PHYSIOGNOMY 57 



one-sided and exaggerated impression to a very 

 common natural phenomenon. 



Mimicry, in the wide sense of the term, in- 

 volves the entire superficial aspect of the body ; 

 the moment the details are analysed the like- 

 ness disappears ; it is absolutely essential to its 

 success that structural details should be disre- 

 garded. We may define mimicry broadly as a 

 physiognomical convergence between two or 

 more species of animals, in this way distinguish- 

 ing it from homoplasy, which depends upon a 

 more deep - seated organic or structural con- 

 vergence. Such coincidences of form and 

 function as those presented by the mole - like 

 burrowing mammals referred to above, by other 

 marsupial and placental mammals, and by some 

 arboreal mammals, e.g., Tupaiidse (tree-shrews) 

 and Sciuridse (squirrels), the flying Insectivore 

 Galeopithecus and the flying squirrel Pteromys, 

 in so far as the whole bodily appearance is 

 involved, afford examples of a third way of 

 convergence known as parallel evolution ; it will 

 soon be clear how convergence is not incom- 

 patible with parallelism. They resemble each 

 other because of their approximation to funda- 

 mental forms, e.g., the burrowing form, the 

 arboreal form, and so on. A carnivorous Mar- 

 supial must necessarily bear some resemblance 

 to a true Carnivore, the fact being that it is 

 an extraordinarily close one. 



