PRESIDENTIAL ADDRESS. 445 



Having now defined or explained, as well as I am able, the terms of which 

 I am about to make use, I return to my main theme, the cell and its evolution. 

 To summarise the points already discussed, a typical cell ie a mass of proto- 

 plasm differentiated into two principal parts or regions, the cytoplasm and 

 the nucleus, or, it may be, two or more nuclei. The cytoplasm may or may 

 not contain chromatin-grains in addition to other enclosures, and may possess 

 cell-organs of various kinds. The nucleus, highly variable in minute structure, 

 possesses one invariable constituent, the chromatin-material in the form of 

 grams and masses of various sizes. 



The cell, therefore, in its complete and typical form, is an organism 

 of very considerable complexity of structure and multiplicity of parts. The 

 truth of this proposition is sufficiently obvious even from simple inspection of 

 the structural details revealed by the microscope in cells in the so-called 

 ' resting condition,' but still more so from a study of their activities and 

 functions. The vital processes exhibited by the cell indicate a complexity of 

 organisation and a minuteness in the details of its mechanism which transcend 

 our comprehension and baffle the human imagination, to the same extent as do 

 the immensities of the stellar universe. If such language seems hyperbolic, it 

 is but necessary to reflect on some of the established discoveries of cytology, 

 such as the extraordinary degree of complication! attained in the process of 

 division of the nucleus by karyokinesis, or the bewildering series of events 

 that take place in the nuclei of germ-cells in the processes of maturation and 

 fertilisation. Such examples of cell-activity give us, as it were, a glimpse into 

 the workshop of life and teach us that the subtlety and intricacy of the cell- 

 microcosm can scarcely be exaggerated. 



On the assumption that an organism so complex and potent was not 

 created suddenly, perfect and complete as it stands, but arose, like all other 

 organisms, by progressive evolution and elaboration of some simpler form and 

 type of structure, it is legitimate to inquire which of the various parts of the 

 cell are the older and more primitive and which are more recent acquisitions 

 in the course of evolution. But it must be clearly pointed out. to start with, 

 that the problem posed in such an inquiry is perfectly distinct from, and 

 independent of, another point which has often been discussed at length, namely, 

 the question whether any parts of the cell, and if so which parts, are to be 

 regarded as ' living ' or ' active ' in distinction to other parts which are to be 

 regarded as 'not-living' or 'passive.' This discussion, in my opinion, is a 

 perfectly futile one, of which I intend to steer clear. 



We may agree that in any given cell or living organism, simple or complex 

 in structure, all the parts are equally 'living' and equally indispensable for 

 the maintenance of life, or at least for the continuance of the vital functions 

 in the normal, specific manner, without losing the right to inquire which of 

 those parts are the phylogenetically older. A simple analogy will serve to 

 point my meaning. A man could not continue to live for long if deprived 

 either of his brain, his digestive tract, his lungs, his heart, or his kidneys, 

 and each of these organs is both ' living ' in itself and at the same time an 

 integral part of the entire organisation of the human body; yet no one would 

 think of forbidding comparative anatomists to discuss, from the data at their 

 command, which of these organs appeared earlier, and which later, in the 

 evolution of the phylum Vertebrata. Moreover, speculative though such dis- 

 cussions must necessarily be, there is no one possessing even a first-year 

 student's knowledge of the facts who would controvert the statement that the 

 digestive tract of man is phylogenetically older than the lung. Speculative 

 conclusions are not always those that carry the least conviction. 



The evolution of the cell may be discussed as a morphological problem of 

 the same order as that of the phylogeny of any other class or phylum of living 

 beings, and by the same methods of inquiry. In the first place there is the 

 comparative method, whereby different types of cell-structure can be compared 

 with one aiiotlier and with organisms in which the cell-structure is imperfectly 

 developed, in order to determine what parts are invariable and essential an<l 

 wh.Tt are sporadic in occurrence and of secondary importance, and if possible 

 to arrange the various structural types in one or more evolutionary series. 

 Secondly there is the developmental or ontogenetic method, the study of the 

 mode and setjuence of the formation of the parts of the cell as they come into 



