462 TRANSACTIONS OF SECTION D. 



Ciliates. In the Metazoa the individual cells may be highly specialised for 

 some particular function of life ; but a Ciliate is a complete and independent 

 organism and is specialised for each and all of the vital functions performed 

 by the Metazoan body as a whole. From the physiological standpoint a Ciliate 

 (or any other Protist) is equivalent and analogous to a complete Metazoon, 

 say a man, but I cannot for a moment agree -with Dobell '" that the body of 

 a "Ciliate is homologous with that of a Metazoon— not at least if the word 

 homologous be used in its usual biological sense of homogenetic as opposed to 

 homoplastic. Dobell appears to me to negative his own conclusion when he 

 maintains that the body of a Ciliate is ' non-cellular ' while admitting that 

 the Metazoon is multicellular ; how then can they be said to be homologous ? 

 Only if the term homologous be used in a sense quite different from its ordinary 

 significance.'^ 



In addition to the highly-developed structural difFerentiation of the body 

 the Infusoria exhibit the extreme of specialisation of the nuclear apparatus in 

 that they possess, as a rule, two distinct kinds of nuclei, micronuclei and 

 macronuclei, composed respectively of generative and trophic chromatin, as 

 already pointed out. This feature is, however, but the culminating point in a 

 process of functional specialisation of the chromatin which can be observed in 

 many Protozoa of other classes, and which, moreover, is not found invariably 

 in its complete form in all Ciliata. 



In this address I have set forth my conceptions of the natare of the simplest 

 forms of life and of the course taken by the earliest stages of evolution, 

 striving all through to treat the problem from a strictly objective standpoint, 

 and avoiding as far as possible the purely speculative and metaphysical questions 

 which beset like pitfalls the path of those who attack the problem of life and 

 vitalism. I have, therefore, refrained as far as possible from discussing such 

 indefinable abstractions as 'living substance' or 'life,' phrases to which no 

 clear meaning can be attached. 



How far my personal ideas may correspond to objective truth I could not, 

 of course, pretend to judge. It may be that the mental pictures which I have 

 attempted to draw are to be assigned, on the most charitable interpretation, 

 to the realm of poetry, as defined by the greatest of poets, rather than of science. 



' The lunatic, the lover and the poet 

 Are of imagination all compact ; 



And as imagination bodies forth 

 The forms of things unknown, the poet's pen 

 Turns them to shapes and gives to airy nothings 

 A local habitation and a name.' 



If I might be permitted to attempt an impartial criticism of my own scheme, 

 I think it miglit be claimed that the various forms and types of organisms in 

 my evolutionary series, namely, the simple cell or protocyte, the cytode or 

 pseudomoneral stage, the micrococcus, even the biococcus, are founded on con- 

 crete evidence and can be regarded as types actually existent in the present 

 or past. On the other hand the role assigned by me to each type in the pageant 

 of evolution is naturally open to dispute. For example, I agree with those 

 who derive the Bacteria as primitive, truly non-cellular organisms, directly 

 from the biococcus through an ancestral form, and not at all with those who 

 would regard the Bacteria as degenerate or highly-specialised cells. But the 

 crux of my scheme is the homology postulated between the biococcus and the 

 chromatinic particle — chromidiosome or chromiole — of true cells. In support 

 of this view, of which I am not the originator, I have set forth the reasons 

 which have convinced me that the extraordinary powers and activities 

 exhibited by the chromatin in ordinary cells are such as can only be explained 

 on the hypothesis that the ultimate chromatinic units are to be regarded as 

 independent living beings, as much so as the cells composing the bodies of 

 multicellular organisms ; and, so far as I am concerned, I must leave the 

 matter to the judgment of my fellow-biologists. 



" Journal of Genetics, iv. (1914), p. 136. 

 " See Appendix A. 



