422 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi. 



division of the cell. Division of a cell means, however, a 

 restoration to its pristine condition. 



Such would be the life-history of an asexual unicellular 

 organism, which has been developed along such lines as to 

 enable it to procure not only a definite kind, but also a 

 certain amount of that special nourishment. If, however, 

 any increase or decrease in the amount of nourishment to 

 which the cell has been accustomed occur, then the nutrition 

 of the trophic centre within the cell will be altered in one of 

 two directions : — 



A. Excess of Food. — "When this obtains, the organs of 

 the cell are able to manufacture food for the trophic centre 

 in such quantities that the latter, always finding sufficient 

 material for its wants, loses the habit of urging the organs 

 to increased activity. This diminution of trophic influence 

 will allow the cell to become larger than normal, and may 

 even end in loss of power of division. 



B. Deficiency of Food. — This condition results in one 

 of two conditions, either, firstly, in death by starvation, or, 

 secondly, in diminution of food elaborated by the organs ; 

 hunger of the centre, and increased stimulation of the 

 organs, the latter leading to movement in search of food, i.e., 

 the cell as a whole becomes active. But this activity neces- 

 sitates greater expenditure, hence still greater food-supply. 

 The cell will be directed by its centre to go where it can 

 obtain the greatest amount of food with the least possible 

 expenditure, i.e., it will tend to go towards a cell of its own 

 species, which is over-fed, and which can therefore supply it 

 with an abundance of exactly such food as, under more 

 favourable conditions, it itself would have elaborated. 



Although in the way just described a varying amount of 

 available food may lead either to a loss of infiuence of the 

 trophic centre over its organs, (jr, on the other hand, to a 

 display of excessive energy, we must ask ourselves are there 

 yet other causes which could produce the same effect ? I 

 believe there are ; for quite a])art from the food-supply, two 

 cells resulting from one division need not be constituted alike. 

 One cell may be abnormally strong on the trophic side, but 

 weak in its organs, or vice versa; or a cell's trophic centre 

 may be normal, but the organs not able to maintain the 

 wants of the centre ; or the organs may be able to perform 



