432 HARPER— ORGANIZATION, REPRODUCTION 



and the degree of difference between the interior and peripheral 

 cells. It is obvious in Pediastriim that such characters are deter- 

 mined directly by the characters of the cells, but it is equally clear 

 that except in their simplest features they are incommensurable 

 with those of the individual cells and cannot be represented directly 

 as such in the germ cell. It is the form, adhesiveness, polarities, 

 etc., of the cells that determine the character of the colony and 

 these characteristics of the cells as noted can best be conceived as 

 characters of the cells as wholes rather than as determined by par- 

 ticular unit parts of cell organs or even by entire cell organs. The 

 general growth tendencies of the cell are characters of the cell not 

 of the colony as a whole and can come to expression regardless of 

 whether the colony is formed or not. 



Ezndence of Polarity in the Cells. — Furthermore it is obvious as 

 shown above that each cell has a specific orientation in the typical 

 colony, and yet there is no mosaic heredity. Any one cell can re- 

 place any other cell in the colony and the shape of the cell is in many 

 species in no notable degree a function of its position or interrela- 

 tions with the other cells. Each cell in the typical arrangement has 

 its major axis in a definite relation to the major axis of the colony. 

 The long pair of lobes or spines point in general radially outward 

 from the center. This, as I have shown, is not at all because, as 

 one might suspect at first glance, the cell tends to grow its longer 

 spines on whichever side happens to be turned outward. The ir- 

 regular colonies demonstrate this over and over (Figs 26-28). If 

 in the swarming period the cell does not achieve its normal position 

 with its short axis placed radially and the spine-bearing side out- 

 ward the maladjustment is never overcome. The long spines push 

 out from the side predestined to produce them and develop as fully 

 as they can under the pressure relations in which they are placed. 

 There is surprisingly little evidence of adaptability in the cells in 

 this regard. Apparently the cell axes are already fixed unalterably 

 in the swarmspore stage and are quite independent of any contact 

 relations then or later established. The presence of a polar dift'eren- 

 tiation of the axes of the cells in addition to the operation of the 

 principles of binary fission, surface tension, adhesion, functional 

 hypertrophy, etc., is certainly essential in the morphogenetic proc- 



