306 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



termining whether such an agglutination will or will not take place and 

 whether the union will be temporary or permanent. Similar factors, and in 

 particular agglutination processes, may perhaps be concerned also in the 

 joining together of parts of more primitive adult organisms, such as Hyla, 

 Planaria, Lumbricus, and even in the transplantation of extremity buds in 

 Triton, or of extremities in the larvae of Salamander, although the processes 

 underlying these latter phenomena have not yet been analyzed from this point 

 of view. 



6. Even in still higher organisms, as, for instance, in mammals, when a 

 wound is made in the epidermis, reactions follow, not unlike those observed 

 in experimental amoebocyte tissue, and in all probability the factors under- 

 lying both these phenomena are likewise similar. However in the more dif- 

 ferentiated tissues more complex structures, which connect neighboring 

 cells or tissues to one another, have developed, and these may vary in the 

 different tissues ; but even in the mammalian skin these complex structures 

 disappear during wound healing, at least temporarily, and then the primitive 

 reactions, which are common to so many organisms and which we have 

 analyzed in this chapter, have a chance to set in. In addition, we have reason 

 for assuming that in the tissues of higher animals there are at work finely 

 graded substances carrying individuality differentials and regulating the 

 interaction of tissues of the same type, as well as of different types adjoining 

 each other within the same organism. These autogenous morphogenic regu- 

 lators have already been discussed. 



It may therefore be assumed that also tissue cells of higher organisms still 

 possess the fundamental properties of amoebocytes, at least potentially, and 

 that only secondarily other, more complicated structures and functions are 

 superimposed upon these primary characteristics and that especially in certain 

 artificial or pathological conditions, such as those leading to wound healing, 

 these primary modes of reaction come again into play. But there are found 

 even in higher organisms certain types of cells which, within the normal 

 organisms, remain isolated; among them are the erythrocytes, especially the 

 nucleated ones, the various types of leucocytes and the spindle cells, which as 

 far as their function is concerned, take the place of mammalian blood plate- 

 lets in other vertebrates. These, as well as the blood platelets, possess in 

 various degrees the characteristics of the amoebocytes. The tendency to 

 agglutinate is most markedly developed in the avian spindle cells of the 

 blood and in the mammalian blood platelets, but it is to a lesser degree also 

 found in the other types of cells. In all these elements, and particularly in 

 the spindles and blood platelets, the stickiness of the outer cell layer is lack- 

 ing under normal conditions within the blood channels. It is only under the 

 influence of abnormal stimulation that their protoplasm undergoes changes 

 which, in principle, are presumably similar to those we have analyzed in the 

 case of amoebocytes, and which lead to agglutination and thrombus forma- 

 tion, or to tissue or cell reactions of a so-called inflammatory kind. As to the 

 role which organismal differentials play in these latter processes, no definite 

 knowledge exists. 



