76 Dr. Wallich, on the Polycystina. 
and contractile vesicle as of primary importance in the deter- 
mination of the Ordinal unity of the families grouped together 
in the Proteina. I have already cited my reasons for re- 
garding variations in the apparent degree of differentiation 
of the protoplasmic mass, and in the shape, size, number, and 
tendency to coalesce of the pseudopodia, as of but secondary, 
or, in other words, merely generic, value. But, after a laborious 
study of the principal fresh-water Puoteina, extending over 
nearly two years without any important intermission, I am 
satisfied that, even regarded as generic characters, these are 
subject to a much wider range of variation than is usually 
imagined, not only in the same genus, but in the same in- 
dividual at different periods of its existence. 
It appears to me that, with all this tendency to va- 
riability (even assuming a higher significance to attach to 
differences in the degree of differentiation attained by the 
sarcode than I am at all prepared to allow) the association in 
the same Order, of families in which these differences show 
themselves to the utmost, is far less open to question than the 
grouping, in the same order, families exhibiting pseudopodia 
framed on the Actinophryan type with such a family as 
Thalassicollttj in which there is not a trace of a true pseudo- 
podial appendage ; and even the guardedly defined " active 
motion of granules^^ amongst the fibrils, " as if circulating,^' 
was only observed once> and then not in the typical T. punc- 
lata (Hux.), but in the form which he preferred to associate 
with Noctiluca ! 
Bearing this in view, it may be stated that the various 
genera of the order Proteina may be divided into two sec- 
tions — the first, in which the pseudopodia assume the Acti- 
nophryan character, and rarely deviate from it ; the second, 
in which these organs, though normally lobose,'' frequently 
merge into the Actinophryan type. Hence the division into 
'^Monomorphous'^ and Polymorphous'' families. 
Commencing, then, with the assumption (reasons for 
which have been already given) that our knowledge of the 
animal of the Polycystina, as well as of the other lower 
Hhizopods, is not yet sufficiently matured to enable us to 
determine specific differences in this portion of their struc- 
ture, we must obviously search for some basis on which to 
classify them in the mineral skeleton which accompanies the 
soft parts. This basis, I conceive, is furnished by the plan of 
growth of the embryonic skeleton, and by its subsequent stages 
of development. In this very important respect, therefore, 
does the system now offered for the systematic classification 
of the Polycystina differ from that founded on mere varia- 
