The Scottish Naturalist. 163 



textbook, the lists of the names of the various forms of plant and 

 animal life found in these strata. All further discovery of the 

 presence in, or absence from, certain strata of certain fossils is a 

 biological discovery, and has to be discussed under the distribution 

 in time of the group to which the discovery refers. It would be 

 always instructive no doubt to indicate the leading features of the 

 organic world at the same time as the characteristic physical fea- 

 tures of any epoch ; but all details I would leave to be studied 

 under Biology. 



Looked at from the Biological side what are the advantages to 

 be gained by this rearrangement ? 



The advantages it seems to me are many ; and first, with 

 regard to classification. 



It is only of late years that a true conception has been arrived 

 at, as to what classification really is. For ages physiological 

 classifications, which introduced such absurdities as the grouping 

 together of whales and fish, of birds and bats, were discussed 

 seriously. Artificial classifications like that of Linnaeus, founded 

 on the morphology of the organ or system, failed of necessity to 

 throw any light on the phenomena of plant or of animal phyllo- 

 geny. The accurate morphological researches of Cuvier, the 

 embryological work of Von Baer, and the profound generalisations 

 of Lamarck and Darwin were needed ere classification was seen in 

 its true light. 



" Some deeper bond is included in classification " says Darwin, 

 " than mere resemblance. I believe that community of descent, 

 the one known cause of close similarity in organic things, is that 

 bond." 



But acceptance of the view of community of descent from a 

 generalised ancestral stock of necessity signifies the acceptance of 

 the unity and continuity of plant and animal life since its origin. 

 It means that all the innumerable plant and animal forms that 

 exist now, that have existed in past ages, whether preserved in 

 the rocks or not, are leaves, twigs, branches, of one great tree, 

 whose roots are hid deep in the unknown pregeological time, 

 whose latest blossoms are unfolding around us to-day. 



" We can understand," writes our great master in Biology, " how 

 it is that all the forms of life, ancient and recent, make together a 

 few grand classes ; we can understand from the continued tend- 

 ency to divergence of character, why the more ancient a form is, 



