P^irf TTT ^ e Significance of Organismal Differentials in 



the Interaction Between Single Cells 



Chapter I 



The Role of Organismal Differentials in the 

 Union of Free-living Cells 



We have so far considered the significance of organismal differen- 

 tials in the grafting of pieces of tissues or organs, or of whole 

 organs, to embryonal or adult organisms, as well as in the union of 

 larger parts of primitive organisms and in parabiosis. As a further step in 

 the analysis of individuality, we shall now study the role which genetic rela- 

 tionship and the organismal differentials play in the joining together of parts 

 of cells or of whole cells, which latter may function as independent, free- 

 living organisms. In these experiments we have not to deal with transplan- 

 tations in the usual restricted meaning of the term, but with related processes. 

 The methods used and the problems considered in this part are similar to 

 those studied in the previous parts. We should naturally have to include in 

 these chapters also experiments in which unsegmented eggs or ova in early 

 stages of segmentation were joined together; however, these have already 

 been discussed in earlier chapters, in which in experiments with the eggs of 

 Ascaris distinct effects of the organismal differentials or their percursors 

 were noted, and this was true also in the experiments of Mangold on the 

 combinations of eggs in amphibia. We have also reported already on investiga- 

 tions in which early embryos or parts of embryos were united. 



In this chapter analogous phenomena in certain protozoa and unicellular 

 plants will be analyzed. 



1. The union of free-living protozoa or of parts of protozoa. As early as 

 1863, Max Schultze observed that pseudopods from different individual 

 protozoa belonging to the same species did not unite when they were brought 

 into close contact with each other; but it was only in 1897 that Jensen noted 

 a difference in the behavior towards each other of protoplasmic particles from 

 the same and from other protozoan individuals. In experiments especially 

 with the polythalamous rhizopod Orbitholites, he observed that two pseudo- 

 pods from the same individual readily joined each other at the point of con- 

 tact to form one single organ, and in particular, adjoining small pseudopods 

 could unite into a single larger one by the flowing together of the protoplasm 

 at the points of contact; furthermore, a pseudopod of large size could in- 

 corporate a smaller one. In these cases we have to deal with autogenous 

 reactions. On the other hand, if two pseudopods which belonged to two differ- 



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