AND  PHYSIOLOGY  OF  THE  SPONGIAD^. 
331 
Fig.  20.  Third  stage  of  development  of  a birotulate  spiculum  from  the  gemmule  of 
Spongilla plumosa,  Caetee,  x660  linear:  page  317. 
Fig.  21.  Adult  eecuevo-de]s:tate  bieotulate  spiculum,  shaft  entirely  spined,  from  the 
gemmule  of  Spongilla plmnosa,  Caetee,  x660  linear:  page  318. 
Fig.  22.  A view  of  the  inner  surface  of  one  of  the  rotulsB  of  the  spiculum  represented 
by  fig.  21,  showing  the  amount  and  irregularity  of  the  dentation  of  its  margin, 
X660  linear:  page  318. 
Fig.  23.  Bieotulate,  maegins  of  the  eotula:  ehtiee,  from  Spongilla  gregarea,  Bo  wee- 
bane,  MS.  A side  view  of  an  averaged-sized  specimen,  xHOO  linear:  page 
317. 
Fig.  24.  A view  of  the  external  surface  of  one  of  the  rotulse  of  the  same  form  of  spicu- 
lum as  that  represented  by  fig.  23,  xHOO  linear:  page  317. 
Fig.  25.  A young  imperfectly  developed  spiculum  of  the  same  description  as  represented 
by  fig.  23,  xllOO  linear:  page  317. 
Fig.  26.  A spiculum  of  the  same  description  as  represented  by  fig.  23,  developed  to  a 
greater  extent  than  usual,  x660  linear:  page  317. 
Fig.  27.  Bieotulate,  eotula:  ieeegulaely  and  deeply  dentate,  from  Spongilla  fluvia- 
tilis,  Johnston,  x660  linear:  page  317. 
Fig.  28.  A view  of  the  external  surface  of  one  of  the  rotulse  of  the  same  description  of 
spiculum  represented  by  fig.  27,  x660  linear:  page  317. 
Fig.  29.  Bieotulate,  eotula:  ieeegulaely  and  deeply  dentate,  shaft  medially  spined, 
from  Spongilla  Meyeni^  Caetee,  x660  linear:  page  318. 
Fig.  30.  Multihamate  bieotulate,  from  the  gemmules  of  Spongilla  recurvata^  Bowee- 
BANK,  MS.,  x660  linear:  page  318. 
Fig.  31.  Inequi-bieotulate,  from  the  gemmule  of  Spongilla  paulula,  Boweebank,  MS., 
x660  linear:  page  318. 
Fig.  32.  View  of  the  inner  surface  of  a large  rotula  of  an  inequi-birotulate  spiculum 
from  Spongilla  paidula,  showing  the  radiating  canals,  xl060  linear:  page 
318. 
Fig.  33.  Boletifoem,  from  gemmule  of  Spongilla  Boweebank,  MS.,  x660 
linear:  page  319. 
Fig.  34.  Boletifoem,  slendee,  from  the  gemmule  of  Spongilla  recurvata,  Boweebank, 
MS.,  X 660  linear:  page  319. 
Fig.  35.  View  of  the  inner  surface  of  a rotula  of  a slender  boletiform  spiculum  from 
Spongilla  recurmta^  Boweebank,  MS.,  x660  linear:  page  319. 
Fig.  36.  Umbonato-scutulate,  from  Spongilla  Brownii,  Boweebank,  MS.  View  of 
external  surface,  x660  linear:  page  319. 
Fig.  37.  Umbonato-scutulate,  from  Spongilla  Brownii,  Boweebank,  MS.  Side  view, 
showing  length  and  form  of  the  umbo,  X 660  linear:  page  319. 
Fig.  38.  Inequi-teieotulate.  Sponge  unknown,  x660  linear:  page  319. 
Fig.  39.  Inequi-fusifoemi-aceeate,  from  the  gemmule  of  Tethea  cranium,  Johnston, 
Xl30  linear:  page  320. 
