Interrelationships of the Cellular Characters of Several Species of Columba.

MMUNOLOGICAL methods have so often been employed as a means of I differentiating species, particularly in animals but also in plants, that it is almost a truism to state that antigenic differences are one of the more important criteria by which qualitative differences between species may be assayed. In animal species, the serum antigens have been somewhat more widely used in such comparisons than have the antigens of the tissues or blood cells. LANDSTEINER and MILLER (1925”) suggested that this was due to the presumption that the species specificities of the precipitins and of the hemagglutinins are of the same order and that species specificity means protein specificity, whereas there is definite evidence that the antigens which engender antibodies against red blood cells do not consist simply of proteins. Various reports from this laboratory (IRWIN and COLE 1936a, 1940; IRWIN, COLE, and GORDON 1936; IRWIN 1939) have shown that, following a comparison of the relationships of the cellular characters of several pairs of species of pigeons and doves, certain general statements may be made. First, each species possessed antigenic components in common with the other and, secondly, in addition to the common substances, each species possessed cellular constituents peculiar to itself (that is, species-specific characters). The hybrids between any two species studied invariably contained all the common components of the two parental species and all or nearly all the species-specific properties of both parents. Furthermore, segregation of the species-specific characters has been observed, by virtue of successive backcrosses of the species hybrid and selected backcross hybrids to one or both parental species. Thus, in thiee different species crosses-Pearlneck (Streptopelia chinensis) X Ring dove (St. risoria), Pearlneck X Senegal (St. senPgalensis), and Columba guinea XC. livia domeslica, respectively-at least certain of the cellular characters peculiar to Pearlneck in the first two crosses and to guinea in the third have been obtained in unit form-that is, no further separation of these characters has been observed following the appropriate backcrosses. It has also been shown, first by immunological procedures and then verified by genetical findings, that some of the cellular characters which distinguish one species (Pearlneck) from another (Ring dove) may be shared with still a third species (Senegal) (IRWIN and COLE 1940). Also, a t least one, and probably two, of the antigenic substances which differentiate C. guinea from C. livia