
1905. | | the English Species of Nummulites, etc. 313 
diameters thé microspheres are remarkably uniform in size, all falling 
between 15 and 19 w in diameter. In most of the other species which 
I have examined in section, the calcite filling of the tests obscures the 
central chambers so much that it is rarely possible to obtain an accurate 
measurement of a body so minute as the microsphere. However, in one 
specimen of NV. gizehensis this can be done, and the value -of m corresponds 
closely with that found in the three English species, being 20 w. From 
these few cases (and I am not aware of any other records of the actual 
size of the microsphere in this genus) it would appear that the size of the 
microsphere is independent alike of the size of the megalospheric form and 
of the ultimate size of the microspheric test into which it grows. 
In view of the facts (a) that there is good ground for concluding that the 
microsphere arises by the conjugation of zoospores produced by individuals 
of the megalospheric form, and (0) that the megalosphere arises by an asexual 
process, the results so far obtained may be stated for the genus Nummulttes 
as follows :— | 
The size of the asexually produced megalosphere is approximately proportional 
to the volume of the protoplasmue contents of the microspheric parent. 
The size of the (probably) sexually produced nucrosphere is uniform, or nearly 
80, throughout. | 
Turning now to the eighth column in the table, showing the ratios of the 
volume of the megalospheric tests to that of the megalospheres, it will be 
noticed that as the series of species is followed down, the ratios increase, 
though with some irregularity, from the top to the bottom. In the little 
N. variolarius, this ratio is almost the same as that for the microspheric 
form—the tests of the two forms being, as we have seen, almost of the same 
size. In the other species as the volume of the microspheric form increases 
so does the proportion which the volume of the megalospheric form bears to 
the megalosphere decrease. 
In the case of variolarius, as the tests of the two forms attain about equal 
sizes, we may suppose that each took about the same time to grow, or, in 
other words, that the complete cycle of the life-history was divided in two 
nearly equal parts between the alternating generations. But in the other 
Species it would appear that in proportion as the period of growth of the 
microspheric form preponderated in the life history, so did that of the 
megalospheric form diminish—not only in proportion to the microspheric 
form of the same species, but in proportion also (allowing for the difference 
in volume) to the period of growth of the megalospheric form in a species 
such as variolarius. Thus, to compare this species with WV. complanatus, its 
VOL. LXXVI.—B, Y 
