398 WILSON. 



EXPLANATION OF PLATE XXL 

 ( Tedania Brn€t'i.) 



Fig. 75. Section of gemmule, in which the ectoderm layer is clearly differen- 

 tiated. D.4. 



Fig. 76'. Part of Fig. 76. D.4. 



Fig. 78. Longitudinal section through unpigmented pole of swimming larva, 

 shortly after birth. D.4. 



Fig. 79. Surface view of larva just born. A. 4. 



Fig. 80. Surface view of older larva — unpigmented "plug" now conspicu- 

 ous. A.4. 



Fig. 81. Longitudinal section through swimming larva, a day old. C.4. 



Fig. 82. Attached larva with spicular pole pulled in. A. 4. 



Fig. 83. Vertical section through sponge just attached. Ciliated ectoderm 

 entirely metamorphosed, unpigmented pole still recognizable. C.4. 



Fig. 84. Surface view of recently attached sponge — spicular pole lost. A.4. 



Fig. 85. Surface view of sponge just attached — shows how spicular pole 

 loses its identity — spicules are being distributed to various parts of sponge. A. 4. 



Fig. 86. Surface view. Sponge is solid, and margin is thrown into irregular 

 lobes (fir.st stage in formation of ectodermal membrane). A.4. 



Fig. 87. Part of periphery of preceding figure. D.4. 



Fig. 89. Part of periphery of Fig. 88. D.4. 



