198 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



to fifteen concentric zones. The arrangement and connexions of these zones may 

 be made out in the thinnest and most translucent specimens, by examining them 

 by transmitted light, after mounting them in Canada balsam ; this, however, gives 

 such transparence to the thin shelly layer which is continuous over both surfaces, 

 that it may escape notice (if not carefully looked for), so as to lead to the conclu- 

 sion that the cells are open. Most specimens require to be somewhat reduced in 

 thickness, by slightly grinding down one surface, to enable the arrangement of their 

 interior to be distinctly made out ; and this may be examined either by transmitted 

 or by reflected light. Each zone thus seen in horizontal section (Plate V. fig. 1, c, c), 

 consists of a circular set of small ovate cells, excavated, as it were, in the shelly sub- 

 stance of the disk, and communicating with each other laterally by passages which 

 unite them together into a continuous annulus. The zone which immediately sur- 

 rounds the nucleus is connected with it by passages which extend from the outer 

 margin of the large circumambient segment to the several cells of which it is itself 

 composed ; and each zone communicates with the one on its exterior by similar 

 passages, which usually extend, however, not from the cells of the inner zone to those 

 of the outer, but from the connecting passages of the inner zone to the cells of the 

 outer (Plate IV. figs. 8, 9) ; and thus it comes to pass, that the cells of each zone 

 usually alternate with those of the zones that are internal and external to it. A ver- 

 tical section of the disk, such as is shown in Plate V. figs. 4, 5, exhibits the same 

 arrangement under a different aspect. The cells of the concentric zones are seen to 

 be much higher than they are broad, so that they present a somewhat columnar 

 form ; the proportion of their height to their breadth, however, may vary greatly in 

 different parts of the same disk, the former often increasing from the centre towards 

 the periphery (fig. 4), whilst the latter remains constant, or nearly so ; and the 

 columns, instead of being straight, are generally more or less curved, and are some- 

 times bent in the middle at an obtuse angle (Plate V. fig. 7, a, b). The gradation 

 which presents itself from one of these forms to the other, and their coexistence even 

 in the same specimens, clearly proves that no value can be attached to the form and 

 proportions of the cells, thus seen in a vertical section, as furnishing specific charac- 

 ters. In every perfect specimen, the columnar cells are seen to be closed at their 

 two extremities by a thin shelly wall ; and this is sometimes flat, sometimes more or 

 less convex *. The meaning of these arrangements is clearly seen, when we turn our 

 attention to the structure of the animal (Plate IV. fig. 1). For the outer margin of 



* In a large proportion of the specimens obtained from sands or dredging, the cells have been laid open by 

 attrition ; either throughout the surface of the disk, if it should be flat, or at its margin only, if it should be 

 at all saucer-shaped. The constancy of this last character in a certain set of forms, resembling that repre- 

 sented in Plate VII. figs. 8, 10, might at first sight lead to the idea that they constitute a distinct specific type ; 

 but, as will hereafter appear, these plate-shaped disks cannot be separated by any definite line of demarcation 

 from such as are quite plane ; and in specimens of them which have not suffered attrition, the marginal cells 

 are closed, like all the rest. 



