25 



basal wall of the one and obtuse angles with the other of the two zooecia, 

 between which it serves as connection (PI. XVII, fig. 10 c). The outer wall 

 of the chamber forms obtuse angles with the frontal wall of the zocecium and 

 the pore-bearing, somewhat slightly concave inner wall forms obtuse angles in- 

 wardly and pointed angles outwardly with the base. What is said here applies 

 to the pore-chambers of both the lateral and distal walls. Though rosette-plates 

 and pore-chambers seem at first glance to be of quite different structure, they 

 are connected by transitions. If we imagine a rosette-plate placed in such a way 

 that its lower edge goes down into the angle between a lateral wall (or distal wall) 

 and the basal wall, a removal of this edge into the basal wall would produce a 

 pore-chamber, as what is just characteristic for such a formation is, that it belongs 

 to two adjoining walls. I have found such transitions between common rosette-plates 

 and pore-chambers in colonies of ^Lepralia"^ Pallasiana from Sebastopol, which 

 together with Electra Zostericola forms incrustations on Zostera marina. While 

 colonies of this species from Denmark and from Port Jackson, New S. Wales, 

 have only ordinary multiporous rosette-plates, we find more or fewer zooecia in 

 the colonies mentioned from Sebastopol, in which more or fewer rosette-plates 

 are replaced by pore-chambers with differently developed basal wall. We can 

 also find such transitions in the very variable species Porella concinna between 

 rosette-plates and pore-chambers, which replace one another in different colonies. 

 In contrast to the multiporous chambers which can be found in ^Lepralia' Palla- 

 siana and Porella concinna the few-pored chambers are usually constant within 

 the species, and even sometimes in the genus or family. Besides in all members 

 of the families Hippothoidae and Celleporidae typical pore-chambers appear in the 

 genera Callopora, Cribrilina, Puellina, Escharina and in a number of species of 

 the genera Escharoides and Microporella. In the members of the family Celle- 

 poridae, the colonies of which increase by superficial budding, the pore-chambers 

 are only to be found in the zooecia which form the first incrusting layer of 

 the colony; in species of Escharella (PI. XVII, fig. 1 c) the originally long and 

 narrow pore-chambers, which are provided with a row of small single-pored ro- 

 sette-plates, are divided by partition walls into a number of uniporous chambers, 

 and the pore-chambers may be tubularly lengthened in species of the genus 

 Hippothoa. 



Before discussing the relation of a rosette-plate to the two zocecia which it 

 connects, we may again recall that on using boiling alkali or cold eau de Ja- 

 velle we can not only loosen a colony from its support, but even as a rule sepa- 

 rate it into single rows of zocecia, on which we can without difficulty study the 



