88 
perceptible excepting the month, showing that at this stage 
the numerous large holes which are afterwards formed have 
no existence. The great thickness of the outer walls com- 
pared with that of the internal parts of the shell shows 
that the animal must have existed for a considerable time 
in ' this condition, during which the surface has been 
strengthened by repeated deposits of calcareous matter 
from its coating of external sarcode, and the smoothness 
and evenness of this surface shows that the coating was at 
that time spread uniformly over the whole of it. But 
broken specimens of P. tubulosa show that a change in the 
disposition of the external sarcode has been afterwards 
made, for in these it is found to have collected itself into 
two or three irregular bands, always commencing by one 
end at the mouth and extending towards the base of the 
shell, an arrangement clearly mapped out by the remains 
of its ultimately formed shell-covering, fragments of which 
are seen still attached to the surface of the smooth rounded 
nucleus. 
The next event in the life of this Polymorphina is the 
formation of those numerous openings through the thick 
shell- walls, the observation of which in the specimens before 
you has chiefly led me to introduce them to your notice. 
These show, by their definite position and the evidence 
they give of their progressive formation, that when the 
external sarcode has once taken the form of bands it 
remains permanently in that state, and that these bands 
hold a fixed position on the parts of the shell where they 
were first placed. Among the specimens shown are some 
which only differ from ordinary shells of P. communis in 
being remarkably smooth on the surface and in having 
numerous large holes arranged in several rows radiating 
from the mouth towards the base of the shell, exactly as in 
undoubted specimens of P. tubulosa, but they are without 
the slightest trace of the external arched coverings and 
