1 82 Studies in Animal Behavior 



tactic influence that drew these cells to certain re- 

 gions of the embryo much as white blood corpuscles 

 are attracted to substances produced by certain bac- 

 teria; or possibly it may have been some form of 

 reaction to contact stimuli ; but, anyway, the result is 

 of interest in showing the role played by cell migra- 

 tion in establishing the structure of the embryo. 



The mesenchyme cells of the embryo are the 

 parents of most of the connective tissue cells of the 

 adult organism. The latter have long been known 

 to be more or less migratory under certain condi- 

 tions, and the recent work on the cultivation of 

 tissues outside the body has shown that they pos- 

 sess considerable power of amoeboid movement. 

 When a piece of tissue, especially from an embryo 

 or young animal, is mounted in a hanging drop of 

 blood plasma there soon appears around it a ring 

 of more or less spindle-shaped cells radiating into 

 the surrounding medium. These spindle-shaped 

 cells are derived mostly from connective tissue, and 

 the ring that is formed results chiefly from the out- 

 wandering of cells, although in some cases the 

 growth and multiplication of cells undoubtedly con- 

 tribute to its formation. The writer has often 

 watched the movements of these cells under the 

 microscope. The locomotion is essentially amoe- 

 boid, and the cells show a pronounced thigmotaxis, 

 or tendency to keep in contact with solid bodies. 



The pigment cells of many animals are related to 

 connective tissue cells both in origin and mode of 



