Geological Society of London. 115 
few and far between, and lose their strength and their im- 
portance. | 
The exquisite symmetry and regularity of conformation of 
the shells of most recent and fossil Rhizopoda were the chief 
sources of the errors that prevailed so long about their nature 
and zoological position. The true explanation of their struc- 
ture appears to me to be that given in detail by our fellow- 
_member Dr Carpenter, to the effect that the entire mass, how- 
ever symmetrical or regular, represents the products by suc- 
cessive gemmation originating from a single ovum. It mat- 
ters little whether we regard each “joint” or cell of a Num- 
mulite as representing an individual or a zooid, provided we 
regard it as an element of the same essential nature with each 
polype of a polypidom, each cell-animal of a polyzoon, or in- 
dividual of a Botryllus. The value of the regularity of the 
whole is not invalidated, becausg that whole is a compound and 
not a unity, and our faith in the specific value of the fossil, and 
its consequent geological importance, may beas strongly based 
on the constancy of characters whose diagnosis is drawn from 
the features presented by a congeries of individuals as from 
those presented bya single being. I make this remark, because 
the only serious objection that I can take of the views of M. 
d’Archiac touching the nature of the Nummulite concerns this 
 fandamental point.. When he states as an argument against 
its compound nature, that, if each of the cells were the proper 
envelope of a particular individual, we ought to find a greater 
irregularity in their development in the same shell, and asks 
why, if this theory were true, should the heights of different 
coils of the same spiral present constant relations, and why 
the first and last cells should be less large than those of the 
median whorls,—we cannot accept the objections, for a crowd 
of comparable phenomena presented by the sertularian zoo- 
phytes, animals having considerable affinity with the Polyzoa, 
although of higher organization, come to our recollection. 
The variations of the Hydroida, their morphology and repro- 
duction, bear too close a relation to the phenomena exhibi- 
ted by the rhizopodous organism, to permit us to regard the 
Nummulite and its allies as simple bodies, or to dispute the 
_ theory of their gemmigerous constitution ; in other words 
H 2 
