CARPENTER ON THE STTJDT OE THE EORAMINIFERA. 383 
paratively large, and in Miliola are reduced to the condition of mere 
constrictions, furnished with a tongue-like projection, or ‘valve,’ 
while in Nubecularia and Vertebralina they almost wholly disappear. 
And thus we are led to such pseudo-polythalamous forms as the 
nautiloid Cornuspira , in which the cavity of the shell is quite un¬ 
divided. In extreme contrast with this low type of structure we 
may cite the family of Nummulinida , among which, with one excep¬ 
tion, the septal planes are double, so that each chamber of the shell 
is furnished with a wall of its own. 
This duplication of the septa is accompanied bv the presence of 
another and highly important advance in organization; tlie develop¬ 
ment, namely, of an ‘ intermediate’ or ‘ supplemental skeleton,’ for 
the nutrition of which a peculiar system of ‘interseptal canals’ is 
provided. The interior of these canals, as of the interspace-system 
(their apparent representative) in the non-perforate Dactylopora , is 
quite distinct from though connected with the cavities of the 
chambers. In the higher members of the Eotaline group a sup¬ 
plemental skeleton also occurs, and in Calcarina constitutes the 
entire substance of the large club-shaped processes with which 
this curious form is ornamented. In other spiral shells, it “ not 
“ only fills up what would otherwise be superficial hollows at the 
“junctions of the chambers, or (as in Polystomella ) at the umbilical 
“ depression, but often forms a layer of considerable thickness over 
“ the whole surface, thus separating each whorl from that which en- 
“ closes it.” When this deposit is very scantily developed, an inter¬ 
septal system ceases to be necessary. “ The passages which make 
“ up this ‘system’ are not true vessels, but are mere sinuses, left in some 
“ cases by the incomplete adhesion of the two contiguous walls which 
“ separate the adjacent chambers, and in other cases apparently 
“ originating in the incomplete calcification of the sarcode which 
“ forms the basis of the solid skeleton; certain portions of that sub- 
“ stance remaining in their original condition so as to maintain a 
“ communication between the contents of the chambers and the parts 
“ of the calcareous skeleton most removed from them, analogous to 
“ that which the Haversian canals afford in the case of laminae of bone 
“ not in the immediate vicinity of a vascular surface. As, therefore, 
“ the development of the Haversian system is related to the thick- 
“ ness of the bone-sub stance to be nourished, so does that of the 
“ canal-system in Foraminifera seem to be related to the amount of 
“ consolidating substance which constitutes the supplemental skele- 
“ ton. There is good reason to believe that these canals are occupied 
“ in the living state by prolongations of the sarcode-body, which 
“ pass from the chambers into the portions of the system in nearest 
“ relation to them, and proceed to its peripheral extensions; and 
“ they are largest and most numerous when nutriment has thus to 
“ be conveved to parts of the supplemental skeleton, which (like the 
“ outgrowths of Calearina ) are very far removed from the segments 
“ of the ordinary sarcode-body.” 
