43 



regular manner suggesting mosaic. Tlie slit-like narial 

 apertures are directed laterally, and tlieir margins are 

 entirely naked. The posterior limit of the rhinarium becomes 

 more defined in later embryos as the snout region becomes 

 pubescent (see fig. 6). 



Fig. 6. 



Rhinarium (from Specimen 

 Male A, Perth). 



External Ear. — In no embryo of the genus Isoodon that 

 I have so far had the opportunity of examining is the ear 

 laid forward at the younger stages. In /. harrowensis the 

 pointed ear stands well out from the side of the head with the 



Fig. 7. 

 The form of the external ear 

 (Embryo Male A, Perth). 



tip directed backwards. The processus antihelicis (the_ so- 

 called metatragus) is large in all stages; the characteristic 

 adult twist in its length becoming more pronounced as growth 



