Plate 16. 



Fig. 1. 



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Poecillastra cribraria. From a section ; c. w., 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. 



2. Polymastia maeandria. From a photograph ; from the side ; |. 



3. Poecillastra cribraria. From a photograph ; oscular surface ; \. 



4. Polymastia maeandria. 



Transverse section through wall of oscular papilla; 



wall of axial canal. Above are the surface 



c. w. 



brushes of small tylotes. Two longitudinal spicular 

 bundles are cut ; x 70. 



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5. 

 6. 



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a 



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Spicules; x 70. 



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 subdermal 



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, I. &., appears ; skeletal 

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



From a photograph ; from the side ; -|-. 



" 8. 



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