GENUS CALCARINA. 221 



384. The canal-system of Calcarina presents a development so extraordinary in itself, 

 and so obviously related to that of the " supplemental skeleton," as to throw great light upon its 

 special functional destination. We do not here observe any such peculiar but limited distri- 

 bution of systematically arranged passages, as that which constitutes so remarkable a feature 

 in Polystomella ; but every portion of the supplemental skeleton, with the exception of certain 

 solid cones presently to be noticed, is traversed by canals which run very close together, 

 with frequent inosculations, and which thus form a continuous network with long narrow 

 meshes, that commences from the parietes of the chambers and extends itself to the very 

 extremities of the spines (figs. 3, 4, 8). The proper walls of the chambers, as already stated, are 

 uniformly perforated, like those of the chambers of Discorbina, by foramina of considerable size 

 (averaging about 1 -3000th of an inch in diameter) ; with these the canals of the supplemental 

 skeleton do not seem to be directly continuous, for they are of about double the diameter and 

 lie further apart from one another ; but immediately round the proper walls of the chambers 

 (as shown in fig. 3) there seem to be irregular lacunar spaces, into which their foramina open 

 externally, and from which the passages of the canal-systern originate. How numerous and 

 closely-set these passages are, is shown in fig. 9, which is taken (under a much higher 

 magnifying power than the rest of the figures) from a section that passes through the 

 supplemental skeleton just outside the walls of one of the chambers, in such a direction as to 

 cut through the passages transversely or obliquely. These passages run in different 

 directions ; some proceeding directly towards the external margin of the convolution, and 

 being continued into the spines where these are given off from it ; whilst others pass not less 

 directly towards the two convex surfaces of the disk. In the earlier whorls of the spire, as 

 shown at fig. 4, a, indications of spiral canals, commencing (as in Poli/stomella, ^ 478) in a 

 central lacunar system, are frequently traceable ; and sometimes we may make out a general 

 distribution of the canal-system of the earlier whorls, that strongly reminds us of that which 

 prevails in Polystomella (^477), the canals of the spines originating (as seen at a) in diverging 

 branches which radiate outwards through spaces left between the two layers of the earlier 

 septa. But this arrangement soon seems to be merged, as it were, in the much more copious 

 distribution of passages that arise from the lacunae round the proper walls of the chambers. 

 The canals which pass towards the tw,o lateral surfaces soon lose the general uniformity of 

 arrangement which they elsewhere present; for they become crowded together in some situa- 

 tions and separated in others, so as to leave a number of columnar spaces untraversed, whilst 

 the intercolumnar spaces are copiously penetrated by them, — as is seen at e, e, e, in figs. 3 

 and 10, the former showing the solid columns divided longitudinally, and the latter showing 

 them as they are cut transversely. The varying appearances of the external surface, as 

 described in 1 381, will now be understood. When, as commonly happens, the summits of 

 the columns rise above the general level of the surface, they will show themselves as rounded 

 tubercles. But when they are not thus elevated, they will merely be distinguished as circular 

 spots surrounded by the punctations which are the orifices of the canals. In the spines, on 

 the other hand, the canals form a longitudinally inosculating system (figs. 4, S), of which the 

 branches near the surface usually reach it so obliquely as to pass along it for some distance 

 as open furrows, the punctations seen in which are the orifices of branches that strike 

 the surface at a greater angle. 



