554 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



successive convolutions. Thus the spine e is one of the oldest, being traceable inwards 

 to the earlier whorls ; whilst those marked e\ e 2 , e 3 , e 4 , e 5 are obviously of progressively 

 later production, their respective origins being further and further removed from the 

 centre of the spire. It is, moreover, to be observed that each spine receives an augmen- 

 tation in thickness as the convolution from which it sprang is encircled by others ; this 

 augmentation, however, is not marked (as in the spines of Echini) by lines of demarca- 

 tion between the earlier and the later formations ; and there is every reason to believe 

 that the growth of the spines, both in length and in diameter, is continuous rather than 

 interrupted. Although it might seem, from the examination of such sections only as 

 are taken in the direction of the equatorial plane or in one parallel to it, as if the course 

 of the spire must be seriously interrupted by the radiation of the spines (which some- 

 times appear to be so interposed between consecutive chambers as completely to separate 

 them); yet the fact is that owing to the turbinoid form of the spire, a spine projecting 

 from an earlier whorl is very little in the way of even the next convolution ; for as this 

 passes by the spine on a different level, its chambers are but slightly encroached-on, and 

 this only upon the side which looks towards the apex of the spire, as will be readily 

 understood by examining the relation of the last half-convolution, visible in such a 

 specimen as the one delineated in Plate XIX. fig. 4, to the pre-formed spines, or by an 

 inspection of the ideal represented in Plate XIX. fig. 12. 



204. 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 distribution 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 con- 

 tinuous network with long narrow meshes, that commences from the parietes of the 

 chambers and extends itself to the very extremities of the spines (Plate XX. figs. 1, 2, 4). 

 The proper walls of the chambers, as already stated, are uniformly perforated, like those 

 of the chambers of Rotalice, by foramina of considerable size (averaging about 3-^5-0 th 

 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 Plate XX. fig. 1) there seem to be irregular lacunar spaces, 

 into which their foramina open externally, and from . which the passages of the 

 canal-system originate. How numerous and closely-set these passages are, is shown 

 in Plate XX. fig. 3, 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 



