80 Dr. G. C. Wallich on the Process of 
ternal sarcode of the chamber on which the spinous processes 
occur has no direct share in their production, from the cireum- 
stance of there being no aperture or pit at the interior point of 
the calcareous chamber which corresponds to the base of the 
process exteriorly. It may be stated, therefore, that the process 
of spine-formation in the Foraminifera is brought about by the 
secretion of calcareous matter upon an already existing calea- 
reous surface, each successive layer being received into the 
mould progressively made for it by the outward extension of its 
investing chitosarc. Fig. 5 diagrammatically represents the 
process, sP being the first. and sp! the second stage of spine- 
formation referred to. 
On these grounds, then, coupled with the fact that no Fora- 
minifera secrete silex, although several genera build up their 
shells by the addition of siliceous and other mineral particles 
derived from extraneous sources, I base my opinion that the’ 
spicules met with occasionally in Polytrema, Carpenteria, and 
Dujardinia* do not constitute integral portions of these or- 
ganisms, but have their origin in entozootic growth; and 
further, that the process of mineral deposit in the Sponges, as 
compared with that prevalent in the Foraminifera, is absolutely 
incompatible with the formation of true spicular growth. 
In the Polycystina the plan of mineral deposit is in every es- 
sential respect identical with that observable in the Foraminifera. 
That is to say, the siliceous portions (which do not constitute a 
shell, but ought to be regarded as an internal skeleton or frame- 
work) are formed by the addition of siliceous matter at right 
angles to the principal line of growth, and in one direction only. 
They are never formed around stolons, and consequently are not 
tubular—the finer threads of silex being projected from point to 
point of the reticulations, much after the same fashion that the 
threads of melted glass are fashioned by the glass-worker into 
miniature baskets, &c.,—the spinous processes so largely deve- 
loped in this family forming no exception to the rule, and it 
being only in the earliest rudiment of the siliceous structure 
that the silex is deposited in the shape of an extremely minute 
composite but solid spicule within the sarcoblast. This identity 
in the plan of deposit in the Foraminifera and Polycystina, not- 
withstanding the difference in the mineral material and the cha- 
racter of the hard parts, therefore yields a reason in addition to 
those derivable from the organization of the soft parts for the 
view advanced by me regarding the ordinal unity of these two 
families. 
* On similar grounds I consider the marginal cord in Operculina to be 
an ordinary secondary growth, in no wise analogous to spicular develop- 
ment. 
