Position of " centre" of Attraction 



77 



If there is a form of energy which is an attribute of living cells 

 and which under certain conditions is manifest as an attractive 

 force acting from a centre, the "centre" must be the centre of the 

 living substance, and if the protoplasm is vacuolated through part 

 of its mass by dead material, for instance, food yolk, then the 

 centre will be driven away from the yolk mass just as the centre 

 of gravity is driven away from the centre of a mass by vacuolation 

 such as one may get in part of a lump of slag. Further it must 

 be supposed that the divisions of the blastomeres take place in 

 such a way that the more yolk-laden parts of the cells are directed 



Fig. 37. Diagrams illustrating how a mass of inert material within an ovum 

 causing eccentricity of the centre of attraction may be divided in the vertical 

 plane without disturbing the original proportion of its distribution between 

 upper and lower segments of the segmented ovum, but how a horizontal plane 

 of division upsets this arrangement. 



inwards, and that therefore the disproportion between the segments 

 set up by the first horizontal furrow, that is to say, at the third 

 generation of blastomeres, is retained till the end of segmentation. 



The material which vacuolates the protoplasm and causes the 

 eccentricity of the centre of attraction in the case of Amphioxus is 

 no doubt the food yolk, small though the amount of it may be. 



It is clear that on the above hypothesis the distribution and 

 quantity of yolk relative to the upper and lower poles, is an all 

 important factor in the process of invagination of the blastula, and 

 anything which would interfere with the normal distribution of yolk 

 would probably render the invagination imperfect or impossible. 



