126 



EEV. T. HINCKS ON POLYZOA. 



outer wall (ectocyst) has been removed, the cells in the centre of 

 the colony, and in a zone extending for a short distance round it, 

 are furnished with an internal calcareous lamina, more or less 

 complete and perforated — in some cases closing in the cavity of 

 the cell entirely, and with a line of punctures round the margin. 

 The cells in the outer zone of the colony (towards the margin), 

 occupying about two thirds of the disk, show no trace of a lamina. 

 The inner margin of the cells is minutely but strongly granu- 

 lated, the dividing line between them thin and smooth, and the 

 aperture irregular-oblong, occasionally oval. Both Smitt and 

 Manzoni figure a calcareous lamina with a single line of rather 

 large pores round the edge, and at the upper extremity a semi- 

 circular opening (opesia of Jullien), distinct from the true 

 orifice in the membranous outer wall. This condition I have 

 not been able to observe, owing to the presence of the ectocyst 

 in almost all the specimens. The cells in the centre of one 

 of the colonies, to which I have just referred as possessing a 

 lamina which completely fills in the cavity, and is altogether 

 destitute of an opening (opesia), are no doubt abnormally deve- 

 loped. In every colony the centre is occupied by the primary 

 zocecium, which is oval in shape, and is surrounded by a belt 

 of seven or eight cells which are disposed radiately about it. 

 These are partially developed, and are destitute of an oral valve, 

 although furnished with the membranous front wall. Probably 

 in this region of the zoarium the internal calcareous lamina 

 also is abnormal. The dorsal surface presents a very different 

 appearance, according to the degree in which calcification has 

 taken place. In young states the centre is occupied by a 

 fragment of stone or coral (?), the base on which the colony 

 was originally planted. This disappears after a time and its 

 place is occupied by a central depression or hollow. The 

 large vibracular cells, which project round the margin of the 

 colony, are traversed by a smooth, keel-like raised line, on each 

 side of which small granules are ranged. The divisions between 

 the zocucia show distinctly on the inferior surface of the disk, 

 which i« more or less covered with minute granules. In the 

 youngest states these are very feebly developed. In older colo- 

 nics the dorsal surface is covered with elongate, radiating areas, 

 separated by grooved, bifurcating lines, on which the granules are 

 disposed longitudinally. As calcification proceeds a large part of 

 the surface becomes coarsely granulous, while at the same time 



