C. DOBELL 181 



such as this, it may be stated now with considerable confidence, as a 

 concrete proposition, that conjugation in the ciliates does not result in 

 rejuvenation — no matter whether a literal or metaphorical meaning be 

 attached to the word. 



128. Experimental inquiries into the factors which determine division 

 and hereditary transmission of characters ; into the factors which deter- 

 mine or inhibit conjugation ; into the results which conjugation itself 

 determines, whether in originating or eliminating variations ; and into 

 the origin of variations, — all these investigations have yielded a great 

 mass of facts of great interest and suggestiveness. But these facts — 

 in my opinion — throw little light upon the great central problems 

 concerned. Rather do they throw into vivid relief the formidable 

 complexity of all biological problems as presented by the Protozoa. 

 It is safe to prophesy that when the known facts have been doubled 

 or trebled, the ironical statement — which now prefaces so many memoirs 

 on the ciliates — that " the Protozoa are the simplest organisms in which 

 to study the great problems of biology " will disappear from biological 

 literature. 



129. The tradition which finds expression in such statements as 

 this is at present almost universally received. It is believed that the 

 non-cellular organisms display vital phenomena in a more elementary 

 and therefore more easily comprehensible form than other organisms. 

 From his earlier physiological studies Jennings (1906) rightly con- 

 cluded that " the behaviour of the Protozoa appears to be no more 

 and no less machine-like than that of the Metazoa." " Action is as 

 spontaneous in the Protozoa as in man." This truth should never be 

 forgotten. It is vain to seek for simple mechanical factors which 

 " induce conjugation " in ciliates. For conjugation is the resultant 

 of many external and internal factors — environmental opportunities, 

 inherent inclinations and potencies — which are no less complex and 

 no more easily comprehensible than the factors which result in com- 

 parable phenomena in man. They are really less easy to understand, 

 because we have no conception of what the " motives " may be which 

 actuate a brainless, non-cellular creature. 



130. In the foregoing pages I have confined myself to recording 

 and analysing facts and concrete questions. It is often asked " What 

 is the significance, or meaning, of conjugation?" This question is 

 itself meaningless. As well might one inquire the meaning of the 

 moon. I have purposely avoided all such questions, though they have 

 been freely debated by others. I have also avoided all discussion of 



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