PLATE IV. 



PAGE 



The soft parts of Euplectella aspergillum, Owen, . . 64 



Fig. 1. Part of the outer surface of the tube- wall, from a specimen preserved in 

 absolute alcohol ; natural size. 



Fig. 2. Part of the inner surface of the tube-wall of the same specimen ; natural 

 size. 



Fig. 3. Transverse section of a ridge, with part of the tube-wall of the same 

 sponge. The section corresponds to one of the larger efferent 

 openings of the exhalent canal system (combination figure) ; x 16. 



Fig. 4. Outer portion of a thin section, perpendicular to the outer surface, through 

 the side wall of a ridge ; x 150. 



Fig. 5. External view of a small piece of the outer membrane from the side wall 

 of a ridge ; x 400. 



Fig. 6. Transverse section of a layer of ciliated chambers with a sperm-mass ; 

 x400. 



Fig. 7. Part of the wall of a ciliated chamber ; x 600. 



Fig. 8. A small portion of the network of the efferent lacunar system of a ridge ; 

 X 600. 



