86 
development characteristic of P. tubulosa. It consists in 
the mature state of the rounded shell of P. communis more 
or less concealed by several covered passages commencing 
at the mouth and taking a direction towards the base of 
the shell. These passages have their arched walls developed 
into tubular prolongations, extending in all directions, 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 sarcode 
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 representa- 
tion of the ordinary appearance of this external sarcode, 
with its pseudopodia protruded, the probable suddenness 
of the process being illustrated by the cauliflower excres- 
cences 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 enfeebled 
vital power being insufficient to gather together the sarcode 
for the formation of another regular chamber, and there- 
fore, properly speaking, the shell is fully formed and perfect 
before this last addition is made to it. There is evi- 
dence, however, in the specimens I have now to show, 
that the animal must have lived for a considerable time in 
