THE LAPSE OF TIME. 299 



of paper, eighty-three feet four inches in length, and stretch 

 it along the wall of a large hall ; then mark off at one end 

 the tenth of an inch. This tenth of an inch will represent 

 one hundred years, and the entire strip a million years. But 

 let it be borne in mind, in relation to the subject of this 

 work, what a hundred years implies, represented as it is by 

 a measure utterly insignificant in a hall of the above dimen- 

 sions. Several eminent breeders, during a single lifetime, 

 have so largely modified some of the higher animals, which 

 propagate their kind much more slowly than most of the 

 lower animals, that they have formed what well deserves to 

 be called a new sub-breed. Few men have attended with 

 due care to any one strain for more than half a century, so 

 that a hundred years represents the work of two breeders in 

 succession. It is not to be supposed that species in a state 

 of nature ever change so quickly as domestic animals under 

 the guidance of methodical selection. The comparison would 

 be in every way fairer with the effects which follow from 

 unconscious selection, that is, the preservation of the most 

 useful or beautiful animals, with no intention of modifying 

 the breed ; but by this process of unconscious selection, vari- 

 ous breeds have been sensibly changed in the course of two 

 or three centuries. 



Species, however, probably change much more slowly, 

 and within the same country only a few change at the same 

 time. This slowness follows from all the inhabitants of the 

 same country being already so well adapted to each other, 

 that new places in the polity of nature do not occur until 

 after long intervals, due to the occurrence of physical 

 changes of some kind, or through the immigration of new 

 forms. Moreover, variations or individual differences of 

 the right nature, by which some of the inhabitants might 

 be better fitted to their new places under the altered circum- 

 stances, would not always occur at once. Unfortunately we 

 have no means of determining, according to the standard of 

 years, how long a period it takes to modify a species j but 

 to the subject of time we must return. 



ON THE POORNESS OF PAL^EONTOLOGICAL COLLECTIONS. 



Now let us turn to our richest geological museums, and 

 what a paltry display we behold ! That our collections are 

 imperfect, is admitted by every one. The remark of that 

 admirable palaeontologist, Edward Forbes, should never be 



