238 PROCEEDINGS: OF SOUIETIES. 
walls developed into tubular prolongations, extending in all direc- 
tions, and soon dividing irregularly into small branches, which, in 
one or two instances in the specimens shown will be found to 
anastomose ; they are either closed at their tips, as a small glass 
tube might be closed in the flame of a blowpipe, or they expand 
into little cauliflower-like excrescences, which are also apparently 
closed. The shell composing the parts just described is very 
delicate and thin compared with that forming the rounded nucleus, 
and its outer surface is frosted with small glassy projections of an 
irregularly squared figure, like imperfectly formed crystals, It is 
evident that this is a hastily deposited shell-covering on the sar- 
code developed since the last regular chamber of the shell was 
formed, and which, instead of collecting itself into a definite shape 
to produce a chamber similar to the others, had been surprised, 
as it were, while fully expanded by the calcifying process, which 
consequently gives us a petrified representation of the ordinary 
appearance of this external sarcode, with its pseudopodia pro- 
truded, the probable suddenness of the process being illustrated 
by the cauliflower excrescences which terminate many of the 
branches, and which have resulted from the contraction of the 
extremely fine terminal filaments of sarcode. It would appear 
that this is the final act in the life of the Polymorphina, its en- 
feebled vital power being insufficient to gather together the sar- 
code for the formation of another regular chamber, and therefore, 
properly speaking, the shell is fully formed and perfect before 
this last addition is made to it. There is evidence, however, in 
the specimens I have now to show, that the animal must have 
lived for a considerable time in 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 circular, 
but oftener oval or kidney-shaped, and so numerous as to open a 
- very free communication between the external sarcode 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 deposited, and this gives them a physiological interest, 
