UNION OF FREE-LIVING CELLS 297 



agglutination and coalescence of the cells, while under other conditions a more 

 complete liquefaction and a subsequent shattering reaction may occur, result- 

 ing in the disintegration of the protoplasm into separate droplets in accordance 

 with the alterations in surface tension of the liquids concerned in these reac- 

 tions. 



In the case of the amoebocytes of Limulus it can be shown that numerous 

 environmental changes may produce variations in the consistency of the outer 

 layer of the protoplasm, which in some instances cause agglutination, and in 

 others amoeboid movement. It is therefore conceivable that in other unicellular 

 organisms stimuli, which sometimes lead to agglutination and coalescence, 

 may under different circumstances initiate amoeboid movements of cells in a 

 direction towards each other, influenced in this process by substances which 

 are hormone-like and which may not, themselves, possess organismal differ- 

 entials. Also, the movements of embryonal cells in the direction towards other 

 tissues may be explained as due to surface reactions similar to those which 

 lead to agglutination, coalescence, or migration in unicellular organisms. 



