Plate 16. 



Fig. 1. Poecillastra cribraria. From a section ; c. n\y canal wall. A flagellated chamber 



occupies a thin trabecula. It opens, to the right, by 

 a wide aperture into efferent canal. Its boundary 

 membrane, to the left, is perforated by a single 

 chamber pore. Collar cells extend between boundary 

 membrane and Sollas's membrane ; the latter shown 

 in section and perspective; x 1000. 

 From a photograph ; from the side ; \. 

 From a photograph ; oscular surface ; \. 

 Transverse section through wall of oscular papilla; 

 c. w., wall of axial canal. Above are the surface 

 brushes of small tylotes. Two longitudinal spicular 

 bundles are cut ; x 70. 



« « Spicules ; X 70. 



" " Section vertical to surface of sponge and through a 



mammillar}' protuberance. Beneath superficial layer 

 of small spicules lies layer of more or less tan- 

 gentially arranged tylostyles. Five radial skeletal 

 bundles appear. Main afferent canal in mammillary 

 protuberance connects with a larger internal canal 

 through a chone-like structure. Small subdermal 

 spaces with pore canals are seen, especially in region 

 of mammillary protuberance ; x 10. 

 Pachychalina acapulcensis. Longitudinal section, vertical to surface, of mace- 

 rated sponge. Surface of sponge to the right. A 

 longitudinal skeletal bundle, I. b., appears ; skeletal 

 network in general irregular ; $. v., surface villi ; x 20. 



" " From a photograph ; from the side ; ^. 



2. Polymastia maeandria. 



3. Poecillastra cribraria. 



4. Polymastia maeandria. 



5. 

 6. 



