SPECULATIONS ON THE ORIGIN OF LIFE 307 



its earliest ancestors, though still microscopic to our limited 

 senses ; it would be a mass of cytoplasm containing numerous 

 chromidial grains and it is only in this sense that I can accept 

 Haeckel's Monera. The next step in evolution would be the 

 concentration and organisation of the scattered chromidia into a 

 definite compact structure, the nucleus ; with this step completed 

 the condition of the true cell would have been reached. Unless 

 the word " cell " is to become quite vague and meaningless, a mere 

 synonym of such terms as microbe or micro-organism, it should 

 in my opinion be restricted in its application to those organisms 

 which have reached the degree of structural complexity found in 

 the tissue-elements to which the term "cell" was originally applied 

 — that is to say, to organisms in which the protoplasm is differen- 

 tiated into cytoplasm and nucleus definitely marked off from one 

 another. By this criterion the Bacteria and their allies should 

 not be termed cells at all. For me the term "cell" connotes a stage 

 in the evolution of living beings which the Bacteria have not 

 reached. 



The evolution of the cellular type of structure may be regarded 

 as the most momentous event in the evolution of living beings 

 on this globe. As I have pointed out elsewhere, 1 the cell, in the 

 sense in which I use the word, should be regarded as the 

 starting-point in the evolution of the entire animal and vegetable 

 kingdoms, the elementary structural component of the bodies of 

 ordinary plants and animals. Moreover it is probable that the 

 peculiar phenomena of sex and sexual behaviour did not come 

 into existence until the cellular type of structure had been 

 evolved ; in my opinion, without sex there can be no true species 

 in living organisms. 2 



1 Presidential Address to the Quekett Microscopical Club, 191 1. 



3 In the course of the discussion, my views with regard to the fundamental 

 importance of chromatin in all living substance were criticised by Prof. MacDonald 

 on the ground that some of the most essential and important activities of the 

 human body were due to purely cytoplasmic structures, as for example all muscular 

 and nervous mechanisms. I am well aware that in the course of evolution of the 

 cell and of its adaptation to various functions, the cytoplasm becomes of great 

 importance and shows an amount of structural differentiation in excess of that 

 exhibited (visibly at least) in the nucleus. It is not necessary to take cells of the 

 human body as examples of this ; the ciliate infusoria furnish instances of cells 

 far more complicated in structure than any found in the human body. It seems to 

 me, however, that any attempt to gain a notion of the most primitive type of living 

 being must begin by seeking to discover what, if anything, is common to all forms, 

 moods or shapes of life, rather than by dealing with the complex structures 



