  younger. 
Most  of  these  children  inherit  the  mental  condition  of 
their  parents,  and  where  both  parents  are  known  to 
be  feebleminded,  there  is  no  record  of  their  having  given 
birth  to  a  normal  child.  In  one  workhouse  there  were 
sixteen  feebleminded  women  who  had  produced  between 
them  116  children  with  a  large  proportion  of  mental 
defect.  Out  of  one  such  family  of  fourteen,  only  four 
could  be  trained  to  do  remunerative  work. 

"With  regard  to  the  fertility  of  feebleminded  stocks, 
it  has  been  pointed  out  that  the  feebleminded  children 
from  the  degenerate  families  who  use  the  special  schools 
in  London,  come,  sometimes  two  or  more  at  a  time,  from 
households  averaging  about  seven  offspring,  whereas 
the  average  number  of  children  in  the  families  who  now 
use  the  public  elementary  school  is  about  four." 

Most  of  the  feebleminded  are  not  confined  in  institu- 
tions. Of  the  1 0,000  known  cases  in  Pennsylvania ,  accord- 
ing to  Dr.  Barr,  6500  are  free.  In  many  cases  women  in 
almshouses  continue  to  produce  children  most  of  whom 
are  below  par  mentally.  In  England  a  few  years  ago 
the  girls  born  in  workhouses  were  set  adrift  at  sixteen. 
They  frequently  returned  repeatedly  to  give  birth  to 
illegitimate  children  who  were  raised  at  the  county's 
expense  until  old  enough  to  follow  the  mother's  example, 
an  effective  system  for  encouraging  the  increase  of 
undesirable  stock. 

The  race  can  improve  its  heritable  qualities  only  by 
breeding  from  the  best  and  preventing  the  breeding  of  its 
worst.  To  bring  this  about  so  far  as  it  is  possible  is  the 


386  ANIMAL  BIOLOGY 

practical  aim  of  the  science  of  Eugenics.  At  the  present 
time  there  are  various  agencies  working  toward  the 
deterioration  of  the  inborn  qualities  of  the  race  and  others 
which  have  the  opposite  tendency  and  the  trend  of  our 
biological  development  depends  upon  which  set  of  ten- 
dencies is  the  more  potent.  One  very  serious  condition 
which  has  come  into  existence  largely  during  the  last 
half  century  is  the  diminishing  size  of  the  family  among  the 
educated  and  successful  classes.  While  there  has  been  a 
general  decline  in  the  birth  rate  in  most  civilized  coun- 
tries this  decline  does  not  affect  all  classes  of  society  alike. 
A  decreasing  birth  rate  is  in  itself  no  menace  so  long  as  it 
is  not  so  low  as  to  cause,  as  in  France,  an  actual  decrease 
of  population.  But  when  the  defective  classes  and  those 
with  inferior  inheritance  continue  to  produce  many 
children  while  the  birth  rate  of  those  with  superior  endow- 
ments becomes  greatly  reduced,  a  deterioration  of  the 
hereditary  qualities  of  the  race  will  inevitably  result. 

Seventy-five  years  ago  the  educated  classes  had  as  a 
rule  large  families,  but  their  birth  rate  has  gradually 
decreased  until  they  average  in  the  United  States  between 
two  and  three  children.  The  average  number  of  children 
of  graduates  of  Yale  and  Harvard  is  scarcely  over  two  per 
family  and  the  families  of  most  other  college  graduates 
are  but  little  larger.  It  is  much  the  same  with  successful 
men  of  business  and  the  higher  classes  of  artizans.  The 
birth  rate  of  foreign  immigrants  is  much  higher,  the  average 
family  in  Massachusetts  for  instance  having  4.7  children 
while  the  families  of  the  American  born  have  only  2.7 
children.  It  requires  nearly  four  children  per  family  to 
replenish  the  population;  many  fail  to  marry  or  else  die 
before  reaching  maturity  so  that,  starting  with  four,  only 
two  (or  a  little  over)  take  the  places  of  their  parents  and 
become  producers  of  children.  It  follows  that  stocks  with 


HEREDITY   AND   HUMAN   IMPROVEMENT  387 

smaller  families  of  two  or  three  children  are  bound  to  be- 
come extinct  in  a  few  generations.  At  the  present  time  we 
are  rapidly  losing  the  blood  that  formerly  gave  us  our  schol- 
ars, legislators  and  leaders  of  men.  While  people  of  very 
moderate  natural  abilities  are  found  in  the  so-called  educa- 
ted classes,  there  is  little  doubt  that  the  latter  have  an 
average  inheritance  above  that  of  the  general  population. 
But  however  this  may  be,  it  is  the  duty  of  those  who  have 
been  blest  with  good  hereditary  qualities  to  see  that  their 
race  does  not  perish.  If  such  people  shirk  the  responsibili- 
ties of  parenthood,  as  they  are  nowadays  so  prone  to  do, 
and  leave  the  perpetuation  of  the  race  to  inferior  strains 
who  tend  to  be  only  too  prolific,  the  race  cannot  fail  to 
deteriorate.  Man,  to  a  great  extent,  has  abolished  the 
struggle  for  existence,  and  now  his  future  lies  largely  in 
his  own  hands  to  make  or  to  mar. 


INDEX 


abdomen,  of  grasshopper,  2,  5 

of     crustaceans,     84-88,     91 
Acridiidae,  18,  19 
adductors,  98 
adrenalin,  281 
adrenals,  281 
air  bladder,  160,  167,  168 
air  cells,  273 
air  sacs,  188 
albinos,  372,  376,  377 
alcohol,  how  made,  237,  238 

effect  on  digestion,  257,  258 
on  heart  and  circulation,  268 
on  kidneys,  279 

general  effects,  311-314 

hereditary  effects  of,  383-384 
alimentary  canal,  of  bee,  58 

of  bird,  187 

of  crayfish,  86,  87 

of  grasshopper,  6,  7 

of  man,  249-251 
alligators,  176,  180 
alternation  of  generations,  135 
Amazon  ant,  68 
Amia,  161,  167,  338 
ammonites,  105 
Amoeba,    146,  147,  151,  240,  241, 

33i 

Amphibians,  157,  169-175 
Amphioxus,  155,  156,  337 
amphipods,  94 
amylopsin,  251 
anaconda,  179 
anal  fin,  158 


analogous  organs,  343 
Ancon  sheep,  356,  372 
anemones,  130,  1-36 
Anguilla,  163 
Annelida,  114 
Anopheles,  47 
ant  eater,  214,  215 
Ants,  36,  56,  65-69 
antelopes,  222 
antenna  cleaner,  58 
antennae,  3,  68 
anthropoids,  227 
antitoxins,  326 
antlers',  221,  222 
Anura,  169-175 
anvil,  310 
aorta,  263 

arches  of,  347 
apes,  227,  230 
aphids,  35,  36,  68 
aqueous  humor,  307 
Arachnida,  18,  76-83 
Archseopteryx,  350,  351 
Argentine  ant,  69 
Armadillo,  214,  215 
arteries,  88,  100,  262-265,  267 
artificial  selection,  356-359 
Artiodactyla,  220 
Ascaris  lumbricoides,  122 
Ascaris  megatocephala,  122 
Asellus,  93 
assassin  bugs,  32 
assimilation,  239,  252 
asteroids,  108-110 
astigmatism,  308 
atavism,  370 


389 


390 


INDEX 


atoms,  233 
auricles,  100,  262 
axis  cylinder,  296 

B 

bacillus,  317,  323-326 

Bacillus  tuberculosis,  322,  323 

backswimmers,  33,  34 

bacteria,  150,  261 

balancers,  40 

Balanoglossus,  155 

barnacles,  94-97 

Basilarchia  archippus,  23 

bass,  167 

bathing,  286 

Batrachians,  157,  169-175 

bats,  185.  218 

beak,  84 

bears,  223 

beavers,  216,  217 

bedbugs,  32 

bees,  56-64 

beetles,  18,  51-55 

Behring,  von,  326 

bile,  251 

birds,  183-208,  338-340,  350-352 

birth  rate,  386 

bladder,  277 

bladder  worm,  127-129 

Blattidae,  18,  19 

blood,  of  clam,  100 

of  crayfish,  88 

of  earthworm,  117 

of  grasshopper,  7,  8 

of  man,  259-265 
blow  flies,  42 
boa  constrictor,  179 
boils,  321 

Bombyx  mori,  26,  27 
bones,  287-291 
bot  flies,  43 
Bovidae,  221 
brain,  of  Amphioxus,  155,  156 

of  clam,  100,  101 


brain,  of  crayfish,  88 

of  earthworm,  118 

of  grasshopper,  8 

of  man,    230,    231,    294,    295, 

298-303 

branchiae,  85,  86 
Bright's  disease,  279,  377 
brittle  stars,  no 
bronchi,  273 
Buffalo  gnats,  44 
Bufonidae,  173 
bugs,  31-34 
bull-frog,  172,  173 
bumble  bees,  63 
Burbank,  L.,  358 
Burroughs,  J.,  207 
byssus,  102 


cabbage  butterfly,  20,  2 1 

caddis  flies,  70,  73 

calciferous  glands,  117 

camel,  220 

canine  or  eye  teeth,  247 

capillaries,  264-266 

carapace,  84,  86 

carbohydrates,  237,  249,  251,  255 

carbon,  233,  234,  235,  236 

carbon  dioxide,  236,  238,  239,  240, 

269,  271,  273,  275,  276 
Carboniferous  period,  349 
Carnivora,'223 
Carolina  locust,  1 2 
carpals,  290 
cartilage,  243,  287 
casein,  260 
cats,  207,  208,  223 
cells,  240-244 
centipedes,  75,  76 
Cephalopoda,  105-107 
Cephalothorax,  84,  88 
cerebellum,  299-301 
cerebral  hemispheres,  300-303 
cerebro-spinal  system,  296 


INDEX 


391 


Cervidae,  221 

Cestodes,  126-129 

Cetacea,  225,  226 

chalk,  148 

chambered  nautilus,  105,  106 

chameleons,  179 

cheese  mites,  82 

Cheiroptera,  218 

chelae,  85 

chelipeds,  85 

Chelonia,  176,  181 

Chelonians,  176,  181,  182 

chemical  changes,  232-234,  245 

chimpanzees,  227,  229,  230 

chinch  bug,  31,  32 

chitin,  2 

chitons,  105 

chlorine,  236 

chlorophyll,  145 

chocolate,  257 

Chordata,  156 

choroid  coat,  307 

cicada,  34,  35 

cilia,  242 

clams,  98-102,  151 

class,  1 8 

classification,  17-19 

clavicle,  290 

cleavage,  336 

clitellum,  115,  119 

clot,  259 

clothes  moths,  30 

clotting  of  blood,  260 

cobra,  179 

Coccidae,  36-38 

Coccidea,  148 

cochlea,  310 

cockroaches,  15,  18,  19 

cocoons,  of  insects,  26,  27,  67 

of  earthworms,  119 

of  spiders,  77,  338 
cod,  167,  339,  360 
codling  moth,  29 
Ccecilians,  169,  180 


ccecum,  250,  345 

Coelenterates,  130-139 

Ccenurus  cerebralis,  129 

coffee,  257 

cold  spots,  305 

colds,  275,  320-323 

Coleoptera,  18,  51-55 

Colorado  potato  beetle,  52,  53,  204 

comb,  58,  60,  61 

commensals,  366 

commissures,  8,  100,  101 

compounds,  232 

conjugation,  143,  332 

connective  tissue,  242,  243 

consumption,  275 

contractile  vacuoles,  142,  147 

convolutions,  300 

copepods,  97,  151 

copperhead,  179 

coral  polyps,  130,  136-138 

coral  snake,  178 

corals,  136-138 

corium,  283 

cornea,  3,  307 

corpus  callosum,  300 

corpuscles,  of  blood,  259,  261,  265, 

266 

cortex,  300 

cottony-cushion  scale,  38 
coughing,  299 
courtship,  80,  160,  194-197 
crabs,  91-93 
cranium,  160,  289 
crayfish,  84-90 
cremaster,  21 
cretinism,  281 
crickets,  14,  15,  18,  19 
Crinoids,  or  sea  lilies,  112 
crocodiles,  176,  180,  181 
Crocodilia,  176 
crop,  of  birds,  187 

of  earthworm,  116 

of  grasshopper,  6 

of  honey  bee,  58 


392 


INDEX 


cross  fertilization,  367-369 
Crustacea,  18,  84-97,  337 
crystalline  lens,  307 
Ctenophores,  139 
cuckoos,  198 
curculios,  55 
cuticle,  283 
cutis,  283 
cuttle  fish,  1 06 
Cyclostomes,  156,  157 
Cynipidae,  69 
cysticercoid,  127 
cysticercus,  127 
cysts,  144,  147 

D 

damsel  flies,  70,  72 
Daphnia,  97 

Darwin,    C.,    on    cross    and    self- 
fertilization,  367 

on  earthworms,  119 

on  natural  selection,  358,  360 

on  sexral  selection,  195,  196 

on  species,  17,  342 
Davenport,  C.  B.,  380 
deafness,  377 
Decapoda,  93 
deer,  220-222 
degeneration,  96,  365,  366 
Demodex,  83 
dentine,  248 
devil-fish,  98,  107 
dextrose,  251,  234,  266 
diaphragm,  274 
digestion,  in  Amoeba,  147 

in  birds,  187,  188  .  , 

in  crayfish,  87 

in  grasshopper,  7 

in  Hydra,  131 

in  man,  245-251 

in  Paramcecium,  142 

in  starfish,  109,  no 
diphtheria,  326 


Dipnoi,   or  lung  fishes,    160,    167, 

1 68 

Diptera,  18,  40-50 
disinfectants,  320 
Dissosteira,  18 
dobson,  or  hellgrammite,  74 
dogfish,  161,  166,  167 
dogs,  210,  223,  358,  359 
dorsal  fins,  158 
dorsal  vessel,  117 
dragon  flies,  70-72 
drones,  56,  60 
drum  membrane,  309 
duck  bills,  211,  212 
ductless  glands,  280-282 
Dytiscidae,  55 


ear,  309,  344 

earthworms,  114-120,  276,  334 

Echidna,  212 

Echinococcus,  129 

Echinoderms,  108-113 

Echinoids,  110-113 

ectoderm,  131,  139,  336 

ectoplasm,  147 

Edentata,  214,  215 

eels,  163,  167 

eggs,  233-236 

care  of,  337~34o 

of  amphibians,  170,  171 

of  ants,  67 

of  birds,   188,   189,   191,    192, 
198,    206 

of  bot-fly,  43 

of  butterfly,  21 

of  clam,  101 

of  cockroach,  15 

of  crocodiles,  181 

of  crustaceans,  85,  90,  96 

of  dragon  flies,  70 

of  earthworm,  118,  119 

of  fishes,  160,  238,  239, 
161,  163,  164,  166 


INDEX 


393 


eggs,  of  fleas,  49 

of  fluke,  125,  126 

of  grasshopper,  10 

of  hookworm,  123 

of  house-fly,  41,  42 

of  Hydra,  130,  132,  133 

of  jelly  fish,  135 

of  katydid,  14 

of  mosquitoes,  45,  46 

of  moths,  28-30 

of  spiders,  78,  80 

of  sponges,  140 

of  tapeworm,  127 

Elasmobranchs,  164-166 

electric-light  bugs,  33 

elements,  232 

elephants,  220,  360 

elk,  222 

embryology,  334,  346,  347 

enamel,  248 

endoplasm,  142,  147 

English  sparrow,  205,  206 

entoderm,  131,  133,  139,  336 

enzymes,  238 

Ephemeridas,  72 

epidermis,  283 

epiglottis,  272 

epilepsy,  303,  378,  384 

epinephrin,  281 

epiphragm,  104 

epithelium,  244,  283 

esophagus,  of  birds,  187 
of  crayfish,  87,  88 
of  earthworm,  116,  117 
of  grasshopper,  6 
of  man,  248,  249 

Eudorina,  333 

Eugenics,  386 

Euglena  viridis,  144,  145 

Eustachian  tube,  310,  347 

evolution,  341-369 

excretion,  8,  239,  277-279 

exercise,  292,  293 

expiration,  274 


eyes,  of  Amphioxus,  156 

of  crustaceans,  84,  88,  89,  93, 

94 

of  grasshopper,  2,  3 
of  man,  305-309 
of  snail,  103 
of  spiders,  76 
of  squid,  106 
rudiments  of,  349 


family,  18 

Fasciola  hcpatica,  124-126 

fats,  237,  249,  251,  255 

feathers,  183-185,  195-197 

feeblemindedness,     378-381,     384, 

385 

Felidae,    223 
femur,  of  grasshopper,  4 

of  man,  290 
fermentation,  237,  238 
ferments,  238 
Fernald,  G.  G.,  380 
fertilization,    160,    163,    164,    334, 

367-369 

fiber,  243,  244,  291 
fibrillae,  243 
fibrin,  259 
fibrinogen,  260 
fibula,  290 

Fishes,  48,  157,  158-168 
fission,  143,  145,  147.  331 
flagella,  139,  141,  144-146 
Flagellata,  141, 144-146 
flat  worms,  122,  124-129 
fleas,  48,  49 
flesh  flies,  42 
flukes,  124-126 
foot,  99,  103,  105 
Foraminifera,  148 
Forbush,  E.  H.,  204 
frogs,  169,  171-175 
fungi,  317 


394 


INDEX 


G 

gall,  251 

gall  bladder,  251 

gall  flies,  69 

galls,  69 

Galton,  F.,  371 

ganglia,  8,  9,  88,  99-101,  118,  296 

ganglion  cells,  296 

ganoids,  166 

gastric  coeca,  6 

Gastropoda,  102-105 

gastrula,  336 

gavial,  181 

Geiger,  J.  C.,  327 

genus,  17,  1 8 

geology,  341,  348,  355 

germ  cells,  370 

germ  plasm,  continuity  of,  370,  371 

germicides,  320 

gibbons,  227 

Gila  monster,  180 

gill-slits,  154,  155,  159,  346,  347 

gills,  276 

of  amphibians,  170 

of  Amphioxus,  155 

of  crayfish,  85,  86 

of  cyclostomes,  157 

of  fishes,  159 

of  May-fly  larvae,  72 

of  mollusk,  98,  99,   103,  104, 

106 

gipsy  moth,  28 
gizzard,  116,  187 
glomerulus,  278 
glycogen,  251,  254,  255 
Glyptodon,  215 
Goddard,  H.  H.,  378 
goiter,  281 
Goltz,  F.,  301 
Gordius,  124 
gorillas,  227,  230 
Grantia,  139 
grasshopper,  1-14,  17-19 


green  gland,  84,  88 
Gregarines,  148 
Grillidae,  18,  19 
grizzly  bear,  224 

H 

Haeckel,  E.,  114,  155 

haemoglobin,  260,  270 

Haemosporidia,  148-150 

hag-fishes,  156,  157 

hair,  209,  284,  285 

halteres,  40 

hammer,  310 

harvest  fly,  34 

hawks,  204,  205,  338 

hearing,  6,  304,  309,  310 

heart,  7,  8,  88,  100,  154,  156,  262- 

268 

hearts,  of  earthworms,  116,  117 
heat  spots,  305 
hedgehogs,  209,  216 
Helix,  103 
Helmholtz,  H.,  313 
Hemiptera,  31-39 
heredity,  370-387 
hermaphrodites,  334 
hermit  crabs,  40,  91,  367 
Herrick,  F.  H.,  191-194 
Hessian  fly,  45 
Heteroptera,  31-34 
hibernation,  171 
hippopotamus,  219,  220 
Hodge,  C.  F.,  311 
holophytic  forms,  144 
Holothurians,  112 
Homarus  americanus,  90 
Hominidae,  230 
Homo,  230,  231 
Homo  sapiens,  231 
homologous  organs,  343 
Homoptera,  35-39 
honey-sac,  58 
hookworm,  123,  124 


INDEX 


395 


hopper-dozers,  14 
horned  toads,  179,  180 
hornets,  65 
horse,  evolution  of,  353,  354 

improvement  of,  356 
horse  flies,  44 
horse-hair  snake,  124 
house  fly,  40,  41,  42 
Hudson,  W.  H.,  191 
humerus,  290 

Huxley,  T.  H.,  84,  230,  238 
Hydra,  130-133,  240,  241,  276 
Hydra  viridis,  133 
hydrogen,  234,  236-238 
hydroids,  130,  133-135 
Hydrophilidae,  55 
hydrophobia,  326,  327 
Hyla,  175 
Hylidae,  174,  1 75 
Hymenoptera,  56-69,  338 
hyoid  bone,  347,  348 


ichneumons,  69 
imago,  12,  73 
immunity,  326 
incubation,  188-190 
Infusoria,  141-144 
insanity,  303,  377,  378 
Insectivora,  216 
inspiration,  274 
instinct,  190,  191 
intelligence,  seat  of,  300-303 
internal  secretion,  280-282 
intestine,  of  clam,  100 

of  crayfish,  87 

of  earthworm,  116,  117 

of  grasshopper,  7 

of  man,  249,  251 
Invertebrates,  153,  348 
iodine,  236 
iris,  307 
iron,  236 


Isopoda,  93 
itch  mites,  83 


jaws,  76,  84 

jelly  fish,  130,  134,  135 

Jenner,  £.,328 

Jordan,  O.  S.,  167,  168.  360 

Jukes  family,  380,  382 

June-bugs,  51,  53 

K 

Kallikak    Family,    The,  379,   380, 

382 

Kallima  butterfly,  363 
kangaroos,  213 
katydids,  13,  14 
kidneys,  8,  100,  277-281 
kissing  bug,  32 
Kitchener,  312 
Koch,  R.,  323 
Koebele,  38 
Krsepelin,  312 


labial  palpi,  of  grasshopper,  3,  4 

of  clam,  99,  100 
labium,  4,  31,  58 
Lacertilia,  176 
lachrymal  glands,  306 
lacteals,  266 
lady  beetles,  54 
lamellae,  98 
lamellibranch,  98 
lampreys,  156,  157 
lancelet,  155 
larvae,  of  amphibians,  175 

of  clam,  101 

of  echinoderms,  113 

of  tunicata,  154 

of    insects,     12,    20,    21,    26, 
28,    29,    30,    41-49,    51, 
52,  62,  66,  67,  70-74 
larynx,  272 


396 


INDEX 


Latrodectes,  80 
leaf  insect,  15,  363 
leeches,  120,  121,  334 
lemurs,  227 
lens,  307,  308 
Lepidoptera,  20-30 
leucocytes,  260,  261,  265 
ligaments,  287 
Limnaea,  104 
Limnoria  lignorum,  93 
lions,  223 
lipase,  251 
liver,  of  clam,  100 

of  crayfish,  86,  87 

of  man,  250,  251-254,  255,  257, 

277,  279,  280 
liver  fluke,  124—126 
lizards,  176,  179,  180 
lobster,  90 
Locustidae,  18,  19 
Loeb,  J.,  334 
Loligo  pealii,  106 
Lubbock,  Sir  J.,  66 
Lumbricus  terrestria,  114-120 
lung  books,  77 
lung  fishes,  160,  167,  168 
lungs,  103,  168,  170,  270-276 
lymph,  266 
lymphatics,  266 


M 


mackerel,  167 
malaria,  47,  48,  148,  150 
Malpighian  corpuscle,  278 
Malpighian  tubules,  7,  8 
Mammalia,     209-231,     338,     339 

.340,  352 
Mammals,     209-231,     338,     339, 

340,  352 

mammary  glands,  209,  339 
mammoth,  355 
man,  227,  230,  231,  355 
mandibles,  3,  31,  58,  84 


Mantidae,  16,  19 
mantids,  16 
mantle,  98 
manubrium,  134 
marrow,  289 
Marsupialia,  212-214 
maternal  impressions,  372,  373 
mating,  194-197 
maxillae,  4,  31,  58,  76,  84 
maxillipeds,  84 
May-beetles,  51,  52 
May  flies,  70,  72,  73 
measly  pork,  128 
medulla,  300,  301 
medullary  sheath,  296 
medusae,  134,  135 
meganucleus,  142,  143 
Melanoplus,  18 
M  elanoplus  femur-rubrum,  18 
Melanoplus  spretus,  18 
Mendel,  G.,  373 
Mendel's  law,  373-378 
Merino  sheep,  356 
mesenteries,  136 
mesoderm,  336 
mesothorax,  4 
metabolism,  246 
metacarpals,  290 
metamorphosis,  337 

of  amphibians,  175 

of  echinoderms,  113 

of  insects,  n,  12,  20,  31,  35, 

Si 

metatarsals,  291 
metathorax,  4 
Meylan,  Dr.,  315 
mice,  216 

micronucleus,  142,  143 
migration,  of  birds,  199-201 

of  fishes,  162,  163 
milk,  souring  of,  319 
milkweed  butterfly,  23 
millipeds,  75,  76 
mimmicry,  23-25,  364 


INDEX 


397 


minnows,  167 

mites,  81-83 

molecules,  233,  234 

moles,  216 

molluscs,  98-107 

molt,  21 

molting,  10,  n,  21,  71,  72,  89 

monarch  butterfly,  23 

monkeys,  227,  228 

Monotremes,  211,  212 

moose,  222 

morphology,  232,  355 

mosquitoes,  45-48,  148,  150 

moths,  25-30 

motor  area,  302,  303 

motor  nerves,  296-298 

motor  reflex,  144 

Musca  domestica,  40,  41,  42 

muscles,  243,  291-293 

Muscular  tissue,  243 

mussels,  102 

mutations,"356 

My  a  arenaria,  102 

Myriapoda,  75,  76 

N 

Nam  Family,  380 

narcotics,  257' 

natural  selection,  360-362 

nauplius,  94 

nautilus,  105,  106 

Necturus,  170 

nematocysts,  131,  136 

nematodes,  122-124 

nephridia,  117 

nerve  cells,  296 

nerve  cord,  of  Amphioxus,  155,  156 

of  Balanoglossus,  155 

of  crayfish,  88 

of  earthworm,  118,  156 

of  grasshopper,  8,  9 

of  tunicate  larva,  154 
nerves,  294-299 


nervous  system,  of  Amphioxus,  155 
156 

of  clam,  100,  101 

of  crayfish,  88 

of  earthworm,  118 

of  grasshopper,  8, 9 

of  man,  294-303 
nervous  tissue,  244 
nests,  189,  191-194,  197,  338,  339 
nettling  cells,  131 
newts,  169 

nitrogen,  234,  236,  237,  238 
Noctuidae,  28 
notochord,  154-159 
Notonecta,  33 

Novius  (Vedalia)  cardinalis,  38,  54 
nuclei,  142,  241 


ocelli,  3 
Octopus,  107 
oil  glands,  283,  284 
olfactory  pits,  3 
operculum,  158-160 
Ophidia,  176 
Ophiurans,  no 
opossum,  214 
orang-utans,  227 
organs,  240 

Ornithorynchus,  211,  212 
orthoceratites,  105 
Orthoptera,  1-16',  18,  19,  51 
osculum,  139 
ossicles,  87 
ostia,  88 
ova,  333 
ovaries,  9 
oviduct,  9 
ovipositor,  5,  14,  19 
owls,  204,  206,  207 
ox,  220 

oxidation,  235,  239,  270 
oxygen,  234,    235-239,    260,    269, 
271,  273,  275,  276 


398 


INDEX 


oyster  drill,  105 
oysters,  102,  105,  no 


pain,  305 

palp,  3,  76 

pancreas,  250,  251,  281,  282 

Pandorina,   331,   333 

paper  nautilus,  105 

Paramoecium  141-144,  331,  332 

parasites,  124-129,  144,  364,  366 

parasitism,  96,  364-366 

Parkes,  Dr.,  311 

parthenogenesis,  35,  36,  333 

Pasteur,  L.,  149,  319,  327 

patella,  291 

patent  medicines,  330 

Peabody,  J.  E.,  316 

pearls,  101,  102 

pebrine,  149 

Peckham,  G.  W.,  64 

Pecten,  102 

pectoral  arch,  160 

pectoral  fins,  158 

pedal  ganglia,  101 

pedicellariae,  no 

pelvic  arch,  160,  176 

pelvic  fins,  158 

pelvis,  290 

pepsin,  238,  249 

peptone,  249 

perch,  158,  167 

pericardium,  88,  100 

Perissodactyla,  220 

phagocytes,  326 

phalanges,  290,  291 

pharynx,  116,  118,  154,  272 

Phasmidae,  19 

phosphorus,  236,  238 

phrenology,  302,  303 

Phylloxera,  36 

phylum,  1 8,  19 

Physa,  104 

physical  changes,  232 


physics,  233 

physiology,  232 

pig,  220 

pigeon,  301,  357,  358 

pill  bugs,  94 

pineal  gland,  346 

Pinnipedia,  224 

Pithecanthropus  erectus,  355 

placenta,  214,  335 

plague,  49,  50 

planarians,  124 

PJanorbis,  104 

plant  lice,  35,  36 

plasma,  259 

Plasmodium,  148 

pleura,  273 

pleurisy,  274 

pluteus,  113 

pneumonia,  314 

poison  gland,  76 

pollen  basket,  59 

pollen  combs,  59 

polyp,  136-138 

pond  skaters,  34 

porcupines,  209,  216 

Porifera,  139 

portal  vein,  266 

Portuguese  man-of-war,  135,  136 

potassium,  234,  236,  238 

prawns,  90 

Primates,  227-230 

Proboscidea,  220 

proglottids,  126,  127 

pro-legs,  21 

propolis,  62 

prostomium,  114 

protective    resemblance,    25,    363, 

364 
proteins,  237,  238,  249,  251,  252, 

253,  255 
Proteus,  170 
pro  thorax,  4 
protoplasm,  238,  252 
Protozoa,  141-152,  317,  331 


INDEX 


399 


Psammophila,  64 

pseudopodia,  140,  146 

ptarmigan,  184 

pterodactyls,  183 

ptyalin,  238,  248 

pulmonary  arteries,  263 

pulmonary  veins,  263 

puma,  223,  224 

pupae,  of   insects,   12,   21,   22,   26, 

41-43.    45,    46,    49,     5i, 

52,  62,  66,  67 
pupil,  307 
pus,  261 
pylorus,  249 
pythons,  176,  179 


queen  ant,  66,  67 
queen  bee,  56-58,  60-63 


rabbits,  360 

rabies,  326,  327 

Radiates,  108 

Radiolaria,  148,  149 

radius,  290 

Rana  catesbiana,  172,  173 

Rana  pipiens,  172 

Ranidae,  172 

rats,  49,  50,  216 

rattlesnakes,  177,  178 

Ray  Lankester,  E.,  76 

rays,  158,  164,  165 

rectum,  7,  249 

red-legged  grasshopper,  18 

reflex  acts,  297-299 

regeneration,  of  amphibians,  170 

of  earthworm,  119 

of  Hydra,  133 

of  starfish,  no 
reindeer,  222 
renal  artery,  277,  278 
renal  vein,  277,  278 
26 


reproduction,  331-340 

in  Amoeba,  147,  331 

in  amphibians,  171 

in  ants,  67 

in  aphids,  35,  36 

in  bees,  61-63 

in  birds,  188,  194,  338,  339 

in  clam,  101 

in  crayfish,  89 

in  earthworm,  118,  119 

in  fishes,  160-164,  33 8 

in      flies      and      mosquitoes, 
41-46 

in  grasshopper,  9,  10 

in  hookworm,  1 23 

in  Hydra,  132 

in  jelly  fish,  134,  135 

in  liver  fluke,  125,  126 

in  mammals,  335 

in  Paramoecium,  143,  331,  332 

in  spiders,  80 

in  sponges,  140 

in  tapeworm,  127-129 

in  Trichina,  123 

in  Volvox,  332,  333 
reptiles,    176-182,    338,    349,   350, 

352 
respiration,  239 

in  amphibians,  170,  172 

in  birds,  188 

in  clam,  100 

in  crayfish,  86 

in  fishes,  159,  160 

in  grasshopper,  5 

in  man,  269-276 

in  Protozoa,  151 

in  snails,  103,  104 

in  spiders,  77 
retina,  307,  308 
reversion,  370 
ribs,  274,  288,  290 
Roberts,  312 
robin,  119,  191-194,  207 
Rocky  Mountain  fever,  82 


4oo 


INDEX 


Rocky  Mountain  locust,  12,  13,  18 

Rodentia,  216,  217 

rostrum,  84 

round  worms,  122-124 

rudimentary  organs,  343-346 

ruminants,  220 


Sacculina,  96,  97,  365 

sacrum,  290 

salamanders,  169,  170,  364 

salivary  glands,  248 

salmon,  162,  163 

salts,  256 

San  Jose  scale,  37 

sand  dollars,  112 

saprophytes,  144 

Sarcodina,  141, '146-148 

scale  bugs,  36-38 

scales,  159,  176,  177,  183 

scallop,  102 

scapula,  290 

sclerotic,  306 

scorpions,  76,  81 

screw  worm,  42 

sea  anemones,  130,  136 

sea  cows,  226,  227 

sea  cucumbers,  112 

sea-horse,  167 

sea-lions,  224,  225 

sea  urchins,  110-112 

seals,  224,  225 

Sebaceous  glands,  283,  284 

segments,  126 

semicircular  canals,  310 

sensations,  294,  297,  304-310 

sense  organs,  304-310 

sensory  nerves,  296-298 

septa,  116 

serum,  260,  283 

setae,  115 

seventeen-year  cicada,  35 

sexual  selection,  195,  196 

sharks,  164,  165 


sheep,  220,  223 

shell,  98 

shrews,  216 

shrimps,  90,  91 

silk- worm  moth,  26,  27,  149 

Silurian  period,  349 

sinuses,  88 

siphon,  99,  102,  106 

Siphonaptera,  49 

Siphonophores,  135 

Sirenia,  226 

skates,  164,  165 

skeleton,  188,  287-291 

skin,  277,  279,  283-286 

skull,  1 60,  289 

skunk,  210 

sleep,  303 

sleeping  sickness,  146 

smallpox,  325,  328 

smell,  3,  209,  210,  305 

snails,  98,  103,  104 

snakes,  176 

sneezing,  299 

sodium,  234,  236 

somites,  84 

sow  bugs,  94 

species,  17,  18,  341,  342 

Spencer,  H.,  313 

sperm  cells,  160,  333,  334 

spermaceti,  226 

spermaries,  9,  10 

spermatozoa,  333,  334 

of  earthworm,  118,  140 

of  fishes,  1 60 

of  grasshopper,  10 

sphinx  moths,  27,  28 

spiders,  76-81 

spiracles,  5 

sponges,  130,  138,  139,  140 

Spongilla,  140 

spores,  141,  147,  148,  331 

Sporozoa,  141,  148-150 

sports,  356 

squash  bug,  31 


INDEX 


401 


squid,  106,  107 
squirrels,  216 
starfishes,  108-110 
Stegomyia,  48 
sternum,  188,  274,  290 
stimulants,  256 
sting.  60 
sting-rays,  165 
stirrup,  310 
Stockard,  C.  R.,  383 
stomach,  of  grasshopper,  6 

of  clam,  100,  101 

of  crayfish,  87 

of  man,  248,  249,  254 

of  starfish,  109,  no 
stone  flies,  70,  73 
sturgeon,  166 

subesophageal  ganglia,  in  crayfish, 
88 

in  grasshopper,  8,  9 

of  clam,  99-101 
Sullivan,  Dr.,  313 
sulphur,  234,  236,  238 
sunfish,  158 
suprarenal  bodies,  281 
swimming  bladder,  160 
symbiosis,  133,  366,  367 
sympathetic  system,  296 
synovial  membrane,  287 
systemic  circulation,  263 


Tabanidae,  44 

Tachinidae,  44 

Tania  solium,  127,  128 

tail,  184,  185,  195,  196 

tail  fin,  158 

tapeworm,  126-129 

tarsals,  291 

tarsus,  4 

taste  buds,  305 

tea,  257 

teeth,  177,  247,  248,  346 


Teleostomi,  164,  166 

teleosts,  167 

telson,  84,  85 

tendons,  243,  291,  292 

tentacles,  103,  130,  132,  134,  135 

testes,  9,  10 

Texas  fever,  82,  148,  317 

thoracic  duct,  266 

thorax,  of  crab,  91 

of  crayfish,  84-88 

of  grasshopper,  2,  4 
thyroid  extract,  281 
thyroid  gland,  281 
tibia,  of  grasshopper,  4 

of  man,  290 
ticks,  81,  82,  149 
tigers,  223 

tissues,  240,  241-244 
toads,  169,  171,  173-175 
tobacco,  257,  268,  3i4~3l6 
tonsils,  267 
torpedo,  166 
tortoise,  176,  181,  182 
touch,  3,  304 
toxin,  326 
trachea,  272 
tracheae,  5,  77 
tracheal  gills,  72 
tree  frogs,  174,  175 
Trematodes,  124-126 
Trichina,  122,  123 
Trichinella  spiralis>  122,  123 
trichinosis,  317 
Triton,  170 
trypanosomes,  146 
trypsin,  251 
tsetse-fly,  146 
tube  feet,  108,  109,  112 
tuberculosis,  314,  322-324,  377 
tunicates,  iS^iSS,  334 
Turbellaria,  124 
turtles,  176,  181,  182 
tympanic  membrane,  309 
typhoid  fever,  324-326,  328,  329 


402 


INDEX 


U 

ulna,  290 

Ungulata,  220 

urea,  278 

ureter,  277,  278 

urinary  tubules,  7,  8,  277,  278 

Urodeles,  169 

Ursus  americanus,  18 

Ursus  arctos,  18 

Ursus  horribilis,  18,  224 


vaccination,  328 
vagus  nerve,  300 
valves  of  heart,  7,  88,  262 

of  shell,  98 

of  veins,  265 
variation,  356,  372 
varieties,  17,  356-359 
veins,  5,  262-266 
ventricles,  100,  262 
vermiform  appendix,  250,  344,  345 
vertebrae,  160,  289,  290 
vertebral  column,  160,  289 
Vertebrates,  153-157 
viceroy  butterfly,  23 
villi,  250 

visceral  ganglia,  100 
vision,  3,  307,  308 
vitreous  humor,  307 
vocal  sacs,  171 
Volvox,  332,  333 
vultures,  202 


W 

walking-stick,  16 

Wallace,  A.  R.,  358 

walruses,  224 

warble  flies,  43 

warning  colors,  170,  364 

wasps,  56,  64,  65 

water  fleas,  97 

water  moccasin,  179 

water  scorpion,  33 

water  striders,  34 

wax  glands,  60 

wax  pincers,  59 

web,  77-80 

weevils,  55 

Weismann,  A.,  370 

whalebone,  226 

whales,  225,  226,  346 

Whetham,  385 

whirling  beetles,  54 

White,  A.  D.,  315 

white  corpuscles,  see  Leucocytes 

Wiedersheim,  R.,  346 

windpipe,  272 

winking,  299 

wolves,  223 

worker  bees,  56-62 

worms,  114-121 

wrigglers,  45-48 


yellow  fever,  48 
yellow  jackets,  65 


MAY  2  9  1967 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 


This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


•;; 

OCT    9 

196819 

OCT  2 

/«/»•» 

8  1368 

OCT  2  8 

1368  If 

j/*  y>y%. 

UDV 

OCT  2 

3  -  1969 

0  1969     2 

LD  21-40m-10,'65 
(P7763slO)476 


General  Library 

University  of  California 

Berkeley