AND INHERITANCE IN PEDIASTRUM. 435 



such morphogenetic factors are organic characteristics of the in- 

 dividual cell rather than the expression of any mysterious form, de- 

 termining principle residing in the organism as a whole is suf- 

 ficiently clear, as it seems to me, from the fact that the cell can de- 

 velop its specific form in entire independence of its interrelations 

 with the other cells of the colony. If, as I think is necessary, one 

 must assume that the cells are characterized by these definite polar 

 dififerentiations, it becomes still more obvious that the swarming 

 period in its later stages at least when the cells writhe and glide and 

 turn upon each other is not one of aimless movement hither and 

 thither with a final chance distribution of the cells but a definitely 

 directed effort to achieve for each cell a_ specific relation to its fel- 

 lows. If the swarmers already had the four-lobed biaxial form we 

 could regard this as a mere matter of physical adjustment analogous 

 to the putting together of the parts of a Chinese puzzle, but as I have 

 pointed out and as earlier students have observed, the cells get their 

 position in the colony as mere oval or egg-shaped jelly droplets. 

 The four-lobed biaxial form appears instantly with the beginning 

 of growth but not before growth begins nor before the cells have 

 their fixed position in the group. It would be highly interesting to 

 know how the cilium-bearing tip, the so-called mouthpiece, of the 

 swarmspore is placed at the moment when the cells come to rest, 

 but I have been unable to determine this point. 



It seems to me evident, then, from the shape of the cells and 

 their orientation in the normal colony that they must be regarded 

 as at least biaxial in their relations to each other, the polar differen- 

 tiations corresponding with their major axes. They are not in equi- 

 librium in their interrelations till the opposite right and left and basal 

 and peripheral poles of their axes are in a general way juxtaposed. . 

 In the sixteen-celled colony of P. asperiim and P. Boryanum this 

 would hold for all the cells except the central cell, whose polar re- 

 lations with the surrounding cells are not easy to analyze. It is 

 perhaps for this reason that the center of the colony is left vacant 

 in the sixteen-celled colonies of P. clatJiraftim and the ring-shaped 

 eight-celled colonies of P. simplex. The tendency to irregularity in 

 the arrangement of the interior cells of the sixteen-celled colonies 

 of P. simplex may also be related to this same difficulty in the polar 

 relations of a central cell in such a group. 



