24 



area in most cases consists of an outer calcified, and an inner uncalcified part, 

 and in strongly calcified species (e. g. ^Lepralio" Pallasiana) the inner uncalcified 

 portion of the outer area is very small. The single small plates in a compound 

 rosette-plate often show only a slight indication of a pore-ring, and when they 

 are not much hollowed out the calcified portion of their outer area is often so 

 little distinct from the large area, that it is only possible to find it by very favour- 

 able light. Just as we rather frequently find two rosette-plates fused together 

 into a double plate with an outer area in common and two pore-areas in species, 

 the distal wall of which is provided with a number of uniporous rosette-plates 

 (e. g. in Flustra foliacea, Fl. carbacea and Membranipora pilosd), we also find in 

 a multiporous rosette-plate a fusion of two or more small plates into one. A 

 great deal of variation and very different kinds of fusion take place in the distal 

 wall in Membr. membranacea^. In this appear as a rule two pear-shaped multi- 

 porous rosette-plates, but in many zooecia each of these is replaced by a whole 

 series of smaller plates, of which some are uniporous, others multiporous with a 

 very varying number of pores; the conditions may even be quite different on the 

 two sides of the distal wall. 



Pore- Chambers. I have used this name^ for the small spaces which are situated 

 in the angle between the basal wall of a zooecium and one of the perpendicular 

 walls. In their typical form they have a triangular tranverse section, and we 

 can distinguish between a basal wall, an inner wall and an outer one. The basal 

 wall is a portion of the basal wall of the zooecium, the small rosette-plates are 

 situated on the inner wall, and on the outer wall is the entrance to the chamber 

 (PI. XVII, fig. 10 c). If we examine their development in the newly formed zooe- 

 cia in the growing part of the colony, we see that the inner wall is the part 

 first formed and that the basal wall and outer wall are formed later. We can 

 best make sure of their presence if we loosen a colony from its support and 

 look at it from the basal surface; for in this position the inner walls of the 

 elongated pore-chambers form curves within the lateral margins of the zooecium 

 (PI. IX, figs. 11 g, 12 a, PI. XV, figs. 3 c, 4 c, PI. XVIII, figs. 14 b, 11 a). There is as 

 a rule only a small number of small plates placed in a single row and the neigh- 

 bouring chambers are in most cases moved up so close together that the curves 

 touch one another, or even so that the chambers have a common separating wall. 

 While the vertical walls in all zooecia, which are furnished with ordinary 

 rosette-plates, form right angles with the basal wall, the pore chambers are 

 placed in such a way that their outer wall forms pointed angles with the 



' 54, Tab. II, fig. 17; 55, PI. IV, fig. 5; " 54, p. 250; 55, p. 7. 



