284 Dr. G.C. Wallich on the Extent and Causes of 
already stated, the appearances just indicated are to be found not 
only in the lageniform and mitriform, but also in the globular 
series, and in the exceptional variety Difflugia spiralis. 
Lastly, I may mention that in certain individuals (as for ex- 
ample in figs. 13, 23, 24, & 24 a) the whole of the test is covered 
with minute cylindrical rods evidently of similar origin, Some- 
times these little cylinders are straight, sometimes irregularly 
curved ; but, as in the former examples, they are arranged side 
by side, and without any very distinct regularity *. 
It has been already stated that no effect is produced by the 
rectangular plates when seen by polarized light. When, how- 
ever, the discs (which in common with the rectangular plates and 
cylindrical bodies are themselves perfectly colourless) are seen by 
polarized light, the alternating changes of tint are not only 
distinctly visible over the test generally, but to the same extent 
in each particular disc,—thus indicating that the effect is not due 
to the presence of micaceous or other mineral films such as 
usually underlie the external coarse layer of sandy particles—a 
fact which is verified when such forms as those now under notice 
are broken up under the microscope. 
The inference which I draw from this singularly complete 
series of transitionary forms is, that the chitinoid basal substance 
of the test, or (as is quite possible when we take into considera- 
tion the facts I shall presently adduce with regard to the mode 
in which mineral particles are arranged by an external sarcode- 
layer such as we see in Gromia) a portion of the viscid sarcode 
mass, combines, under the law of “molecular coalescence” ft, 
with the siliceous or other mineral elements, and thus serves to 
produce all the transitionary colloid bodies which occur, from 
the first alteration in shape of the mineral particles themselves, 
to the development of the crystalline tablets which were first 
described. One thing is quite manifest, namely, that the whole 
series of bodies now under notice are derived in some way from 
the animal, and no¢ directly from the medium in which it lives ; 
for none are traceable in a free condition in the material in 
which the specimens occur. On the other hand, notwithstanding 
the selective and adaptive faculty already shown to belong to the 
Rhizopod, we are not warranted in assigning to it a special 
formatwe power. The origin of the minute crystalloids, so 
abundantly present in the Amoeban and Difflugian forms gene- 
rally, is thus also accounted for; and step by step we are 
arriving at a knowledge of the mode in which the vital and 
* These bodies were accurately described by me in the ‘Annals’ for 
December 1863, p. 456. 
+ See Mr. Rainey’s valuable papers on “ Molecular Coalescence ”’ 
vols. vi. and vii. of the Journal of Microscopical Science. 
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