
1905. | the English Species of Nummulites, ete. 309 
In the life-history of Polystomella crispa we know that the megalospheric form 
arises by an asexual process; the protoplasmic contents of the microspheric 
form emerging from the test, and dividing up into a large number of 
megalospheres. These shortly separate and proceed to develop into full grown 
individuals of the megalospheric form (14, pp. 67 and 68). 
In the light of this ascertained fact in the life-history of Polystomella, a 
simple member of the Nummulitide, the question under consideration may 
be put in a different manner: Is there a definite relation between the volume 
of the protoplasm of the microspheric form and the size of the megalospheres 
into which it divides ? 
For a satisfactory answer it was evidently desirable to extend the observa- 
tions to a wider series of species, and, thanks to the stores of material in the 
collection presented to this University by the late Dr. H. B. Brady, I have 
been able to examine six other species (or “ pairs of species” on the old view) 
ranging up to IV. complanata, the microspheric form of which attains the 
gigantic proportions of 3 inches in diameter. 
As an index of the volume of the megalosphere the cube of its mean 
diameter has been taken. Similarly for an index of the volume of the 
protoplasmic contents of the complete test the square of the diameter (qd) 
multiplied by its greatest thickness, z.¢., the length of the spiral axis (a) has 
been taken. Thus ad? is the index of the volume of the complete tests, 
megalospheric and microspheric. 
If the tests were all of the same shape and the chambers and septa between 
them were of the same proportional dimensions and thickness in all the 
species, the values of ad? would give accurately comparable indices of the 
protoplasmic contents of the tests throughout the series. This is, however, far 
from being the case. In some species the tests are highly biconvex, in others 
they are nearly flat; some have large chambers and thin walls, others small 
chambers and thick walls; and the species differ also in the degree of develop- 
ment and the disposition of the alar prolongations of the chambers. In those 
sometimes separated under the distinct generic name Assilina, the latter are 
altogether absent. When comparing the results the characters of each species 
in these respects must be taken into account. 
It should be stated further that the measurements which follow can only 
be regarded as approximately correct. In some cases the only specimens 
available were glued on museum tablets, and many are more or less worn 
at the edges. Whenever possible the two forms of a species selected for 
measurement are from the same locality. 
The list of species with the localities of the specimens examined is as 
follows :— 
