Dr. WallicH; on the Polycystina. 59 
manner in which the term ^' nucleus'^ has been employed^ in 
Miiller's work, to signify a portion of the structure totally 
distinct from that to which it usually, or indeed legitimately, 
applies, not only has his classification been impaired, but, on 
his authority, has an error been promulgated by other writers, 
the importance of which can hardly be over-estimated. For, 
if it be admitted, as I presume is the case, that physiological 
advance is deducible from the gradually increasing com- 
plexity of a creature^s organization, the presence or absence of 
such an appendage as the nucleus must necessarily be regarded 
as of higher significance than the degree of frequency with 
which the pseudopodia coalesce, or the form these processes 
assume when projected beyond the general mass of sarcode. 
The next important addition to our knowledge of the 
Rhizopods is contained in the work of MM. Claparede and 
Lachmann {' Etudes sur les Infusoires et les RMzopodes' pub- 
lished at Geneva almost immediately after the appearance of 
Miiller^s memoir. According to these writers, the Rhizopods 
may be arranged as follows : 
Neither calcare- f Pseudopodia f Siliceous"] 
ous test nor 
multiple fora- 
minated cham- 
bers. 
rarely inos- 
culating 
with each 
other. 
spicules 
absent. 
No yel- 
low cel- 
lules. J 
^ Peoteina. 
r Amoeba. 
1_ Actinophrys. 
r Siliceous") 
< spicules I 
[ present. | 
r Acanthometra. 
r Yellow 
X cellules 
[ present.^ 
Pseudopodia forming 
numerous inoscula- 
tions with each other. 
^ ECHINOCYSTIDA < Tholassicolla. 
|_ Polycystina. 
Gromida 
CrTomia. 
Test generally calcareous, and constituting"] 
several chambers; but at times single 
Its walls pierced with multitudinous 
minute apertures. 
Foraminifera 
f MonotTialamia. 
\ Polythalamia. 
In this system, in which we have presented to us the first 
really comprehensive view of the principal Ehizopodal families, 
there occur some striking peculiarities. To these must be 
accorded more than a passing notice, inasmuch as they involve 
not only characters but conclusions somewhat at variance with 
what is known of the organisms to which they relate. 
Thus, although the invariable absence of a calcareous test 
VOL. XIII. / 
