TRANSACTIONS OF SECTION P. — PRESIDENTIAL ATJDRESS. 437 



SECTION D.— ZOOLOGY. 



PilCSlDRNT OF THE SECTION : —PeOFES SOU E. A MiN'CHIN, 



M.A., Hon. Ph.D., F.R.S. 



WKDXESDAY, SEPTEMBER 8. 

 The Presiilenfs Ai.ldfe.'^s was read in liis absence, as fallows :— 



The Evolution of Uie Cell. 



When addressing an audience of biologists it would be superfluous to insist 

 upon the importance of the study of the cell and its activities. It is now- 

 recognised almost universally that the minute corpuscles known by the some- 

 what unsuitable term ' cells ' are the vital units of which the bodies of animals 

 and plants are built up, and that all distinctive vital processes — metabolism, 

 growth and reproduction, sexual phenomena and heredity — reduce themselves 

 ultimately to activities taking place in, and carried on by, the individual 

 cells which build up the body as a whole. Each cell must be regarded as 

 a living, individual organism which, however much it may be specialised 

 for some particular function or form of vital activity, is capable of main- 

 taining its life and existence in a suitable environment by carrying on all 

 the necessary processes of metabolism which are tre essential and distinctive 

 characteristics of living beings. In the case of cells composing the complex 

 body of the higher animals and plants the cells are mutually interdependent, 

 and, with the exception of the mature germ-cells, cannot maintain their exist- 

 ence apart from their fellows ; that is to say, the only natural i environment 

 suitable for their continued existence is the complex body or cell-commonwealth 

 of which they form an integral part. But in the simplest forms of life the whole 

 body of the living individual may reach no higher degree of complexity than 

 the single cell, which is then seen as an organism physiologically complete in 

 every respect, living a free and independent life in Nature and competing 

 with other organisms of all kinds, simple or complex, in the universal struggle 

 for existence amongst living beings. This statement of the ' cell-theory ' is 

 that with which, I believe, the majority of modern biologists would agree; 

 not without, however, some dissentients, amongst whom I personally am not to 

 be numbered.^ 



The fundamental importance of the cell as a complete living organism, 

 whether maintaining itself singly and independently or in union with other 

 similar but individually specialised units, has made it the object of intensive 

 and concentrated study, not only by those who group themselves according to 

 their special points of view as zoologists, botanists, physiologists, &c., but also 

 by a class of investigators who take the cell itself as the subject of a branch 



* It is not necessary to do more than refer here to the investigations that 

 have been carried on in recent years with regard to the viability and multiplica- 

 tion of tissue-cells removed from the body in artificial culture-media. These 

 experiments afford strong support to the view that the cell is to be regarded 

 primarily a6 an independent living organism. 



* See Appendix A. 



