The  figures  which  follow  (from  339  to  345)  are  represen-
tations, of  the  natural  size,  of  the  dorsal  vessel  of  the  Sphinx
ligustriy  or  Privet  Hawk-moth,  which  has  been  dissected  in  its
three  different  stages,  with  great  care,  by  Mr.  Newport,  from


<  IBCULATIUN   IN   INSECTS.  '245

-  The  discovery  of  the  circulation  in  insects,  and
of  its  varying  energy  at  different   periods  of

whose  drawings  these  figures  liave  been  engraved,  and  to  whom
I  am  indebted  also  for  the  description  which  follows : —

The  dorsal  vessel  of  this  insect  is  an  elongated  and  gradually
tapering  vessel,  extending  from  the  hinder  part  of  the  alxlomeo,
along  the  back,  towards  the  head ;  and  furnished  with  valves.
K


m


Mh  Milk  ..^ma^^^^^


cocrespond  very  nearly  in  their  situation  to  the  incisions  of
i^ody.  During  the  changes  of  the  insect  from  the  larva  to  the
mago  stale,  it  undergoes  a  slight  modification  of  fonn.  In
every  stale  il  may  be  distinguished  into  tno  portions,  a  (kr«ai  and
an  aortal.  The  dorsal  portion,  which  is  the  one  in  which  a  pulsa-
tion is  chiefly  observable,  is  furnished  with  distinct  valves,  is  at-
tached along  the  dorsal  part  of  the  body  by  lateral  muscles,  and
has  vessels  which  ent«r  it  laterally,  pouring  into  it  the  circulating
fluid,  which  is  returning  from  the  sides  and  inferior  portions  of
ibfi  body.  In  the  caterpillar,  this  portion  of  the  dorsal  vessel  ex-
tends from  ihe  twelfth  lo  the  anterior  part  of  the  fifth  segment.
It  is  furnished  with  eight  double  valves,  which  are  formed  as
Mr.  Bowerbank  has  correctly  described  them  in  the  Ephemera
mar^nata;  namely,  the  upper  valve  "  by  a  reflecting  inwards


246  THE  VITAL  FUNCTIONS.
