SYMBIOSIS 53 



complete parasitism, for which temporary advantages the animal 

 surrenders its birthright of genuine symbiosis and its chances 

 of future symbiogenesis. Convolutal association is thus a 

 makeshift arrangement, retrogressively come to. It is not on 

 the lines of progressive reciprocal differentiation, and the 

 limitations incurred are not balanced by a commensurate 

 physiological or bio-economic advantage as in the case of the 

 lichen, to which we shall have to refer again later on. 



Prof. Keeble's evidence confirms the view that the green 

 cells in Convoluta are degenerates. They show nuclear 

 degeneration. The great majority of them occurring in the 

 adult animal are not complete cells, but cells which show all 

 stages of diminishing nuclear substance. " Those green cells 

 whose nuclei are least degenerate are capable of division, but 

 even they have suffered. They are no longer able to form a 

 cell-wall nor to exist as independent organisms." 



The algal cells in these associations, therefore, are not on 

 the road to progressive reciprocal differentiation, but, on the 

 contrary, "on that which leads to complete loss of 

 independence." Hence they lose their progressive bio- 

 economic value, and as the advent of the enucleate stage in the 

 green cells may be " the signal to the animal to devour them," 

 so it may well have been the lack of progressive inclination 

 associated with a desire for surfeit which originally singled out 

 certain cells for a career of failure for a merry though a short 

 life. The idea that the essential degeneration of the green 

 cells as here depicted may be the signal to the animal to devour 

 them, and thus end a short period of inadequate symbiosis, 

 according to my interpretation, is of great significance, for I 

 believe it adumbrates the fact that cessation of due symbiotic 

 labour marks the starting point of the phenomena of disease 

 and of extinction in the biological world. 



This I have recognised for some time, and it is a recogni- 

 tion I am convinced of some considerable importance. To be 

 able to diagnose the earliest phases of (biological) disease is no 

 small matter. To be able to say where physiology ceases and 



