NO.    5      MALE  GENITALIA  OF  ORTHOPTEROID  INSECTS — SNODGRASS 
Fig.  I. — Development  of  the  testis  of  Mclanoplus  differenfialis  (Thomas). 
(From  Nelsen,  1931,  1934.) 
A,  an  embryo  at  age  when  the  germ  cells  are  first  distinguishable  as  such 
lying  along  sides  of  ectoderm  of  abdomen.  B,  transverse  section  of  unseg- 
mented  part  of  abdomen  at  stage  of  fig.  A,  showing  masses  of  germ  cells 
(GCls)  proximal  to  amniotic  folds  (Am)  at  sides  of  abdominal  ectoderm 
(Ecd).  C,  transverse  section  of  lateral  half  of  germ  band  at  later  stage,  with 
germ  cells  folded  inward  upon  upper  end  of  mesoderm.  D,  still  later  stage, 
germ  cells  now  transferred  to  splanchnic  wall  of  mesoderm.  E,  transverse 
section  of  testis  just  after  revolution  of  embryo,  showing  group  of  germ  cells 
(GCls)  and  undifferentiated  mesoderm  cells  (MsdCIs)  in  germinal  area  of 
gonad,  with  dorsal  strand  of  mesoderm  cells  above  (DStr)  and  ventral  strand 
(VStr)  below,  the  whole  surrounded  by  a  mesodermal  epithelial  sheath  (ESh) 
continuous  with  a  body  of  fat  tissue  (Ft)  below.  F,  transverse  section  of  testis 
near  close  of  first  postembryonic  instar,  showing  rudiments  of  sperm  tubes 
(ST),  each  containing  an  apical  cell  (ApCl)  surrounded  by  primary  spermato- 
gonia, with  vasa  efferentia  (Vc)  forming  from  germinal  center  (GCn).  G, 
section  of  young  sperm  tube  during  latter  part  of  second  instar,  with  apical 
complex  (ApCmplx)  in  its  distal  end,  and  encysting  spermatogonia  (Spg")  in 
its  proximal  part. 
Am,  amnion ;  ApCI,  apical  cell ;  ApCmplx,  apical  complex ;  Coel,  coelomic 
cavity ;  CpslCI,  capsular  cell ;  CstCI,  cyst  cell ;  DStr,  dorsal  strand ;  Ecd,  ecto- 
derm ;  ESh,  epithelial  sheath  of  testis ;  Ft,  body  of  fat  tissue ;  GCls,  germ  cells ; 
GCn,  germinal  center;  Msd,  mesoderm;  MdsCls,  undifferentiated  mesodermal 
cells  of  gonad ;  Spg' ,  primary  spermatogonia :  Spg" ,  secondary  spermatogonia ; 
ST,  rudiments  of  sperm  tubes  (testicular  "follicles")  ;  Ve,  vas  efferens ;  VStr, 
ventral  strand. 
