180 Studies in Animal Behavior 



means of osmotic changes or growth processes occur- 

 ring in other parts. But it is coming to be recognized 

 more and more that many of the processes of embry- 

 onic development are the result of active cell move- 

 ment. Many cells in early development have a con- 

 siderable power of locomotion, and, like the soldiers 

 of a well-disciplined army, they move into their ap- 

 pointed places at the proper time. To gain an in- 

 sight into this feature of their development, to un- 

 derstand why it is that these cells act as they do, 

 we are naturally led to a study of cell behavior. 

 To a considerable extent the form of our bodies is 

 an expression of shall we say cell psychology? Or, 

 at any rate, it is in part the expression of that kind 

 of behavior which is embraced under comparative 

 psychology when found among lower organisms. 



A few years ago Wilhelm Roux, an investigator 

 of especial prominence among the experimental em- 

 bryologists, found that if the cells of the frog's 

 egg are shaken apart during early stages of seg- 

 mentation, and placed in water a short distance apart 

 they would slowly approach one another until they 

 came into contact. This peculiar behavior, which 

 was later observed also by Rhumbler, was called 

 by Roux Cytotropism. Whether it is a form of 

 chemotaxis, or just how it is brought about is un- 

 certain. Cells of the early cleavage stages also show 

 a marked tendency to come into contact with one an- 

 other as closely as possible. While they round up 

 during division, during the resting stages the cells 



