Differential migration of sex- and age-groups as shown by the larger samples taken at Topeka (Catbird, Red-eyed Vireo, Nashville Warbler, Yellow-throat, Mourning Warbler, Dickcissel, Lincoln Sparrow) is discussed and the history of theories on this subject reviewed. It is shown that age and sex must both be taken into account in studies of differential migration. Several patterns of migration are displayed by the species analyzed, adults migrating earlier than immatures in some instances, young earlier than adults in others, but all seemingly being complicated to varying degrees by differential migration of sexes within age groups. It is suggested that explanations of these patterns may be sought in the life histories of the species involved. Molt in relation to migration is discussed briefly, and it is held that there is an important relationship between molt and time of migration. Specimens noted to be in molt are listed. Size differences, in wing length, tail length, and weight are discussed in relation to sex and age, and variation in one or more of these characters is analyzed as found in the Topeka samples of Nashville Warbler, Mourning Warbler, Yellow-throat, Dickcissel, and Lincoln Sparrow. It seems that in some instances significant size differences prevail between adults and immatures and that these age classes should be separated in taxonomic work with species where differences in size are known to exist. When the facts are not known they should be determined, and the large samples collected in accidents to nocturnal migrants present excellent opportunities for ascertaining the facts. Other uses of material obtained in large migration accidents are discussed, such as computations of longevity and the problems of processing large, accidentally-killed samples. Care should be taken to select samples as nearly random as possible when all birds cannot be processed. Repeated and thorough analysis of accidental kills should provide a mass of valuable data bearing on many questions and problems which have thus far been little studied. Literature Cited ALLEN, J. A. 1880. Destruction of birds by light-houses. Bull. Nuttall Orn. Club, 5(3):131-138, July. 1896. Gätke's 'Heligoland.' Auk, 13(2):137-153, April. 1901. Barrington's 'The Migration of Birds at Irish Light Stations.' [Review.] Auk, 18(2):205-206, April. 1909. An American's views of bird migration. Brit. Birds, 3(1):12-19, June 1. BARRINGTON, R. M. 1900. The migration of birds as observed at Irish lighthouses and lightships [_etc._]. London, R. H. Porter; Dublin, Edward Ponsonby. Pp. XXV, 285, 667. (Not seen; citation from Mullens and Swann, Bibliogr. Brit. Orn., 1917, p. 43 and Zimmer, Cat. Ayer Coll., I, p. 40, 1926; see also reviews, Ibis, 1900:677-679, Auk, 1901:205-206; some sources list pagination as XXV + 667, possibly in error.) BEHLE, W. H.