10 
mediately on the surface of tlie zooecium, but subsequently they get 
surrounded by raised lines and the small compartments formed in 
this manner can be regarded as superficial pore-chambers. In the 
figure of Smittia reticulata, given by H i n c k s the whole row of 
these chambers on each side is externally limited by a raised line, 
forming an immediate continuation of the lateral wall of the zooe¬ 
cium, while the single chambers are separated from each other by 
a row of parallel raised lines, forming right angles with the longitudinal 
one. The latter meets a corresponding line from the neighbouring 
zooecia and by the splitting of a colony in singular rows of zooe- 
cia these raised longitudinal lines which are the lateral walls of 
the superficial pore-chambers will separate from each others. When 
regarded from the side-wall of an isolated zooecium these pore- 
chambers will shine through as channels Crossing the side-wall of 
the zooecium. In species possessing both such marginal rosette- 
plates and a median avicularium behind the orifice the avicularium 
is connected with the first, and sometimes also with the second 
pair^) of these rosette-plates, through two or four channels which 
originate from the fore-part of the avicularium. 
In Myrizoum coarctatum the whole front wall is perforated by 
closely set backward-directed bag-shaped tubes, each of which ends 
in a rosette-plate with a single pore. In every tube can be seen 
a string of mesenchymal tissue dilating towards the rosette-plate. 
All the othei, so-called pores in the Cheilostomata, hitherto looked 
upon as perforations of the calcified wall, are really in the bottom 
closed by a membrane without pores, but in a number of species 
• 
this membranous bottom is calcified in a greater or lesser part of 
its surface. In the species of Tuhucellaria and of Haswellia the 
greater part of it is calcified and only a little median circular part 
is membranous. In Micropora horealis the membranous part of 
Hincks, British marine Polyzoa, PI. 48, fig. 1. 
*) Sometimes only with a single rosette-plate. G. M. R. Levinsen, Op. 
cit., Tab. IV, Pig. 18. 
