2  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
unity  of  these  forms  is  attested  in  the  structure  of  the  male  repro- 
ductive system  by  the  compounding  of  the  so-called  accessory  genital 
glands  that  appear,  in  the  adult  condition,  to  arise  from  the  inner  end 
of  the  ductus  ejaculatorius,  but  which  in  their  development  are  out- 
growths of  the  mesodermal  coelomic  ampullae  into  which  the  vasa 
deferentia  discharge.  Qosely  associated  with  the  true  Orthoptera  by 
the  same  feature  of  the  male  genitalia  are  the  Termitidae,  Embiidae, 
Grylloblattidae,  Phasmatidae,  and  probably  the  Zorotypidae.  On  the 
other  hand,  the  Plecoptera  and  the  Dermaptera  would  appear  to  be 
distinct  orders  having  no  close  relationship  with  the  Orthoptera,  since 
in  each  of  these  groups  the  male  reproductive  system  is  specialized  in 
its  own  way.  and  shows  none  of  the  features  characteristic  of  the 
orthopteroid  insects.  Concerning  Dermaptera,  Favrelle  (1934)  says, 
not  only  the  structure  of  their  reproductive  organs,  but  also  the 
cytology  of  their  spermatogenesis  shows  that  they  are  entirely  dis- 
tinct from  Orthoptera. 
Development  of  the  male  gonads. — The  primary  germ  cells  of 
Orthoptera,  so  far  as  their  history  is  known,  are  differentiated  from 
the  somatic  cells  at  a  relatively  late  stage  of  development  as  compared 
with  those  of  insects  in  which  they  appear  at  the  time  of  blastoderm 
formation.  In  Blafta,  Blattella,  Gryllus,  and  Melanoplus  the  germ 
cells  have  been  first  recognized  as  such  after  the  differentiation  of  the 
inner  germ  layer,  but  before  the  formation  of  the  coelomic  sacs  (Hey- 
mons,  1895  ;  Nelsen,  1934),  in  Conocephalits  and  Locusta  not  until  the 
coelomic  cavities  have  been  formed  in  the  mesoderm  (Wheeler,  1893  ; 
Roonwal,  1937).  The  germ  cells  of  Melanoplus  differentialis,  ac- 
cording to  Nelsen  (1934),  are  first  distinguishable  from  the  ectoderm 
of  the  germ  band  when  metamerism  is  about  to  begin  in  the  abdomen  ; 
they  now  appear  as  bands  of  weakly  staining  cells  bordering  the 
abdomen  (fig.  i  A,  GCls)  from  the  region  of  the  first  to  that  of  the 
ninth  prospective  somite,  and  are  seen  in  sections  (B,  GCls)  as 
masses  of  cells  at  the  sides  of  the  abdominal  ectoderm  projecting 
laterad  of  the  bases  of  the  amniotic  folds  (Am).  The  mesoderm 
rudiment  (Msd)  has  already  been  formed  as  a  solid  band  of  cells 
lying  above  the  midline  of  the  ectoderm.  During  the  subsequent 
growth  of  the  embryo  the  mesoderm  spreads  laterally  to  the  edges  of 
the  ectoderm  (C),  and  the  germ  cell  bands  are  now  folded  inward 
upon  the  mesoderm.  When  the  coelomic  sacs  are  later  formed  (D, 
Coel),  the  germ  cells  (GCls)  have  come  to  lie  on  their  dorsal  walls, 
and  from  this  position  they  soon  invade  the  mesoderm  and  inter- 
mingle with  the  mesoderm  cells  in  the  upper  parts  of  the  splanchnic 
