ON THE RADIOLARIA AS AN ORDER OF THE PROTOZOA. 275 
(as the nucleus of the higher order of Khizopods invariably does) 
a membranous covering. For these combined reasons which 
had obviously made the term u yellow cells ” a dangerous mis- 
nomer, I designated them sarcoblasts. Whether, in the fresh 
water, the littoral, or oceanic Khizopods, the sarcoblasts in- 
variably constitute , when liberated from the parent organism 
(as they are always eventually destined to be), either at once the 
infant shell-less organism, as in the naked Khizopods ; or the 
nidus , and at the same time the infant mass of sarcode, within 
which the rudiment of the shell or other mineral framework of 
the organism is secreted. Thus, in the Amcebans , the sarco- 
blasts speedily assume, one by one, the whole of the typical 
characters of the parent form. In the Foraminifera and Poly- 
cystina , they are the nidus , within which, in the former family, 
the primordial calcareous chamber of the shell is secreted, and 
in the latter family, the earliest siliceous rudiment of the siliceous 
framework or perforated shell ; whilst in the Acanthometrina and 
other families constituting the second Order, in which an en- 
capsuled nucleus first presents itself, they form the nidus , not 
only within which the axial portion of the siliceous framework 
is secreted, but also within the peripheral portion of which the 
earliest discernible vestige of the membranous capsule is secreted, 
in the condition of a most subtle membrane. Indeed, so fully 
is this fact borne out by observation that it may, I venture to 
believe, be laid down that until the sarcoblast has already 
become freed from the parent structure, no trace whatever of 
the nuclear capsule exists. 
For the above stated reasons, (which I submit, demand some- 
thing more for their refutation than speculative disquisitions 
about the unicellular or multicellular potentialities of the Kadio- 
laria, or about their incipient Liver- systems and parasites ), I 
have considered it absolutely necessary to substitute the term 
sarcoblasts for that of yellow-cells , as being not only suggestive 
of the derivation and function of these bodies, but as avoiding 
a condition as to colour, which is altogether untrue in the case 
of the fresh- water Khizopods. 
But after what has been stated concerning the opinions of 
Professors Haeckel and Hertwig, Sir Wyville Thomson, and 
Mr. Mivart himself on the nature and origin of the y elloiu -cells , 
; it can surprise no one that the term sarcoblasts should not have 
j been very readily adopted by any of these writers. Mr. Mivart 
; tells us at the outset of his observations, that 66 each individual 
j Kadiolarian consists of two portions of coloured or colourless 
sarcode ; one portion nucleated and central ; the other portion 
peripheral and almost always containing certain yellow-cells ; 
J these portions being separated by a porous membrane , called 
the capsule ” (Memoir, p. 137), it being added in a footnote 
