422 



HARPER— ORGANIZATION, REPRODUCTION 



in which by some accident certain cells are only attached at one 

 point to the remainder of the group. 



In Fig. 29 we have an eight-celled colony of P. asperum in 

 which one cell, a, is attached by only one of its basal lobes and 

 yet is quite symmetrically developed. The second base lobe is 

 rounded rather than sharply wedge-shaped and this difference 

 may be taken as the measure of the influence of the epigenetic 

 pressure and contact relations as compard with heredity in de- 

 termining the form of the cell. The asymmetric positions of the 

 two central cells in this colony also have produced characteristic 

 effects on their form and it is plain that the relatively free cell has 

 much more nearly achieved its full development than have these 



Figs. 29 and 30. P. asperum. Irregular, eight-celled colonies, one cell 

 in each case attached by one lobe only, but quite typical in outline. X about 

 550. 



cells with their asymmetric contact relations. In Fig. 30 we have 

 a colony with only seven cells visible, one cell, a, attached by only 

 one basal lobe, another by a basal and a peripheral lobe, h. It is 

 plain here that in neither case has the free basal lobe tended in any 

 degree to assume the more tapering form of a peripheral lobe, nor 

 have the long and short axes of the cells been reversed. In this 

 colony the eighth cell may have been present in its early life and 

 possibly may have been connected with some of the cells now partly 

 free. The form of cell h, however, has certainly been achieved 

 under the same contact conditions in which it appears in the figure. 

 The rounded end of its free basal lobe as well as that of cell a 

 shows that the wedge fonn is an environmental eft'ect. 



Figs. 31 and 32 (less highly magnified) also show cells which 

 have attained the normal form while attached by only one basal 



