564 
DR. CARPENTER’S RESEARCHES ON THE FORAMINIFERA. 
ing in NmnmuUte), and that the chamber of the row abutting on the preceding whorl 
is nearly always much larger than the rest, and gives origin to two or even three 
chambers in the next row. Further, it is sliown by vertical sections (Plate XXXI. 
fig. 7), that the innermost chambers of the whorl are not only broader but thicker, 
their upper and under walls diverging from each other where they are to be con- 
tinued over the spire they invest. Hence it is pretty obvious, that this portion of the 
whorl is that wherein the most active nutrition takes place ; and it is here that the 
marked accession to the number of chambers occurs, Vv^hich tends to carry the later 
rows around the whole circumference of the disk. 
1 15. Each of the early turns of the spire not only surrounds, but completely invests 
its predecessor; as is best shown by a vertical section, such as that represented in 
fig. 7- The investing whorl does not, in the younger part of the spire, come into 
immediate contact with the two surfaces of that which it includes, but is separated 
from it by the prolongation of the chambers and of their septa, very much as in 
ordinary NiimmuUtes. But between the later whorls, there are no such interspaces. 
4’he successive layers come into absolute continuity with one another ; both the tubuli 
and the cones of non-tubular substance being continued from each into the one 
external to it. From the time that the rapid thinning-away and opening-out of the 
spire commences, the investment of the previously-formed whoi'ls seems to discon- 
tinue, It is at the margin of each whorl, that we find the intermediate or additional 
skeleton most remarkably developed ; and the canal-systefn sometimes forms quite a 
network in its substance (fig. 11). 
1 16. General Summary. — It is obvious, from the foregoing details, that the physio- 
logical condition of each individual segment of the animal of Heterostegina must be 
essentially the same as that of each segment of Cycloclypeus \ and that the only 
difference in the condition of the two organisms arises out of the mode in which 
these segments are increased in number. In Cycloclypeus, in which each row of seg- 
ments is (normally at least) a complete annulus, a new annulus is formed around its 
predecessor by gemmation from its several segments along the entire circumference; 
and this mode of increase may be traced-back to the central cell, which buds-out 
equally on all sides. But in Heterostegina, each row is limited by the breadth of the 
spire; and while most of its chambers are formed by the like kind of gemmation 
from their predecessors, there is a special provision for an augmentation in the 
number of chambers at the end of the row nearest the previous whorl. Tracing-back 
the spire to its origin, we find that it commences in the one-sided gemmation of the 
central cell, just as we found it to do in Orbicidina (^ 85) and in those forms of 
Orhitolites which have a spiral commencement (^ 54). lienee there is nothing but 
the plan of increase, which separates Heterostegina from Cycloclypeus and their 
relation is exactly the same as that of Orhiculina and Orhitolites. For in Heterostegina, 
as in Orhiculina, the first-formed portion is a spire, of which each turn invests its 
predecessors; but after three or four turns have been made, the spire spreads-out, 
