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 yu.) 

 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. 6, 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 aiiproach. The distances between 

 horizontal lines = 4 f^ ; between vertical lines, 

 75 seconds. (From Roux, '94.) 



