MAMMALIAN CONVERGENCE 79 



example of the three principles of divergence, 

 convergence and parallelism, at one and the 

 same time, is of course that which is afforded by 

 the parallel series presented by the Marsupial 

 Mammals or Metatheria, on the one hand, and 

 the ordinary Placental Mammals or Eutheria, on 

 the other. I have compiled a table and give 

 a graphic representation of it in Fig. 5. 1 The 

 inward bends of the parallel waved lines indicate 

 particular features of convergence selected for 

 the purpose of the diagram. A similar diagram 

 could be constructed for comparing the series of 

 Insectivora and Rodentia, the spiny armature of 

 the hedgehogs approximating to that of the 

 porcupines, the arboreal habit of tree-shrews 

 (Tupaiidae) to that of squirrels (Sciuridae), the 

 terrestrial, nocturnal, and semi-domesticated habit 

 of land-shrews to that of mice and rats, while 

 the aquatic habit and the parachute flight are 

 also met with in both orders. The musk-shrew, 

 Crocidura murina, is very rat -like in general 

 deportment, although its eyes are small and its 

 dentition that of Insectivora. 



Parallel evolution accompanied by convergence 

 is the expression of analogous formations in two 

 or more animals belonging to different subdivi- 

 sions, which may have acquired a similar differ- 

 entiation of outward appearance or internal 



1 The items are gathered from Flower and Lydekker's textbook 

 on Mammals, with reference also to Max Weber's " Saiigethiere," 



