PLATE 6. 



Sidonops oxyastra Lendenfeld. 

 Figures 1-23. 



1, 2. — Parts of sections showing strands of spindle-cells traversing the choanosome; haematoxylin, 

 aniline-blue: 



1, magnified 400; phot., Zeiss, apochr. 4, compens. oc. 6; 



2, magnified 200; phot., Zeiss, apochr. 8, compens. oc. 6. 



3. — Part of section through the choanosome showing canal-end branches and flagellate chambers; 



haematoxylin, aniline-blue; magnified 400; phot. Zeiss, apochr. 4, compens. oc. 6. 



4. — A lobe of the sponges showing a group of uniporal efferents; magnified 3; phot., Zeiss, anastig. 167. 



5. — View of the largest specimen, attached to a flat stone; reduced 1 :0.63; phot., Zeiss, anastig. 480 / 



412 



6-13. — Plagiotriaenes ; magnified 43; phot., Zeiss, achr. aa, compens. oc. 6: 



6, with all the clades shortened and blunt; 



7, with one reduced, blunt clade; 

 8-13, with pointed clades; 



7, 8, 10, with unequal clades; 

 6, 9, 11-13, with equal clades. 

 14. — Two large choanosomal amphioxes from a spicule-preparation ; magnified 43; phot. Zeiss, achr. 



aa, compens. oc. 6. 

 15-18. — Cladomes of minute dermal anaclades; magnified 300: 

 15, 17, 18, phot., Zeiss, apochr. 8, compens. oc. 12; 

 19 phot., Zeiss, apochr. 4, compens. oc. 6; 



15, a regular mesanatriaene; 



16, an irregular mesanatriaene; 



17, 18, more or less irregular anatriaenes. 



19, 20. — Parts of a radial section through a region of the cortex bearing afferent pores: 



19, magnified 300; phot. Zeiss, apochr. 4, compens. oc. 6; 



20, magnified 200; phot. Zeiss, apochr. 8, compens. oc. 6; 



a, monaxonid sponge attached to this part of the surface of the Sidonops; b, minute dermal 

 anaclades of the Sidonops; c, dermal membrane of the Sidonops occupied by masses of 

 small oxysphaerasters (oxyasters). 



21. — Part of a radial section through a region of the cortex bearing efferent pores, showing the dermal 



layer occupied by dense masses of minute dermal rhabds; magnified 200; phot. Zeiss, apochr. 8, 

 compens. oc. 6. 



22. — A minute dermal rhabd; magnified 300; phot. Zeiss, apochr. 4, compens. oc. 6. 



23. — Part of a radial section through a region of the cortex bearing afferent pores, showing numerous 



minute protruding dermal anaclades; magnified 50; phot., Zeiss, achr. aa, compens. oc. 6. 



