87 
a full-grown state before it thus terminated its existence, 
by producing a permanent likeness of its living self. These 
specimens have their arched coverings, with the branches 
proceeding from them, more or less broken away, so as to 
expose the floor beneath them, which consists of parts of the 
strong outer wall of the rounded nucleus, and which in all the 
cases examined presents the same peculiar appearance. It is 
riddled through with many large holes sometimes nearly cir- 
cular but oftener oval or kidney-shaped, and so numerous as 
to open a very free communication between the external sar- 
code and that in the interior of the shell. It is not unusual 
to find Polymorphinas of a different type from these with a 
few small round holes in their outer walls, but they are 
scattered irregularly, are few in number, and have no evident 
relation either with one another or with any structural 
peculiarity of the animal ; whereas in the present case they 
are invariably contained within the area of the floor of the 
covered passages, and are so numerous and encroach so 
much on each other that in some parts they leave only 
narrow isthmuses of the original shell-wall between them, 
and the larger holes have every appearance of having been 
formed by the union of several smaller ones. It is evident 
from a consideration of their character that they have been 
produced by the removal of shell-material previously depo- 
sited, and this gives them a physiological interest, for though 
it is natural to suppose that a creature which has the power 
of precipitating carbonate of lime on its surface would also 
have the power of removing portions of it by solution or 
absorption if required, the foraminifera are so structureless 
that we should hesitate to attribute to them this function 
without clear and positive proof. 
In order to follow the successive changes in the latter 
part of the life of this Polymorphina, as they are illustrated 
in the specimens before you, the large rounded shells of P. 
communis should be first noticed, in which no opening is 
