Plate XIX. 



Fig. 1 a. Trypostega venusta (Norman). A zooecium 

 and two dwarf-zooecia. X 75. 



— 1 b. The same species, from the basal surface. 



Two ocecia are seen surrounded by dwarf- 

 zooecia, which, like the ordinary zooecia, 

 are furnished with pore-chambers. X 40. 



— 1 c. An operculum of the same species. X 149. 



— Id. An operculum of a dwarf-zocEcium. X 200. 



— 2 a. Discopora pavonella (Alder.). A portion of 



the margin of a colony with all the zooecia 

 undeveloped. On the oldest zocecia the devel- 

 opment of- the avicularia has just begun, 

 but the frontal surface of these is still a 

 continuous membrane, and on four zooecia 

 the frontal surface still consists of a row 

 of independent calcareous plates separated 

 by sutures. Distally to these plates is seen 

 a dark curved line, the growing end of the 

 fold which encloses the cryptocyst, and the 

 internal layer of which becomes the exter- 

 nal wall of the compensation-sac. X 23. 



— 2 b. A sagittal section through a zocecium of the 



same species to show the compensation-sac 

 (cs). The above-mentioned fold surrounds 

 parts of the decalcified, broken cryptocyst 

 (cr.). X 75. 



— 3 a. The zooecia of Smittina propinqua (Smitt), 



from the basal surface, which consists of a 

 number of striated plates meeting in sutures. 

 X 40. 



— 4 a. Smittina Smitti (Kirchenp.). A developing 



ooecium. The ectoooecium still consists of 

 two separate halves. X 40. 



— 5 a. Smittina palmata (Sars), var. A developing 



ooecium. X 40. 



— 5 b. The basal surface of a zooecium of the same 



species. Plate-mosaic with centres of calci- 

 fication. A multiporous rosette-plate. X 40. 



— 6 a. A zooecium of Smittina Lansborovi (Johnst.) 



with ooecium. An ooecial cover is seen, which 

 paith- appears in the margin of the zooe- 

 cium partly forms two projections distally 

 to the aperture. X 40. 



— 6 b. An ooecium of the same species, through 



the broken ectoiecium of which the endo- 

 ooecium is seen. X 100. 



— 7 a. Two ooecia of Smittina trispinosa, var. ciicul- 



lana n. with a hood-shaped ooecial cover. X 40. 



— 8 a. Some zooecia of Flustra securifrons (Pall.) 



after boiling in potash, to show the process 

 of calcification of the basal wall (see pages 

 4—5). X 33. 



— 8 b — f. Sagittal sections through a series of devel- 



oping ooecia of the same species (see page 

 57). X 40. 



— 8 g. A very early rudiment of an ooecium of the 



same species seen partly from the proxi- 

 mal end. The distal curved line is the line 

 in which the distal wall joins the frontal 

 membrane (fig. 8 b), and the bilobate part 

 seen within the operculum belongs to the 

 horizontal part of the distal wall. The 

 rounded sinus is the beginning of the ro- 

 sette-plate. X 40. 



Fig. 8 h — n. A series of developmental stages of the 

 endoooecium of the same species, seen from 

 the surface. X 40. 



— 9 a. Some zooecia of Flustra (Flustra) foliacea L., 



from the basal surface, after boiling in po- 

 tash. The distal wall with its rosette-plates 

 is seen and the composition of the basal 

 wall in small plates (see page 6). A very 

 fine striation parallel to the distal lines 

 cannot be seen in this figure. X 40. 



— 9 b. Two zooecia of the same species after boil- 



ing in potash. The lateral wall's composi- 

 tion of small plates is seen. X 40. 



— 1 a. A transverse section through a branch of 



Flustra iSpiralis) denticulata Busk, cr. : 

 cryptocyst. X 55. 



— 1 b. A sagittal section through an avicularian 



mandible of the same species, to show the 

 internal cavity which corresponds with the 

 vestibular cavity in the operculum. 



— 10 c. A portion of the basal surface of the same 



species, to show its composition of cell-like 

 small plates (cell- mosaic). Immers. 



— 11a. Operculum of Flustra pisciformis. X 23. 



— 1 2 a. A transverse section through a branch of 



Flustra (Flustra) carbacea Sol. cr. : crypto- 

 cyst. X 40. 



— 13 a. An avicularian mandible of Sarsiflustra 



abyssicola (Sars.), to show the internal 

 cavity. X 23. 



— 13 b. A transverse section through the same 



mandible in its middle part. X 23. 



— 14 a. A transverse section through an avicularian 



mandible of an Onychocella species, to show 

 the mandibular cavity. X 40. 



— 15 a. The avicularian mandible of Scuticella 



plagiostoma Busk. X 75. 



— 15 b. A transverse section through the end of 



the same mandible. X 75. 



— 16 a. Pore-canals of Myriozoum subgracile d'Ovh. 



Each of them contains an endosarcal cord 

 and is, at its proximal part, furnished 

 with a uniporous rosette-plate. Immers. 

 •— 17 a. Haswellia auriculata (Busk). Each of the 

 two-layered stalked, developing ooecia is 

 placed in a hollow. X 40. 



— 18 a. A sagittal section through some oceciura- 



bearing zocecia of Sclerodomus denticulatus 

 (Busk). The avicularium is seen on the 

 internal surface of the peristome and the 

 plate originating from the distal wall. X 23. 



— 18 b. A sagittal section through a zooecium with 



ooecium, more highly magnified. X 40. 



— 18 c. The same species. As a portion of the 



frontal surface has been ground away, the 

 flat proximal part of the ooecial frontal 

 surface is seen and the broadened crenul- 

 ated margin of the plate originating from 

 the distal wall. X 40. 



— 19 a. Discopora plicata (Smitt.). The distal of the 



two angular lines is the growing end of 

 the fold or outpushing formed by the 

 frontal membrane and enclosing the cryp- 

 tocyst whose growing end forms another 

 angular line. X 40. 



