(a) In the Dickcissel (Fig. 1, F) and the Mourning Warbler (Fig. 1, G), immatures decrease more markedly than adults (visible in samples of Mourning Warbler; inferred in Dickcissel), leaving the adults in the majority in the closing phase of migration. The distinctive and interesting feature in each of these two species is the ascendancy in numbers of adults _despite_ the almost complete disappearance of adult males. The relative increase of adults is here caused by a retarded migration of adult females, which linger conspicuously behind all other classes. Something of this nature was suggested, in theory, by Dixon (1892:70) who thought that adult females are delayed by "maternal duties." It was hinted at also by Dwight (1900:127) who thought that in some species females molted later than males as a result of prolongation of parental responsibilities. As mentioned already, there is need for caution in interpreting the present samples because the Dickcissel is represented only by one sample and two of the three samples of Mourning Warblers are small. In the case of the Mourning Warbler, the samples may be regarded as one, nearly lacking in adult males. The progressive increase of adult females, however, may be significant; at least there are enough of these to make division of the birds into three samples enlightening. There is, of course, some chance that the majority of adult males have not yet migrated, or are migrating by a different route. This seems unlikely in both cases. October 1 is late in the migration of the Dickcissel and it seems that large-scale migration would not occur much later, and in the case of the Mourning Warbler adult males are rare in all three samples, extending over a considerable period and reaching late into the probable migration period of the species. It is interesting to conjecture just when and where adult male Mourning Warblers do migrate in autumn. Brewster (1886:16) wrote: "This species arrives at Cambridge [Massachusetts] about September 12, and during the remainder of the month is ... abundant.... The adults, however, are so very uncommon that I have never known them [to] represent more than five per cent of the total number of individuals. They do not seem to be more numerous in the earlier flights than towards the close of the month, and I am very sure that they cannot be found in this locality before the young begin to appear." While the present samples show an abundance of adult _females_ of this species (could Brewster have failed to recognize these as adults?) the whereabouts of the adult males remains a mystery.