C. DOBELL 179 



of the same species'. The case to which I refer is given by Simpson 

 (1901), who states that twice (out of 21 attempts) he succeeded in 

 getting conjugations between Paramecium caudatum and P. aurelia. 

 "After separation each of the exconjugants divided once: on the third 

 day they died off." The account is extremely unconvincing, and I think 

 it is infinitely more probable that Simpson was deceived than that 

 cross-conj ugation occurred. 



CHAPTER IV. 



General Conclusions. 



123. In this final chapter I propose to consider very briefly certain 

 results of the genetic study of the Ciliata. I would point out that this 

 chapter is not a summary of previous chapter.s ; nor is it intended to be 

 a substitute for them — to enable the reader to dispense with the facts 

 there set forth. Each of the preceding chapters is itself a series of very 

 brief and incomplete summaries, which form — in part — the premisses 

 from which the following conclusions are drawn. If my conclusions 

 appear absurd and wrong, they may nevertheless incite further inquiry 

 into the evidence upon which they rest. This is my desire. 



124. It is quite clear to me — and I have every confidence that 

 sooner or later it will be equally clear to others — that many of the 

 problems now associated with the ciliates do not exist in nature. They 

 are really dialectic — not problems of concrete biology. They are off- 

 shoots of the fallacies involved in the " cell theory," and of the unbridled 

 academic speculations concerning evolution which were fashionable at 

 the end of last century. 



125. The fundamental error in the conceptions of Maupas and his 

 followers is due to the "cell theory." The ciliate has been called a 

 " cell," and certain constituent elements of the metazoan body have 

 been given the same name. Consequently it has been assumed that 

 an exconjugant is the homologue of a fertilized metazoan ovum ; and 

 that the whole succession of its descendants is homologous with the 

 entire body of a multicellular animal^. It has thus become possible 



' "Assortative mating has clearly the effect of keeping differentiated races from 

 mixing. ...When a culture containing two species conjugates, the two as a result of the 

 assortative mating remain quite distinct" (Jennings, 1911a). 



- This view has been advocated most strongly in recent times by Calkins (1909). The 

 reader who wishes for a fuller analysis of the matters here merely touched upon, will find 

 it in an earlier publication (Dobell, 1911). 



