392 



WILSON. 



EXPLANATION OF TLATE XVIII. 

 (Esperella Jihrexilis.) 



Fig. 47. Part of section through young sponge, showing formation of canal 

 wall, ^j Immersion 4. 



Fig. 48. Section of young sponge, shomng osculum. D.4. 



Fig. 49. Section through peripheral part of young sponge. D.4. 



Figs. 51, 52, 53. Sections of young sponges, for canal system. C.4. 



Fig. 54. Surface view of young sponge with surrounding ectodermal membrane 

 covered with debris. A. 4. 



Fig. 55. Combined surface view and horizontal optical section of young sponge 

 — note abundance of formative cells and absence of chambers. A. 4. 



Fig. 56. Horizontal optical section of peripheral part of young sponge — for- 

 mation of peripheral mesodermic zone and canals. D.4. 



Fig. 57. Horizontal optical section of older sponge in which flagellated cham- 

 bers have formed. D.4. 



Fig. 58. .Surface view of sponge with openings into subdermal spaces. A. 4. 



Fig. 59. Part of periphery of preceding figure, to show pores. D.4. 



