64 SECTIONAL ADDRESSES. 



by Miss Kobertson and the late Professor Minchin 1S ; and they showed 

 that the little bead at the base of the flagelluni, known as the blepharo- 

 plast, is the first thing in the cell to divide, and forms two daughter ble- 

 pharoplasts which take the part of centrosornes and induce the division 

 of the nucleus into two daughter-nuclei, followed by the division of the 

 cell into two daughter-cells. In each of these daughter-cells the new 

 blepharoplast grows a new flagellum. It will be seen that the part of the 

 blepharoplast which was last in contact with its sister is, as it were, a 

 healed wound, and the strip of flagellum which grows from this has there- 

 fore a different parentage from that which grows from the opposite surface 

 of the blepharoplast, which is an intact part of the parent surface. 



There is no nervous system in sponges, and no sign of nervous control 

 of the flagella, either from the individual cell or from the community. 

 The direction and timing of their beat is wholly uncorrelated, and though 

 the frequency of two neighbouring cells generally approximates to equality 

 it is not exactly the same. The frequency varies when the temperature 

 and soluble contents of the water vary. Except in certain cases where a 

 wandering ovum (Grantia) or pore-cell (Clathrina) is laid over a collar-cell, 

 I have never seen a flagellum motionless in a cell which was not moribund. 16 

 I believe the motion to be ceaseless, unconscious, and uncontrolled, a direct 

 function of the chemical and physical environment. 



What has this to do with the history of animals ? Our ancestors were 

 flagellates, or lower than flagellates, for as many generations as they have 

 been anything else, for perhaps five or fifty times as many generations as 

 they have been vertebrates, at least two hundred times as many generations 

 as they have been mammals, and our ancestors were flagellates for at least 

 five thousand times as many generations as they have been men. All 

 those flagellate ancestors of ours passed their whole active lives in this 

 continual rhythm of accumulating energy and building, accumulating 

 energy and building, twenty or more to the second through the whole of 

 their short lives. Do you believe we have forgotten that rhythm ? I 

 believe that all through our growth, from infancy to prime, we added our 

 molecules to every unit of protoplasm, rhythmically, as our flagellate 

 ancestors did. And when we have passed our prime, our units keep their 

 rhythmic reconstruction ; only now, because we are land-animals and must 

 not grow any bigger for fear that our limbs should snap, the rhythm or the 

 chemical change is readjusted, so as only each beat to add as many mole- 

 cules as we use up between the beats. But the adjustment is not perfect, 

 so that when we have done growing, our protein units do not keep abso- 

 lutely constant — they lose a little each beat on the balance of gain and 

 expenditure. 17 So that as we grow older our muscles shrink, and our 

 nerves shrink, and our cartilages shrink, and our brain shrinks, 

 and we become what other people call ' senile ' ; and at length we die — 

 a thing which none of our twelve thousand million flagellate ancestors 

 ever did. 



Incidentally, I believe that to that same metabolic rhythm, inherited 



" Q.J. M.S. 1910, vol. 55, p. 611 ; 1912, vol. 57, p. 129. 



16 Cf. J. Gray, 1926 : P.R.8., B, xcix, p. 398, and G. H. Parker, 1910 : Journ. Exp. 

 Zool. viii, p. 795 (or 31) ; and cf. Journ. Linn. Soc. 1921, vol. xxxiv, p. 317. 



17 Proc. Linn. Soc. 1925, p. 17 ; 1926, p. 19. 



