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Fig. 1. 



it 



2. 



3. 

 4. 



5. 



Plate 17. 



PachychaVma acapulcensis . Dermal membrane. Pores and dermal reticulum 



with villi. Surface preparation ; x 70. 



" " Horizontal section, vertical to surface, of macerated 



sponge. Surface of sponge above. A longitudinal 

 skeletal bundle, /. b., is cut transversely. Skeletal 

 network comparatively regular ; s. v., surface 



villi; x20. 



Large radial skeletal fibre ; x 300. 



Small connective ; x 300. 



One of the finest fibres, subdividing a skeletal mesh ; 



a 



a 



u 



a 



« 



a 



x 3 



00. 



6. Petrosia variabilis crassa. Oxeas, with spongin ; x 100. 



7. Petrosia similis densissima. Prom a photograph ; \. 



8. Oceanapia bacillifera. Surface of fistula ; x 100. 



9. Petrosia variabilis crassa. From a photograph ; \. 



10. Petrosia similis densissima. Oxea and flagellated chambers, one of which opens 



. into efferent canal; x 250. 



11. Gellius perforates. End of skeletal oxea, with sigmata; x 450. 



12. Petrosia variabilis crassa. From a photograph ; \. 



13. Pachychalina acapnlcensis. Longitudinal section through macerated conulus. 



An axial bundle of spiculo-fibre gives off, and 

 ultimately divides into, radial fibres ; s. v., surface 

 villi ; x 20. 











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