Dr. WallicHj on the Polycystma. 
79 
The more extensive our experience/^ he observes^ " the 
weaker become our convictions respecting the limits of varia- 
tion in any species of Foraminifera. . . . That species 
do exist among the Foraminifera as elsewhere, analogy would 
lead us to infer ; but I believe there are several actual indi- 
cations of the fact more substantial than what can be sup- 
plied by mere analogy. But we have hitherto failed to detect 
their real specific peculiarities, or even to ascertain in what 
part of the living organism they are likely to be found. As 
yet they are but unseen potentialities, of which the eye has 
hitherto been unable to detect any concrete or objective 
manifestations ; and I strongly suspect that the remark is 
equally applicable to the entire group of the RhizopodaJ""^ 
It is in view of this opinion, to which I cordially subscribe, 
that I now offer the following systematic classification of the 
Polycystina. 
It will be seen that one universal character distinguishes 
the skeleton of the Polycystina from that of the Foraminifera. 
It is always purely siliceous, of crystalline transparence, 
solid, invariably composed of one continuous unbroken piece, 
perfectly rigid, and unafi*ected by any chemical agents except 
those which are the known solvents of silex. Hence in this 
family we are deprived of those distinctive features in the 
composition and construction of the skeleton which, in Car- 
penter's system, are applied to the Foraminifera and afford 
so admirable a means of determining the sub-families. In 
the Polycystina, moreover, we have no distinction afforded by 
Perforate and Imperforate forms, since, virtually, all are 
perforate. That is to say, there is no exception to the rule 
that the siliceous skeleton is so pierced by apertures, in every 
portion (excepting the spinous projections, which are so but 
rarely), that the most complete communication may be said 
to exist between the contents of every chamber and the 
investing film of sarcode on the exterior. Even in the oldest 
individuals, in which siliceous deposit has gone on tiU the 
walls are so unusually thick as materially to increase the 
space between the sarcode within and the sarcode without, 
some of the apertures are rarely, but all are never, obliterated. 
The growth of the mineral portion in this, as in all the 
other siliceous-shelled Rhizopods, except the Bictyochidce, is 
essentially the same. That is to say, the material is deposited 
* Williamson's 'Hecent British Eoraminifera/ published by the Hay 
Society, 1857. Introduction, p. 10. 
f See " Remarks on the Process of Mineral Deposit in the Rhizopods 
and Sponges," by G. C. Wallich, M.D., ' Annals and Magazine of Natural 
History,' January, 18 64, p. 72. 
