212 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



take place between adjoining tissues which are of a regulatory character and 

 keep the animal equilibrated. However, distance substances, in the form of 

 hormones, may also participate in this equilibrium as secondary factors, 

 though their action is less important and more specialized. In the case of 

 hydrozoa, conditions are in some essential respects similar to those of higher 

 organisms ; the equilibrium depends on local and distant factors and it can be 

 disturbed through local as well as through distant changes ; also, there is reason 

 for assuming that in both instances definite substances mediate these effects. 

 Furthermore, in these primitive organisms the organismal differentials, as well 

 as what corresponds to organ and tissue differentials in higher organisms, par- 

 ticipate in the maintenance of an equilibrium; but the particular structure 

 and function of adjoining autogenous parts of the organisms seem to be better 

 able to induce growth processes of various kinds in hydrozoa than in higher 

 organisms, on account of the greater plasticity of the tissues and organs in 

 the former. Important also in these lower forms are specific distance sub- 

 stances, which, acting in a stimulating or an inhibiting manner, are able to 

 modify the structure of the organism. There is a third difference between 

 higher organisms and hydrozoa in the stabilization of the equilibrium. In 

 higher organisms the equilibria depend upon the local interaction of tissues 

 bearing the same individuality differential and they are therefore essentially 

 autogenous in character. In hydrozoa, on the contrary, parts of an organism 

 differing in the character of their individuality differentials may, in general, 

 substitute for each other; incompatibilities, with resulting disturbance of the 

 formative equilibria, as a rule become manifest only if distinct differences in 

 species differentials exist between adjoining tissues. We cannot therefore con- 

 sider this equilibrium in lower forms as strictly autogenous in character ; it is 

 of a homoiogenous, as well as of an autogenous nature. 



The next problem to be considered concerns the incompatibilities and dis- 

 turbances of equilibrium which may take place, in organisms bearing heterog- 

 enous differentials, after a primary union and an apparently complete forma- 

 tive equilibrium have been established. These changes may be due to two 

 different causes: (1) The primary incompatibility of the organismal differ- 

 entials may gradually increase, the resulting disturbance of the equilibrium 

 becoming manifest in the appearance of growth processes in whole organ- 

 isms, which otherwise would occur only in isolated parts; or (2) the original 

 incompatibility of the organismal differentials may lead to a primary separa- 

 tion of the adjoining surfaces of the heterogenous parts and this process may 

 be followed by regenerative changes. We believe that the* first interpretation 

 is the more probable one for several reasons: (1) In certain cases, when the 

 union between adjoining homoiogenous pieces was apparently perfect, sec- 

 ondarily a separation also took place. Presumably a formative change at the 

 point of union was here the primary process, which was followed by separa- 

 tion; (2) the separation may occur in some classes of animals not exactly at 

 the junction of the two surfaces, but at a neighboring point. This indicates 

 that either growth processes or changes of a degenerative character induced 

 the separation; (3) one of the mechanisms which help to reestablish a stable 



