REPORT ON THE GENUS ORBITOLITES. 33 



The circumambient chamber is completely enclosed peripherally by a circular wall ; 

 and this is traversed by a series of passages at regular intervals all around, each of which 

 leads into a separate chamberlet, — the very first series of chamberlets thus formino- a 

 complete annulus. The sarcodic body which occupies the cavity of the nucleus, consists 

 of a large pyriform primordial segment (PL V. fig. 18, a), from the small end of which 

 proceeds the stolon-process that connects it with the circumambient segment h, b'. This 

 last is very large, a portion of it (c) being usually in part separated from it by a partition 

 in the shelly chamber (fig. 3, p. 13) ; and it buds off", all round its periphery, a succession 

 of radial stolon-processes, of which one traverses each passage in the surrounding wall, to 

 become the origin of one of the sub-segments forming the first annulus. 



Each of the chambered zones by which the " nucleus " is surrounded, even from the 

 first, consists of two superjicial layers, between which is interposed an intermediate 

 stratum. 



The superficial layer of each annulus (PI. VI. fig. 4) is made up of oblong chamberlets, 

 the partitions between which correspond with the radial surface-lines. These jjartitions 

 extend continuously across the annulus, so that the adjacent chamberlets have no lateral 

 communication. And as the circular septa that form the end-walls of these superficial 

 chamberlets are alike imperforate, the chamberlets of the successive annuli have no 

 direct communication with each other. When, however, the chamberlets have been 

 so laid open by grinding or by the application of acid (as at /, /), that their floors are 

 brought into view, a pore is seen at either end ; and each of these pores is shown by ver- 

 tical sections to open into an annular gallery {g, g', g") that passes beneath it ; so that, 

 as each superficial chamberlet lies across the interval between two galleries, and com- 

 municates with both of them, an indirect connection is established, through their 

 intermediation, between each annular gallery and that which is internal and external to 

 it, and thus throughout the entire system. This will be best understood by looking at the 

 disposition of the sub-segments of the sarcodic body which occupy the chamberlets, so as 

 to form its surface-layer (PI. V. fig. 11). These present themselves under a low 

 amplification as narrow elongated blocks, very uniform in size and figure, arranged in 

 concentric annuli ; and when a portion of the layer is more highly magnified (fig. 13), it 

 is noticeable that though these sub-segments generally alternate in jjosition in successive 

 annuli, this arrangement is by no means constant, there being no direct connection 

 between them. Their relations to other parts of the sarcodic body are best brought 

 into view by vertical sections (fig. 14), which show that every block of each of the 

 superficial rows (c, c') is connected by a pedicle at either end with one of the annular 

 stolons (a, h, b') that intervene between the superficial layers of sub-segments and the 

 sarcodic columns {d, e) of the intermediate stratum. Each stolon thus gives off two 

 series of pedicles : one to the row of sub-segments internal to it, and the other to the 

 row external to it ; and these usually (though not always) alternate in position. 



(ZOOL. OHALL. EXP. — PAET XXI. — 1883.) X 5 



