258 On the Sponge-Fauna of Norway. 



i, incurrent tube ; e, excurrent tube ; c, concentric canals ; 

 e', a deeper-seated excurrent tube ; i', a deeper-seated incurrent 

 tube ( X 24). 

 Fig. 6 a. Ciliated chambers in longitudinal optical section and from a 

 view face on ( X 435). 



Plate XI. 



Fig. 7. Section through the cortex, showing the structure of the chone 

 and the ligamentous connexions of the globates (c) : /, the 

 fibrous layer (X 104). 



Figs. 8, 9. Porrecto- and recurvo-ternate spicules with long slender 

 shafts. 



Fig. 10. Fusiform acerate spicule. 



Fig. 11. Bifurcated ternate spicule. 



Fig. 12. Globate spicule. 



Fig. 13. Small acerate from the cortex. 



Fig. 14. Small ternate from the upper angle of one of the crypts. 

 Figs. 8-14 all magnified 21 diameters. 



Fig. 15. Fusiform fibres of different kinds : g, granular mark-cell from 

 pillar of a crypt ; v, vacuolated cell from same place ; s, axial 

 thread of a muscle-fibre from a sphincter ; /, fibres from the 

 wall of one of the large excurrent tubes (X 435). 



Fig. 16. Porrecto-ternate spicule (X 21). 



Fig. 17. Cylindro-stellate from the mark (X 315). 



Fig. 18. Globate spicide, showing the nucleus at one side (X 435). 



Fig. 19. Young globate as seen in Canada balsam (X 435). 



Fig. 20. Stellate with sharp-pointed rays, from the mark (X 315). 



Fig. 21. Cylindro-stellate from the epidermis (X 435). 



Fig. 22. Stellate-cell with its contained spicule (X 435). 



Fig. 23. Section of a chone with widely opened sphincter (x 30). 



Plate XII. 



Vacuolate connective tissue from the dermis (X 435). 

 An unaltered mark-cell occurring associated with vacuolated 

 connective-tissue cells : a-e, various stages in the development 

 of these cells (X 435). 



Section across the outer part of the cortex, showing — e, epidermis 

 and c, dermis, resting upon the globate-layer. 

 Wall of a crypt, taken from one of its upper corners, showing 

 epithelium overlying a layer of vacuolate connective- tissue cells 

 (X217). 



A typical mark-cell, showing nucleus and nucleolus imbedded 

 in fine granular sarcode (X 435). 



Nuclei which occur dispersed through the granular substance of 

 the mark (x 435). 



Section of a chone, showing obliteration of endochone through 

 the contraction of its muscular walls (X 26). 

 A trabecula of one of the excurrent canals, to show the general 

 character of its constituent mark-substance (X 435). 

 A transverse section through a small canal in the mark; the 

 surrounding mark-cells are distinguished by faintly defined out- 

 lines (x 435). 



A transverse section through a dermal ostium, showing stellate- 

 bearing external layer and central fibrous layer (X 217). 

 Section through cortex and mark, in which the incurrent canals 



