10 ProL 
PROTOZOA. 
vided with a perforate membrane, one large branched or many minute 
nucleoli, &c., in opposition to those which, like Collozoum, Sphcerozoum, 
Thalassophceray Thalassoplaneta, CystidcBf DiscidfB^ Acanthometridce^ &c., 
have, from the first, numerous nuclei of a simple homogeneous structure ; 
on the Co/ZiWu, however, several small nuclei are developed by-and-by, 
and before the formation of the “zoospores,” a retrograde transformation 
of the large central nucleus takes place, resulting in an organization similar 
to that of the majority of Radiolaria, The Radiolaria (the organization 
of which is, after all, more simple than hitherto supposed before Hertwig’s 
researches) are especially characterized by the central capsule, its external 
gelatinous layer, the yellow cells (only wanting in AcanthometridcB), and 
the propagation through uniflagellate zoospores, the mode of develop- 
ment of those elements, &c. Their nearest allies (in shape, skeleton, 
&c,), are the fresh- water Heliozoa, characterized by the absence of a 
true central capsule, and the presence of contractile vacuoles and of 
axial filaments traversing the pseudopodia and the body to the central 
granule ; the zoospores are biflagellate, provided with several contractile 
vacuoles, a more differentiated nucleus, &c. They might, however, be 
considered as subclasses (Heliozoa, Cytophord) of a class (^Radiolaria) 
forming, with the Thalamophora, the realm of Sarcodina or Rhizopoda 
(sensu latiore). 
Carter (8) has published detailed descriptions of Polyirema miniaceum 
(Linn.), P. halaniforme^ Cart., utriculare, sp. n., 1. c. p. 210, pi. xiii. figs. 11- 
16, and P. planum^ p. 211, figs. 18 & 19 (Australia). P. halaniforme is 
identical with the genus Carpenteria of Gray, which is not a connecting 
link between Rhizopods and Sponges, the sponge spicules and similar 
foreign bodies being found embedded in its shell-substance or in its interior, 
drawn in with the sarcode, as is also often the case in P. miniaceum. 
Carpenter (7), on the other hand, urges the necessity of retaining 
Carpenteria as a distinct genus, because the arrangement of the primary 
chambers is distinctly spiral, Glohigerina-\\k.Q^ while Polytrema (like 
Tinoporus) is an extraordinary development of the Planorbuline type ; 
“the branching canals or utricular dilatations of Polytrema are mere 
cavitary interspaces in the midst of a fabric built up by the aggregation 
of minute chambers ; the cavities of Carpenteria are its true chambers, 
arranged in regular spiral succession, and separated from each other by 
complete septa, whilst partially subdivided into chamberlets by imperfect 
septa.” ^\Polytr. miniaceum differs externally from all other known i^^ora- 
minifera through its fixed calcareous arborescent test with superior aper- 
tures, internally from most Foramini/era in possessing a cancellous struc- 
ture void of the canal system, but permeated with cavernous excavations 
communicating with the apertures, and more or less filled with sponge- 
spicules and other foreign objects ” (Carter). 
Fossil Ehizopoda. 
J. Bennie, Note on range of Saccammina carteri^ Br., in the car- 
boniferous series ; Geol. Mag. (2) iii. p. 47. H. B. Brady, Monograph 
of carboniferous and permian Foraminifera ; London : 1876, 166 pp. 
