42  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
The  lypt:  of  ])liallic  structure  perlaiuinj^  to  tlie  P>lattinae  cousists 
of  a  highly  integrated  complex  of  parts  belonging  to  three  phallic 
organs,  which  apjiear  in  the  nymph  as  three  simple  lobes  of  the  genital 
chamber  wall  immediately  surrounding  the  gonopore.  This  type  of 
structure  is  ilkistrated  in  the  following  descriptions  of  Blatta  orient  alls 
and  Periplaneta  americana. 
The  abdomen  of  an  adult  male  of  Blatta  oriciitalis  (fig.  12  A)  ends 
with  the  broadly  truncate  and  somewhat  emarginate  tenth  tergum 
above  (XT),  and  the  large  rounded  ninth  sternum  below  (B,  IXS), 
which  latter  bears  the  elongate  styli  (Sty).  Beneath  the  margin  of 
the  tenth  tergum  are  the  paraprocts  (C,  Papf),  and  a  small  membra- 
nous area  or  lobe  (Eppt)  representing  the  epiproct.  Between  the 
paraprocts  and  the  ninth  sternum  is  the  mouth  of  a  deep  cavity,  the 
genital  chamber  (GC),  containing  the  phallic  organs.  In  a  nymphal 
male  the  abdomen  is  relatively  short  and  broad  (D)  and  the  small 
ninth  sternum  does  not  completely  conceal  the  paraprocts.  If  the 
genital  chamber  of  a  median-sized  nymph  is  opened  (E)  there  will  be 
seen  three  small,  soft  lobes  projecting  from  its  anterior  wall  around 
the  opening  of  the  ejaculatory  duct  (Dej).  These  lobes  are  the  left 
phallomere  (IPhm) ,  the  right  phallomere  {rPhm),  and  the  ventral 
phallomere  {vPhm).  In  a  later  nymphal  instar  (F)  the  phallomeres 
have  increased  in  size  and  the  lateral  ones  show  the  development  of 
accessory  lobes.  The  ejaculatory  duct  {Dej)  opens  above  the  base  of 
the  broad  ventral  phallomere.  From  this  simple  beginning  are  evolved 
the  extraordinarily  complex  genital  organs  of  the  adult  roach. 
The  mature  phallomeres  of  Blatta  orieiitalis,  as  seen  from  above 
in  their  usual  position  within  the  genital  chamber,  are  shown  at  A  of 
figure  13.  The  right  phallomere  (rPJim)  has  taken  a  more  median 
position  above  the  genital  opening,  the  elaborately  subdivided  left 
phallomere  (IPhm)  forms  a  group  of  lobes  and  horny  processes  on 
the  right,  and  the  broad  ventral  phallomere  (vPhni)  projects  to  the 
right  from  beneath  the  other  two.  The  base  of  the  right  phallomere 
is  produced  forward  on  the  right  into  a  deep  pocket  (y)  oi  the  genital 
chamber  wall,  and  the  base  of  the  left  phallomere  is  sunken  into  a 
similar  but  shallower  pocket  on  the  left  (s).  Beneath  the  right  phal- 
lomere is  a  deep,  transverse,  oval  cavity  (C)  within  a  large,  strongly 
convex  capsular  sclerite  (A,  B,  C,  m),  which  is  normally  closed  from 
below  by  a  flat  valvular  sclerite  (C,  n).  Between  the  dorsal  right 
phallomere  and  the  left  phallomere  is  an  obliquely  transverse  fold, 
which,  beginning  on  the  left  (A,  fd),  goes  downward  to  the  right 
and  expands  on  the  dorsal  surface  of  the  ventral  phallomere  (fig.  14  B, 
fd).  Within  the  lower  end  of  this  fold  above  the  base  of  the  ventral 
