Chap. IV.] ORGANISATION TENDS TO ADVANCE. 155 



and be still advancing throughout the world, yet the 

 scale will always present many degrees of perfection ; 

 for the high advancement of certain whole classes, or of 

 certain members of each class, does not at all necessarily 

 lead to the extinction of those groups with which they 

 do not enter into close competition. In some cases, as 

 we shall hereafter see, lowly organised forms appear to 

 have been preserved to the present day, from inhabiting 

 confined or peculiar stations, where they have been sub- 

 jected to less severe competition, and where their scanty 

 numbers have retarded the chance of favourable varia- 

 tions arising. 



Finally, I believe that many lowly organised forms 

 now exist throughout the world, from various causes. 

 In some cases variations or individual differences of a 

 favourable nature may never have arisen for natural 

 selection to act on and accumulate. In no case, probably, 

 has time sufficed for the utmost possible amount of 

 development. In some few cases there has been what 

 we must call retrogression of organisation. But the 

 main cause lies in the fact that under very simple con- 

 ditions of life a high organisation would be of no service, 

 — possibly would be of actual disservice, as being of a 

 more delicate nature, and more liable to be put out of 

 order and injured. 



Looking to the first dawn of life, when all organic 

 beings, as we may believe, presented the simplest struc- 

 ture, how, it has been asked, could the first steps in the 

 advancement or differentiation of parts have arisen ? 

 Mr. Herbert Spencer would probably answer that, as 

 soon as simple unicellular organism came by growth 

 or division to be compounded of several cells, or became 

 attached to any supporting surface, his law "that 



