218 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



those of the zone 7 7, which not only surrounds it, but extends further backwards 

 upon the nucleus. So the cells of the zones 8 8, 9 9, 10 10, 1111, and 12 12, pro- 

 gressively increase in number, and each zone extends itself further back upon the 

 nucleus, until those of the last of these zones nearly meet upon its yet unenclosed 

 margin. The cells of zone 13 13 do actually meet there, so as to form a complete 

 circle; and zones 14 14 and 15 15 are formed with cyclical regularity, as would be 

 any other zones subsequently produced. A still more complete spiral, in which 

 twenty-two zones (commencing with the central segment) succeed one another before 

 the first complete annul us is formed, is shown in Plate IX. fig. 2. Both figs. 2 and 4 

 (the latter of which is diagrammatized) represent the central portions of large disks, 

 whose peripheral portions grow on the regular cyclical plan. 



55. Now if these two plans of growth the one cyclical from the beginning, the 

 other cyclical only after having been at first spiral were constantly presented in well- 

 marked contrast with each other, there would be good ground for considering them 

 (as Professor WILLIAMSON has done*) to be characteristic of distinct specific types. 

 But this idea cannot be entertained, when a large number of individuals are examined. 

 For it then becomes apparent, that the number of cases in which the nucleus is 

 surrounded on all sides by the same number of zones, indicating that the concentric 

 mode of growth has prevailed from the very first, are very few ; but that in by far 

 the larger proportion of specimens, there is a slight excentricity of the nucleus, with 

 a larger number of zones on one side than on the other, as in Plate IX. figs. 1,3; 

 indicating that the first-formed zones have been incomplete circles, owing to a 

 restriction of the gemmation of the nucleus to one part of its periphery. This is 

 shown extremely well by decalcified specimens of the animal, no two of which, in 

 fact, precisely resemble one another as to the mode in which the first zone of segments 

 originates in the nucleus. Thus in the specimen represented in Plate IV. fig. 1, of 

 which the nucleus is represented on a larger scale in fig. 12, the circumambient 

 segment of the nucleus gives off only three stolons, at the end most remote from its 

 connexion with the central mass ; and the first zone of segments is far from being 

 entire, the cyclical type not being completely attained until two or three successive 

 additions have been made. In fig. 13, eight stolons are given off from the nucleus; 

 and from the half-zone which they form, an entire circle is next produced; thus 

 affording a remarkable confirmation to the idea I have already suggested (^[ 37.), as 

 to the capacity of a portion of a zone to give origin to a complete annulus, by the 

 lateral extension of its bands of sarcode. In fig. 10, the nucleus gives off eleven 

 stolons on one side, and there are indications of three or four on the other. In fig. 6, 

 the stolons come forth from a still larger proportion of the periphery of the nucleus ; 

 the zone which first surrounds it, however, is still incomplete in some parts, though 

 the succeeding zone forms an entire circle. Finally, in the specimen represented in 

 fig. 5, which is almost the exact counterpart of the disk represented in Plate VII. fig. 2, 

 * Transactions of the Microscopical Society, 1st series, vol. iii. pp. 116, 119. 



