INTRODUCTION. 



Like the previous work, dealing with the gastro- 

 intestinal tract in Monotremes and Marsupials, the 

 present volume, though structural in character, has been 

 written from the point of view of physiology, i.e., func- 

 tion This also applies to the illustrations of the dissec- 

 tions. By a study of the two above-mentioned orders 

 light is thrown on the nature of the primitive liver from 

 which the human liver has been evolved; in the Platypus 

 we have a multilobed liver, whilst some varieties of the 

 Victorian Wombat may have a liver practically resemb- 

 ling the human in type. In this maimer, i.e., viewed from 

 the comparative standpoint, anomalies of the human 

 liver, which are not infrequent, become intelligible. As the 

 function of the hepatic cells are multiple, and as these 

 functions must bear an evolutionary sequence one to 

 another, it is possible that in the near future the classi- 

 fication of diseases of the liver will be based on that 

 sequence. Thus it is conceivable that there may be a loss 

 of one, or some, but not necessarily all, of the functions 

 of the hepatic cell. Again, the question might well arise 

 — Does one portion of the human liver or spleen perform 

 functions differing from those of some other? The pos- 

 sible differentiation in their action on cells of vital stains, 

 for the interpretation of which we are so much indebted 

 to Professor Herbert Evans of the University of Cali- 

 fornia, holds out some promise of results in this direction. 



If we compare the "highest" form of Australian rep- 

 tile with the "lowest" mammal, the Platypus, three dis- 

 tinctive features stand out in the latter as compared with 

 the former. These are — (a) the presence of a diaphragm 



