APPENDIX CYTOTAXIS 



53 



and when several pairs of cells were in the field, this movement 

 took place in various directions, indicating that their move- 

 ment was not determined by conditions outside the approaching 

 cells. To get further light on the migration of the cells, their 

 distance apart was meas- 

 ured at short intervals 

 of time. The results of 

 two series of such meas- 

 urements are represented 

 graphically in Figs. 6 and 

 7. In both of these dia- 

 grams the heavy lines 

 indicate the successive 

 positions assumed by 

 four points ; namely, the 

 points of the two cells 

 which are nearest each 

 other and those which 

 are most distant. In 

 the first case the cells 

 .traverse the distance of 

 their diameters (58 /A) 

 in about 10.5 minutes. 

 The rate of migration 

 is, however, extremely 

 variable. In some cases 

 the cells seem even to 

 move apart (negative 

 cytotaxis?). 



Certain special cases 

 are worthy of considera- 

 tion. When a third cell 

 lies near an approaching 

 pair, the path of migra- 

 tion of the pair may become convex towards the third cell. 

 Two cell-complexes, each composed of three or four cells, 

 may approach and connect. But masses composed of a 

 larger number of cells form " closed complexes ' which 

 show no cytotactic activity. The isolated cells of differ- 



FIGS. fi, 7. Two sets of curves, showing the 

 course of "cytotactic" movements of the 

 cleavage cells of the frog. In each figure 

 the dotted line represents a diameter of the 

 cell. The full line represents the successive 

 positions of the extremities of the diameters 

 as the cells approach. The distances between 

 horizontal lines = 4^ ; between vertical lines, 

 75 seconds. (From Roux, '94.) 



