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SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
evidently  are  the  rudiments  of  the  adult  armature  (H,  h,  i).  The  ma- 
ture structure  of  the  phallus  (H)  apparently  is  attained  at  the  last 
moult;  it  involves  principally  the  thickening  of  the  dorsal  lobe,  the 
invagination  of  the  upper  surface  of  the  latter,  and  the  development 
of  the  dorsal  armature  characteristic  of  the  species. 
The  adult  modifications  of  the  tettigoniid  phallus  consist  principally 
of  variations  in  the  relative  size  of  the  several  terminal  lobes,  and  in 
the  form  and  development  of  the  armature  of  the  dorsal  lobe.  In 
the  Decticinae,  however,  the  cavity  of  the  dorsal  lobe  becomes  con- 
verted into  a  pocket  by  the  posterior  extension  of  its  anterior  margin, 
which  condition  leads  into  that  characteristic  of  the  Rhaphidophorinae 
(fig.  22  F),  and  finally  to  an  extreme  type  of  modification  that  dis- 
tinguishes the  Gryllidae  from  the  Tettigoniidae, 
Fig.    24. — Tettigonioidea-Tettigoniidae :     external    male   genitalia   of    Micro- 
centrum  retinerz'e  (Burnieister). 
A,  end  of  abdomen,  lateral  view.  B,  phallus,  posterior  \iew.    C,  same,  median 
longitudinal  section. 
For  letter  explanation,  see  fig.  22. 
For  a  concrete  example  of  a  phallic  structure  that  comes  close  to 
the  hypothetical  generalized  structure  shown  at  C  of  figure  22  we 
may  select  the  genus  Microcentrum.  The  phallus  of  M.  retinerve 
(fig.  24  B)  is  a  low,  rounded  organ  with  a  basinlike  cavity  (dc)  in  the 
dorsal  wall,  a  pair  of  folded  lateral  lobes  (//),  and  a  thick,  bifurcate 
ventral  lobe  (vl).  The  phallotreme  (Phtr)  is  a  wide,  transverse  open- 
ing between  the  distal  lip  (g)  of  the  dorsal  lobe  above,  and  the  lateral 
and  ventral  lobes  below.  The  dorsal  cavity  contains  two  large,  oval, 
strongly  convex  protuberances  (h),  transversely  ribbed  on  their 
lateral  surfaces  with  finely  toothed  ridges,  but  there  is  no  other  acces- 
sory armature.  Attached  on  the  inner  surfaces  of  these  dorsal  organs 
are  large  masses  of  muscle  fibers  converging  from  the  lateral  parts 
of  the  base  of  the  phallus.  The  dorsal  and  ventral  retractor  muscles 
(rpd,  rpv)  have  the  typical  arrangement  and  are  inserted  on  the 
phallic  base.    A  median  section  of  the  organ   (C)  shows  clearly  the 
