PORPOISES AND DOLPHINS 2gi 



the species. The back is black and the belly white. Just 

 behind and above the eye is a lens-shaped area of white which 

 projects backwards and slightly upwards. Behind the dorsal 

 fiii is an ill-defined saddle-shaped light area enclosed in the 

 blackness of the back ; this patch is sometimes absent, and 

 when present is rather variable in form. The chin is white ; 

 the flippers, which are black on upper and under surfaces, are 

 inserted in the black area on the sides of the body, which 

 here is extended downward almost to the under surface. 

 Towards the tail end on either side of the body the white of 

 the under surface invades the predominating black of the 

 sides in an upward and backward direction. This lateral 

 white patch is a most conspicuous and very constant feature. 

 The under surface of the tail is white. 



In this as in other dolphins the number of teeth and their 

 size are useful guides in determining the species to which the 

 animal belongs, and in stranded specimens where an oppor- 

 tunity for detailed examination presents itself the mouth 

 should always be inspected. The Killer Whale has 10 to 12 

 large and powerful, conically-pointed teeth on each side of 

 upper and lower jaws. The teeth are flattened in front and 

 behind so that their cross-section is not circular, but roughly 

 elliptical. The major axis is thus in the transverse plane of 

 the head and may be up to 2 inches in length. The upper and 

 lower teeth interlock and, being set in massive jaws, demon- 

 strate that the animal is most efficiently equipped for its 

 predatory mode of life. 



A feature unusual in cetaceans is the great discrepancy in 

 size between the male and female Killer Whale, the only 

 other instance in any way comparable being found in the 

 Sperm Whale. The fully-grown male Killer attains a length 

 of about 30 feet and the female approximately half that 

 size. 



Very little is known of the breeding habits of the Killer, but 

 it is believed from the scanty evidence available that pairing 

 takes place about the end of the year, that the gestation 

 period is twelve months, and that the young are about 7 feet 

 long at birth. In this connection it is interesting to note the 

 stranding of a specimen 7 feet 9 inches long on the Yorkshire 

 coast in November, 1927. The time of stranding ;md the size 



