522 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



cytes of the hybrid either did not possess all the antigens of the parental 

 genera, or they did not possess them in the same quantity as the corpuscles 

 of the parents. An additional interesting observation was the following: 

 when the anti-hybrid rabbit serum was absorbed by the erythrocytes of both 

 parents in succession there still remained in the immune serum a remnant 

 of agglutinin, which could not be removed by such absorption ; and further- 

 more, after absorption of the anti-hybrid immune serum by the red corpuscles 

 of one of the parents, there still remained a greater amount of agglutinin 

 against the erythrocytes of the hybrid than against those of the other parental 

 genus. Irwin concludes that a new antigen (agglutinogen) must have devel- 

 oped in the erythrocytes of the hybrid as a result of fertilization, and that a 

 new agglutinin may thus be produced in the immune serum. A combination 

 of the gene sets belonging to the two parent genera would, therefore, give 

 rise to something different from both component sets. Furthermore, it may be 

 stated that the haploid number of chromosomes present in the germ cells of 

 each of the parents is evidently able to produce in the hybrid almost the 

 same amount of antigenic substance as the diploid number does in each of the 

 parents. 



Subsequently, Irwin and Cole investigated, by similar methods, the ag- 

 glutinogens in the backcross generation from hybrid F 1 (Ring dove X 

 Pearlneck) to Ring dove parent ("one-fourth Pearlneck"). In addition, the 

 "one-eighth Pearlneck" backcross generation was studied ; these were obtained 

 by mating the one-fourth Pearlneck backcross a second time to a Ring dove 

 parent. In these backcross hybrids a separation of the pearlneck genes took 

 place, so that all possible random combinations were found, according to 

 the rules of Mendelian segregation. The presence or absence of Pearlneck 

 agglutinogens in the two backcross generations was tested as usual by the 

 anti-hybrid F x rabbit serum which had been exhausted once or twice by 

 various types of erythrocytes. The results showed that in the Pearlneck 

 erythrocytes multiple, and at least ten, agglutinogens are present, which are 

 distributed in a specific way in the backcross birds, so that each individual 

 can be differentiated from the others, if a sufficient number of agglutination 

 tests are made with anti-F x hybrid (Ring dove X Pearlneck) rabbit serum, 

 after certain agglutinins have been absorbed with various kinds of erythro- 

 cytes. Besides, there was present in many, but not in all, of the backcross in- 

 dividuals the newly formed hybrid L agglutinogen, which did not exist in the 

 erythrocytes of either parent, but formed as a result of the union of the genes 

 of both parents in the F x generation. 



However, these results were obtained only if immune serum from a certain 

 rabbit was used for these tests. An immune serum from another rabbit might 

 have given different results, and it is conceivable that if the immune sera had 

 been used from a different species, additional differentiations would have 

 appeared and the number of agglutinogens found in the Pearlneck erythro- 

 cytes would have been still further increased. Moreover, the question may 

 be asked as to whether these species-specific multiple agglutinogens which 

 were present in the erythrocytes were peculiar to these cells, or whether they 



