31 



towards the cenlre of the zod'cium. [ii JhiswvUin (iiistraliensis and Hasiv. coronata 

 the frontal wall is furnished with muiuMoiis pore-canals, each ending inwardly 

 in a uniporous roselte-plate and as the rosette-plates helonging to the marginal 

 pore-canals have their place in the outer pari of the lateral walls, these rosette- 

 plates thus form a connecting link hetween the common lateral rosette-plates and 

 those belonging to the frontal wall. In species of the genus Myriozoum the whole of 

 the frontal wall is furnished with closely placed, posteriorly directed sac-like pore- 

 canals, each ending in a uniporous rosetle-plate (PI. XIX, lig. Hi a). In each canal is 

 a chord of mesenchymatous tissue, which has a club-shaped widening towards the ro- 

 sette-plate. In Srlerodoinns denticiilatux (PI. XIX, fig. 18 a, 18 b) the frontal wall of the 

 zoo'cium is furnished with minieious curved, sac-like and widened pore-canals, which 

 contain a similar chord of mesenchymatous tissue. Finallj', I may mention that 

 in all the species which have marginal pores and at the same time a median 

 avicularium proximally to the aperture, the avicularium stands in connection with 

 the llrst or sometimes also with the second pair of superficial rosette-plates, respec- 

 tively through two or four shorter or longer canals, which issue from the distal 

 part of the avicularian chambers. This is the case for instance with most species 

 of the genus Porella. 



AH other so-called pores in the Cheilostonmta are, as Per gens has already 

 remarked, not real pores, and when this writer' states »ces petits pores sont, en 

 realite, des cavites intersqueletliques occupees par du tissu epidermiijue, en con- 

 nection avec ies parties scjuelettiques et avec le parenchyme«, this so far agrees 

 with my observations, as I have always found the bottom of these pores closed 

 by a membrane, which adheres directly to the calcareous skeleton and may with 

 age be calcified to a more or less extent. In some of the species, for instance in 

 'Lepralid' Pallasiana, a larger or smaller number of these pores may eventually 

 become closed, and in Siniltina jmrifera they may assume a very dilTerent appea- 

 rance according to the different manner in which calcification proceeds. This 

 membranous area in Microporina horealis is divided into a number of small areas 

 by radiating calcareous ridges. The difference between such a j)ore and a rosette- 

 plate is therefore only, that the latter is furnished with one or more very fine 

 perforations, which are absent in the former. The pores as well as the marginal 

 rosette-plates may as time goes on become surrounded by small chambers, and 

 for instance in Sinittiim povifera and ■ Lepralia« Pullasinna a meshwork of ridges 

 is formed over the whole surface. Regarding the pores of the ooecia, I need 

 only remark that they are similar to those of the zoo^cia. 



' 93, p. 308. 



