200 MESSRS. BRADY, PARKER, AND JONES 
relationship with surviving genera, and, so far from breaking the zoological continuity of 
the series, do but serve to fill up some of the links previously wanting to complete the 
chain. 
It is quite true that, for some reasons, of which we know nothing, certain “ genera ” 
and * species" have become prominent at one period, and lapsed into insignificance at 
another; but the number of types which, so far as our present knowledge goes, are abso- 
lutely lost is comparatively trifling. Nor is this surprising ; for it is seldom that we 
have evidence of sudden upheavals of the sea-bed extending over large areas; and even 
in such cases the displaced water would carry with it sufficient of its microzoa to stock 
a new area, should the fresh conditions be favourable to their development and increase ; 
but in the far commoner process of gradual deposit the Rhizopoda would naturally 
follow, as it receded, the area of depth most favourable to their habits. 
These considerations are merely brought forward to show that we have no evidence of 
want of “continuity” in respect to the forms of marine Microzoa recurring in successive 
strata, and that there is no valid reason for regarding morphological characters, wher- 
ever shown, in any other than a zoological light. It need not be assumed that there is 
absolute and direct descent in the trifling peculiarities which have been made the bases 
for so many *' specific” subdivisions ; indeed it is almost certain that the largest number 
of such modifications are brought about, gradually perhaps and within certain limits for 
each type, by external conditions. 
The arguments employed to uphold the renaming of the same varietal form on its 
reappearance in successive beds would be as applicable, if well grounded, to geographi- 
cal as to geological range, and must be held to be also true in case of the recurrence 
of the same variety in areas widely separated. It would be easy, for instance, to 
give a list of Foraminifera common on our own coast and equally at home at similar 
depths on the shores of North America; to trace direct relationship would be impos- 
sible; for we have the strongest negative evidence that the same varieties, or even the 
same types, do not occur in the abyssal depths that separate Europe from America; yet 
no naturalist would suggest the ** specific " separation of specimens found in the eastern 
from those found in the western habitat, or would hesitate to accept zoological characters 
alone as sufficient basis for identification. 
In one word, the following history of the genus is as purely zoological as we have 
been able to make it; and the subdivisions adopted are based solely on external physical 
characters. We can see no consistency in any other course; and the present aspect of 
the nomenclature of this little section of the animal kingdom shows sufficiently the 
practical contradictions which accrue from the admission of time as a primary element in 
systematic zoology. 
We have no hesitation in saying that, read in the light of the older definitions, the 
whole of the widely differing shells referable to the Polymorphine type must be regarded 
as a single species. From end to end of the long series it embraces there is no single 
break ; the successive modifications of the typical form, however well defined when judged 
by central and characteristic specimens, are seen, as the number of examples is multiplied, 
