400 



WILSON. 



EXPLANATION OF PLATE XXIL 

 (Tedania Brucei.') 



Fig. 88. Surface view. Cavities have formed in sponge, and mesoderm no 

 longer extends to edge of body. A.4. 



Fig. 90. Surface view — ectodermal membrane well developed e.xcept in one 

 region — central canal. A.4. 



Fig. 91. Surface view — sponge of very irregular shape, which is, however, 

 common, i-inch objective. 



Fig. 92. Vertical section of recently attached sponge — no ectodermal mem- 

 brane. C.4. 



Fig. 93. Vertical section of sponge with developed canal system. C.4. 



Fig. 94. Peripheral region of same sponge — double nature of ectodermal 

 membrane. D.4. 



{ Tt'danionc fot'tida.) 



Fig. 95. Section through oscular papilla. X 4. 

 Fig. 96. Vertical section through body of sponge. X 3. 

 Fig. 97. Vertical section of adult — canal system and arrangement of skeleton. 

 3-inch objective. 



Fig. 98. Section of adult — disposition of ultimate branches of canals. D.4. 

 Fig. ioi. Modified oxea — very common form of spicule. 



