{Margaropus  annulatus  auslraLis)  ;  others  have  two  hosts ;  and,  like 
the  silver  tick  (Amdlyonmia  cajanense),  others  again  require  three 
hosts.  With  the  first  named,  all  the  meals  and  both  moults  are 
effected  on  the  same  animal.  The  second  kind  moults  on  the  first 
host  as  a  larva,  and  leaves  the  host  as  a  fully  engorged  nymph,  moults 
for  the  second  time  on  the  ground,  and  when  sexually  mature  seeks 
another  host.  The  last  named  undergoes  both  moults  upon  the 
ground  ;  the  first  as  a  larva,  the  second  as  a  nymph,  so  that  in  this 
way  three  different  hosts  are  required.  With  such  ticks  as  these, 
there  are  three  non-parasitic  periods,  and  for  this  reason  the  complete 
life-cycle  must  often  be  greatly  prolonged  in  the  absence  of  a  host, 
and  the  probabilities  are  that  large  numbers  perish  for  the  want  of 
food.  With  the  fowl  tick  {Argas  persicus)  the  parasitic  periods,  with 
the  exception  of  that  of  the  larva,  are  all  of  short  duration,  and  the 
female  may  live  for  a  very  long  period  producing  many  batches  of 
eggs  at  irregular  intervals. 
STRUCTURAL  CHARACTERS  OF  TICKS 
These  animals  are  divided  into  two  families:  i,  the  Argasidae  ; 
2,  the  Ixodidae.  There  are  representatives  of  both  groups  in 
Jamaica,  though  the  prevailing  forms  belong  to  the  second  division. 
It  IS  not  intended  to  enter  fully  into  the  structural  details,  but  to 
point  out  some  of  their  more  salient  characteristics. 
Argasidae.  Distinguished  chiefly  by  the  absence  of  a  scutum  or 
shield  on  the  upper  surface  of  the  body.  The  fowl  tick  {Argas 
persicus^  is  the  only  representative  of  this  group  hitherto  found  in 
Jamaica. 
Ixodidae.  All  the  members  of  this  family  are  provided  with  a 
shield  or  scutum  (fig.  i)  and  the  mouth  parts  (capitulum,  figs,  i,  2) 
project  in  front  of  the  body.  The  males  differ  from  the  females  in 
having  nearly  the  whole  of  the  upper  parts  of  the  body  covered  with  a 
shield  ;  in  the  females  this  is  not  so  ;  in  some  species  the  shield  is 
extremely  small,  especially  so  in  the  genus  Margaropus,  in  which  it 
is  scarcely  visible  in  the  engorged  female.  With  the  exception  of 
Argas  persicus  all  the  other  known  species  found  in  Jamaica  belong 
to  this  group.  The  structural  details  of  one  of  the  members  of  this 
family  {Amhlyomma  cajanense)  are  shown  in  the  accompanying 
