CONCLUSIONS 



137 



because he is aware of the correlation between changes in the 

 function of these systems in different species. 



Table 12 

 Vertebrate ventilation mechanisms 



4. When comparing the structure and physiology of animals, 

 a zoologist should consider the evolution of the systems under 

 consideration. Functional continuity is just as characteristic of 

 evolutionary processes as a sequence of structural modifications. 

 In this instance a clear evolutionary change in the respiratory 

 organs and circulatory systems has been established, and what 

 is known of their physiology assists in the interpretation of these 

 changes. 



In order to summarise the main modifications that have been 

 mentioned, the phylogenetic tree given on pp. 138-139 has been 

 constructed. Some of the major changes in the evolution of verte- 

 brates are indicated and it also serves to show the relationships 

 of the different groups that have been mentioned in this book. 

 Although there are many dangers involved in deducing relation- 

 ships from the study of comparative physiology and morphology, 

 a constant reference to the palaeontological record enables some 

 of the major pitfalls to be avoided. It is from this point of view 

 that a study of the functional morphology of vertebrates has 

 considerable advantages over that of ^ny other |roup. 



