280 



VARIATION IN THE TENTH KIB OE THE PENGUIN. 



BY 



J. E. DuEiiDEN, M.Sc, Ph.D., 

 Professor of Zoology, Rhodes University College, 



AND 

 YlVIAX ElTZSlMOXS, ]3.Sc. 



With Plates VI— \' 111. 



Read July 13, 1922. 



Before the Mendehan conception of the discreteness of 

 characters obtained recognition, it was generally held that varia- 

 tions appearing in Nature would tend to be " swamped," so long 

 as inter-breeding was possible; a measure of isolation, geographical 

 or phj'siological, was demanded for the persistence and spread 

 of a new variation. It is manifest that on the supposition that 

 characters would blend, it was to be expected that the inter- 

 mingling of forms differing but slightly would tend to produce an 

 approximate uniformity in development of any one of the 

 characters. Now that attention is concentrated upon the actual 

 behaviour of characters in breeding, practically all the results are 

 seen to be a contradiction of the notion of blending or swam])ing. 

 Results procured from a study of variation in the highly gregarious 

 penguin, Spheniscus dermersus, Linn., seem deserving of record 

 as illustrating the persistence of variations among individuals of 

 the same species, living and breeding in the closest association 

 with one another. 



A collection of fifteen joung penguins, some just hatched and 

 others about to hatch, was obtained from Bird Island,* and an 

 examination of the skeletal and other characters for evidences of 

 variation revealed certain marked differences in connection with 

 the last pair of ribs. In Vol. VJI of the " Challenger Reports," 

 Dr. ]\Iorrison Watson contributes a full account of the skeleton 

 of the Spheniscidae, but records very few variations among the 

 ribs. Ten vertebral ribs are stated to occur throughout the 

 family. Where, as in Eudyptes c]irysoco))ic. only nine are given 

 by some writers, it is held that as the tenth is always very slender 



* Bird Island is one of the many islands, rocks and reefs, comprised in the 

 large group of the Government Guano Islands, situated off the western 

 and southern coasts of South Africa, Iving between latitudes 24° 30' 

 and 35° South; and longitude 14° 20' and 26° 30' East. We are under 

 obligations to the Superintendent of the Islands, Mr. 11. Jackson, for 

 permission to obtain specimens. 



