BY W. A. HASWELL, M.A., B.So. 201 



of the polyzoarium, and become closed in by a punctated calcareous 

 lamina, which grows over the mouth and is usually perforated in 

 the centre by a slender projecting tube, the orifice of which is 

 also sometimes in turn closed in ; this tube is usually about a 

 sixth to an eighth of the whole diameter of the mouth, but 

 sometimes much less, and projects from the mouth of the cell to 

 a length equal usually to about four or five times its own diameter. 

 The form of these cells is nearly that figured by Busk as occurring 

 in M. meandrina, with the exception of the central tubule, the 

 place of which seems to be taken in the latter by a simple pore 

 with a slight raised margin. 



In process of growth the polyzoarium pushes out from its 

 periphery radiating processes the cells in which have the same 

 divergent tendency as in the original subcircular colony, and 

 neighbouring processes as they widen come into contact in such 

 a manner that the mouths of their marginal cells of each process 

 are obliquely opposed to those of the margin of the contiguous 

 process, and the result is that, in order to make room for further 

 growth, there is a curving upwards of the margins of these 

 processes as they come into contact — a thick septum being formed 

 between the cells of the contiguous processes. The outcome of 

 this mode of growth is the formation of a series of radiating, low, 

 thick, ribs or walls rising from the plane surface of the polyzoarium 

 — each rib essentially consisting of the upturned edges of two 

 contiguous lobes of the latter, separated by a mesial vertical 

 septum. The flat portion of the polyzoarium meanwhile grows 

 out from between these ribs until by a repetition of the same 

 process, a second series of ribs may become formed external to 

 the first. These ribs are usually not very high, rarely projecting 

 more than a tenth of an inch above the general surface ; a few 

 of their marginal cells on either side are usually greatly elongated, 

 projecting far beyond the others ; the septum projects as a thin 

 lamina well up beyond the cells contiguous to it. 



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