Plate 16. 



Polymastia maeandria. 

 Poecillastra cribruria. 

 Polymastia maeandria. 



Fig. 1. Poecillastra cribraria. From a section ; c. ?<'., canal wall. A flagellated chamber 



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

 a wide aperture into efferent canal. Its bounchiry 

 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; 

 f. n\, wall of axial canal. Above are the surface 

 brushes of small tylotes. Two longitudinal spicular 

 bundles are cut ; x 70. 



5. " « Spicules ; x 70. 



6. " " Section vertical to surface of sponge and through a 



mam miliary 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 subderinal 

 spaces with pore canals are seen, especially in region 

 of mammillary protuberance ; x 10. 



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

 rated sponge. Surface of sponge to the right. A 

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

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



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



