VESTIGIAL STRUCTURES. 



89 



if not entirely, due to the gradual acquisition of 

 terrestrial habits by animals originally aquatic, is 

 largely supported by the condition of the pinna in 

 aquatic mammalia. The adult whale has no pinna or 

 external auditory meatus ; Howes has detected vestiges 

 of the pinna in the embryo of the white whale (Beluga 

 leucas}'. the pinna was almost microscopic in size 



FIG. 46. The head of a Seal (Otaria gillespii], showing the 

 small pinna. (After Forbes.) 



and pointed, resembling in a very striking manner the 

 small cervical auricles in man. 



In most seals the pinnae are wanting, and when 

 present they are short, pointed, and vestigial, as in the 

 eared-seals (Otaridcz), fig. 46. 



If the Cetaceans and Phocidcs are to be regarded as 

 land mammals which have taken to the water which 

 is the most consistent manner of studying them we 



