BIOCHEMICAL STUDIES OF PHYLOGENY 113 



This table indicates that most of the invertebrates have one type 

 of phosphagen (arginine phosphate) whilst the vertebrates have 

 another (creatine phosphate). The echinoderms and the proto- 

 chordates have both types of phosphagen and this makes it seem 

 likely that they are the group of invertebrates most closely related 

 to the vertebrates. 



Let us now consider the situation in a little more detail. 



In 1927 Eggleton and Eggleton showed that one could extract 

 a labile organic phosphorus-containing compound from vertebrate 

 muscle. This compound was called phosphagen and later workers 

 showed that it was in fact creatine phosphate. After isolation crea- 

 tine phosphate broke down to form creatine and phosphoric acid. 



NH.OP(OH)., 



/ 

 HN = = C + H 2 



N— CH 2 .COOH 



CH 3 



Creatine phosphate. 



NH 2 



HN = C + H 3 P0 4 



N— CH 2 .COOH 



CH 3 



Creatine and phosphoric acid. 



