Dr. Wallich, on the Polycystina. 
83 
ence. The canal thus formed, however, is not deposited as a 
tube, but originally as a series of short spines arranged in cir- 
cular order at right angles to the axis of the disc; the canal being 
subsequently completed by the projection of a film of silex 
from each pair of spines, which renders the canal in reality 
polygonal. But this only occurs in those specimens in which 
the spongy structure of the outer layers is so dense as 
probably to have impeded the animal during its efforts to 
extend its velvety layer of minute pseudopodia. The little 
canal may therefore be said to represent the analogue of the 
aperture of a Monothalamous Foraminifera. This statement, 
however, is only offered as a surmise. 
Lastly, I have to speak of those singular examples in the 
Monodinal subdivision in which a repetition of parts, some- 
times similar in external contour to the type of the Cyclodina 
occurs along the course of a monstrously developed spine, 
and might thus countenance the idea that the boundary line 
above laid down is untenable. It will be found, however, on 
breaking up such growths, that we have before us merely a 
more or less dense network of siliceous filaments interwoven 
around the spine, and that nothing at all similar to the 
Omphalostype, or a true chamber, exists within. It is impor- 
tant to bear this in recollection, for, perhaps, in no series of 
organisms does monstrosity seem to attain such a limit. We 
are thus enabled to account for the difficulty which has been 
supposed to hedge in these beautiful structures and has be- 
come a barrier to their systematic distribution heretofore. 
It only remains to be stated that, perhaps, in no other 
family of the animal kingdom is the tendency to assume 
varietal form more signally manifest, at the same time that 
the line of demarcation remains clear between such characters 
as are constant and such as are accidental in their nature. 
Hence, notwithstanding the wide range of configuration 
which the Folycystina present, the number of species is 
extremely limited ; and these furnish the strongest evidence 
that the only permanent types are those which are recognisable 
in the earliest condition of the structure. 
The following is a tabular view of the classification of the 
Polycystina now proposed : 
VOL. XIII. 
h 
