166 LEO LOEB. 



bryos of the same species can be readily grafted upon each other. 

 The homoiodifferential does apparently not play any role. These 

 embryos on the other hand react against union with the part of 

 an embryo belonging to a different species, against an heterodif- 

 f erential ; the reaction, however, seems to be less marked than in 

 mammals. Similar are the results obtained with transplantation 

 of gonads in larvae of lepidopterse (Meisenheimer, Kopec). In 

 nearly related species the results of grafting are better than in 

 distant species. 



It is similar in adult invertebrates. Here also no difference 

 seems to exist between auto- and homoiotransplantation and while 

 a reaction takes place against heterotransplants, it is again con- 

 siderably less pronounced than in the higher animals. Of value 

 are here especialy the experiments of Joest, Harms, Leypoldt 

 and Rabes in Lumbricidae and of Wetzel in Hydra. While hetero- 

 differentials and also reactions against heterodifferentials exist 

 here, the reactions are much less intense, if we make allowance 

 for the lower temperature at which these reactions take place and 

 which would naturally retard the reaction considerably. In Lum- 

 bricidae the heterotransplant may remain alive in toto, while even 

 in amphibia part of the heterotransplant becomes necrotic. In 

 adult invertebrates also heterotransplantation succeeds only in 

 certain, not too distant, species. We studied recently the species 

 differential in such simple forms as the blood cells of arthropods. 

 We found that the blood cells of limulus are specifically adapted 

 to their own blood serum. Their activities are optimal in Limu- 

 lus serum. Limulus serum surpasses any other serum so far 

 tested. 



In order to determine this relationship we made use of experi- 

 mental amcebocyte tissue and we compared the rapidity and quan- 

 tity of outgrowth from this tissue in different sera. The pictures 

 we obtain under those conditions are very similar to those pre- 

 sented by outgrowing embryonic connective tissue. We find then 

 even in the blood cells of invertebrates a specific adaptation be- 

 tween the species differential of the blood cells and the supple- 

 mentary species differential of the body fluids. 



If we pass to the lower vertebrates, we note in amphibian larvae 

 a condition somewhat analogous to that in invertebrates. Espe- 



