ARREST 129 



Thus, the Hydra zooid's tissue cells are arrested owing 

 to Continuity, but the zooid as a whole is unarrested owing 

 to its Discontinuity, and can become sexual. Similarly, the 

 vegetative zooids of the marine colony are arrested, but 

 the colony as a whole becomes sexual. Or again, a free- 

 swimming medusoid produces sexual elements, but in the 

 segmental organism no elements are produced by the great 

 majority of those continuous regions we term segments. 



It is customary to call Nature prodigal in that she 

 produces sexual elements far in excess of the number that 

 could possibly realise new Individuals in existing conditions. 

 She appears to be wasteful. The truth is that she is sparing, 

 arresting in the higher living types the greater part of the 

 developing Individual. If we take the earthworm, for 

 example, we find that of one hundred and fifty segments 

 only the tenth, eleventh, and thirteenth produce sexual 

 elements ; or if we turn to a typical fish like the salmon 

 it is clear that the huge number of ova it produces is nothing 

 in comparison with what would be produced were all the 

 segments to have sexual organs. So that it would appear 

 that Nature has had to economise in producing the structural 

 wonders of living Continuity. 



While the development of a vertebrate embryo is pro- 

 ceeding active cell-division is no doubt general, though it 

 is probable that many cells are from time to time temporarily 

 stopped in the process of multiplication according to the 

 requirements of the evolving body-plan. It is with the 

 first divisions of the fertilised ovum that the evolution of 

 the fixed cell-species begins. There is commencing variation. 

 The main road of growth-cycle evolution no sooner starts 

 than side-paths begin to branch out ; and while the main 

 road ends in the restoration of sexual elements, the side- 

 paths end in the arrested somatic cells. These somatic 

 cells are not arrested in the sense that they do not grow 

 and divide during the life of the Individual, but once their 

 type is fixed or differentiated their division-products are 

 true to type. Thus the fat cell in the human body becomes 

 other fat cells, just as the starfish in the body Nature gives 

 rise to other starfishes. In both cases this is a reflection 

 of magnificent Control. 



