GENUS ORB1TOLITES: 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 Forarninifera, such as Orbitolite or Nutnmulite, is to be regarded 

 as a single individual, or as a colony or clutter of individuals. All 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 hornolo- 

 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) the 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 

 'individual,' 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 denned, 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 Acalephae, &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. HUXLEY'S observations on this subject, in Philosophical Transactions, 1851, pp. 578, 580. 

 I 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 



