486 POPULAR SCIENCE MONTHLY. 



It would lead too far were I to enter here upon the various points 

 on which their theories differ; let it be sufficient to note some parts of 

 Scott's treatise, since this gives the sharpest and clearest contrast to 

 the reigning view. In the long ancestral trees which have been 

 brought to light by the study of prehistoric animals, one form leads 

 gradually to another. When the strata are sufficiently known there 

 remain no breaks in the pedigree. Breaks are met with only where 

 the strata are wanting or where it has as yet been impossible to study 

 them thoroughly. Each ancestral tree consists of an uninterrupted 

 series of forms. Between two adjacent ones there exists no greater 

 difference than between the two most closely related species of the pres- 

 ent day. And in the successive strata they follow each other up in 

 such a manner as corresponds to the gradual development of the ances- 

 tral tree. 



But how did each form originate from the one immediately pre- 

 ceding it? Gradually or suddenly? Directly, paleontology can of 

 course not teach us anything upon this subject. Did the species orig- 

 inate suddenly, then there can have been no intermediate forms, but 

 even if they originated gradually the chances that such intermediate 

 forms would have become fossilized, are exceedingly slight. For how 

 small is the proportion of fossilized specimens to those which once 

 must have existed ! In any case, no such intermediate forms have 

 been found, and it is for this reason that many paleontologists accept 

 a sudden formation of new forms from the older ones. The transition 

 is slight, as slight for instance as the well-known differences between 

 the local races of slugs; but as these races are constant, so in paleon- 

 tology are the closest related forms sharply separated from one an- 

 other. 



The contrast between the views of Scott and those of the majority 

 of botanists and zoologists has, I believe, been sufficiently shown here. 

 According to Scott species did not originate gradually, but by small 

 jumps. By each jump a limit was passed, but after that the species 

 remained constant until, perhaps many centuries later, a new shock 

 produced a new form. Each species, each subspecies, or even each 

 variety, is constant in all its characters; they remain the same from 

 the beginning till the end, until, later on, either after having pro- 

 duced other species, or without having done so, they succumb in the 

 struggle for life. 



This theory restores the doctrine of the invariability of species to 

 its old place. And this invariability is so general a matter of expe- 

 rience that it has always remained an exceedingly weak point of Dar- 

 win's theory of descent. The continual, slow, even inappreciable 

 changes of species, which Darwin, but more especially Wallace and his 

 disciples, accepted, and which are so lineally opposed to every-day expe- 



