- ON THE GENUS POLYMORPHINA. 247 
by the continuatiou of the shelly investment; and the question has been raised, whether 
this may not be their normal condition. Further observations on living specimens are 
much needed; without them it can scarcely be admitted that the open ends are due to 
the breakage or erosion of the caleareous investment. It is not uncommon to meet with 
Polymorphine having irregular perforations of considerable size in the shell-wall. The 
same peculiarity may be and is observed from time to time in other genera; but in none 
does it exist to the same extent as a habit of growth, and in the particular varieties at 
present under notice it is a distinguishing feature. Soldani, as early as 1791, makes 
those frequent, large, irregular or rounded orifices very prominent in some of his figures, 
and appears to have suspected that they were indications of importance; and they have : 
not been passed over by subsequent writers. Dr. Aleock, however, in some interesting 
observations on Polymorphina tubulosa*, draws from them an ingenious argument in 
favour of the view that Foraminifera have the power of absorbing and re-precipitating por- 
tions of the carbonate of lime of which the shell-wall is formed, and supports the theory 
by collateral evidence. Thus, in specimens having the supplementary fistulose chamber, 
we find that the primary shell has the thickened homogeneous wall usual amongst fully 
erown Foraminifera of the same class, whilst the wild-growing portion of the test is of 
much more delieate texture. Individuals in which the irregular growths have been 
broken away (Pl. XLII. figs. 38, y, k, 7) commonly exhibit a’ number of the perforations 
alluded to, in the region of the primary shell which formed the floor of the fistulose 
chamber. It might be supposed that the irregular segment was the result of the cover- 
ing in of a lobe of sarcode issuing from those large perforations—in other words, that the 
perforations were the cause rather than the effect of the aberrant chamber; but this sup- 
position is inconsistent with the well-observed fact, that the shell-wall is uniformly dimi- 
nished in thickness over those portions which are so covered in. In old and worn 
specimens in which the fistulose chamber, from the tenuity of its wall, has been quite lost, 
its exact extent may commonly be traced by observing the outline of the area on the pri- 
mary shell so thinned away. 1t would scarcely be necessary to insist on this, were it not 
that the Protozoa are seldom accredited with the power of performing any but the most 
simple vital processes. In some of the Mollusca the habit of thinning the interior por- 
tions of the calcareous spire as its growth advances is well ascertained; and a section of 
one of these shells presents some curious resemblances to our drawing, Pl. XL. fig. 12, e, 
taken from an accidentally broken specimen of a common thick-walled variety. It has 
been noticed, also, that, not unfrequently, the stolon-passages between the older chambers 
of large individuals are very free and patulous, whilst the terminal orifice of the last seg- 
ment consists only of constricted radiate slits. It is fair to assume that this difference is 
due to resorption of calcareous material. 
The shelly investment of the cervicorn chamber differs much in appearance and texture 
* Proc. Lit. and Phil. Soc. Manchester, vol. vi. p. 85. See also note on Polymorphina lactea in a memoir by 
W. K. Parker and T. R: Jones, on “ Some Foraminifera from the North Atlantic and Arctic Oceans,” Phil. Trans. vol. clv. 
p- 361, in which the opening of foraminal communication by absorption had previously been suggested as a possible 
explanation of the rows of orifices sometimes met with on the side of the antepenultimate, and even of the earlier 
chambers in these free-growing varieties. 
