ORGANISMAL DIFFERENTIALS OF HYBRIDS 523 



were found also in the cells of other tissues and organs. In the first named 

 possibility we would have to deal with species-specific organ or tissue differen- 

 tials. However, of special interest is the formation, in the hybrids, of a new 

 agglutinogen, which is not present in the erythrocytes of either parent. This 

 would indicate that new combinations of genes may give rise not only to 

 corresponding combinations of substances which are present in the parents, 

 but also to new substances which are not represented by any of the genes 

 as such, but which depend upon the way in which the genes are sorted out. 



In these various experiments we have to deal with different generic or 

 species (or race) differentials in the parents and with combinations of such 

 differentials in the hybrids. In the hybrids we note in all instances characteris- 

 tics transmitted from both of the parents. In the mule, as well as in the 

 hybrids between Ring dove and Pearlneck dove, it was observed that the 

 hybrid red corpuscles contained combinations of the parental characters, 

 either in smaller amounts or in the same complete assortment as the erythro- 

 cytes of the parent species. On the other hand, it may be recalled that by 

 means of serological methods Todd found that the individuality differentials 

 of children within the same race and species resembled either those of the 

 father or those of the mother. 



Furthermore, it would seem that some characteristics of the hybrids are 

 constant and common to all individuals of the hybrid generation, while others 

 are variable and may differ in different hybrids derived from the same parents. 

 To the latter class belong, for instance, the blood-group characteristics ; 

 neither these nor their precursors can, as such, constitute or be a significant 

 part of the species or hybrid differential. Also, the individual hybrids between 

 domestic and wild Brazilian guinea pigs varied greatly in certain characteris- 

 tics other than in those determining species or race, and behaved in this respect 

 similar to the hybrids between inbred families of rats and guinea pigs when 

 they were analyzed by means of transplantation ; here also, all kinds of 

 quantitatively graded, intermediate conditions could be established in the trans- 

 mission of the individuality differentials. 



An experiment similar to those reported in this chapter and dealing with 

 animal species has more recently been performed by O. Moritz with plant 

 species. He crossed Berberis empetri folia with Berberis Darwinii and thus 

 obtained the species hybrid, Berberis stenophylla. He then sensitized animals 

 by injecting extracts from the leaves and young shoots of these three kinds of 

 plants and by means of the anaphylaxis reaction he could show that the hybrid 

 antigen contained constituents of both parent species. This experiment repre- 

 sents only a beginning in the analysis of plant hybrids by serological methods, 

 but the results so far indicate that similar modes of distribution of the parent 

 differentials in species hybrids will probably be found in plants and in 

 animals. 



