92 Geometrical relation of Nuclei 



infinitely more complex processes of later development, we should 

 find so mystical an explanation as entelechy necessary ? In other 

 words, may not this simple force be the sole factor in the develop- 

 ment of organisms which is to be regarded as "vitalistic," that is 

 to say peculiar to living matter exhibiting the essential character 

 which distinguishes living from non-living substances. 



For by this supposed form of energy, I do not mean a mysterious 

 metaphysical influence, but a form of energy comparable to gravity, 

 electricity, or magnetism in some respects similar to these but in 

 other respects differing from each, and a form which could be in- 

 vestigated by the ordinary methods of mensuration and computa- 

 tion available to the mathematician. 



Professor Bateson, who was so good as to read the foregoing 

 pages, pointed out to me (among other kind and valuable criticisms, 

 for which I desire to express my thanks) with reference to the 

 hypothesis of an intercellular attraction as a possible cause of 

 invagination, that, given the fact that the pull between cell and 

 cell is eccentric at one part of a ring, or over one area of a hollow 

 sphere, invagination would occur if the mutual pull were due to 

 a contraction of protoplasm just as much as it would on the 

 hypothesis of intercellular attraction. 



No doubt that is so; and it must be admitted that whereas 

 contractility is recognised as an attribute of protoplasm, the 

 attraction between cell and cell as indicative of a special vitalistic 

 property is "not proven." 



If contraction is the cause of invagination it is necessary to 

 assume either: 



(a) that there is an early differentiation into contractile tissue 

 for the special purpose of causing gastrulation by- invagination, or 



(b) that there is a relationship between more contractile and 

 less contractile protoplasm so as to exert a greater pull eccentrically 

 over a certain area as regards the cellular units corresponding in 

 effect to the result of the forces postulated by the attraction hypo- 

 thesis. 



It must be admitted, that there is nothing visibly present which 

 suggests a differentiation into more and less contractile protoplasm. 



The contraction hypothesis necessitates a cement, or other firm 

 means of attachment between cell and cell, or the units would be 



