42q 
of  common  commercial  glue.  As  incubation  advances,  a  small  whitish 
spot  appears  beneath  the  cuticle,  evidently  formed  by  the  excreta  of 
the  embryo.  The  incubation  period  varies  in  the  different  species, 
and  temperature  has  evidently  a  marked  effect  upon  the  development 
of  the  embryo.  These  produce  :  — 
Larvae,  'grass  lice'  or  'seed  ticks!  All  larvae  are  six-legged; 
and  the  sexes  are  not  distinguishable.  On  hatching  from  the  egg 
they  crawl  up  the  stems  of  grasses  and  other  plants,  usually  to  the 
topmost  leaf  or  stem,  congregating  together,  sometimes  in  enormous 
numbers.  The  ‘  clusters  ’  or  '  nests  ’  are  as  a  rule  the  progeny  of  one 
parent.  They  remain  in  such  situations  for  a  host ;  meanwhile  no 
kind  of  food  is  taken  as  a  substitute  for  blood ;  and  they  are  capable 
of  fasting  for  very  long  periods,  though  it  is  highly  probable  that 
nature  provides  them  with  a  store  of  food  which  may  tide  them  over 
the  first  few  weeks.  When  a  host  is  secured  they  take  a  meal  of 
blood,  filling  and  distending  their  bodies  considerably.  The  first 
moult  takes  place  afterwards,  and  the  eight-legged  or  nymphal  stage 
is  reached. 
Nymph  (PI.  XIII,  figs,  i,  2).  In  this  stage  also  there  is  no  sexual 
distinction.  The  animal  has  now  increased  in  size,  though  it  may  be, 
and  often  is,  smaller  than  a  fully  engorged  larva.  Again  the  tick  fills 
itself  to  repletion,  the  body  becoming  greatly  distended  during  the 
process.  Shortly  after  feeding,  the  nymphal  skin  is  cast  and  the 
sexually  mature  stage  is  reached. 
Adult  Tick  (PI.  XIII,  figs.  I,  2).  The  sexually  mature  male  and 
female  are  often  identical  in  size  immediately  after  the  change  from 
nymph  to  adult,  and  females  of  small  size  may  frequently  be  found  in 
coitu  (Mar garopus  annulatus  australis').  Little  change  takes  place 
in  the  male  after  feeding ;  but  the  female  in  filling  her  body  to 
repletion  becomes  enormously  distended,  increasing  in  size  from 
thirty  to  forty  diameters.  She  falls  from  the  host  when  fully 
engorged,  and  after  the  lapse  of  a  few  days  begins  to  lay  her  eggs. 
This  process  is  continued  over  several  days  ;  and  in  the  end  the 
female  dies,  leaving  her  body  attached  to  the  little  mass  of  eggs. 
This  is  briefly  the  metamorphosis  of  the  cattle  ticks,  and  the  cycle  is 
practically  the  same  in  all  other  known  .species  of  this  division  of  the 
Ixodoidea.  In  habits,  however,  they  vary  considerably  :  some  species 
require  but  one  host,  such,  for  instance,  as  the  cattle  tick  of  Jamaica 
