8  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
would  suggest,  the  primitive  genital  ducts  of  insects  are  then  quite  com- 
parable with  the  outlet  ducts  of  Onychophora  and  of  those  arthropods 
in  which  they  are  known  to  be  of  coelomic  origin.  The  lumen  of  the 
gonad  and  of  the  definitive  lateral  genital  duct  of  insects  and  of  some 
other  arthropods  appears  to  be  a  secondary  cleavage  space  formed  in 
the  originally  solid  genital  ridge.  However,  the  observation  of  Hey- 
mons  (1892)  that  the  embryonic  germ  cells  of  Blat fella  are  overgrown 
by  folds  of  the  splanchnic  mesoderm,  might  be  interpreted  as  evi- 
dence of  the  closure  of  a  dorsal  gohadial  compartment  of  the  coelome, 
and  thus  give  the  insect  gonad  the  same  morphological  status  as 
that  of  Onychophora  and  Chilopoda  (see  Snodgrass,  1936,  pp.  7-12). 
The  terminations  of  the  embryonic  genital  ducts  of  the  male  in  the 
appendage  rudiments  of  the  tenth  abdominal  segment  (fig.  2  A) 
would  seem  to  imply  that  the  primitive  ducts,  represented  by  the 
coelomic  ampullae,  opened  on  the  bases  of  these  appendages  when 
the  latter  had  a  more  leglike  form.  The  gonopores  have  a  similar 
position  in  many  other  arthropods,  though  on  dififerent  pairs  of  ap- 
pendages. It  might  be  assumed  also  that  the  ducts  discharged  through 
a  pair  of  papillae  or  short  tubular  penes  arising  from  the  appendage 
bases,  though  such  organs  are  not  reproduced  in  the  embryo ;  but  it 
seems  improbable  that  the  appendages  themselves  containing  the  duct 
exits  ever  formed  an  intromittent  organ,  since  in  other  arthropods  the 
intromittent  organs,  if  present,  are  formed  from  neighboring  ap- 
pendages that  have  no  direct  relation  to  the  genital  ducts. 
As  the  development  of  the  male  exit  system  of  the  Orthoptera 
progresses  toward  the  mature  condition,  the  appendage  rudiments  of 
the  tenth  abdominal  segment  shift  toward  the  median  line  (fig.  2  B), 
but  the  enlarging  ampullae  (Amp)  leave  the  appendages  and  inde- 
pendentl}'  migrate  forward  and  mesally  into  the  posterior  part  of  the 
ninth  abdominal  segment.  Here  the  ampullae  unite  with  each  other  to 
form  a  bilobed  mesodermal  vesicle  into  which  open  the  two  vasa 
deferentia  (C,  Amp).  At  the  same  time  a  median,  tubular  ingrowth 
of  the  ectoderm  has  formed  between  the  ninth  and  tenth  segments, 
which  is  the  primary  ejaculatory  duct  (Dej).  The  ectodermal  duct 
unites  with  the  mesodermal  vesicle,  and  the  lumina  of  the  two  organs 
eventually  become  continuous.  The  definitive  median  genital  exit 
passage  in  the  Orthoptera,  commonly  called  the  "  ductus  ejacula- 
torius  ",  is  therefore  a  composite  structure  formed  of  a  posterior 
ectodermal  part,  and  an  anterior  mesodermal  part  (D,  Dej,  Amp). 
The  outgrowth  of  numerous  vesicular  or  tubular  diverticula  from 
the  ampullar  part  of  the  definitive  ductus  ejaculatorius  is  a  feature 
characteristic  of  all  the  true  Orthoptera  and  of  most  of  the  orthop- 
