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SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.   96 
arising  posteriorly  on  the  ninth  sternum,  inserted  ventrally  on  the 
phallomere  base  (fig.  13  D)  ;  12,  a  large  bundle  of  fibers  within  the 
left  phallomere  (fig.  13  E),  arising  in  the  base  of  the  appendage  and 
inserted  distally  in  the  lateral  lobe  (g),  giving  independent  movement 
to  the  distal  process  of  the  latter;  jj_,  1/^,  two  small  muscles  within 
the  left  phallomere  (not  shown  in  the  figures). 
The  ventral  phallomere  has  but  one  muscle  attached  upon  it ;  this 
is  a  short  muscle  (fig.  14  B,  i^^  attached  to  the  right  margin  of  the 
IPhm 
vPKm 
Fig.  15. — Blattoidea :  male  and  female  genitalia  of  Pcriplaiwla  americana 
(Linnaeus). 
A,  male  nymph,  31  mm  long,  end  of  abdomen,  ventral  view.  B,  same,  external 
genitalia,  dorsal  view.  C,  genitalia  of  following  nymphal  instar  taken  from 
within  cuticle  of  B.  D,  adult  male,  external  and  part  of  internal  genitalia, 
dorsal  view.  E,  same,  accessory  glands  and  vesiculae  seminales,  ventral  view. 
F,  spermatheca.  G,  spermathecal  aperture  and  surrounding  structures  in  dorsal 
wall  of  female  genital  chamber. 
a,  b,  smaller  and  larger  tubules  of  accessory  glands ;  c,  d,  sclerites  in  dorsal 
wall  of  female  genital  chamber  associated  with  spermathecal  aperture  (Spr)  ; 
Ovp,  base  of  ovipositor ;  Vsm,  vesiculae  seminales.    Other  lettering  as  on  fig.  13. 
ventral  plate  (iv),  which  extends  downward  from  the  right  marginal 
angle  of  the  valvular  plate  (fig.  13  C,  n)  beneath  the  right  phallomere. 
The  external  genitalia  of  Periplaneta  (fig.  15  D)  differ  only  in 
details  from  those  of  Blatta.  The  three  phallomeres  have  essentially 
the  same  structure  and  the  same  relations  to  one  another  in  the  two 
genera,  but  in  minor  characters  they  present  many  differences.  The 
left  phallomere  of  Periplaneta  aniericana  is  somewhat  more  deeply 
sunken  into  its  basal  pouch  (s)  than  in  Blatta  orienlalis,  but  the  right 
phallomere  has  the  same  basal  structure  as  that  of  Blatta,  and  beneath 
