206 Proceedings of the Boycd Physical Society. 



of the colony. In these sessile forms a continuance of high 

 nutrition would tend to the re-establishment of a more stable 

 type of growth, but a medium, nutrition would tend to the 

 more unstable form of specialisation, with increasing predomin- 

 ance of cells of a more active and governable katabolism ; and 

 should the conditions of nutrition become unfavourable, parts 

 of the colony, with the corresponding increasing instability of 

 the form of tissue, might again take to the tow-net method of 

 procuring their existence. In the evolution of this series the 

 organism is not allowed to rest; permanence is a disadvantage 

 to it ; over-nutrition, leading to the degenerate mode of life, 

 could only be successful under particularly advantageous 

 circumstances, as the impaired nutrition, resulting from a 

 sedentary existence, would lead to its wandering once more, 

 and to its forming tissues of greater instability. This 

 bringing about a constantly increasing need of more nutritious 

 food would tend further and further to the selection by 

 nature of those forms whose activity and co-operation of cells 

 allowed of them capturing larger prey or ingesting food in 

 greater quantities. 



In applying the law laid down by Herbert Spencer, that 

 division of the cell is forced upon it, so long as its shape is 

 more or less of a spherical one, by the inequality increasingly 

 brought about during growth bebween the surface and the 

 volume contained, it becomes apparent that the cell of this 

 kind, which requires the greatest nourishment to keep 

 pace with its kind of anabolism, would be obliged to divide 

 more frequently than the cell whose form of anabolism went 

 to the building up of a more stable form of protoplasm. In 

 other words, a cell whose form of anabolism was to the 

 building up of unstable products, and which wasted a great 

 deal on katabolism, requiring as it would a quicker and more 

 nutritious supply of food for the renewal and building up of 

 its protoplasm, would have its limit of growth of a smaller 

 size, or the surface would have to be greater in propor- 

 tion to the bulk of the cell. On the other hand, the cell, 

 whose form of anabolism was to the building up of a more 

 stable form of protoplasm, and which would require less 

 nutritious food, and could take greater time in procuring it, 



