74 THE MICROSCOPE AND ITS REVELATIONS. 



such disks are subjected to microscopic examination, they are found (if 

 uninjured by abrasion) to present the structure represented in Fig. 316; 

 where we see on the surface (by incident light) a number of rounded ele- 

 vations, arranged in concentric zones around a sort of nucleus (which has 

 been laid-open in the figure to show its internal structure); whilst at the 

 margin we observe a row of rounded projections, with a single aperture 

 or pore in each of the intervening depressions. In very thin disks the 

 structure may often be brought into view by mounting them in Canada 

 balsam and transmitting light through them; but in those which are too 

 opaque to be thus seen-through, it is sufficient to rub-down one of the 

 surfaces upon a stone, and then to mount the specimen in balsam. Each 

 of the superficial elevations will then be found to be the roof or cover of 

 an ovate cavity or i chamberlet,' which communicates by means of a 

 lateral passage with the chamberlet on either side of it in the same ring; 

 so that each circular zone of chamberlets might be described as a continu- 

 ous annular passage, dilated into cavities at intervals. On the other hand, 

 each zone communicates with the zones that are internal and external to 

 it, by means of passages in a radiating direction; these passages run, 

 however, not from the chamberlets of the inner zone to tnose of the 

 outer, but from the connecting passages of the former to the chamberlets 

 of the latter; so that the chamberlets of each zone alternate in position 

 with those of the zones internal and external to it. The radial passages 

 from the outermost annulus make their way at once to the margin, where 

 they terminate, forming the ' pores ' which (as already mentioned) are to 

 be seen on its exterior. The central nucleus, when rendered sufficiently 

 transparent by the means just adverted-to, is found to consist of a 'pri- 

 mordial chamber' (a), usually somewhat pear-shaped, that communicates 

 by a narrow passage with a much larger ' circumambient chamber' (b), 

 which nearly surrounds it, and which sends off a variable number of ra- 

 diating passages towards the chamberlets of the first zone, which forms a 

 complete ring around the circumambient chamber. 1 



467. The idea of the nature of the living occupant of these cavities 

 which might be suggested by the foregoing account of their arrangement, 

 is fully borne-out by the results of the examination of the sarcode-body, 

 which may be obtained by the maceration in dilute acid (so as to remove 

 the shelly investment) of specimens of Orbitolite that have been gathered 

 fresh and preserved in spirit. For this body is found to be composed 

 (Fig. 317) of a multitude of segments of sarcode, presenting not the least 

 trace of higher organization in any part, and connected together by 

 * stolons' of the like substance. The ' primordial' pear-shaped segment, 

 a, is seen to have budded-off its 'circumambient' segment, Z, by a narrow 

 footstalk or stolon; and this circumambient segment, after passing almost 

 entirely round the primordial, has budded-off three stolons, which swell 

 into new sub-segments from which the first ring is formed. Scarcely any 

 two specimens are precisely alike as to the mode in which the first ring 



1 Although the above may be considered the typical form of the Orbitolite, 

 yet, in a very large proportion of specimens, the first few zones are not complete 

 circles, the early growth having taken place from one side only; and there is a 

 very beautiful variety in which this one-sidedness of increase imparts a distinctly 

 spiral character to the early growth, which soon, however, gives place to the 

 cyclical. In the Orbitolites tenuissimus (Fig. 318) brought u-p from depths of 

 1,500 fathoms or more, the ' nucleus' is formed by three or four turns of a spiral 

 closely resembling that of a Cornuspira ( 462), with an interruption at every 

 half -turn as in Spiroloculina; the growth afterwards becoming purely concentric. 



