58 
pR. Wallich^ on the Polycystina. 
Rhizopods; to describing their plan of development and 
(so far as I know) their mode of reproduction; and, lastly, 
to pointing out how the rudimentary siliceous skeleton of this 
family may be rendered available for its classification on a 
natural system. 
In order to accomplish ttiese objects, however, it becomes 
imperative on me to review the various systems hereto- 
fore proposed in classifying the Rhizopods, and I shall strive 
to do so as briefly as is consistent with the necessity for 
an explanation of the grounds on which I seek to eff'ect a 
modification of these systems ; and, amongst other changes, to 
remove the Polycystina to a lower position in the series than 
has heretofore been assigned to them. 
To the late Professor L. Miiller, of Berlin, is due the credit 
of having established the true nature of the Polycystina, In 
his admirable memoir ' Uber die Thalassicollen Polycystinen 
und Acanthemetren des Mittelmeeres ' (published in 1858) 
they are associated, as stated in the title, with two other 
families, under the designation of the " Rhizopoda Radiaria 
seu Radiolaria.^^ The definitions, as found in the above 
work (pp. 16, 17), are as follows : 
Rhizopoda Radiaria seu Radiolaria, 
A. Solitary. Radiolaria solitaria. 
1. Without shell; with or without siliceous spicules. 
Thalassicollina, restricted to Thalassicolla. 
2. Animal enclosed in a siliceous foraminated shell. 
Polycystina. 
3. Animal naked, with siliceous radiate spines. Acan- 
thometrina, 
B. Compound. Radiolaria poly zoa. 
4. Naked, or with siliceous spicules. BphcerozoidiS, 
Sphcerozoum. 
5. Enclosed in a siliceous foraminated shell. Collo- 
sphceridce. 
As I shall have occasion to state my views regarding the 
expediency or otherwise of accepting variations in the charac- 
ters of the pseudopodia as distinctive of the Orders into which 
the Rhizopods are divisible, I would merely observe, at 
present, that, under the system thus constructed, the Poly- 
cystina which have no nucleus, are associated with two 
families which possess this organ in a highly developed 
degree. And further, that, in consequence of the unguarded 
