396 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



regard to their morphological development. A similar state of 

 affairs exists with regard to our knowledge of the chemical phy- 

 logeny of living forms. The paleontologist has access in the sedi- 

 mentary rocks to records of extinct species from which he can recon- 

 struct at least some of their morphology. But as a rule the chemical 

 characters of extinct organisms do not leave any direct record in 

 the rocks. The information which we have as to the composition 

 of extinct organisms is largely based on analogies drawn from our 

 knowledge of the composition of existing structures homologous with 

 those observed in fossil remains, or from the persistence of structures 

 which were mainly composed of inorganic material. 



Fortunately this rule is not entirely without exceptions. In one 

 or two rare instances there is reason to believe that organic com- 

 pounds present in long extinct organisms have been preserved from 

 the remote past. It is a matter of pride to us to know that the 

 latest of these rare discoveries has been made by a distinguished 

 member of this society, our esteemed past president, Sir Edgeworth 

 David. In the course of the examinations made in connection with 

 his discovery of structures of living origin in pre-Cambrian strata, 

 David (1928) observed that some of these structures consist of or- 

 ganic matter which is apparently the original chitin of which the 

 skeletons of these animals (annelids) were largely composed. 



Direct glimpses like this into what has been termed the paleochem- 

 istry of living things are of great importance. They give direct 

 support to the otherwise very indirect evidence upon which is based 

 our belief in the stability of some of the chemical characters of 

 living organisms. 



The paucity of our knowledge of the detailed composition of living 

 things does not permit us to classify them in such small subdivi- 

 sions as are made possible by our more detailed knowledge of their 

 morphology. In this connection, however, the pioneering work of 

 Smith and Baker (1920) must receive due mention. These in- 

 vestigators in their now classical researches followed out the relation 

 between certain of the chemical constituents and the structure of a 

 group of Australian plants. 



Investigations of this kind, however, relate rather to the associa- 

 tion which is to be found between highly specialized structures and 

 compounds in living things. They bring out the changes which 

 have taken place during the evolution of the chemical characters 

 of living things rather than emphasize the relative permanence of 

 some of the more primitive of these characters. 



When we wish to consider the more fundamental chemical char- 

 acters of the living organism, we must examine the less highly spe- 

 cialized tissues, and the wider divisions of morphological differentia- 



