378 
POPULAR SCIENCE REVIEW. 
As the Dictyochidce have often been met with by me in tropical 
seas, grouped together in numbers in a common sarcodic matrix, 
and they possess the characteristic tubularity of which I have 
spoken, it appears to me that they form the only true connecting 
link between the Rhizopods and the Sponges. 
It has already been shown by me why I hold that the Poly - 
cystina — which have of late years been seized upon to help to 
build up the motley group called Radiolaria , are disqualified 
through the absence of an encapsuled and definite nucleus, 
from being placed in any other position amongst the Rhizopods, 
than with the Foraminifera. It is, however, only because they 
have been classified in like manner with the other groups 
arranged under the term Radiolaria , without any further result, 
so far as I can see, than to increase the list of so-called genera 
and species, and without due weight being ascribed to their ex- 
treme varietal tendencies : that I avail myself of the present 
opportunity to furnish a somewhat more complete, though neces- 
sarily brief outline of their classification and characters than has 
heretofore been offered by me. 
In the earliest observable stage of the siliceous skeleton of 
the Polycystina , two very definite and important formations 
take place within the sarcoblast. These, apparently, never vary 
so far as to render their characters uncertain at any subsequent 
period in the history of the organism. To these two formations 
(in consequence of their extreme value for determining their 
typical starting-points), I have given the names of Omphalostype 
and Omphalic chamber. The first constitutes the axis of all future 
development of the siliceous structure. The latter constitutes 
the omphalic chamber, which answers to the primordial chamber 
of the closely related Foraminifera. Both are secreted, one, how- 
ever, after the other within the nucleus and peripheral portion of 
the sarcoblast which produces them ; the omphalostype con- 
sisting in the Symmetrical or Oyclodinal division of the Poly - 
cystina , of two, or four, rarely more, intensely delicate and 
minute spinelets , united at their bases, but upon and around 
the free extremities of which the first little spherical chamberlet 
or omphalic chamber is secreted, whilst as yet the dimensions of 
the sarcoblast have but very slightly increased ; the second and 
each succeeding chamber of the series being constructed on pre- 
cisely the same plan ; that is to say, by the continuous growth, 
radially outwards of the spines, and the repetition, at stated 
intervals, of the formation of another perforated siliceous cham- 
ber ; until at last there exists a series of gradually increasing 
hollow spheres, retained one within the other, and in situ , by 
the spines. In the Non-symmetrical or Monodinal division, the 
omphalostype consists of extremely delicate siliceous fibres, 
