THE UNIQUENESS OF LIFE 151 



another and touch; they actually become pressed and flat- 

 tened up against one another. This interesting attraction 

 was called by Roux cytotropism or cytotaxis, and it has been 

 observed in other cases. Assheton was particularly concerned 

 with the development of the lancelet or Amphioxus, where 

 the ovum divides into a hollow ball of cells, which again is 

 indimpled or invaginated to form a two-layered sac of cells, 

 the gastrula. Assheton sought to show that, if there were 

 an attractive force between cell and cell, acting from centres 

 represented by the nuclei of the cells, the hollow ball of cells 

 would at a certain stage become invaginated. The explana- 

 tion of how gastrulation might come about was put forward 

 as indirect evidence in favour of the existence of some force 

 acting from a centre like gravitation or magnetism or statical 

 electricity, but probably of a different nature and with dif- 

 ferent laws, and an attribute of living matter alone. Asshe- 

 ton meant definitely a kind of physical energy " which could 

 be investigated by the ordinary methods of mensuration and 

 computation available to the mathematician ". 



Herbst made the remarkable observation that if the ova 

 of the sea-urchin be allowed to develop in sea water deprived 

 of its calcium salts, the blastomeres separate from one an- 

 other, instead of adhering. What looks like repulsion be- 

 tween two centres is seen in the normal process of cell- 

 division, where the incipient daughter-nuclei, while still parts 

 of the parent cell, seem to repel one another, and yet imme- 

 diately after separation appear to attract one another strongly. 

 Assheton suggested that the hypothetical form of energy ex- 

 hibits an unceasing recurrence of a bipolar state out of a 

 unipolar state. " The attraction and repulsion observed be- 

 tween cell and cell are certain of the manifestations of this 

 supposed form of energy but probably not by any means 



