ON MEELIA N0E5[ANI. 699 



siliceous spicules, e. Clavidiscs. /. Tiibercles of calcareous skeleton. 

 g. Skeletal wall showing zones of fibrillar fanning out. x 125. 



Fig. 11. — Crypt-cells in glycerine. X 1500. 



Fig. 12. — Youngest specimen (a) forming a minute red. spot on a 

 shell. X 25. 



PLATE 33. 



Fig. 1. — Upi^er surface of decalcified specimen showing '"nodal" 

 masses, a, of flagellated chaml^ers joined by radial Imnds, h, of flagel- 

 lated chambers, c. Spaces left by decalcified tubercles, x 100. 



Fig. 2. — Under surface of another specimen (decalcified), a. Masses 

 of choanosome filling uppermost spaces of calcareous skeleton, h. Radial 

 " spokes " joining these masses, c. Spaces left by decalcified tubercles. 

 d. Crypt cells, x 120. 



Fig. 3. — ^Decalcified vertical section of well-expanded specimen 

 (showing only one mass of crypt-cells), a. Subdermal space, h. Flagel- 

 lated chambers, c. Soft tissues (in uppermost crypts), d. Soft tissues, 

 mostly calcocytes, in a lower cryjDt. e. Bundles of siliceous spicules. 

 /. Clavidiscs. g. Inhalant pore, x 140. 



Fig. 4. — Flagellated chambers, a. Apopyle in sjjhinctrate membrane. 

 h. Sphincter " muscle "-cell. X 750. 



Fig. 5. — Flagellated chambers. Lateral view, x 750. 



Fig. 6. — Flagellated chamber, convex surface, showing prosopyles 

 between stellate bases of collar-cells. X 1600. 



Fig. 7. — Section of a flagellated chamljer. x 2425. 



Figs. 8-11. — Collar-cells in different conditions of contraction, drawn 

 from the same section, x 1800. 



Fig. 12. — Collar-cell showing flagellum passing down to nucleus, x 

 1800. 



Fig. 13. — Growing edge of young specimen, o. Flagellated chambers. 

 h. Radiating tufts of spicules, c. Clavidisc. X 175. 



PLATE 34. 



Fig. 1. — Section of a small decalcified specimen showing gradual 

 development of calcareous skeleton from edge to centre of the crust 

 (the skeleton being represented by spaces in figure), x 25. 



Fig. 2.— Surface of a young specimen, a. Oscule. h. Pores, x 425. 



Fig. 3. — Decalcified tubercle and upper edge of wall of skeleton, 

 showing large granular cells (calcocytes) and radiating fibrillar structure 

 of organic matrix, a. Granular cells, h. Radiating fibrillse in body of 

 tubercle, c. Flagellated chamber, x 375. 



