6  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
attaching  themselves  to  the  secondary  spermatogonia,  become  the 
c}-st  cells  (CstCl)  that  give  rise  to  the  sperm  cysts.  The  encysted 
secondary  spermatogonia  by  subsequent  divisions  produce  the  cell 
groups  that  eventually  form  the  spermatocytes  and  spermatozoa.  The 
formation  of  the  cysts  from  mesoderm  cells,  as  described  by  Nelsen, 
seems  much,  more  reasonable  than  the  idea  that  the  cyst  cells  are 
derived  from  the  spermatogonia,  as  some  writers  have  claimed.  The 
cyst  cells  of  the  testis  are  thus  seen  to  be  entirely  analogous  in  their 
origin  to  the  follicle  cells  of  the  ovary.  During  the  formation  of  the 
cysts  the  sperm  tubes  increase  in  size,  and  the  interstices  between 
the  cysts  become  occupied  by  a  continuously  growing  interfollicular 
framework  of  connective  tissue  cells  derived  mostly  from  the  germinal 
center.  A  central  core  of  cells  also  is  produced  from  the  same  source. 
Since  the  cysts  first  formed  lie  between  the  apical  complex  and  the 
rudiment  of  the  outlet  duct,  these  cysts  remain  in  the  neighborhood 
of  the  duct  as  younger  ones  are  formed  in  the  upper  part  of  the  tube, 
which  later  elongates  in  the  apical  direction  to  form  a  zone  of  growth 
to  accommodate  the  increasing  number  of  cysts. 
Finally,  there  is  formed  from  the  ventral  strand  and  the  germinal 
center  beneath  the  sperm  tubes  the  gonadial  part  of  the  vas  deferens, 
which  is  continuous  with  a  cell  strand  proceeding  posteriorly  that 
becomes  the  free  part  of  the  duct.  The  lumen  is  formed  as  an 
internal  cleavage  space  between  the  cells  of  the  strand.  The  individual 
ducts  of  the  sperm  tubes,  or  vasa  efferentia,  which  are  connected  with 
the  vas  deferens,  Nelsen  says,  do  not  acquire  distinct  lumina  until 
just  before  the  last  moult.  The  mature  testis  of  Melanoplus  differen- 
tialis,  according  to  Nelsen,  includes  about  i88  sperm  tubes. 
The  mature  testes  of  the  Orthoptera  in  general  vary  in  size  and 
shape  according  to  the  number,  form,  and  arrangement  of  the  sperm 
tubes.  In  the  more  generalized  condition  the  testicular  tubes  are  small 
pear-shaped  or  oval  bodies  arranged  in  series  on  the  gonadial  parts 
of  the  ducts  (figs.  7  B,  11  A,  B,  Tcs)  ;  in  Blattella  (fig.  16  A)  each 
organ  is  reduced  to  four  globular  bodies  on  the  end  of  the  duct. 
Generally,  however,  the  testis  is  a  large  oval  compact  mass  of  elongate 
tubules  enveloped  in  a  common  peritoneal  sheath  (figs.  9  A,  20  A. 
34  A,  39  A).  An  exceptional  condition  occurs  in  some  of  the  Phas- 
matidae,  in  which  the  testes  are  long  cylindrical  organs  having  no 
subdivision  into  sperm  tubes  (fig.  7  A,  Tes). 
The  male  genital  ducts. — The  embryonic  vasa  def  erentia  of  Orthop- 
tera (fig.  2  A,  Vd)  end  posteriorly  with  hollow  terminal  enlargements, 
or  ampullae  {Amp),  inserted  into  the  appendage  rudiments  of  the 
tenth  abdominal  somite  (XApd) .  This  condition  has  long  been  known 
