TRANSPLANTATION AND INDIVIDUALITY. 169 



place. An individuality differential seems to be present in these 

 protozoa and to lead to a marked direct interaction of proto- 

 plasms. There exist, perhaps, a few similar reactions in certain 

 other unicellular organisms. In other similar protozoa, however, 

 the reaction has not been observed by more recent investigators. 



If it were possible to generalize from this observation, we 

 should conclude that the individuality differential is present in all 

 animal tissues ; and that the lack of reaction must be due to one 

 of the two other causes. On the other hand there are some indi- 

 cations that the chemical constitutions of the cell proteins of the 

 embryo differ from those of the fully developed forms. To men- 

 tion only one fact of this kind: while according to Roessle em- 

 bryonic tissue contains the same antigen for hemolysins as the 

 adult tissue, it lacks according to Braus the substance which after 

 injection into animals of a different species or class calls forth the 

 production of precipitins ; neither does embryonic tissue bind 

 precipitin which had previously been produced through hetero 

 injection of adult material. Probably the precipitin reaction is in 

 this case a less reliable indicator of the presence of the differen- 

 tial than the hemolysin reaction, which seems to be positive. It 

 is possible that the absence or presence of the supplementary sub- 

 stance in the body fluids may at least in part, be responsible for 

 the hetero reaction ; this is suggested by the observation of Braus 

 according to whom extremities of amphibian embryos grafted on 

 hosts which are as yet in an embryonic stage show the effect of 

 the unsuitable soil, as soon as the body fluids of the host begin to 

 circulate in the grafts. 



If we take all these facts into consideration, it seems on the 

 whole more probable that the individuality differentials exist in 

 all animal organisms, but that the individuality reactions are lack- 

 ing in lower forms. 



INDIVIDUALITY AND SPECIES DIFFERENTIAL AND FERTILIZATION. 

 There exists an interesting correlation between the lack of the 

 individuality differential in lower ontogenetic and phylogenetic 

 forms on the one hand and between the lack of an individuality 

 reaction on the part of egg and sperm chromosomes throughout 

 all classes on animals. Homoiofertilization is the normal occur- 



