I) E GENERA TION. 



225 



left, by natural selection, unimproved or but little improved, and 

 might remain for ages in their present lowly condition. And geology 

 tells us that some of the lowest forms, as the foraminifera (Fig. 9), in- 

 fusoria, and rhizopods, have remained for an enormous period in nearly 

 their present state. But," adds Darwin, wdth a characteristically im- 

 partial view of matters, " to suppose that most of the many now ex- 

 istino- low forms have not in the least advanced since the first dawn 

 of life w^ould be extremely rash ; for every naturalist who has dissected 

 some of the beings now ranked as very low in the scale must have been 

 struck with their really wondrous and beautiful organization." 



Thus one of the plainest facts 

 of natural history, namely, that in 

 even one group or class of animals 

 we find forms of exceedingly low 

 structure included along with ani- 

 mals of high organization the 

 apparently diverse bodies being 

 really modeled on the one and the 

 same type is explained by the 

 consideration that with different 

 conditions, or with various condi- ' 

 tions acting differently upon un- 

 like constitutions, we expect to 

 find extreme differences in the rank 

 to which the members of a class 

 may attain. In the class of fishes 

 we find the worm-like, clear-bodied 

 lancelet of an inch lono; associated 

 with the ferocious shark, the active 

 dogfish, or the agile food-fishes of 

 our table. But, as Darwin re- 

 marks, the shark would not tend 

 to supplant the lancelet, their 



spheres and their conditions of existence being of diverse nature. 

 The same remark applies to many other classes of living beings. So 

 that lowly beings still live as such among us, and preserve the primi- 

 tive simplicity of their race, firstly, because the conditions of life and 

 their limited numbers may not have induced any great competition or 

 struggle for existence. On the " let-well-alone " principle we may un- 

 derstand why some animals, such as the lancelet itself, have lagged be- 

 hind in the race after progress. Then, secondly, as Darwin remarks, 

 favorable variations, by way of beginning the work of progress, may 

 never have appeared a result due, probably, as much to hidden causes 

 within the living being as to outside conditions. AVe may not fail to 

 note, lastly, that the simpler and more uniform these latter conditions 

 are as rejoresented in the abysses of the ocean, for example the less 



VOL. XIX. 15 



Fig. 9. Globigeeina, etc. 



