GENUS ORBITOLITES: — PHYSIOLOGY; QUESTION OF INDIVIDUALITY. 211 
seems partly to consist in the limitation of the new growth to the natural margins of 
the zones ; no such growth taking place from the edge of a fracture which has 
crossed the zones transversely, although it may proceed from the remains of a zone 
which has been broken off by a fracture that partly follows its course. 
42. Question of Individuality . — It has been frequently discussed, whether each of the 
composite forms of Foraminifera, such as Orbitolite or Nummulite, is to be regarded 
as a single individual, or as a colony or cluster of individuals. Ail occasion for this 
discussion would, I think, be removed by the adoption of philosophical views as to 
what really constitutes an individual, and as to the relationship between the parts 
which, having a common origin in one generative act, are multiplied by a process of 
gemmation. As I have elsewhere endeavoured to show*, the entire product of every 
generative act, whether developing itself into a body of high organization, distin- 
guished by the structural differentiation of its parts, or evolving itself as an almost 
homogeneous aggregate of equal and similar segments, must be regarded as homolo- 
gically the same ; and the essential difference between the two, as living beings, lies 
in the functional relations of their respective parts. For whilst in the former there 
is so close an interdependence amongst them all, that no one can exist without the 
rest, and the life of the whole is (as it were) ihe product of the lives of the component 
parts, there may be in the latter such a mutual independence, that each part can con- 
tinue to live, grow, and reproduce itself when separated from the rest, so that the life 
of the whole is (so to speak) but the sum of that of its components. Now the term 
Mndividual,’ being commonly applied to the entire organism in the first case, and to 
only a small Segment of it, perhaps, in the second, is obviously inappropriate either to 
one or to the other, except in so far as it expresses the fact of independent existence. 
But the limits of such individuality as this cannot be strictly defined, and they 
even differ widely in animals whose general plan of structure is the same-f'. Hence in 
regard to the Foraminifera, as in regard to Zoophytes, Composite Acalephee, &c., we 
are to regard the entire mass originating in a generative act, as a single organism ; 
and the question in regard to the functional independence of its multiple segments, is 
one of degree in each particular type. Thus, as we have seen, this independence 
exists in the case of the Orbitolite to such a degree as to make each part entirely 
self-sustaining, and to prevent the existence of any definite limit to the growth of the 
whole ; yet it is quite possible that in a form so much more elevated as Nummulite, 
there may be, as maintained by MM. d’Archiac and Haime {op. cit. p. 69), such a 
degree of mutual dependence among the segments, and of unity in their aggregate 
life, that the latter predominates sufficiently to limit the growth of the organism to a 
tolerably determinate size^. 
* Principles of Comparative Physiology, chap. xi. sect. 1. 
t See also Mr. Huxlev’s observations on this subject, in Philosophical Transactions, 1851, pp. 578, 580. 
t Whilst admitting the possibility of this view, I shall hereafter have occasion to question its correctness ; 
since the evidence on which it is based appears to me by no means satisfactory. In fact, when I come to 
