Distribution of Sacrammiaa splhierica, etc. 15 



Saccaminina sphserica (M. Sars). 



As regards the earliest stage of this Ehizopod, recognizable as 

 such, the dredgings offer no definite evidence. The smallest recog- 

 nizable specimens of Saccammina sphmrica differ from the adults 

 only in their relatively small size, their comparatively rough (ix- 

 terior,and the fact that the aperture is a mere chink between the sand- 

 grains at the somewhat produced end of the shell, which is often 

 rather pear-shaped tlian spherical. The nipple-like })rotuberance 

 bearing the aperture has not as yet begun to be formed. These 

 earliest specimens have a maximum diameter of about 0'3mm., 

 which is considerably less than anything heretofore recorded for 

 the species, and in our opinion a sufficiently small beginning for 

 such a large organism. Prior to the formation of these young speci- 

 mens, it is probable that Saccammina may live in a naked amoeboid 

 form, but as regards the manner of its origination, whether by 

 budding and fission, or from zoospores, there is absolutely no 

 evidence producible. The young individuals are, as already stated, 

 of apparently rougher external surface-contour than the adults, but 

 this is very largely due to the difference in the relative sizes of the 

 young and of the adult tests. The constituent sand-grains do not 

 vary greatly in size in the two stages, but they are as a general rule 

 less neatly and regularly arranged in the earlier. Thus, while in 

 the adult shell the trains are cemented togrether with their flat sur- 



o o 



faces forming the external contour-surface of the sphere, in the young 

 shell they are as frequently as not embedded without any attempt at 

 orderly arrangement. The " comparatively rough exterior" referred 

 to above is, we think, to a large extent merely superficial. Fissures 

 of identical depth on the exterior surface of spheres of differing 

 dimensions, would appear more pronounced and deeper on a smaller 

 sphere than on a larger. Moreover, in any Saccammina gathering 

 there are generally two distinct types of structure observable in 

 all stages of growth. One type habitually uses smaller material 

 and consequently builds a smoother test than the other which uses 

 larger sand-grains. (Plate I, figs. 13, 14.) 



From these minute specimens it is easy to trace the gradual 

 development of the species (Plate I, figs. 1-12). The shells increase 

 in size and become less pear-shaped and more spherical. The aper- 

 ture, however, remains a mere chink and the surface is still very 

 rough. At this stage Saccammina is with difficulty separable from 

 a spherical and smooth form of Psammosphadra fusca. The onlv 

 certain method of discriminating between the two is to turn the test 

 over and over until one is satisfied that it possesses no aperture what- 

 ever, in which case it should be referred to Psammosphaera fusca, or 

 until one finds an angular " chink " or opening between several con- 

 tiguous sand-grains, formed by their angularities, in which case 

 the test is referable to Saccammina sphserica. This " chink " is the 

 oral aperture of the test, and its development from a mere cranny, 



