Plate 15. 



Fig. 1. Poecillastra cribraria. From a radial vertical section, showing oscular surface. 



Parenchyma with abundant conspicuous granular cells ; 

 xlOO. 

 " 2. " " From a section. Posterior wall of flagellated chamber 



showing several chamber-pores. Boundary membrane 

 of chamber is a thin, finely granular membrane show- 

 ing no cell-boundaries. On it rest the cell-bodies 

 (wide apart) of the collar cells, appearing as dense 

 angular masses, each enclosing a nucleus ; x 1000. 



Oscular surface ; surface preparation ; x 30. 



Pore surface ; " " x 30. 



From a section. A flagellated chamber opens to the 

 right into its efferent canaliculus ; afferent canaliculus 

 abutting against boundary membrane of chamber, to 

 left; Sullas's membrane in perspective. Two other 

 flagellated chambers are cut. In right lower corner, 

 a part of an ovum {nv.) with part of its nucleus is 

 included; x 1000. 

 G. " " From a section vertical to surface of sponge, showing 



choanosome with a number of small efferent canals 

 cut lengthwise; some canals leading in the section to 

 the flagellated chambers from which they start. The 

 small efferent canals unite to form the two larger 

 canals of the figure. These unite in the next section. 

 Other canals, some cut transversely, appear ; some 

 of them, afferent canals; c.iv., canal wall ; x 70. 



7. " " Surface ; from a photograph ; \. 



8. " " Microrhabds ; x 250. 



9. " " Vertical section showing ectosome and adjoining choano- 

 some. Two radial pore canals open, each into a sub- 

 dermal chamber ; x 30. 



10. " « Oxyasters ; x 600. 



11. " " Surface, showing arrangement of pores and cladomes of 



the triaenes. Microrhabds with which dermal mem- 

 brane is densely filled, and which extend over the 

 cladomes as well as throughout the pore areas, are 

 omitted. Surface preparation ; x 30. 



