208 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



plastic, modifiable condition. It is due to this plasticity of organ differentials 

 and to the readiness with which transformations and newformations of organ 

 systems and parts of the body take place that individuals are restituted from 

 parts. But this factor alone would not insure the ready restitution of in- 

 dividuality. There must be added to it a certain autogenous state in which 

 organ systems interact perfectly in such a manner that a relatively stable 

 equilibrium is maintained. Some of the mechanisms which participate in the 

 maintenance of this equilibrium we have analyzed in the preceding pages. 

 Any disturbance in this autogenous equilibrium, consisting in the balancing 

 of these organ systems, activates mechanisms which result in the integration 

 of the organism. It is the relative lack of fixity in organ differentials, their 

 ability to change within certain limits, that make possible the integrative activity 

 of the mechanisms leading to the restoration of the individual. 



So far, we have analyzed the interaction of organs and organ differentials 

 and their significance in the maintenance of the equilibrium which makes 

 possible the integration of parts into the individual organism. We shall now 

 compare with the nature of this equilibrium, the mode of action of the or- 

 ganismal differentials in this class of animals. Here we notice that the plas- 

 ticity of the organ differentials is somehow bound up with a relative lack of 

 fixity of the organismal differentials, or at least of the effects which differ- 

 ences in organismal differentials would induce in higher organisms. 



We find, accordingly, that in Hydra auto- and homoiotransplantations seem 

 to succeed equally well ; similarly, there seems to be no difference in the results 

 when several autogenous or homoiogenous pieces are joined together, the 

 integrative as well as the organizer impulses being transmitted in a normal 

 manner from one piece to the other. At the point of union corresponding 

 tissues of homoiotransplants and host may unite perfectly in Hydra, without 

 any scar remaining visible. Homoiotransplantation in Hydra succeeds very 

 well, even if the two partners have been made unequal in their contents in 

 algae. However, we must not necessarily conclude from these experiments that 

 homoiodifferentials do not exist in these organisms. While this may per- 

 haps be the case, there still remains the possibility that they do exist in a 

 rudimentary form, but that they are not strongly enough developed to lead 

 to noticeable reactions and that the tissues have a power of resistance suffi- 

 cient to overcome unfavorable conditions caused by a difference in organismal 

 differentials. With this conclusion harmonizes also the observation that while 

 in organisms like Tubularia homoiotransplantation may apparently be per- 

 fect, yet in some cases separation between host and transplant takes place 

 after a time. 



The results of heterotransplantation differ noticeably from those of homoio- 

 transplantation. Even if the transplantation succeeds, the differences in race 

 or species differentials may cause the union to take place more slowly and the 

 resulting combination may only be temporary, separation occurring perhaps 

 at a later date. On the other hand, it seems that union of different species may 

 permanently succeed in certain instances. In Hydra the union of heterografts 

 may, however, not be so firm as that of homoiograf ts ; the surface of contact 

 between the species may at first become smaller, until at last some mechanical 



